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Nucleotide-binding leucine-rich repeat (NLR) proteins are crucial intracellular immune receptors in plants, responsible for detecting invading pathogens and initiating defense responses. While previous studies on the evolution and function of NLR genes were mainly limited to land plants, the evolutionary trajectory and immune-activating character of NLR genes in algae remain less explored. In this study, genome-wide NLR gene analysis was conducted on 44 chlorophyte species across seven classes and seven charophyte species across five classes. A few but variable number of NLR genes, ranging from one to 20, were identified in five chlorophytes and three charophytes, whereas no NLR gene was identified from the remaining algal genomes. Compared with land plants, algal genomes possess fewer or usually no NLR genes, implying that the expansion of NLR genes in land plants can be attributed to their adaptation to the more complex terrestrial pathogen environments. Through phylogenetic analysis, domain composition analysis, and conserved motifs profiling of the NBS domain, we detected shared and lineage-specific features between NLR genes in algae and land plants, supporting the common origin and continuous evolution of green plant NLR genes. Immune-activation assays revealed that both TNL and RNL proteins from green algae can elicit hypersensitive responses in Nicotiana benthamiana, indicating the molecular basis for immune activation has emerged in the early evolutionary stage of different types of NLR proteins. In summary, the results from this study suggest that NLR proteins may have taken a role as intracellular immune receptors in the common ancestor of green plants.

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The ecological niche of the recently described limnic microalga Limnomonas gaiensis (Chlamydomonadales) in Northern Europe remains unknown. To decipher the species tolerance capacity to pH, the effects of hydrogen ions on the physiological response of L. gaiensis were investigated. Results showed that L. gaiensis could tolerate exposure from pH 3 up to pH 11, with an optimal survival at pH 5-8. Its physiological response to pH was strain specific. Globally the southernmost strain was more alkaliphilic, had a slightly rounder shape, a slowest growth rate, and a lowest carrying capacity. Despite strain discrepancies among lakes, Swedish strains exhibited similar growth rates, faster at more acidic conditions. The extreme pH conditions affected its morphological features such as the eye spot and papilla shape, especially at acidic pH, and the cell wall integrity, at more alkaline pH. The wide range tolerance of L. gaiensis to pH would not be a hindrance to its dispersal in Swedish lakes (pH 4-8). Notably, the storage of high-energetic reserves over a wide range of pH conditions, as numerous starch grains and oil droplets, makes L. gaiensis a good candidate for bioethanol/fuel industrial production and a key resource to sustain aquatic food chain and microbial loop.

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The Pedinophyceae (Viridiplantae) comprise a class of small uniflagellate algae with a pivotal position in the phylogeny of the Chlorophyta as the sister group of the 'core chlorophytes'. We present a chromosome-level genome assembly of the freshwater type species of the class, Pedinomonas minor. We sequenced the genome using Pacbio, Illumina and Hi-C technologies, performed comparative analyses of genome and gene family evolution, and analyzed the transcriptome under various abiotic stresses. Although the genome is relatively small (55 Mb), it shares many traits with core chlorophytes including number of introns and protein-coding genes, messenger RNA (mRNA) lengths, and abundance of transposable elements. Pedinomonas minor is only bounded by the plasma membrane, thriving in temporary habitats that frequently dry out. Gene family innovations and expansions and transcriptomic responses to abiotic stresses have shed light on adaptations of P. minor to its fluctuating environment. Horizontal gene transfers from bacteria and fungi have possibly contributed to the evolution of some of these traits. We identified a putative endogenization site of a nucleocytoplasmic large DNA virus and hypothesized that endogenous viral elements donated foreign genes to the host genome, their spread enhanced by transposable elements, located at gene boundaries in several of the expanded gene families.

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The characteristics of detached macroalgae (drift) in nearby highly eutrophic and mesotrophic estuaries in south-western Australia are compared to elucidate the magnitude and types of changes that occur in macroalgal drift when estuaries receive excessive nutrient input. Drift characteristics in the large basins of the microtidal, eutrophic Peel-Harvey and mesotrophic Swan-Canning, which is not subjected to large nutrient inputs directly from agricultural land, differed markedly. Biomass (dry weight) in mesotrophic estuary was dominated by rhodophytes (92%), particularly Laurencia and Hypnea, and in eutrophic estuary by opportunistic chlorophytes (68%), especially Chaetomorpha and Ulva. Prevalence and biomass of drift were far greater in the eutrophic estuary, particularly during summer and autumn when macroalgal growth rose sharply. Macroalgal biomass in the eutrophic estuary was positively related to salinity. These results facilitate predictions of how climatic and other anthropogenic changes influence extent of macroalgal growth and thus change the estuarine environment.

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BACKGROUND: Global warming directly influencing ozone layer depletion, which eventually is increasing ultraviolet radiation penetration having far-reaching impacts on living biota. This particularly influences the primary producer microalgae which are the basic unit of food webs in the aquatic habitats. Therefore, it is necessary to concentrate the research at this micro-level to understand the harmful impact of increased UV-B radiation ever before. Consequently, the present attempt aimed to focus on the influence of UV-B on growth criteria, photosynthetic pigments, some metabolites, and ultrastructure of the freshwater cyanobacteria, Planktothrix cryptovaginata (Microcoleaceae), Nostoc carneum (Nostocaceae), Microcystis aeruginosa (Microcystaceae), the Chlorophyte Scenedesmus acutus (Scenedesmaceae), and the marine Cyanobacterium Microcystis (Microcystaceae). METHODS: The cultures of investigated algae were subjected directly to different duration periods (1, 3, 5, and 7 h) of artificial UV-B in addition to unirradiated control culture and allowed to grow for 10 days, after which the algal samples were analyzed for growth, photosynthetic activities, primary metabolities and cellular ultrastructure. RESULTS: A remarkable inhibitory influence of UV-B was observed on growth criteria (measured as optical density and dry weight) and photosynthetic pigments of P. cryptovaginata, N. carneum, M. aeruginosa, S. acutus, and marine Microcystis. Where increasing the exposure time of UV-B was accompanied by increased inhibition. The variation in carbohydrate and protein contents under UV stress was based on the exposure periods and the algal species. The variation in algal ultrastructure by UV-B stress was noticed by an Electron Microscope. Cells damage and lysis, cell wall and cell membrane ruptured and release of intracellular substances, loss of cell inclusion, plasmolysis and necrosis, or apoptosis of the algal cells were observed by exposure to 7 h of UV-B. CONCLUSION: Exposure to UV-B has a marked harmful impact on the growth, pigments, and metabolic activity, as well as the cellular ultrastructure of some cyanobacteria and chlorophytes.

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For a long time, algal chemistry from terrestrial to marine or freshwater bodies, especially chlorophytes, has fascinated numerous investigators to develop new drugs in the nutraceutical and pharmaceutical industries. As such, chlorophytes comprise a diverse structural class of secondary metabolites, having functional groups that are specific to a particular source. All bioactive compounds of chlorophyte are of great interest due to their supplemental/nutritional/pharmacological activities. In this review, a detailed description of the chemical diversity of compounds encompassing alkaloids, terpenes, steroids, fatty acids and glycerides, their subclasses and their structures are discussed. These promising natural products have efficiency in developing new drugs necessary in the treatment of various deadly pathologies (cancer, HIV, SARS-CoV-2, several inflammations, etc.). Marine chlorophyte, therefore, is portrayed as a pivotal treasure in the case of drugs having marine provenience. It is a domain of research expected to probe novel pharmaceutically or nutraceutically important secondary metabolites resulting from marine Chlorophyta. In this regard, our review aims to compile the isolated secondary metabolites having diverse chemical structures from chlorophytes (like Caulerpa ssp., Ulva ssp., Tydemania ssp., Penicillus ssp., Codium ssp., Capsosiphon ssp., Avrainvillea ssp.), their biological properties, applications and possible mode of action.

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Phytohormones are pivotal signaling compounds in higher plants, in which they exert their roles intracellularly, but are also released for cell-to-cell communication. In unicellular organisms, extracellularly released phytohormones can be involved in chemical crosstalk with other organisms. However, compared to higher plants, hardly any knowledge is available on the roles of phytohormones in green algae. Here, we studied phytohormone composition and extracellular release in aero-terrestrial Trebouxiophyceae. We investigated (a) which phytohormones are produced and if they are released extracellularly, and if extracellular phytohormone levels are (b) affected by environmental stimuli, and (c) differ between lichen-forming and non-lichen-forming species. Three free-living microalgae (Apatococcus lobatus, Chloroidium ellipsoideum, and Myrmecia bisecta) and three lichen-forming microalgae (Asterochloris glomerata, Trebouxia decolorans, and Trebouxia sp.) were studied. Algae were grown on solid media and the following cellular phytohormones were identified by ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS): indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), abscisic acid (ABA), gibberellin A4 (GA4 ), and zeatin (ZT). Furthermore, IAA, IBA, ABA, jasmonic acid (JA), gibberellin A3 (GA3 ), and GA4 were found to be released extracellularly. IAA and ABA were released by all six species, and IAA was the most concentrated. Phytohormone release was affected by light and water availability, especially IAA in A. glomerata, Trebouxia sp., and C. ellipsoideum. No clear patterns were observed between lichen-forming and non-lichen-forming species. The results are envisaged to contribute valuable baseline information for further studies into the roles of phytohormones in microalgae.

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Auxin, represented by indole-3-acetic acid (IAA), has for a long time been studied mainly with respect to the development of land plants, and recent evidence confirms that canonical nuclear auxin signaling is a land plant apomorphy. Increasing sequential and physiological data show that the presence of auxin transport machinery pre-dates the emergence of canonical signaling. In this review, we summarize the present state of knowledge regarding the origins of auxin transport in the green lineage (Viridiplantae), integrating both data from wet lab experiments and sequence evidence on the presence of PIN-FORMED (PIN), PIN-LIKES (PILS), and AUXIN RESISTANT 1/LIKE-AUX1 (AUX1/LAX) homologs. We discuss a high divergence of auxin carrier homologs among algal lineages and emphasize the urgent need for the establishment of good molecular biology models from within the streptophyte green algae. We further postulate and discuss two hypotheses for the ancestral role of auxin in the green lineage. First, auxin was present as a by-product of cell metabolism and the evolution of its transport was stimulated by the need for IAA sequestration and cell detoxification. Second, auxin was primarily a signaling compound, possibly of bacterial origin, and its activity in the pre-plant green algae was a consequence of long-term co-existence with bacteria in shared ecological consortia.

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It is generally accepted that land plants evolved from streptophyte algae. However, there are also many chlorophytes (a sister group of streptophyte algae and land plants) that moved to terrestrial habitats and even resemble mosses. This raises the question of why no land plants evolved from chlorophytes. In order to better understand what enabled streptophyte algae to conquer the land, it is necessary to study the chlorophytes as well. This review will introduce the freshwater filamentous chlorophyte alga Draparnaldia sp. (Chaetophorales, Chlorophyceae) as a model for comparative analyses between these two lineages. It will also focus on current knowledge about the evolution of morphological complexity in chlorophytes versus streptophytes and their respective morphological/behavioural adaptations to semi-terrestrial habitats, and will show why Draparnaldia is needed as a new model system.

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The R2R3-MYB transcription factors play critical roles in various processes in embryophytes (land plants). Here, we identified genes encoding R2R3-MYB proteins from rhodophytes, glaucophytes, Chromista, chlorophytes, charophytes, and embryophytes. We classified the R2R3-MYB genes into three subgroups (I, II, and III) based on their evolutionary history and gene structure. The subgroup I is the most ancient group that includes members from all plant lineages. The subgroup II was formed before the divergence of charophytes and embryophytes. The subgroup III genes form a monophyletic group and only comprise members from land plants with conserved exon-intron structure. Each subgroup was further divided into multiple clades. The subgroup I can be divided into I-A, I-B, I-C, and I-D. The I-A, I-B, and I-C are the most basal clades that have originated before the divergence of Archaeplastida. The I-D with the II and III subgroups form a monophyletic group, containing only green plants. The II and III subgroups form another monophyletic group with Streptophyta only. Once on land, the subgroup III genes have experienced two rounds of major expansions. The first round occurred before the origin of land plants, and the second round occurred after the divergence of land plants. Due to significant gene expansion, the subgroup III genes have become the predominant group of R2R3-MYBs in land plants. The highly unbalanced pattern of birth and death evolution of R2R3-MYB genes indicates their important roles in the successful adaptation and massive radiation of land plants to occupy a multitude of terrestrial environments.

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Resumen Las microalgas son organismos fotoautótrofos con un rápido crecimiento y la habilidad de adaptarse a diversos ambientes. Convierten el dióxido de carbono en biomasa y debido a esto, se considera que tienen gran potencial biotecnológico. La biomasa algal puede usarse en la industria alimenticia y de compuestos bioactivos, en la producción de biocombustibles, en la bioremediación y biofertilización. Como biofertilizantes, las microalgas clorofitas y cianofitas, producen polisacáridos (mucílago) que pueden evitar la erosión, mejorar la estructura y el contenido de material orgánica de los suelos, y aumentar la concentración de iones en los cultivos. Reduciendo de esta forma la necesidad de fertilizantes químicos convencionales. El uso de estas microalgas como biofertilizantes se denomina algalización. Durante este proceso se usan principalmente clorofitas por su alta tasa de crecimiento, la facilidad de su cultivo a gran escala, y su adaptación a las condiciones del suelo. El género Chlorella es de gran interés porque diversos estudios han mostrado que puede ayudar en la fijación del nitrógeno, mejorar las propiedades físicas y químicas del suelo, y producir sustancias que promueven el desarrollo de la planta y el control de infecciones. Por esta razón, las microalgas del género Chlorella representan una alternativa viable para la biofertilización, generando beneficios no solo para la producción agrícola sino también para el medio ambiente.

Abstract Microalgae are photoautotrophic organisms with fast growth and the ability to adapt to different environments. They convert carbon dioxide into biomass and are considered to have great biotechnological potential because of it. Algal biomass can be used in food and bioactive compounds industry, in biofuels production, in bioremediation and biofertilization. As biofertilizers, chlorophytes and cyanophytes microalgae produce polysaccharides (mucilage) that can avoid erosion, improve the structure and organic matter content in the soil, and increase the ions concentration for crop plants. Thus, reducing the need for conventional crop chemical fertilizers. The use of this microalgae as biofertilizers is called algalization. Algalization uses mainly chlorophytes due to their high growth rate, their simple large scale cultivation, and their adaptation to soil conditions. Chlorella genus is of special interest because research has shown that it can help with nitrogen fixation, improve physical and chemical properties of the soil, and produce substances that can promote plant development and infections control. Therefore, microalgae from Chlorella genus are a viable alternative for biofertilization, generating benefits for agricultural production and the environment.

Resumo As microalgas são organismos fotoautotróficos com crescimento rápido e capacidade de adaptação a diferentes ambientes. Eles convertem dióxido de carbono em biomassa e, por isso, são considerados com um grande potencial biotecnológico. A biomassa de algas pode ser usada na indústria alimentar e de compostos bioactivos, na produção de biocombustíveis, na biorremediação e biofertilização. Como biofertilizantes, as microalgas clorófitas e cianófitas produzem polissacarídeos (mucilagem) que podem evitar a erosão, melhorar a estrutura e o conteúdo de matéria orgânica do solo, e aumentar a concentração de iões nas culturas, reduzindo assim a necessidade de fertilizantes químicos convencionais. O uso dessas microalgas como biofertilizantes é chamado de algalização. Durante este processo, usam-se eles ​​principalmente clorofíceas por sua alta taxa de crescimento, facilidade de cultura em larga escala, e sua adaptação às condições do solo. A Chlorella é de grande interesse porque vários estudos têm mostrado que pode auxiliar na fixação do nitrogênio, melhorar as propriedades físicas e químicas do solo, e produzir substâncias que promovem o crescimento das plantas e o controle de infecções. Por esta razão, as microalgas do gênero Chlorella representam uma alternativa viável para a biofertilização, gerando benefícios não só para a produção agrícola, mas também para o meio ambiente.

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Se determinó la composición de ácidos grasos de 54 cepas microalgales colectadas del Perú y mantenidas en el Banco de Germoplasma de Organismos Acuáticos (IMARPE) con la finalidad de determinar su uso nutricional en la acuicultura. Para ello se realizaron cultivos en un volumen de 50 mL y se determinaron los porcentajes relativos de ácidos grasos mediante transesterificación directa y cromatografía de gases. En el grupo Chlorophyta las microalgas que presentaron los mayores valores de porcentaje relativo de ácidos grasos fueron Chlamydomonas reinhardtii (16:0; 41.2%), Scenedesmus obtusus (18:1n-7; 33.6%), Acutodesmus dimorphus (18:1n-9; 37.1%), Desmodesmus armatus (18:3n-3; 32.2%) y Tetraselmis contracta (16:4n-3; 16.5%). En cambio en el grupo Bacillariophyta, los ácidos grasos más abundantes fueron 16:1n-7 en Chaetoceros didymus (20.2%), 18:4n-3 en Navicula sp. (28.3%) y EPA en Asterionellopsis sp. (31.5%). Por otro lado, en el grupo Dinophyta, todas las cepas superaron el 20% de DHA, en particular, la cepa de Akashiwo sanguinea presentó el mayor porcentaje relativo de este ácido graso (29.9%) y de los ácidos grasos 16:0 (24.8%) y EPA (16%). Se discute el uso de estas cepas según su contenido de ácidos grasos.

In This work, we determinate the fatty acids composition and their nutritional value in 54 microalgal strains, collected from Peru and stored in Banco de Germoplasma de Organismos Acuáticos (IMARPE). The cultures were grown to 50 mL and analyzed by direct transesterification and gas chromatography. In the Chlorophyta group, the microalgaes that present the highest relative percentage of fatty acids were Chlamydomonas reinhardtii (16:0; 41.2%), Scenedesmus obtusus (18:1n-7; 33.6%), Acutodesmus dimorphus (18:1n-9; 37.1%), Desmodesmus armatus (18:3n-3; 32.2%) and Tetraselmis contracta (16:4n-3; 16.5%). Moreover in the Bacillariophyta group, the most abundant fatty acids were 16:1n-7 in Chaetoceros didymus (20.2%), 18:4n-3 in Navicula sp. (28.3%) and EPA in Asterionellopsis sp. (31.5%). By the other hand, in the Dinophyta group, all strains exceed the 20% of DHA, in particular Akashiwo sanguinea, it was strain to have the highest percentage of this fatty acid (29.9%) in addition to 16: 0 (24.8%) and EPA (16%). We discussed uses of these strains is according to their fatty acids content.

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BACKGROUND: Green plants comprise two lineages: (1) the streptophytes that colonised land and (2) the chlorophytes that have adaptations to land but remained mostly aquatic. To better understand what made streptophytes so successful, we are currently establishing the chlorophyte alga Draparnaldia sp. (Chaetophorales, Chlorophyceae) as a model for comparative analyses between these two lineages. However, establishing Draparnaldia as a valuable model requires that it can be transformed. Thus, our goal is to develop a transformation protocol for this alga. RESULTS: We have established the first transformation protocol for Draparnaldia. This protocol is based on protoplast transformation by electroporation. It includes instructions on protoplast isolation, regeneration and transient transfection. It also provides a list of the effective selective agents for future Draparnaldia transformations. CONCLUSIONS: Our protocol opens a way for Draparnaldia functional genomics analyses. Moreover, it also provides an important base for establishment of stable transformation.

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Hydrogen peroxide (HP) is a feasible algicide to control cyanobacterial blooms, but its application in the waters with strong reductive power is still a problem. The rapid decomposition rate of HP results in a short residence time in the waters, which renders the failure of bloom mitigation. In this study, the damage of Microcystis aeruginosa (M. aeruginosa) by HP, the optimization method for Microcystis bloom control and its field effects were investigated. Results of microcosm experiments indicated M. aeruginosa was vulnerable to HP. The HP-induced damage was mainly attributed to the impairments of HP detoxification pathways and photosystem. Repetitive additions of HP, which could prolong the residence time, were conducted in the mesocosm experiments. HP concentration ranged from 96 µM to 165 µM for 2 h could successfully mitigate Microcystis bloom, even though HP decomposition rate reached 109 µM per h. Besides the removal of M. aeruginosa, contents of total dissolved nitrogen, total dissolved phosphate, dissolved organic carbon and chromophoric dissolved organic matter in water column increased significantly (p < 0.05). The enrichment of nutrients promoted the growth of chlorophytes but the growth of M. aeruginosa couldn't be observed. The dominant species thrived in the HP-treated waters was Chlamydomonas sp. Results in this study confirmed that HP was a promising algicide for cyanobacterial blooms control. The optimization method further demonstrated that repetitive additions of HP could favor the mitigation of cyanobacterial blooms.

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For photosynthetic microbial eukaryotes, the rate-limiting step in NO3- assimilation is its reduction to nitrite (NO2-), which is catalyzed by assimilatory nitrate reductase (NR). Oceanic productivity is primarily limited by available nitrogen and, although nitrate is the most abundant form of available nitrogen in oceanic waters, little is known about the identity of microbial eukaryotes that take up nitrate. This lack of knowledge is especially severe for ice-covered seas that are being profoundly affected by climate change. To address this, we examined the distribution and diversity of NR genes in the Arctic region by way of clone libraries and data mining of available metagenomes (total of 4.24 billion reads). We directly compared NR clone phylogenies with the V4 region of the 18S rRNA gene (DNA pool) and 18S rRNA (RNA pool) at two ice-influenced stations in the Canada Basin (Beaufort Sea). The communities from the two nucleic acid templates were similar at the level of major groups, and species identified by way of NR gene phylogeny and microscopy were a subset of the 18S results. Most NR genes from arctic clone libraries matched diatoms and chromist nanoflagellates, including novel clades, while the NR genes in arctic eukaryote metagenomes were dominated by chlorophyte NR, in keeping with the ubiquitous occurrence of Mamiellophyceae in the Arctic Ocean. Overall, these data suggest that a dynamic and mixed eukaryotic community utilizes nitrate across the Arctic region, and they show the potential utility of NR as a tool to identify ongoing changes in arctic photosynthetic communities.IMPORTANCE To better understand the diversity of primary producers in the Arctic Ocean, we targeted a nitrogen cycle gene, NR, which is required for phytoplankton to assimilate nitrate into organic forms of nitrogen macromolecules. We compared this to the more detailed taxonomy from ice-influenced stations using a general taxonomic gene (18S rRNA). NR genes were ubiquitous and could be classified as belonging to diatoms, dinoflagellates, other flagellates, chlorophytes, and unknown microbial eukaryotes, suggesting novel diversity of both species and metabolism in arctic phytoplankton.

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Globally, eutrophication and warming of aquatic ecosystems has increased the frequency and intensity of cyanobacterial blooms and their associated toxins, with the simultaneous detection of multiple cyanotoxins often occurring. Despite the co-occurrence of cyanotoxins such as microcystins and anatoxin-a (ATX) in water bodies, their effects on phytoplankton communities are poorly understood. The individual and combined effects of microcystin-LR (MC-LR) and ATX on the cyanobacteria Microcystis spp., and Anabaena variabilis (a.k.a. Trichormus variabilis), and the chlorophyte, Selenastrum capricornutum were investigated in the present study. Cell density, chlorophyll-a content, and the maximum quantum efficiency of photosystem II (Fv/Fm) of Microcystis cells were generally lowered after exposure to ATX or MC-LR, while the combined treatment with MC-LR and ATX synergistically reduced the chlorophyll-a concentration of Microcystis strain LE-3. Intracellular levels of microcystin in Microcystis LE-3 significantly increased following exposure to MC-LR + ATX. The maximum quantum efficiency of photosystem II of Anabaena strain UTEX B377 declined during exposure to the cyanotoxins. Nitrogen fixation by Anabaena UTEX B377 was significantly inhibited by exposure to ATX, but was unaffected by MC-LR. In contrast, the combination of both cyanotoxins (MC-LR + ATX) caused a synergistic increase in the growth of S. capricornutum. While the toxins caused an increase in the activity of enzymes that scavenge reactive oxygen species in cyanobacteria, enzyme activity was unchanged or decreased in S. capricornutum. Collectively this study demonstrates that MC-LR and ATX can selectively promote and inhibit the growth and performance of green algae and cyanobacteria, respectively, and that the combined effect of these cyanotoxins was often more intense than their individual effects on some strains. This suggests that the release of multiple cyanotoxins in aquatic ecosystems, following the collapse of blooms, may influence the succession of plankton communities.

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The biodiversity of terrestrial algae is still grossly understudied, and African deserts in particular are barely touched in this respect. Here, four coccoid green algae from oases in the Western Desert of Egypt were characterized using a combination of morphotaxonomic, ecological and 18S rDNA data, with additional carotenoid and lipid analyses for two of the strains. Three strains were identified as affiliated with known taxa: Mychonastes sp., Asterarcys sp. (first report of this genus from a desert soil), and Stichococcus cf. deasonii. The fourth strain is proposed to represent a new cryptic genus Pharao gen. nov., with the type species P. desertorum sp. nov. The new taxon is sister to the clade of uncharacterized North American desert strains of Radiococcaceae (Chlorophyceae, Chlorophyta). The pigment profile of P. desertorum gen. et sp. nov. revealed carotenoids and chlorophylls typical of green algae. Bioorganic analysis showed a complex lipidome based on phospho- (PC), galacto- (MGDG and DGDG), betaine- (DGTS), and sulfoquinovosyl- (SQDG) membrane lipids, besides significant amounts of storage neutral lipids such as diacyl- (DAG) and triacylglycerols (TAG). The presence of saturated alkyl chains within all the membrane lipid classes in P. desertorum and Asterarcys sp. appears to reflect the need to maintain membrane fluidity and viscosity. In summary, African deserts likely still harbor new taxa to be described, and lipidomic analyses of such taxa may provide clues about their ability to survive in the extremely harsh desert habitats.

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Hydrological regimes are key in shaping the structure of phytoplankton communities in estuaries. Because anthropogenic disturbances often alter the quantity and quality of riverine inputs, this research focused on investigating phytoplankton dynamics in the St. Lucia Estuary, since being reconnected to the Mfolozi River. Due to the closed mouth state of the estuary, the input from the river resulted in oligohaline (≥5) conditions and the characteristic reverse salinity gradient to persist throughout the study (i.e. one year). Model results indicated that phytoplankton communities were structured by rainfall, light transmittance and depth, while shifts between dominant groups were driven by salinity and flow season. The persistence of chlorophytes and euglenophytes as the co-dominant functional group indicates the freshening and nutrient-enriched nature of the river. This study provides the first detailed account documenting the response of the phytoplankton community to recent restoration efforts in the St Lucia Estuary, a Ramsar Site.

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Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH4+ ), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (Fv /Fm ) was a sensitive indicator of NH4+ toxicity, manifested by a suppression of Fv /Fm in a dose-dependent manner. Two chlorophytes were the least sensitive to NH4+ inhibition, at concentrations of >3,000 µmoles NH4+  · L-1 , followed by two estuarine diatoms that were sensitive at concentrations >1,000 µmoles NH4+  · L-1 , followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 µmoles NH4+  · L-1 . At non-inhibiting concentrations of NH4+ , the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO3- ), whereas the other grew significantly faster on NH4+ . All four diatoms tested grew faster on NH4+ compared with NO3- . We showed that in cases where growth rates were faster on NH4+ than they were on NO3- , the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH4+ dominates the total N pool and they will also not have a growth advantage when NO3- is dominant, as long as N concentrations are sufficient.

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Species sensitivity distributions (SSDs) are an important predictive tool in risk assessment. Usually, literature data are used to build SSDs that are mostly based on planktonic species. But, to get adequate protective thresholds for environmental communities, one could argue that SSD should be built on ecotoxicological data obtained from species found in the ecosystem that should be protected. This is particularly true when benthic algae are of concern. Due to the lack of literature data, building SSD on benthic microalgae is difficult. This paper aims in comparing SSDs, and thus protective thresholds (hazardous concentration that affects 5% of the species of a community, HC5), built on ecotoxicological data obtained (1) from literature and (2) with specific bioassays on benthic diatoms from a lake. Thresholds were derived for protection against four herbicides separately and for a mixture of them. Sensitivity data obtained from literature were statistically lower than the specific data for all herbicides: Species tested in the literature were usually more sensitive (mainly chlorophytes), leading to more protective lower HC5. The HC5 thresholds (literature or specific) derived for protection against the mixture were also compared to the observed sensitivity of an assemblage of benthic diatom species exposed to an increasing range of herbicide mixture concentrations. We observed that one species within the assemblage (Fragilaria rumpens) was affected at a concentration below both the literature and the specific HC5 thresholds.

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