RESUMO
Antarctica's extreme environmental conditions impose selection pressures on microbial communities. Indeed, a previous study revealed that bacterial assemblages at the Cierva Point Wetland Complex (CPWC) are shaped by strong homogeneous selection. Yet which bacterial phylogenetic clades are shaped by selection processes and their ecological strategies to thrive in such extreme conditions remain unknown. Here, we applied the phyloscore and feature-level ßNTI indexes coupled with phylofactorization to successfully detect bacterial monophyletic clades subjected to homogeneous (HoS) and heterogenous (HeS) selection. Remarkably, only the HoS clades showed high relative abundance across all samples and signs of putative microdiversity. The majority of the amplicon sequence variants (ASVs) within each HoS clade clustered into a unique 97% sequence similarity operational taxonomic unit (OTU) and inhabited a specific environment (lotic, lentic or terrestrial). Our findings suggest the existence of microdiversification leading to sub-taxa niche differentiation, with putative distinct ecotypes (consisting of groups of ASVs) adapted to a specific environment. We hypothesize that HoS clades thriving in the CPWC have phylogenetically conserved traits that accelerate their rate of evolution, enabling them to adapt to strong spatio-temporally variable selection pressures. Variable selection appears to operate within clades to cause very rapid microdiversification without losing key traits that lead to high abundance. Variable and homogeneous selection, therefore, operate simultaneously but on different aspects of organismal ecology. The result is an overall signal of homogeneous selection due to rapid within-clade microdiversification caused by variable selection. It is unknown whether other systems experience this dynamic, and we encourage future work evaluating the transferability of our results.
Assuntos
Microbiota , Áreas Alagadas , Filogenia , Regiões Antárticas , Bactérias/genéticaRESUMO
Natural grasslands provide a valuable resource for livestock grazing. In many parts of South America, legume overseeding and P fertilization are commonly used to enhance primary productivity. The effect of this practice on the plant community is well established. However, how this management regime affects the soil microbiome is less known. Here, to contribute to filling this knowledge gap, we analyzed the effect of Lotus subbiflorus overseeding, together with P fertilization, on soil microbial community diversity and activity in the Uruguayan Pampa region. The results showed that plant communities in the natural grassland paddocks significantly differed from those of the managed paddocks. In contrast, neither microbial biomass and respiration nor microbial diversity was significantly affected by management, although the structure of the bacterial and fungal communities were correlated with those of the plant communities. AM Fungi relative abundance, as well as several enzyme activities, were significantly affected by management. This could have consequences for the C, N, and P content of SOM in these soils, which in turn might affect SOM degradation.
RESUMO
As functional traits are conserved at different phylogenetic depths, the ability to detect community assembly processes can be conditional on the phylogenetic resolution; yet most previous work quantifying their influence has focused on a single level of phylogenetic resolution. Here, we have studied the ecological assembly of bacterial communities from an Antarctic wetland complex, applying null models across different levels of phylogenetic resolution (i.e. clustering ASVs into OTUs with decreasing sequence identity thresholds). We found that the relative influence of the community assembly processes varies with phylogenetic resolution. More specifically, selection processes seem to impose stronger influence at finer (100% sequence similarity ASV) than at coarser (99%-97% sequence similarity OTUs) resolution. We identified environmental features related with the ecological processes and propose a conceptual model for the bacterial community assembly in this Antarctic ecosystem. Briefly, eco-evolutionary processes appear to be leading to different but very closely related ASVs in lotic, lentic and terrestrial environments. In all, this study shows that assessing community assembly processes at different phylogenetic resolutions is key to improve our understanding of microbial ecology. More importantly, a failure to detect selection processes at coarser phylogenetic resolution does not imply the absence of such processes at finer resolutions.
Assuntos
Ecossistema , Áreas Alagadas , Regiões Antárticas , Bactérias/genética , FilogeniaRESUMO
Bacteria play critical roles in peatland ecosystems. However, very little is known of how habitat heterogeneity affects the structure of the bacterial communities in these ecosystems. Here, we used amplicon sequencing of the 16S rRNA and nifH genes to investigate phylogenetic diversity and bacterial community composition in three different sub-Antarctic peat bog aquatic habitats: Sphagnum magellanicum interstitial water, and water from vegetated and non-vegetated pools. Total and putative nitrogen-fixing bacterial communities from Sphagnum interstitial water differed significantly from vegetated and non-vegetated pool communities (which were colonized by the same bacterial populations), probably as a result of differences in water chemistry and biotic interactions. Total bacterial communities from pools contained typically aquatic taxa, and were more dissimilar in composition and less species rich than those from Sphagnum interstitial waters (which were enriched in taxa typically from soils), probably reflecting the reduced connectivity between the former habitats. These results show that bacterial communities in peatland water habitats are highly diverse and structured by multiple concurrent factors.
Assuntos
Bactérias/genética , Ecossistema , Microbiologia Ambiental , Sphagnopsida/microbiologia , Regiões Antárticas , Argentina , Bactérias/classificação , Proteínas de Bactérias/genética , Geografia , Oxirredutases/genética , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Solo , Especificidade da EspécieRESUMO
Bacterioplankton communities inhabiting peatlands have the potential to influence local ecosystem functions. However, most microbial ecology research in such wetlands has been done in ecosystems (mostly peat soils) of the Northern Hemisphere, and very little is known of the factors that drive bacterial community assembly in other regions of the world. In this study, we used high-throughput sequencing to analyse the structure of the bacterial communities in five pools located in a sub-Antarctic peat bog (Tierra del Fuego, Argentina), and tested for relationships between bacterial communities and environmental conditions. Bacterioplankton communities in peat bog pools were diverse and dominated by members of the Proteobacteria, Actinobacteria, Bacteroidetes and Verrucomicrobia. Community structure was largely explained by differences in hydrological connectivity, pH and nutrient status (ombrotrophic versus minerotrophic pools). Bacterioplankton communities in ombrotrophic pools showed phylogenetic clustering, suggesting a dominant role of deterministic processes in shaping these assemblages. These correlations between habitat characteristics and bacterial diversity patterns provide new insights into the factors regulating microbial populations in peatland ecosystems.
Assuntos
Bactérias/classificação , Bactérias/isolamento & purificação , Biota , Microbiologia Ambiental , Regiões Antárticas , Argentina , Análise por Conglomerados , Sequenciamento de Nucleotídeos em Larga Escala , Dados de Sequência Molecular , Filogenia , Homologia de SequênciaRESUMO
During a study of the 'tunta' (frozen-dry potato) production process in Peru, a bacterial strain, LMT03(T), was isolated from the straw grass in which the potatoes are dried. This strain was classified into the genus Pseudomonas on the basis of the 16S rRNA gene sequence analysis, and is most closely related to Pseudomonas argentinensis CH01(T) with 99.3â% identity in this gene and 96â%, 92â% and 86â% identities in rpoB, rpoD and gyrB genes, respectively. Strain LMT03(T) has a single polar flagellum, like other related yellow-pigment-producing pseudomonads. The major quinone is Q-9. The major fatty acids are C18â:â1ω7c in summed feature 8 (40.82â%), C16â:â1ω6c/C16â:â1ω6c in summed feature 3 (23.72â%) and C16â:â0 (15.20â%). The strain produces oxidase but it does not produce gelatinase, indole, urease, arginine dihydrolase or ß-galactosidase. Catalase production was very weak after 28 and 48 h incubation on nutrient agar medium. Nitrate reduction is negative. It does not hydrolyse aesculin. The DNA G+C content is 57.8 mol%. DNA-DNA hybridization results showed lower than 52â% relatedness with respect to the type strain of P. argentinensis, CH01(T). These results, together with other phenotypic characteristics, support the definition of a novel species within the genus Pseudomonas, for which the name Pseudomonas punonensis sp. nov. is proposed. The type strain is LMT03(T) (â=âLMG 26839(T)â=âCECT 8089(T)).
Assuntos
Filogenia , Poaceae/microbiologia , Pseudomonas/classificação , Técnicas de Tipagem Bacteriana , Composição de Bases , DNA Bacteriano/genética , Ácidos Graxos/análise , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Oxirredutases/metabolismo , Peru , Pseudomonas/genética , Pseudomonas/isolamento & purificação , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Microbiologia do Solo , Solanum tuberosumRESUMO
In this work we analysed different chromosomal and symbiotic markers in rhizobial strains nodulating Lupinus albus (white lupin) in several continents. Collectively the analysis of their rrs and atpD genes, and 16S-23S intergenic spacers (ITS), showed that they belong to at least four chromosomal lineages within the genus Bradyrhizobium. Most isolates from the Canary Islands (near to the African continent) grouped with some strains isolated on mainland Spain and were identified as Bradyrhizobium canariense. These strains are divided into two ITS subgroups coincident with those previously described from isolates nodulating Ornithopus. The remaining strains isolated on mainland Spain grouped with most isolates from Chile (American continent) forming a new lineage related to Bradyrhizobium japonicum. The strains BLUT2 and ISLU207 isolated from the Canary Islands and Chile, respectively, formed two new lineages phylogenetically close to different species of Bradyrhizobium depending on the marker analyzed. The analysis of the nodC gene showed that all strains nodulating L. albus belong to the biovar genistearum; nevertheless they form four different nodC lineages of which lineage C is at present exclusively formed by L. albus endosymbionts isolated from different continents.
Assuntos
Bradyrhizobium/classificação , Bradyrhizobium/fisiologia , Lupinus/microbiologia , Lupinus/fisiologia , Nodulação , Simbiose , Proteínas de Bactérias/genética , Bradyrhizobium/genética , Chile , Análise por Conglomerados , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , DNA Espaçador Ribossômico , Dados de Sequência Molecular , N-Acetilglucosaminiltransferases/genética , Filogenia , RNA Ribossômico 16S/genética , RNA Ribossômico 23S/genética , Análise de Sequência de DNA , EspanhaRESUMO
Bacteria have developed mechanisms that allow them maintaining cell viability during starvation and resuming growth when nutrients become available. Among these mechanisms are adaptive mutations and phase variation, which are often associated with DNA rearrangements. Azospirillum brasilense is a Gram-negative, nitrogen-fixing, plant growth-promoting rhizobacterium. Here we report phenotypic variants of A. brasilense that were collected after exposure to prolonged starvation or after re-isolation from maize roots. The variants differed in several features from the parental strains, including pigmentation, aggregation ability, EPS amount and composition and LPS structure. One of the phenotypic variants, overproducing EPS and showing an altered LPS structure, was further characterized and showed differential response to several stresses and antibiotics relative to its parental strain. Characterization of the variants by repetitive-PCR revealed that phenotypic variation was often associated with DNA rearrangements.
RESUMO
Azospirillum brasilense is a plant root-colonizing bacterium that exerts beneficial effects on the growth of many agricultural crops. Extracellular polysaccharides of the bacterium play an important role in its interactions with plant roots. The pRhico plasmid of A. brasilense Sp7, also named p90, carries several genes involved in synthesis and export of cell surface polysaccharides. We generated two Sp7 mutants impaired in two pRhico-located genes, noeJ and noeL, encoding mannose-6-phosphate isomerase and GDP-mannose 4,6-dehydratase, respectively. Our results demonstrate that in A. brasilense Sp7, noeJ and noeL are involved in lipopolysaccharide and exopolysaccharide synthesis. noeJ and noeL mutant strains were significantly altered in their outer membrane and cytoplasmic/periplasmic protein profiles relative to the wild-type strain. Moreover, both noeJ and noeL mutations significantly affected the bacterial responses to several stresses and antimicrobial compounds. Disruption of noeL, but not noeJ, affected the ability of the A. brasilense Sp7 to form biofilms. The pleiotropic alterations observed in the mutants could be due, at least partially, to their altered lipopolysaccharides and exopolysaccharides relative to the wild-type.
Assuntos
Azospirillum brasilense/genética , Azospirillum brasilense/metabolismo , Genes Bacterianos , Polissacarídeos Bacterianos/biossíntese , Sequência de Bases , Biofilmes/crescimento & desenvolvimento , DNA Bacteriano/genética , Hidroliases/genética , Hidroliases/metabolismo , Lipopolissacarídeos/biossíntese , Manose-6-Fosfato Isomerase/genética , Manose-6-Fosfato Isomerase/metabolismo , Mutação , Plasmídeos/genética , Estresse FisiológicoRESUMO
The response regulatory gene flcA controls the differentiation process of Azospirillum brasilense from vegetative state to cyst-like forms, both in culture and in association with plants. In contrast to the wild type parental strain Sp7, strain Sp72002, a Tn5 induced flcA(-) mutant, does not aggregate, does not differentiate from motile, vibroid cells into nonmotile, cyst-like forms and lacks some of the exopolysaccharide material on its cell surface. Here we aimed to identify differentially expressed genes whose expression could be modulated by flcA. Using cDNA-amplified fragment length polymorphism, we detected 81 transcript-derived fragments showing differential expression during exponential growth phase in an aggregation-inducing medium containing high C : N ratio. The fragments were sequenced and analyzed, and expression of ten genes encoding known proteins was compared between the two strains by reverse transcriptase polymerase chain reaction-(RT-PCR). RT-PCR analyses confirmed the differential patterns observed by cDNA-AFLP in nine of those genes. Among them are genes homologous to nodQ, involved in sulfation; narK, involved in nitrite/nitrate transport, and flp, involved in autoaggregation; as well as genes encoding a biopolymer transport protein, and the signal recognition particle. This work demonstrates the usefulness of the cDNA-AFLP approach to reveal genes that are differentially expressed during aggregation in Azospirillum brasilense and provides insights into the aggregation process of this bacterium.
Assuntos
Azospirillum brasilense/genética , Azospirillum brasilense/fisiologia , Proteínas de Bactérias/genética , Regulação Bacteriana da Expressão Gênica/genética , Polissacarídeos Bacterianos/genética , Fatores de Transcrição/genética , Sequência de Aminoácidos , DNA Complementar , Floculação , Perfilação da Expressão Gênica , Dados de Sequência Molecular , Técnicas de Amplificação de Ácido Nucleico , Polimorfismo Genético , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
A Gram-negative, non-spore-forming bacterial strain with the ability to solubilize highly insoluble phosphatic minerals was isolated from a high-phosphorous iron ore from Minas Gerais State, Brazil. This strain, designated FeGl01(T), was subjected to a polyphasic taxonomic investigation. Comparative 16S rRNA gene sequence analysis indicated that it formed a distinct phylogenetic lineage within the genus Burkholderia together with several other species of the genus, e.g. Burkholderia sacchari, Burkholderia tropica and Burkholderia unamae. Partial nucleotide sequencing and analysis of the recA gene roughly corroborated the phylogenetic position of strain FeGl01(T) within the genus Burkholderia. The chemotaxonomic properties of strain FeGl01(T), such as ubiquinone Q-8 as the predominant quinone system and C(16 : 0), C(17 : 0) cyclo, C(18 : 1)omega7c and C(19 : 0)omega8c cyclo as the major fatty acids, were also consistent with its classification within the genus Burkholderia. DNA-DNA hybridization experiments between strain FeGl01(T) and the type strains of B. unamae, B. sacchari and B. tropica yielded reassociation values of 40 % or lower, which, together with qualitative and quantitative differences in fatty acid composition and with differences in several phenotypic traits, support the separation of the new isolate from the phylogenetically most closely related species. Therefore, it is suggested that strain FeGl01(T) represents a novel species of the genus Burkholderia, for which the name Burkholderia ferrariae sp. nov. is proposed. The type strain is FeGl01(T) (=LMG 23612(T)=CECT 7171(T)=DSM 18251(T)).