RESUMO
The halotolerant yeast Debaryomyces hansenii belongs to the CTG-Ser1 clade of fungal species that use the CUG codon to translate as leucine or serine. The ambiguous decoding of the CUG codon is relevant for expanding protein diversity, but little is known about the role of leucine-serine ambiguity in cellular adaptations to extreme environments. Here, we examine sequences and structures of tRNACAG from the CTG-Ser1 clade yeasts, finding that D. hansenii conserves the elements to translate ambiguously. Then, we show that D. hansenii has tolerance to conditions of salinity, acidity, alkalinity, and oxidative stress associated with phenotypic and ultrastructural changes. In these conditions, we found differential expression in both the logarithmic and stationary growth phases of tRNASer, tRNALeu, tRNACAG, LeuRS, and SerRS genes that could be involved in the adaptive process of this yeast. Finally, we compare the proteomic isoelectric points and hydropathy profiles, detecting that the most important variations among the physicochemical characteristics of D. hansenii proteins are in their hydrophobic and hydrophilic interactions with the medium. We propose that the ambiguous translation, i.e., leucylation or serynation, on translation of the CUG-encoded residues, could be linked to adaptation processes in extreme environments.
RESUMO
A number of heterocytous, mat-forming, tapering cyanobacteria in Rivulariaceae have recently been observed in both the Atlantic and Pacific coasts in the rocky intertidal and supratidal zones. These belong to the genera Nunduva, Kyrtuthrix, and Phyllonema and have been the subject of several recent studies. Herein, two new species of Nunduva (N. komarkovae and N. sanagustinensis) and two new species of Kyrtuthrix (K. munecosensis and K. totonaca) are characterized and described from the coasts of Mexico. Genetic separation based on the 16S-23S ITS region was pronounced (>10% in all comparisons). Morphological differences between all existing species in these two genera were also observed, but the group is morphologically complex, and these taxa are considered pseudocryptic. Nunduva and Kyrtuthrix remain morphologically and phylogenetically separate even with the addition of new species. However, how long will this remain the case? Many new genera and species of cyanobacteria have recently been described. Will the taxonomy of cyanobacteria eventually become saturated? Will we start to see multiple populations for the same cryptic species, or will future taxonomists collapse multiple species into fewer species, or multiple genera into single genera. The description of even more Nunduva and Kyrtuthrix species causes us to pause and evaluate the future of cyanobacterial taxonomy. These same questions are faced by algal taxonomists studying other phyla, and the resolution may ultimately be similar.
Assuntos
Cianobactérias , Cianobactérias/genética , México , Filogenia , RNA Ribossômico 16SRESUMO
Two untapered, heterocytous species were observed and collected from the intertidal and supratidal zones of the Mexican coastline of the Pacific Ocean near Oaxaca and from the Gulf of Mexico. These populations were highly similar in morphology to the freshwater taxon Petalonema incrustans in the Scytonemataceae. However, 16S rRNA sequence data and phylogenetic analysis indicated that they were sister taxa to the epiphyllic, Brazilian species Phyllonema aveceniicola in the Rivulariaceae, described from culture material. While genetic identity between the two new species was high, they differed significantly in morphology, 16S rRNA gene sequence identity, and sequence and structure of the 16S-23S ITS region. Their morphology differed markedly from the generitype of the previously monotypic Phyllonema, which has tapered, heteropolar, single-false branched trichomes with very thin or absent sheath. The two new species, Phyllonema ansata and Phyllonema tangolundensis, described from both culture and environmental material, have untapered, isopolar, geminately false branched trichomes with thick, lamellated sheaths, differences so significant that the species would not be placed in Phyllonema without molecular corroboration. The morphological differences are so significant that a formal emendation of the genus is required. These taxa provide a challenge to algal taxonomy because the morphological differences are such that one would logically conclude that they represent different genera, but the phylogenetic evidence for including them all in the same genus is conclusive. This conclusion is counter to the current trend in algal taxonomy in which taxa with minor morphological differences have been repeatedly placed in separate genera based primarily upon DNA sequence evidence.