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Plominsky, A. M., Henriquez-Castillo, C., Delherbe, N., Podell, S., Ramirez-Flandes, S., Ugalde, J. A., et al. (2018). Distinctive Archaeal Composition of an Artisanal Crystallizer Pond and Functional Insights Into Salt-Saturated Hypersaline Environment Adaptation. Front. Microbiol., 9, 13 pp.
Abstract: Hypersaline environments represent some of the most challenging settings for life on Earth. Extremely halophilic microorganisms have been selected to colonize and thrive in these extreme environments by virtue of a broad spectrum of adaptations to counter high salinity and osmotic stress. Although there is substantial data on microbial taxonomic diversity in these challenging ecosystems and their primary osmoadaptation mechanisms, less is known about how hypersaline environments shape the genomes of microbial inhabitants at the functional level. In this study, we analyzed the microbial communities in five ponds along the discontinuous salinity gradient from brackish to salt-saturated environments and sequenced the metagenome of the salt (halite) precipitation pond in the artisanal Cahuil Solar Saltern system. We combined field measurements with spectrophotometric pigment analysis and flow cytometry to characterize the microbial ecology of the pond ecosystems, including primary producers and applied metagenomic sequencing for analysis of archaeal and bacterial taxonomic diversity of the salt crystallizer harvest pond. Comparative metagenomic analysis of the Cahuil salt crystallizer pond against microbial communities from other salt-saturated aquatic environments revealed a dominance of the archaeal genus Halorubrum and showed an unexpectedly low abundance of Haloquadratum in the Cahuil system. Functional comparison of 26 hypersaline microbial metagenomes revealed a high proportion of sequences associated with nucleotide excision repair, helicases, replication and restriction-methylation systems in all of them. Moreover, we found distinctive functional signatures between the microbial communities from salt-saturated (>30% [w/v] total salinity) compared to sub-saturated hypersaline environments mainly due to a higher representation of sequences related to replication, recombination and DNA repair in the former. The current study expands our understanding of the diversity and distribution of halophilic microbial populations inhabiting salt-saturated habitats and the functional attributes that sustain them.
Trefault, N., Guzman, L., Perez, H., Godoy, M., & Gonzalez, B. (2009). Involvement of several transcriptional regulators in the differential expression of tfd genes in Cupriavidus necator JMP134. Int. Microbiol., 12(2), 97–106.
Abstract: Cupriavidus necator JMP134 has been extensively studied because of its ability to degrade chloroaromatic compounds, including the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 3-chlorobenzoic acid (3-CB), which is achieved through the pJP4-encoded chlorocatechol degradation gene clusters: tfdC(I)D(I)E(I)F(I), and tfdD(II)C(II)E(II)F(II). The present work describes a different tfd-genes expression profile depending on whether C. necator cells were induced with 2,4-D or 3-CB. By contrast, in vitro binding assays of the Purified transcriptional activator TfdR showed similar binding to both tfd intergenic regions; these results were confirmed by in Vivo Studies of the expression of transcriptional lacZ fusions for these intergenic regions. Experiments aimed at investigating whether other pJP4 plasmid or chromosomal regulatory proteins could contribute to the differences in the response of both tfd promoters to induction by 2,4-D and 3-CB showed that the transcriptional regulators from the benzoate degradation pathway, CatR I and CatR2, affected 3-CB- and 2,4-D-related growth capabilities. It was also determined that the ISJP4-interrupted protein TfdT decreased growth on 3-CB. In addition, an ORF with 34% amino acid identity to IcIR-type transcriptional regulator members and located near the tfd(II) gene cluster module was shown to modulate the 2,4-D growth capability. Taken together, these results Suggest that tfd transcriptional regulation in C. necator JMP134 is far more complex than previously thought and that it involves proteins from different transcriptional regulator families. [Int Microbiol 2009; 12(2):97-106]