Project description:Abstract Hypersaline lakes are of immense ecological value as they niche some of the most exclusive extremophilic communities dominated by bacterial and archaeal domains, with few eukaryotic algal representatives. A handful reports describe Picocystis as a key primary producer with great production rates in extremely saline habitats. An extremely haloalkaliphilic picoalgal strain, Picocystis salinarum SLJS6 isolated from hypersaline lake Sambhar, Rajasthan, India, grew robustly in an enriched soda lake medium containing mainly Na2CO3, 50 g/L; NaHCO3, 50g/L, NaCl, 50 g/L (salinity ≈150 ‰) at pH 10. To elucidate the molecular basis of such tolerance to high inorganic carbon and NaCl concentrations, a high-throughput LFQ (label-free quantitation) based quantitative proteomics approach was applied. Out of the total 383 proteins identified in treated samples, 225 were Differentially abundant proteins (DAPs), of which 150 were statistically significant (p value <0.05) including 70 upregulated and 64 downregulated proteins after 3 days of salt and alkalinity stress. Gene ontology analysis was done to annotate and classify the DAPs into functional groups. The analysis linked most DAPs to photosynthesis, oxidative phosphorylation, glucose metabolism and ribosomal structural components envisaging that photosynthesis and ATP synthesis were central to the alkalinity-salinity response. Key components of photosynthetic machinery like photosystem reaction centres, ATP synthase, Rubisco, Fructose-bisphosphate aldolase were significantly upregulated. Enzymes Peptidylprolyl isomerases (PPIase), important for correct protein folding showed remarkable marked-up regulation along with other chaperon proteins indicating their role in alleviating stress. Enhanced photosynthetic activity exhibited by Picocystis salinarum in highly saline-alkaline condition is noteworthy as photosynthesis is suppressed by salt stress in most photosynthetic organisms. This study provided the first evidence of a tailored regulatory mechanism of alkalinity and salt tolerance in extremophilic alga P. salinarum, potentially unraveling the basis of resilience in this not so known organism and paves the way for a promising future production host and model or¬ganism for deciphering the molecular mechanisms of os¬motic stress responses.
Project description:To investigate the contribution of ribonucleases to post-transcriptional regulation of mRNA levels, we examined the fitness consequences and gene expression changes of ribonuclease mutants in the extreme halophilic archaeon Halobacterium salinarum NRC-1. H. salinarum NRC-1 is known to use a large repertoire of environment-specific transcriptional regulatory programs, which may be complemented by post-transcriptional regulatory mechanisms. Homology searches identified putative RNase genes in H. salinarum NRC-1 that include likely orthologs for RNases found in prokaryotic and eukaryotic lineages. The VNG2099C protein sequence is significantly similar (e = 2 x 10^-34) to the sequence of the rat liver perchloric acid-soluble protein (L-PSP), which has been shown to have endoribonuclease activity in vitro (Morishita et al 1999). The VNG2099C protein, like the archaeal Sulfolobus tokodaii YjgF/L-PSP protein for which a crystal structure has been solved (Miyakawa et al 2006), shares conservation of residues proposed to constitute the active site of the rat protein. The purpose of this gene expression study was to investigate the role of the putative endoribonuclease VNG2099C on gene regulation.