Effects of salinity on the cellular physiological responses of Natrinema sp. J7-2

Abstract

The halophilic archaea (haloarchaea) live in hyersaline environments such as salt lakes, salt ponds and marine salterns. To cope with the salt stress conditions, haloarchaea have developed two fundamentally different strategies: the "salt-in" strategy and the "compatible-solute" strategy. Although investigation of the molecular mechanisms underlying the tolerance to high salt concentrations has made outstanding achievements, experimental study from the aspect of transcription is rare. In the present study, we monitored cellular physiology of Natrinema sp. J7-2 cells incubated in different salinity media (15%, 25% and 30% NaCl) from several aspects, such as cellular morphology, growth, global transcriptome and the content of intracellular free amino acids. The results showed that the cells were polymorphic and fragile at a low salt concentration (15% NaCl) but had a long, slender rod shape at high salt concentrations (25% and 30% NaCl). The cells grew best in 25% NaCl, mediocre in 30% NaCl and struggled in 15% NaCl. An RNA-seq analysis revealed differentially expressed genes (DEGs) in various salinity media. A total of 1,148 genes were differentially expressed, consisting of 719 DEGs (348 up-regulated and 371 down-regulated genes) between cells in 15% vs 25% NaCl, and 733 DEGs (521 up-regulated and 212 down-regulated genes) between cells in 25% vs 30% NaCl. Moreover, 304 genes were commonly differentially expressed in both 15% vs 25% and 25% vs30% NaCl. The DEGs were enriched in different KEGG metabolic pathways, such as amino acids, glycerolipid, ribosome, nitrogen, protoporphyrin, porphyrin and porhiniods. The intracellular predominant free amino acids consisted of the glutamate family (Glu, Arg and Pro), aspartate family (Asp) and aromatic amino acids (Phe and Trp), especially Glu and Asp.

Hundreds of novel composite genes and chimeric genes with bacterial origins contributed to haloarchaeal evolution

“…2 ). None of the composite gene families identified in this study were significantly regulated in response to salt concentration in previous transcriptome studies [ 35 – 37 ]. However, the predicted function of these families suggests that their acquisition may have been crucial to the adaptation of haloarchaea to hypersaline environments and the salt-in strategy.…”

Differential Gene Expression in Response to Salinity and Temperature in a Haloarcula Strain from Great Salt Lake, Utah

“…High salinity has been reported to stimulate intracellular accumulation of amino acids in haloarchaea [ 74 ], by affecting gene regulation of uptake and transporter proteins or amino acid biosynthesis pathways. However, we noted four genes related to osmophily were repressed or downregulated in the high salinity optimal conditions: (1) the gene for amino acid permease that allows amino acid uptake; (2) the phosphoserine phosphatase gene, which is involved in the biosynthesis of serine and ion transport [ 75 ]; (3) the phenyl acetyl CoA ligase gene, which is involved in the catabolism of phenyl acetic acid [ 73 ]; and (4) an iron ABC (ATP binding cassette) transporter, which also plays an important role in substrate uptake [ 76 ]. Others have noted similar observations regarding genes involved in osmoregulation being upregulated in lower salinities and repressed in higher salinities.…”

The Primary Antisense Transcriptome of Halobacterium salinarum NRC-1

“…Regular strand-specific comparative transcriptome analysis (RNA-seq) is available for other halophiles but only one, in Natrinema sp. J7-2 (formerly H. salinarum J7), focused on salinity adaptation questions [87]. Since regular RNA-seq does not have the resolution power to pinpoint aTSS as dRNA-seq, we inspected differential read distributions between Natrinema sp.…”