Life at high salt concentrations, intracellular KCl concentrations, and acidic proteomes

Abstract

Extremely halophilic microorganisms that accumulate KCl for osmotic balance (the Halobacteriaceae, Salinibacter) have a large excess of acidic amino acids in their proteins. This minireview explores the occurrence of acidic proteomes in halophiles of different physiology and phylogenetic affiliation. For fermentative bacteria of the order Halanaerobiales, known to accumulate KCl, an acidic proteome was predicted. However, this is not confirmed by genome analysis. The reported excess of acidic amino acids is due to a high content of Gln and Asn, which yield Glu and Asp upon acid hydrolysis. The closely related Halorhodospira halophila and Halorhodospira halochloris use different strategies to cope with high salt. The first has an acidic proteome and accumulates high KCl concentrations at high salt concentrations; the second does not accumulate KCl and lacks an acidic proteome. Acidic proteomes can be predicted from the genomes of some moderately halophilic aerobes that accumulate organic osmotic solutes (Halomonas elongata, Chromohalobacter salexigens) and some marine bacteria. Based on the information on cultured species it is possible to understand the pI profiles predicted from metagenomic data from hypersaline environments.

Comparative genomics reveals adaptations of a halotolerant thaumarchaeon in the interfaces of brine pools in the Red Sea

“…Although there is no data of whether ectoine is excreted by thaumarchaea, the potentially one-way-only biosynthesis pathway implies that there is no ectoine turnover; therefore, very little energy would be invested subsequent to its production. 16S rRNA gene-based analyses indicate that thaumarchaea are part of the metabolically active prokaryotic community of the BSI (Yakimov et al, 2007), where the capacity to fix dissolved inorganic CO 2 was also higher than in the bathypelagic waters (Yakimov et al, 2007;2013). The high dissolved inorganic CO 2 -incorporating activity coincidentally matched profiles of amoA-like mRNA gene transcripts (Yakimov et al, 2007), suggesting that most of the AOA are autotrophic.…”

“…Niche adaptations of a halotolerant thaumarchaeon D Kamanda Ngugi et al tend to have acidic residues on their surface and show optimal activity and stability at high salinity (Paul et al, 2008;Oren, 2013). In contrast, moderate halophiles, which grow at 5-20% NaCl (Kanekar et al, 2012), keep their intracellular ionic concentrations at low levels and use organic solutes to produce the necessary osmotic balance without dramatically altering the structure of their proteome (Oren, 2011).…”

Multiple Osmotic Stress Responses in Acidihalobacter prosperus Result in Tolerance to Chloride Ions

“…Given the sensitivity of acidophiles to Cl − , those to be utilized in biomining with seawater must be able to tolerate the dual stresses of low pH and high Cl − concentrations. Adaptations to high salt concentrations exhibited by halophilic/halotolerant microorganisms include: (i) accumulation of cytoplasmic potassium; production of osmo-protectants in the cytoplasm to maintain an even turgor pressure inside and outside of the cell; (ii) alterations in the cell membrane, and (iii) an increase in acidic amino acids on the surface of proteins resulting in an elevated negative potential that aids in keeping the protein in solution (Shivanand and Mugeraya, 2011; Oren, 2013; Graziano and Merlino, 2014). In addition, changes in the surface electrostatic potential of a halophilic/halotolerant electron transport proteins is likely to affect their interactions with redox partners as has been shown for the interaction of the blue copper protein amicyanin with methylamine dehydrogenase (Ma et al, 2007; Choi et al, 2011).…”

From Metagenomics to Pure Culture: Isolation and Characterization of the Moderately Halophilic Bacterium Spiribacter salinus gen. nov., sp. nov

“…Most microbiological studies in these extreme environments have been carried out on aquatic habitats, especially saline lakes and marine salterns, which are used for the commercial production of salt by evaporation of seawater (1,2). One of the salterns that has been most extensively studied during the last 30 years is located in Santa Pola, Alicante, Spain; these studies have been based on culture-dependent (3)(4)(5) as well as culture-independent (6-11) techniques.…”