Different strategies of osmoadaptation in the closely related marine myxobacteria Enhygromyxa salina SWB007 and Plesiocystis pacifica SIR-1

Abstract

Only a few myxobacteria are known to date that are classified as marine, owing to their salt dependency. In this study, the salt tolerance mechanism of these bacteria was investigated. To this end, a growth medium was designed in which the mutated Escherichia coli strain BKA13 served as sole food source for the predatory, heterotrophic myxobacteria. This enabled measurement of the osmolytes without any background and revealed that the closely related strains Enhygromyxa salina SWB007 and Plesiocystis pacifica SIR-1 developed different strategies to handle salt stress. Ple. pacifica SIR-1, which was grown between 1 and 4 % NaCl, relies solely on the accumulation of amino acids, while Enh. salina SWB007, which was grown between 0.5 and 3 % NaCl, employs, besides betaine, hydroxyectoine as the major compatible solute. In accordance with this analysis, only in the latter strain was a locus identified that codes for genes corresponding to the biosynthesis of betaine, ectoine and hydroxyectoine.

Diversity of Bacillus-like bacterial community in the rhizospheric and non-rhizospheric soil of halophytes (Salsola stocksii and Atriplex amnicola), and characterization of osmoregulatory genes in halophilic Bacilli

“…Moderate halophilic bacteria use 'compatible solute' strategy to cope with their external environments by accumulating small, highly water soluble organic compounds such as glycine betaine, proline, glutamine, ectoine, potassium and glutamic acid (Moghaddam et al 2016). Ectoine, a cyclic tetrahydropyrimidine is used as an osmolyte in halotolerant and halophilic bacteria.…”

Metabolic and Biosynthetic Diversity in Marine Myxobacteria

“…To combat this stress, bacteria have developed several strategies, mostly focused on the accumulation of either organic compounds called “osmolytes” or inorganic ions within their cells [ 73 ]. From the plethora of known organic osmolytes [ 74 ], myxobacterial strains studied so far are thought to utilize at least the organic form of osmoregulation, with glutamate, betaine, and hydroxyectoine playing a major role [ 75 ]. The combined betaine or hydroxyectoine biosynthetic gene cluster has been found in E. salina SWB007 (accession code KU237243) [ 75 ].…”

“…From the plethora of known organic osmolytes [ 74 ], myxobacterial strains studied so far are thought to utilize at least the organic form of osmoregulation, with glutamate, betaine, and hydroxyectoine playing a major role [ 75 ]. The combined betaine or hydroxyectoine biosynthetic gene cluster has been found in E. salina SWB007 (accession code KU237243) [ 75 ]. While the hydroxyectoine component of the combined betaine or hydroxyectoine gene cluster is also encoded as a 6-gene operon in the closely related E. salina SWB005 (accession codes for the genes ENSA5_19400-ENSA5_19450), the betaine component is apparently missing.…”

“…Occasionally, genes encoding for ectoine-like products could be found even in terrestrial myxobacteria, such as the ectoine synthase in Stigmatella aurantiaca DW4/3-1 (STAUR_RS25940), highlighting the difficulty in making a clear division between the two sets of myxobacteria and their lifestyles. On the other hand, osmoregulation in P. pacifica SIR-1 seems to be mostly dependent on accumulation of the unmodified amino acids glutamate, glycine, and proline as osmolytes, since experiments have shown no use of betaine, ectoine, or hydroxyectoine as osmotic agents in this bacterium [ 75 ].…”

Marine-derived myxobacteria of the suborder Nannocystineae: An underexplored source of structurally intriguing and biologically active metabolites

“…For instance, E. salina SWB007 biosynthesizes the osmolytes betaine, ectoine, and especially hydroxyectoine under high salt concentrations. In contrast, P. pacifica SIR-1 does not synthesize specialized compatible solutes; this strain rather accumulates amino acids as osmoprotective agents [ 17 ]. Of course, further mechanisms may be involved for osmoregulation, but are not known to date for myxobacteria.…”