Osmoadaptation mechanisms in prokaryotes: distribution of compatible solutes

Microorganisms respond to osmotic stress mostly by accumulating compatible solutes, either by uptake from the medium or by de novo synthesis. These osmotically active molecules preserve the positive turgor pressure required for cell division. The diversity of compatible solutes is large but falls into a few major chemical categories; they are usually small organic molecules such as amino acids or their derivatives, and carbohydrates or their derivatives. Some are widely distributed in nature while others seem to be exclusively present in specific groups of organisms. This review discusses the diversity and distribution of known classes of compatible solutes found in prokaryotes as well as the increasing knowledge of the genes and pathways involved in their synthesis. The alternative roles of some archetypal compatible solutes not subject to osmoregulatory constraints are also discussed (AU)

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Organic solutes in Rubrobacter xylanophilus: the first example of di-myo-inositol-phosphate in a thermophile.

The thermophilic and halotolerant nature of Rubrobacter xylanophilus led us to investigate the accumulation of compatible solutes in this member of the deepest lineage of the Phylum Actinobacteria. Trehalose and mannosylglycerate (MG) were the major compounds accumulated under all conditions examined, including those for optimal growth. The addition of NaCl to a complex medium and a defined medium had a slight or negligible effect on the accumulation of these compatible solutes. Glycine betaine, di-myo-inositol-phosphate (DIP), a new phosphodiester compound, identified as di-N-acetyl-glucosamine phosphate and glutamate were also detected but in low or trace levels. DIP was always present, except at the highest salinity examined (5% NaCl) and at the lowest temperature tested (43 degrees C). Nevertheless, the levels of DIP increased with the growth temperature. This is the first report of MG and DIP in an actinobacterium and includes the identification of the new solute di-N-acetyl-glucosamine phosphate.

Diversity and biosynthesis of compatible solutes in hyper/thermophiles / Diversidad y biosíntesis de solutos compatibles en hiper/termófilos

The accumulation of compatible solutes, either by uptake from the medium or by de novo synthesis, is a general response of microorganisms to osmotic stress. The diversity of compatible solutes is large but falls into a few major chemical categories, such as carbohydrates or their derivatives and amino acids or their derivatives. This review deals with compatible solutes found in thermophilic or hyperthermophilic bacteria and archaea that have not been commonly identified in microorganisms growing at low and moderate temperatures. The response to NaCl stress of Thermus thermophilus is an example of how a thermophilic bacterium responds to osmotic stress by compatible solute accumulation. Emphasis is made on the pathways leading to the synthesis of mannosylglycerate and glucosylglycerate that have been recently elucidated in several hyper/thermophilic microorganisms. The role of compatible solutes in the thermoprotection of these fascinating microorganisms is also discussed (AU)

La acumulación de solutos compatibles por incorporación del medio o mediante síntesis de novo es una respuesta general de los microorganismos al estrés osmótico. La diversidad de solutos compatibles es grande pero cae en unas pocas categorías químicas importantes tales como carbohidratos o sus derivados y aminoácidos o sus derivados. Esta revisión trata de los solutos compatibles encontrados en bacterias y en arqueas termófilas o hipertermófilas y que no se han identificado en microorganismos que viven a temperaturas bajas y moderadas. La respuesta de Thermus thermophilus al estrés causado por el NaCl es un ejemplo de cómo responde una bacteria termófila al estrés osmótico mediante la acumulación de solutos compatibles. Se destacan las vías que conducen a la síntesis del manosilglicerato y del glucosilglicerato que se han descubierto recientemente en varios microorganismos hiper/thermófilos. Se describe también la función de los solutos compatibles en la termoprotección de estos apasionantes microorganismos (AU)

Characterization of glycolipids from Meiothermus spp.

Thin-layer chromatographic analysis of the polar lipids of Meiothermus strains revealed two glycolipid bands with similar chromatographic mobility to the major glycolipid of Thermus strains. In this study the glycolipids from the type strains of Meiothermus ruber, Meiothermus chliarophilus, Meiothermus silvanus and Meiothermus cerbereus were characterized using GC, GC/MS, fast atom bombardment MS and chemical methods. All strains contained dihexosyl-(N-acyl)hexosaminylglucosyl diacylglycerols, related in structure to the major glycolipid of Thermus strains but varying in their fatty acylation pattern. The detection of two glycolipid bands by TLC in Meiothermus spp. was attributable to the invariable presence of 2-hydroxyacyl groups N-linked to the hexosamine of the polar head group which cause the glycolipids to be more strongly retained on silica TLC plates than 3-hydroxy or non-hydroxylated N-acyl glycolipids of similar structure that are also present. M. silvanus contained, in addition to these glyceroglycolipids, several glycolipids which were linked to acylated branched octadecanediols rather than to glycerol. The presence of glycolipids containing 2-hydroxyacyl groups N-linked to hexosamine appears to be a stable phenotypic marker that distinguishes the genus Meiothermus from the genus Thermus.