New triacylglycerol-accumulating bacteria isolated from Altiplano lakes

BEQUER URBANO S.; SILVA R.A.; FARÍAS M.E.; ALVAREZ H.M.

Villa Carlos Paz. Argentina.

Congreso; VI Congreso Argentino de Microbiología General; 2009

Triacylglycerols (TAG) are non-polar, water-insoluble fatty acid triesters of glycerol, which occur in most eukaryotic organisms, including animals, plants, yeast and fungi. For several years it has been considered that the formation of TAG as storage lipids was restricted to eukaryotic cells, and that prokaryotes were unable to synthesize and accumulate them. However, during the last years the occurrence of TAG has been detected in certain groups of prokaryotes as reserve material, such as Gram positive bacteria belonging to the actinomycetes group, such as Mycobacterium, Rhodococcus, Nocardia and Streptomyces, and in some Gram negative bacteria belonging to the gamma-Proteobacteria, such as Acinetobacter, Marinobacter and Alcanivorax. TAG accumulation may provide cells of energetic autonomy and a temporal independence from the environment and contribute for cell survival when they do not have access to energy resources in soil, like in deserts. In a previous study, we demonstrated that survival of Rhodococcus cells under desiccation conditions depended on endogenous metabolism using intracellular TAG for generating energy and precursors, and also as a reservoir of metabolic water. In this study, we partially analyzed an extremophile culture collection from Andean Altiplano in order to identify new TAG-accumulating bacteria. This place presents arid conditions such low nutrients and other extreme environmental conditions. Lipid accumulation was investigated by thin layer and gas chromatography analyses of cells. Desiccation tolerance was analyzed according to the method of Alvarez et al. (2004. FEMS Microbiol. Ecol. 50:75-86). Interestingly, we were able to identify four new TAG-accumulating genera among this extremophile culture collection: Microbacterium arborescens CH5 and Agrococcus jenensis CH9, which belong to actinobacteria group, and Stenotrophomonas maltophilia Ver 10 and Alkalilimnicola sp. Sv 12.18, which belong to gamma-Proteobacteria. Among these strains, only M. arborescens CH5 accumulated significant amounts of storage lipids (app. 20 %, w/w), whereas the other strains produced no more than 2 % (w/w) after cultivation with a carbon source under nitrogen-limiting conditions. In addition, cells of these four strains were resistant to desiccation, and a high fraction of the cells (> 50 %) survived after two weeks under these conditions (20% H. R.). Resuming, after analyzing partially an extremophile culture collection from Andean Altiplano, we identified four new TAG-accumulating genera, such as Microbacterium, Agrococcus, Stenotrophomonas and Alkalilimnicola. As described for other TAGaccumulating bacteria, the studied microorganisms showed high water stress tolerance. Further studies are necessary to determine the relation between the accumulation of TAG and the desiccation tolerance by such bacteria.