DIFFERENTIAL DISTRIBUTION OF FATTY ACIDS BETWEEN INTRACELLULAR AND EXTRACELLULAR TRIGLYCERIDES PRODUCED BY Rhodococcus opacus PD630

VILLALBA MS; ALVAREZ HM

Rosario

Congreso; IX Congreso Argentino de Microbiologia General (SAMIGE); 2013

SAMIGE

Rhodococcus bacteria are able to synthesize and accumulate variable amounts of triglycerides (TAG) during growth on diverse carbon sources. Particularly, R. opacus strain PD630 has become a model for the study of biosynthesis and accumulation of intracellular TAG. However, production of extracellular TAG by this strain and other actinobacteria remains to be investigated. The objective of this study was to analyze the production of extracellular lipids by R. opacus PD630, and the distribution of fatty acids between intra- and extracellular TAG. After cultivation of cells on gluconate (1%, w/v) as sole carbon source under nitrogen-poor conditions, intracellular TAG amounted up to 70% of cellular dry weight (CDW); whereas the extracellular production of TAG was significantly lower (2.04%, TAG of CDW), as revealed by gas chromatography analyses of lipid extracts. Intra- and extracellular TAG of gluconate-grown cells exhibited different fatty acid composition: a mixture of saturated and monounsaturated fatty acids (FA) (C16:0>C18:1>C17:1) occurred in intracellular TAG (with 49% of unsaturated FA), whereas extracellular TAG were composed almost exclusively by saturated FA (C18:0>C16:0) (with 86% of saturated FA). Curiously, when unsaturated FA, such as oleic acid (C18:1) and linolenic acid (C18:3), were used as sole carbon sources for cell cultivation, high proportion of saturated FA occurred in intracellular as well as in extracellular TAG. Oleic acid-grown cells produced intracellular TAG containing 79,7% of saturated FA (29% C16:0 and 38% C18:0) and extracellular TAG with 79% of saturated FA (19% C16:0 and 54% C18:0). In the other hand, cells cultivated with linolenic acid produced intra- and extracellular TAG containing 71,8% of saturated FA (28% C16:0 and 30% C18:0) and 83,9% of saturated FA (22% C16:0 and 56% C18:0), respectively. Results of this study demonstrated that R. opacus PD630 was able to accumulate significant amounts of intracellular TAG, in addition of minor amounts of extracellular lipids. Intra- and extracellular TAG exhibited differential FA compositions, independently on the carbon sources used for cell cultivation. In this context, extracellular TAG were always enriched with saturated FA (>80% of the total FA). These results suggested that lipid occurrence in the extracellular milieu is not simply caused by cell lysis; thus, a selective transport mechanism for lipid export, a mechanism for selective distribution of FA among intra- and extracellular TAG, and/or a modification process of FA in TAG may occur during TAG production by strain PD630. IX