Accumulation of storage lipids in species of Rhodococcus and Nocardia and effect of inhibitors and polyethylene glycol

Members of the genera Rhodococcus and Nocardia corallina were investigated for their capability to accumulate storage lipids that occur in the cytoplasm during cultivation of the cells under nitrogen-limiting conditions in the absence or presence of various effecters. All bacteria were able to accumulate triacylglycerols (TAG) as main compounds plus minor amounts of diacylglycerols and wax esters. In addition to neutral lipids, R. fascians, R. erythropolis, and R, opacus MR22 accumulated small amounts of polyhydroxybutyrate (PHB), and N. corallina and R. ruber accumulated significant amounts of polyhydroxyalkanoates (PHA) consisting of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV) from glucose or valerate. Alloxan or 3-nitropropionate, which are inhibitors of the citric acid cycle, caused a decrease in the content of odd-numbered fatty acids in the TAG accumulated from acetate by R. opacus PD630. Cerulenin, an inhibitor of the fatty acid de novo synthesis, completely inhibited accumulation of TAG from glucose or gluconate but not from hexadecane in all bacteria investigated. In addition, cerulenin caused an increase of the PHA content and resulted in an increase of the relative amounts of 3HB units in the PHA in R. ruber and N. corallina. Acrylic acid, an inhibitor of fatty acid beta-oxidation, completely or partially inhibited accumulation of TAG from hexadecane or valerate, respectively, in R, opacus PD630. In R. ruber, acrylic acid completely inhibited accumulations of TAG from valerate; under these conditions the content of PHA increased twofold, and the polyester consisted exclusively of 3HV. PEG-200 (0.2 to 5%, w/v) caused a decrease in the PHA content, but stimulated the incorporation of 3HV units into the PHA in R. ruber. Therefore, the relative amounts and compositions of both storage lipids can be affected by various compounds in these Gram-positive bacteria.