Biosynthesis of storage compounds by Rhodococcus jostii RHA1 and global identification of genes involved in their metabolism

Abstract

Background: Members of the genus Rhodococcus are frequently found in soil and other natural environments and are highly resistant to stresses common in those environments. The accumulation of storage compounds permits cells to survive and metabolically adapt during fluctuating environmental conditions. The purpose of this study was to perform a genome-wide bioinformatic analysis of key genes encoding metabolism of diverse storage compounds by Rhodococcus jostii RHA1 and to examine its ability to synthesize and accumulate triacylglycerols (TAG), wax esters, polyhydroxyalkanoates (PHA), glycogen and polyphosphate (PolyP). Results: We identified in the RHA1 genome: 14 genes encoding putative wax ester synthase/acyl-CoA: diacylglycerol acyltransferase enzymes (WS/DGATs) likely involved in TAG and wax esters biosynthesis; a total of 54 genes coding for putative lipase/esterase enzymes possibly involved in TAG and wax ester degradation; 3 sets of genes encoding PHA synthases and PHA depolymerases; 6 genes encoding key enzymes for glycogen metabolism, one gene coding for a putative polyphosphate kinase and 3 putative exopolyphosphatase genes. Where possible, key amino acid residues in the above proteins (generally in active sites, effectors binding sites or substrate binding sites) were identified in order to support gene identification. RHA1 cells grown under N-limiting conditions, accumulated TAG as the main storage compounds plus wax esters, PHA (with 3-hydroxybutyrate and 3-hydroxyvalerate monomers), glycogen and PolyP. Rhodococcus members were previously known to accumulate TAG, wax esters, PHAs and polyP, but this is the first report of glycogen accumulation in this genus.

Rhodococcus UKMP-5M, an endogenous lipase producing actinomycete from Peninsular Malaysia

“…MK1 has been suspected for high level of lipase activity due to its excellent level of degradation of waste from food industry and domestic wastewater. However, this actinomycete is minimally assessed for lipase production although the presence of lipase in mobilizing accumulated triacylglycerol (TAG) has been recognized significantly (Hernandez et al 2008). Therefore, in the present study we report lipase production by a local strain ofRhodococcus UKMP-5M as a potential strain in degrading lipid rich wastewater.…”

“…This explains the reason for no growth of R.UKMP-5M which led to no lipase detection at temperature 45 • C and above. As discussed previously, lipase enzyme secretion is triggered to mobilize stored TAG to generate energy for the growth (Hernandez et al 2008). Thus, competent temperature for cell growth, 30…”

<i>Rhodococcus jostii</i> RHA1 TadA-homolog deletion mutants accumulate less polyhydroxyalkanoates (PHAs) than the parental strain

“…For example, the biosynthesis of both PHAs and TAGs share the metabolite acetyl-CoA, and both of these storage polymers are synthesized as membrane-bound inclusion bodies (Alvarez and Steinbuchel, 2002;Valappil et al, 2007). Experimental evidence indicates that when RHA1 is grown on glucose, gluconate or acetate, TAGs represent the majority of storage compounds when compared to PHAs (Hernandez et al, 2008). Additional studies of R. opacus PD630 further demonstrated shifts in the composition of PHAs and TAGs during unbalanced growth that correlated with whether the cells were in an exponential or stationary phase (Alvarez et al, 2000).…”

“…The Actinomycete bacterium Rhodococcus jostii RHA1 is capable of simultaneously accumulating multiple carbon storage compounds, which include polyhydroxyalkanoates (PHAs), triacyglycerols (TAGs) and glycogen (Hernandez et al, 2008). Accumulation of these storage compounds can be heavily influenced by the primary carbon growth substrate.…”

“…Accumulation of these storage compounds can be heavily influenced by the primary carbon growth substrate. Unbalanced growth conditions such as nutrient starvation (usually nitrogen) in the presence of excess carbon (Hernandez et al, 2008), normally induces an increased accumulation of these storage compounds. While many studies have examined either PHA or TAG accumulation in Actinomycete bacteria such as the Rhodococcus (Alvarez and Steinbuchel, 2002;Valappil et al, 2007), very little is known regarding the competition of these storage polymers for common metabolic precursors and/or cellular membrane components.…”