Accumulation of poly(3-hydroxybutyrate) by Microbacterium barkeri DSM 20145

A gram-positive bacterium that accumulated poly(3-hydroxybutyric) acid (PHB) was isolated from petrol bunk soil. From its morphological and physiological properties and the nucleotide sequence (about 1.5 kb) of its 16S rDNA, it was identified as Microbacterium barkeri DSM 20145. Based on the available literature, this is the first report of PHB accumulation by Micro bacterium sp. The isolate accumulated 0.6 g/L, or 29.7%, of PHB under growth conditions in a nitrogen-deficient medium containing glucose and yeast extract (4:1 ratio), with maximum production by 48 h. The capacity of the isolate to produce PHB under different carbon and nitrogen sources was also investigated. The strain produced appreciable levels of PHB by utilizing hemicellulosic sugars such as glucose, xylose, and arabinose, as well as disaccharides such as lactose and sucrose, alternative carbon sources like wheat bran and carboxymethyl cellulose, and organic acids such as propionic acid, with maximum production achieved using xylose (1.7 g/L, 68%). Among the nitrogen sources tested, peptone supported maximum production (1.4 g/L, 16%), followed by casein (0.9 g/L, 22.6%) and sodium nitrate (0.4 g/L, 26.4%), although the PHB yield was not appreciably high. The addition of xylose to the nitrogen-deficient medium increased the values of PHB yield (g/L) by 2.5 and the PHB accumulation (% dry cell weight) by 2.3; the replacement of yeast extract in the medium with peptone increased the PHB yield (g/L) by 2.05. The isolated polymer was highly soluble in chloroform and peaked sharply at 235 nm upon digestion with concentrated H2SO4. This study adds a new species to the family of PHB producers.