Production of biopolyester poly(3-hydroxybutyrate) by Bacillus cereus RCL 02, a leaf endophyte of Ricinus communis L.

Endophytic bacteria colonizing the internal tissues of plants have attracted the attention of scientific communities in recent years for production of biodegradable polyesters like polyhydroxyalkanotaes (PHAs). A newly characterized bacterium, Bacillus cereus RCL 02 (GenBank accession no. KX458035 ), isolated from surface sterilized leaves of Ricinus communis L. has been explored for the production of poly(3-hydroxybutyrate) [P(3HB)], the most common PHA. As revealed by scanning electron microscopy, P(3HB) accumulating cells developed swellings or blebs and released the native granules as a function of autolysis. During growth in glucose containing mineral salts medium under batch fermentation, the isolate produced P(3HB) accounting 68% of its cell dry weight (CDW). Glucose and yeast extract when used in the ratio of 5:1, significantly influenced intracellular biopolyester accumulation (72.2%, CDW and 2.54 g/L). A further increase of polymer production (81%, CDW and 3.17 g/L) was accomplished in presence of 1.5 mM manganese as exogenous metal stress. Moreover, supplementation of the growth medium with non-conventional carbon sources especially refined sugarcane molasses further enhanced the production of both biomass (9.44 g/L) as well as polyester (83.6%, CDW and 7.89 g/L). These finding emphasises exploration of endophytic bacteria of oleaginous plants in general and R. communis L. in particular as potential but hitherto an under exploited bioresource for commercial production of biodegradable polyesters.