Isolation and screening of biopolyester (poly-β-hydroxybutyrate) producing bacteria from compost samples in Bangladesh

Poly-β-hydroxybutyrate (PHB) is the simplest member of polyhydroxyalkanoates (PHAs) that are biological polyesters or biopolymers produced by a wide variety of bacteria as an intracellular storage material of carbon and energy. Compost is one of the richest sources of microorganisms; therefore, an attempt was made to isolate PHB producing bacteria from compost samples. Out of six compost samples, bioslurry showed the highest mesophilic bacterial count of 3.75×109 cfu/g. A total of 48 mesophilic bacteria were isolated by growing samples on nutrient agar medium at pH 7.0 and a temperature of 37°C. All isolates were purified and screened for PHB production using lipophilic stains such as Nile red, Sudan black B, Acridine orange. 16 out of 48 isolates exhibited PHB production ability after screening by plate assay. PHB granule formation was also confirmed by observation under a fluorescent microscope. The number of PHB producer and accumulators in different compost samples were in the order of Bioslurry > Cow dung > Cotton seed > Tobacco dust. Based on morphological, cultural and biochemical characteristics, all isolates were assigned to four genera viz. Bacillus, Micrococcus, Veillonella and Pseudomonas. Batch fermentation in shake flask was carried out using glucose as carbon source. By analyzing photomicrographs of 24-hour old cultures, 7 out of 16 bacterial isolates were found with a good PHB accumulation capacity. These bacteria are being currently studied for biopolymer production using different carbon sources and renewable biomass.