Screening of contaminated soils for biodegradable plastic producing bacteria and profiling of their resistance markers

Polyhydroxyalkanoates (PHA) are the biodegradable polyesters produced by bacteria to overcome the environmental stress. Contaminated environments have a large number of bacteria which can accumulate PHA as their energy reserves. Molasses, oil/ghee and sewerage contaminated soils were selected for the screening of biodegradable plastic- producing bacterial strains. The selected contaminated environments showed great diversity of bacterial flora, Pseudomonas (39.39%) being the most common. The 54 bacterial isolates were further screened by Sudan Black B staining after 48 h of incubation on polyhydroxyalkanoates (PHA) - detection media with glucose as a carbon source and Nile Blue A viable colony staining method. The PHA granules could not be detected in 6 bacterial isolates (AS1, AS2, AP2, AP1, LS13 and VM1). In soil samples contaminated with molasses (sugar industry waste), 95% and in samples contaminated with oil/ghee industry waste all bacterial isolates showed PHA accumulation ability. The accumulated PHA was extracted by direct addition of sodium dodesyl sulphate (SDS). The bacterial isolates SM5, SM11, PG5, UOS2, LS10, AP4 and LS3 accumulated more than 50% PHA of their wet cell mass. No correlation was observed between bacterial growth and the PHA production. The bacterial strains showed multiple resistant markers for selected antibiotics (penicillin and streptomycin) and heavy metals (copper and cadmium). A high level of resistance was observed for penicillin (100 - 4500 µg/ml) and copper (1.5 - 17 mM/ml) in PHA- producing strains.