1. Introduction Environmental pollution due to unscrupulous use consumption of synthetic polymers derived from petroleum has an adverse impact on environment since majority of plastics do not degrade and further incineration of synthetic plastics generates CO2 and dioxin [1,2]. In view of this, some aliphatic polymers have been developed as biodegradable plastics [3]. Poly lactic acid or polylactide (PLA) is aliphatic polyester synthesized by bacteria and fungi utilizing the renewable resources. PLA is the only thermoplastic polymer that is commercially produced on a relatively sizable scale on competitive cost compared with petroleum based polymers. The global attention of PLA is high as it can be used different packaging materials, medical devices and also in agricultural applications as a substitute for synthetic polymers like poly ethylene and poly propylene. The mechanism by which PLA polymers degrade depends on the biological environment to which they are exposed. During degradation, the water insoluble high molecular weight PLA polymer hydrolyzed to water soluble oligomers by microbial attacks and at final stages, these oligomers converted into carbon dioxide, water and humus [4]. Biological processes by both microbial and enzymatic
activities are currently considered to be sustainable recycling methods for PLA. Literature is abounding with degradation of PLA, but understanding on the theme is still inadequate. This is clearly due to the lack of information on the role of microorganisms in the mechanism of PLA degradation. Pranamuda et al., [5] first reported the microbial degradation of PLA by actinomycetes Amycolatopsis strain isolated from soil. Recently, several thermophilic bacteria such as Brevibacillus [6], Bacillussmithii [7] and Geo bacillus thermocatenulatus [6] have been reported to exhibit PLA degrading ability. Bacterial degradation of L- PLA has been reported even at high temperature (>50°C). Brevibacillus, a thermophile, isolated from soil showed degradation at 60°C [8]. Similarly, Bacillus smithii isolated from garbage fermenter exhibited maximum growth in the medium containing 1% L-PLA and caused decrease in the molecular weight of PLA after incubation at 60°C for 3 days [7]. Most of the reported bacteria were thermophilic in nature and some of the bacteria such as Paeni bacillus amylolyticus TB-13 [9], Bordetella petrii PLA-3 (10) and Pseudomonas DS04-T [11] have been reported to be mesophiles involved in degradation of PLA. Keeping in view of the present literature, the present study is designed to understand the role of compost mesophilic bacteria in the degradation of polylactide plastic