Isolation and role of polylactic acid-degrading bacteria on degrading enzymes productions and PLA biodegradability at mesophilic conditions

摘要

Enumeration and isolation of polylactic acid (PLA)-degrading bacteria from soils and wastewater sludge were performed on emulsified PLA agar. Two isolates of potent PLA-degrading bacteria, designated as CH1 and WS3, were selected and identified asStenotrophomonas pavaniiandPseudomonas geniculata, respectively. PLA was presented as a substrate to stimulate production of protease and PLA-degrading enzyme byS. pavaniiCH1 andP. geniculataWS3. The optimal pH values for both protease and PLA-degrading enzyme production byS. pavaniiCH1 andP. geniculataWS3 were 7.5 and 8.0, respectively. The optimal gelatin concentrations for stimulating protease production inS. pavaniiCH1 andP. geniculataWS3 were 0.3% (w/v), while those for PLA-degrading enzyme production inS. pavaniiCH1 andP. geniculataWS3 were 0.1 and 0.3% (w/v), respectively. In addition,P. geniculataWS3 had a higher percentage of PLA film-weight loss than that ofS. pavaniiCH1, corresponding with reduced molecular weight of PLA. A significant increase of lactic acid content in culture broth was directly correlated with the increasing percentage of PLA film-weight loss. Our results clearly demonstrated thatP. geniculataWS3, a novel isolated bacterium, has played a substantial role in PLA biodegradation by producing PLA-degrading enzyme and adhering on PLA surface.