Biodegradable plastics opened a new way for waste management strategies since these materials are
intended to degrade under various conditions. Two complementary parts were conducted to study the ability
of bacteria to degrade bioplastic (polylactic acid) (PLA) under in vitro conditions. The first part was to screen
seven bacterial strains adopted on their ability to produce proteolytic and lipolytic enzymes. As well as, use
lactic acid (LA) as a sole carbon source by estimate dehydrogenase activity (DHA), optical density (OD),
dry weight (DW), consumed and residual LA of the medium. The second part was incubation of those strains
into media supplemented with PLA films as a sole carbon source for two months. Changes in pH,
accumulated LA and weight loss were estimated periodically every 15 days during two months. The tested
seven bacterial strains showed high ability to produce protease and lipase and able to use LA as a sole carbon
source. Concerning PLA biodegradation, results also showed that pH was gradually decreased from the
initial period to reach their maximum after 60 days of incubation. Whereas, the accumulated LA and loss of
PLA films weight were increased and the highest records were observed after 60 days in medium inoculated
with Serratia marcescens (ZH5) followed by Pseudomonas fluorescence (ZH6). Optical and scanning
electron microscopy were conducted to observe changes in PLA films. In this respect, results showed
roughening of the outer surface, formation of holes and cracks in addition changes in color. |
