Exploitation of inexpensive substrates for production of a novel SCL-LCL-PHA co-polymer by Pseudomonas aeruginosa MTCC 7925.

Studies conducted with various inexpensive carbon sources such as whey, vegetable oils (palm, mustard, soybean and coconut), a low-cost source of glucose-D, rice and wheat bran, and mustard and palm oil cakes demonstrated palm oil as the best substrate for accumulation of a novel short-chain-length-long-chain-length polyhydroxyalkanoate (SCL-LCL-PHA) co-polymer containing SCL 3HAs [3-hydroxybutyric acid (3HB) and 3-hydroxyvaleric acid (3HV)] and LCL 3HAs of 3-hydroxyhexadecanoic acid (3HHD) and 3-hydroxyoctadecanoic acid (3HOD) units as constituents by a sludge-isolated Pseudomonas aeruginosa MTCC 7925. The co-polymer content reached up to 60% of dry cell weight (dcw) at 48 h of incubation in 0.5% (v/v) palm oil and the extract of 0.5% (v/v) palm oil cake supplemented vessels. The PHAs pool was further enhanced up to 69 and 75% (dcw), when the above culture was subjected to P- and N-limitation, respectively. The mol fraction of 3HB:3HV:3HHD:3HOD units were, respectively, 83.1:7.7:3.8:5.4 and 87.3:5.1:3.6:4.0 in P- and N-limited cultures. Consequently, a co-polymer yield of 5 g l(-1) (approx.) was achieved, which was about 80-fold higher as compared to 69 mg l(-1) of the control culture. On substrate basis, the accumulation reached up to 0.62 g PHAs per g substrate, which was significantly higher as compared to the yield obtained from starch by Haloferax mediterranei and Azotobacter chroococum, from molasses by A. vinelandii UWD, and from lactose and xylose by Pseudomonas cepacia. This novel P(3HB-co-3HV-co-3HHD-co-3HOD) co-polymer exhibited better thermal and mechanical properties as revealed from the differential scanning calorimetry and mechanical property studies, thus opens up new possibilities for various industrial applications.