Production of Polyhydroxyalkanoates

Abstract

Polyhydroxyalkanoates are a family of bio polyesters. It is produced by many soil and marine bacteria. It is accumulated as energy reserve inside the microbial cell under nutrient imbalance conditions of excess carbon source and deficient phosphorous, nitrogen or oxygen. PHA is a better and safer alternative to plastics because of its biodegradability. Microbes can utilize wide variety of substrate to produce PHAs ranging from simple substrate such as glucose, benzoic acid to complex one as those of lignin. A number of microbes can utilize lignin waste to produce PHA, hence converting lignin into high value product. Studies have shown that lignin metabolism involves depolymerization of lignin to small phenolic derivatives, which then forms central intermediates Protocatechuate or Catechol via upper pathway or funneling. Protocatechuate is the most important intermediate which undergoes β Ketoadipate to form TCA cycle intermediate acetyl CoA. Bacteria have various pathways to transform these intermediates into hydroxyacyl-CoA thioesters, which serves as the target for PHA synthases. In this work, 4 strains isolated from black liquor were grown in growth media plate having PCA as sole carbon source. These four strains were Halomonas sp. 78A, Halomonas sp. 78B, Pseudomonas putida sp. 29A, Halomonas sp. 38. Out of them, only 78B showed growth. Later the screened isolate was grown in liquid growth media and then in production media having higher C: N ratio. Presence of PHA granules in cells was confirmed by Sudan black staining. Effect of co-feeding of PCA was also studied with other carbon sources. For this purpose, glycerol and 8 sugars were used. It was observed that PCA when used with main carbon source showed increased biomass growth. Later, 78B was also screened for its growth in different lignin derived compounds or monomers. The isolate was able to grow well in vanillic acid. This monomer can also be used along with other carbon source to show its effect on their utilization. However this study along with characterization of PHA could not be completed due to covid pandemic related laboratory closure.