Mesorhizobium bacterial strains isolated from the legume Lotus corniculatus are an alternative source for the production of polyhydroxyalkanoates (PHAs) to obtain bioplastics

Polyhydroxyalkanoates, the bioplastics of microbial origin: Properties, biochemical synthesis, and their applications

The rising plastic pollution deteriorates the environment significantly as these petroleum-based plastics are not biodegradable, and their production requires natural fuels (energy source) and other resources. Polyhydroxyalkanoates (PHAs) are bioplastic and a sustainable and eco-friendly alternative to synthetic plastics. PHAs can be entirely synthesized using various microorganisms such as bacteria, algae, and fungi. These value-added biopolymers show promising properties such as enhanced biodegradability, biocompatibility, and other chemo-mechanical properties. Further, it has been established that the properties of PHA polymers depend on the substrates and chemical composition (monomer unit) of these polymers. PHAs hold great potential as an alternative to petroleum-based polymers, and further research for economic production and utilization of these biopolymers is required. The review describes the synthesis mechanism and different properties of microbially synthesized PHAs for various applications. The classification of PHAs and the multiple techniques necessary for their detection and evaluation have been discussed. In addition, the synthesis mechanism involving the genetic regulation of these biopolymers in various microbial groups has been described. This review provides information on various commercially available PHAs and their application in multiple sectors. The industrial production of these microbially synthesized polymers and the different extraction methods have been reviewed in detail. Furthermore, the review provides an insight into the potential applications of this biopolymer in environmental, industrial, and biomedical applications.

Valorization of agro-wastes for the biosynthesis and characterization of polyhydroxybutyrate by Bacillus sp. isolated from rice bran dumping yard

Investigations have been made to determine the usage of inexpensive agro-waste products as an alternative carbon source for the production of degradable bacterial polyester. Among 33 bacterial isolates, a gram-positive bacterium PPECLRB-16 isolated from rice bran dumping yard was found to accumulate a relatively higher quantity of PHB and identified as Bacillus sp. through 16S rRNA gene sequence analysis. The higher PHB producing bacterial isolate was grown with different inexpensive agro-wastes to determine the suitable carbon source for its growth and PHB production. The one-factor-at-a-time approach comparatively enhanced PHB yield (5.64 g/L) when grown for 48 h with 1.5% (w/v) of defatted oil cake at a pH of 7.0. The bacterially accumulated PHB was isolated from the cells, purified, and characterized using solid-state ¹³C NMR, FT-IR, Powder XRD, TGA, GPC, Tensile and HR-SEM analyses. The hydrophobicity and printing accessibility of recovered PHB were demonstrated using contact angle measurement by coating on different surfaces. The results obtained in the present investigation have thrown light on the potential usage of agro-waste by-products, mainly oil cake, as an appropriate carbon source for the commercial production of PHB by Bacillus sp. in a cost-effective way.

Production of polyhydroxyalkanoates by halotolerant bacteria with volatile fatty acids from food waste as carbon source

In this study, a halotolerant strain was isolated from high salinity leachate and identified as Bacillus cereus NT-3. It can produce a high concentration of polyhydroxyalkanoates (PHAs) with no significant changes when NaCl concentration is up to 50 g/L. FTIR and NMR spectra of PHAs synthesized by Bacillus cereus NT-3 were similar to the standard or previous results. Effluent from acidogenic fermentation of food waste and pure volatile fatty acids (VFAs) mixture was used as carbon source to check the effect of non-VFAs compounds of the effluent on PHAs production. The maximum PHAs production was 0.42 g/L for effluent fermentation, whereas it was 0.34 g/L for pure VFAs fermentation, indicating that bacteria could use actual effluent in a better way. Furthermore, a mathematical model was established for describing kinetic behavior of bacteria using different carbon sources. These results provided a promising approach for PHAs biosynthesis with a low-cost carbon source.