Microbial Polyhydroxyalkanoate Co-polymers From Biowastes
Authors: Subhasree Ray, Shikha Koul, Jyotsana Prakash, Vipin Chandra Kalia
Microbial Biotechnology and Genomics, CSIR - Institute of Genomics and Integrative Biology (IGIB), Delhi University Campus, Mall Road, Delhi-110007.


Introduction

Bacteria can produce biopolymers such as polyhydroxyalkanoates (PHAs) from cheap and renewable biowastes. Most bacteria produce homopolymers of hydroxybutyrate (PHB). The economical feasibility of PHBs is low because of their brittle nature, poor strength and elasticity. These limitation can be overcome by producing co-polymers of PHAs.

Co-polymers of polyhydroxyalkanoate (PHAs)

The ability of bacteria to produce co-polymers depends mainly upon carbon (C) source and supplements, etc. These inputs can be procured from pure sugars and volatile fatty acids (VFAs). Alternatively, biowastes can be exploited as feed material with desired kind of C and VFAs. Different bacteria can hydrolyze biowastes which can be metabolize by PHA producers.

Gram-negative bacteria

Ralstonia, Cupriavidus and Pseudomonas species are well known to produce homopolymers and co-polymers: P(3HB-3HV-3HHx), P(HD-HDD-HO-HHx), P(3HB-3HHx) from vegetable oils, and glycerol which have been provided with valeric acid (VA) or levulinic acid, FAME +VA. Azotobacter, Klebsiella, Rhizobium, Sphigomonas, Comamonas and Haloferax have been reported to produce co-polymers of PHA from agricultural wastes, dairy products, oily wastes and industrial wastes.

Gram-positive bacteria

Bacillus, Clostridium , Norcardia, Microlunatus, Streptomyces, Corynebacteria, Rhodococcus, Staphylococcus are among the gram-positive organisms which are capable of producing co-polymers of PHA from: (i) on pea-shell slurry, (ii) crude glycerol, (iii) apple poamace, (iv) potato peels, (v) onion peels, (vi) agricultural waste, and (vii) mahua flowers (Madhuca sp.).

Bacillus sp. such as B. thuringiensis, B. cereus, and B. megaterium can metabolize biowastes to co-polymers, like: P(3HB-3HHx), P(3HB-3HV-3HHx), P(HD-HDD-HO-HHx), etc. in an efficient manner. Here, 3HV, 3HHx, and 3HO can account upto 64.5 mol% of the total PHA co-polymer.

Opinion

In conclusion, we may need to choose a combination of feed material and bacteria to produce PHA co-polymers of the desired composition. Bacillus, a GRAS organism is emerging as a potential PHA co-polymer producer.

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About Author / Additional Info:
Researcher in Microbial Biotechnology and Genomics at CSIR-IGIB, Delhi.