Biosynthesis of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) by a new mangrove-isolated Methylopila oligotropha strain MCSUBH

Polyhydroxyalkanoates (PHAs) are natural polyesters accumulated as intracellular granules to store carbon and energy source, during limited growth conditions by bacteria and archaea. The interest in such alternative materials has increased due to the non-biodegradable nature of petrochemical-derived plastics; also, the natural polyesters exhibit thermoplastic and elastomeric properties. In this work, the strain MCSUBH, a facultative aerobic methylotroph, isolated from mangrove and identified as Methylopila oligotropha, was characterized as a new bacterium able to produce PHAs. The main goal of this study was to verify its ability to produce the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) or P(3HB-co-3HV) from methanol and other auxiliary co-substrates in stress conditions. This strain accumulated P(3HB-co-3HV) when valeric acid was supplied as a co-substrate in the presence of methanol. Still, with other auxiliary-carbon sources (citric acid, propanol, and propionic acid), it was able to accumulate poly(3-hydroxybutyrate) (P3HB) at concentrations between 1.31 and 1.53 g L. In addition, different strategies for copolymer production were tested, such as cultivation time, methanol, and nitrogen concentrations. As a result, the P(3HB-co-3HV) accumulation rates ranged between 0.49 and 0.85 g L, reaching 20.86% of the molar fraction of 3-hydroxyvaleric acid (3HV). Furthermore, our results show that longer cultivation time promoted an increase in the molar fraction of 3HV, which could make the final product promising toward its application. Graphical abstract: [Figure not available: see fulltext.]