Novel thermophilic polyhydroxyalkanoates producing strain Aneurinibacillus thermoaerophilus CCM 8960

Characterization of newly isolated thermotolerant bacterium Cupriavidus sp. CB15 from composting and its ability to produce polyhydroxyalkanoate from glycerol

BACKGROUND

This study aimed to isolate a novel thermotolerant bacterium that is capable of synthesizing polyhydroxyalkanoate from glycerol under high temperature conditions.

RESULTS

A newly thermotolerant polyhydroxyalkanoate (PHA) producing bacterium, Cupriavidus sp. strain CB15, was isolated from corncob compost. The potential ability to synthesize PHA was confirmed by detection of PHA synthase (phaC) gene in the genome. This strain could produce poly(3-hydroxybutyrate) [P(3HB)] with 0.95 g/L (PHA content 75.3 wt% of dry cell weight 1.24 g/L) using glycerol as a carbon source. The concentration of PHA was enhanced and optimized based on one-factor-at-a-time (OFAT) experiments and response surface methodology (RSM). The optimum conditions for growth and PHA biosynthesis were 10 g/L glycerol, 0.78 g/L NH₄Cl, shaking speed at 175 rpm, temperature at 45 °C, and cultivation time at 72 h. Under the optimized conditions, PHA production was enhanced to 2.09 g/L (PHA content of 74.4 wt% and dry cell weight of 2.81 g/L), which is 2.12-fold compared with non-optimized conditions. Nuclear magnetic resonance (NMR) analysis confirmed that the extracted PHA was a homopolyester of 3-hydyoxybutyrate.

CONCLUSION

Cupriavidus sp. strain CB15 exhibited potential for cost-effective production of PHA from glycerol.

Biosynthesis of versatile PHA copolymers by thermophilic members of the genus Aneurinibacillus

Thermophilic members of the genus Aneurinibacillus constitute a remarkable group of microorganisms that exhibit extraordinary flexibility in terms of polyhydroxyalkanoates (PHA) synthesis. In this study, we demonstrate that these Gram-positive bacteria are capable of the utilization of selected lactones, namely, γ-valerolactone (GVL), γ-hexalactone (GHL), and δ-valerolactone (DVL) as the structural precursors of related PHA monomers. In the presence of GVL, a PHA copolymer consisting of 3-hydroxybutyrate, 3-hydroxyvalerate, and also 4-hydroxyvalerate was synthesized, with a 4 HV fraction as high as 53.1 mol%. Similarly, the application of GHL resulted in the synthesis of PHA copolymer containing 4-hydroxyhexanaote (4HHx) (4HHx fraction reached up to 11.5 mol%) and DVL was incorporated into PHA in form of 5-hydroxyvalerate (5 HV) (maximal 5 HV content was 44.2 mol%). The produced materials were characterized by thermoanalytical and spectroscopic methods; the results confirmed extremely appealing material properties of produced copolymers. Further, due to their unique metabolic features and capability of incorporating various PHA monomers into the PHA chain, thermophilic Aneurinibacillus spp. can be considered not only promising chassis for PHA production but also potential donors of PHA-relevant genes to improve PHA production in other thermophiles by using approaches of synthetic biology.