A polyhydroxyalkanoate synthesised by halophilic archaeon Natrialba swarupiae

Abstract

Monomers and heteropolymers known as biodegradable polyhydroxyalkanoates (PHAs) are promising alternatives to fossil fuel-based polymers. During times of nutrient scarcity, microbes like extremophilic archaea store energy by accumulating PHA in the form of inclusions. However, knowledge of the mechanisms and PHA accumulation capabilities of extremophilic archaea is limited. In this study, an extremophilic haloarcheon, Natrialba swarupiae, isolated from a hypersaline lake in India has been investigated for its ability to produce PHA. The Sudan black B staining method was utilized for an initial assessment of potential PHA synthesizing ability. Nile blue A staining confirmed the presence of PHA granules. PHA concentrations were measured using crotonic acid assays. Nab. swarupiae yielded maxima of 0.27 ± 0.0094 g L⁻¹ biomass and 0.14 ± 0.0017 g L⁻¹ PHB, measuring 54.40 ± 1.386% PHB accumulation. The NMR analysis revealed the presence of a copolymer of PHA containing monomers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), and 3-hydroxyoctanoate (3HO), poly-(3HB-co-3HV-co-3HO). The annotated genome sequence was used to detect the presence of the PHA synthase gene in Nab. swarupiae. The genome-scale metabolic model was built based on the ModelSEED pipeline using the Build Metabolic Model app in KBase. The homology model of PHA synthase was built by using SWISS-MODEL. The molecular docking study was carried out between PHA synthase and 3-hydroxybutyryl-CoA (3HBCA) along with 3-hydroxyoctanoyl-CoA (3HOCA) using PATCH-DOCK. The computational studies revealed good hydrogen bonding interactions between PHA synthase and 3-hydroxybutyryl-CoA. The molecular modeling studies could point out that the amino acid residues of PHA synthase such as TYR76, ASP183, MET152, ASN225, ASP235, THR228, ASP235, GLU238, TYR272 and ASN245 might play a major role in enzyme catalysis during PHA granule production.