Extremophilic Bacterium Halomonas desertis G11 as a Cell Factory for Poly-3-Hydroxybutyrate-co-3-Hydroxyvalerate Copolymer’s Production

Abstract

Microbial polyhydroxyalkanoates (PHA) are biodegradable and biocompatible bio-based polyesters, which are used in various applications including packaging, medical and coating materials. In this study, an extremophilic hydrocarbonoclastic bacterium, previously isolated from saline sediment in the Tunisian desert, has been investigated for PHA production. The accumulation of intracellular PHA granules in Halomonas desertis G11 was detected by Nile blue A staining of the colonies. To achieve maximum PHA yield by the strain G11, the culture conditions were optimized through response surface methodology (RSM) employing a Box-Behnken Design (BBD) with three independent variables, namely, substrate concentration (1–5%), inoculum size (1–5%) and incubation time (5–15 days). Under optimized conditions, G11 strain produced 1.5 g/L (68% of DCW) of PHA using glycerol as a substrate. Application of NMR (1H and 13C) and FTIR spectroscopies showed that H. desertis accumulated PHA is a poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). The genome analysis revealed the presence of typical structural genes involved in PHBV metabolism including phaA, phaB, phaC, phaP, phaZ, and phaR, coding for acetyl-CoA acetyltransferase, acetoacetyl-CoA reductase, class I polyhydroxyalkanoates synthases, phasin, polyhydroxyalkanoates depolymerase and polyhydroxyalkanoates synthesis repressor, respectively. Glycerol can be metabolized to 1) acetyl-CoA through the glycolysis pathway and subsequently converted to the 3HB monomer, and 2) to propionyl-CoA via the threonine biosynthetic pathway and subsequently converted to the 3HV monomer. In silico analysis of PhaC1 from H. desertis G11 indicated that this enzyme belongs to Class I PHA synthase family with a “lipase box”-like sequence (SYCVG). All these characteristics make the extremophilic bacterium H. desertis G11 a promising cell factory for the conversion of bio-renewable glycerol to high-value PHBV.

Optimized Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) Production by Moderately Haloalkaliphilic Bacterium Halomonas alkalicola Ext

“…On their part, Tan et al [57] synthesized PHBV copolymers with 4-6% 3-HV fraction from Halomonas TD01. Our findings are consistent with earlier reports that showed the prominence of PHBVs in PHAs extracted from bacteria of the genus Halomonas [26,41,60,61]. However, short-chain polyhydroxyalkanoates have also been recovered from members of the Halomonas genus [62,63].…”

“…Other biopolymers synthesized by Halomonas bacteria have varied 3-HV fractions. For instance, Hammami et al [41] reported a maximum incorporation of 52.04% 3-HV fraction from biopolymer synthesized by Halomonas desertis G11 while Mozejko-Ciesielska et al [42] showed that Halomonas alkaliantarctica could synthesize PHBV with 60.59% HV fraction. On their part, Tan et al [57] synthesized PHBV copolymers with 4-6% 3-HV fraction from Halomonas TD01.…”

“…This was lower than the 3-HV fraction reported in some earlier studies (Table 9). According to Hammami et al [41], a 3-HV fraction of about 10-20% is desirable for PHBV to have some practice use but the attainment of high 3-HV fraction often demands the incorporation of chemical precursors. In the present study, PHBV precursors were not incorporated in the growth media, hence the low 3-HV fraction in the extracted polymer.…”

Halomonas alkaliantarctica as a platform for poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) production from biodiesel‐derived glycerol

“…Nevertheless, PHA copolymers are of high interest due to their favourable thermomechanical properties compared to PHA homopolymers. Incorporation of 3HV monomer to the polymer chain lowers melting temperature, reduces crystallinity, improves flexibility that are important parameters for their future application (Hammami et al, 2022 ). Most bacterial species required precursors to produce P(3HB‐ co ‐3HV) such as Cupriavidus necator (Grousseau et al, 2014 ), Bacillus aryabhattai (Balakrishna Pillai et al, 2020 ) or Halomonas sp.…”

PHBV cycle of life using waste as a starting point: from production to recyclability

“…These latter processes, account for approximately half of the total production cost (Zhang et al, 2024). Nevertheless, due to the growing concern about global pollution due to non-biodegradable plastics as well as growing interest in PHBV application in different biomedical areas and as a substitute for conventional plastic products, multiple research projects are being carried out to look for microorganisms able to produce PHBV efficiently and/or develop processes aiming at the reduction of the cost of their production (Hammami et al, 2022).…”