Enoyl-CoA hydratase mediates polyhydroxyalkanoate mobilization in Haloferax mediterranei

Abstract

Although polyhydroxyalkanoate (PHA) accumulation and mobilization are one of the most general mechanisms for haloarchaea to adapt to the hypersaline environments with changeable carbon sources, the PHA mobilization pathways are still not clear for any haloarchaea. In this study, the functions of five putative (R)-specific enoyl-CoA hydratases (R-ECHs) in Haloferax mediterranei, named PhaJ1 to PhaJ5, respectively, were thoroughly investigated. Through gene deletion and complementation, we demonstrated that only certain of these ECHs had a slight contribution to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biosynthesis. But significantly, PhaJ1, the only R-ECH that is associated with PHA granules, was shown to be involved in PHA mobilization in this haloarchaeon. PhaJ1 catalyzes the dehydration of (R)-3-hydroxyacyl-CoA, the common product of PHA degradation, to enoyl-CoA, the intermediate of the β-oxidation cycle, thus could link PHA mobilization to β-oxidation pathway in H. mediterranei. This linkage was further indicated from the up-regulation of the key genes of β-oxidation under the PHA mobilization condition, as well as the obvious inhibition of PHA degradation upon inhibition of the β-oxidation pathway. Interestingly, 96% of phaJ-containing haloarchaeal species possess both phaC (encoding PHA synthase) and the full set genes of β-oxidation, implying that the mobilization of carbon storage in PHA through the β-oxidation cycle would be general in haloarchaea.

Production of butanol and polyhydroxyalkanoate from industrial waste byClostridium beijerinckiiASU10

“…[58][59][60] For example, the presence of phaEC gene cluster encodes a PHA synthase class III and phaJEC encodes an (R)-enoyl-CoA hydratase that transforms crotonyl-CoA to (R)-3-hydroxybutyryl-CoA, the precursor for P(3HB) synthesis. 61 The current study confirmed that C beijerinckii ASU10 (KF372577) has the potential to accumulate a considerable amount of PHAs (37.93%) from fermentation of molasses. Remarkably, PHAs produced on molasses are composed of 47.5% 3HB (C4) and 52.5% 3HO)C8).…”

“…In that manner, the genome analysis of many strains of Clostridium , eg, Clostridium homopropionicum DSM 5847, Clostridium lundense DSM 17049, and Clostridium tetanomorphum DSM 665, indicated the occurrence of a gene cluster that is essential for P(3HB) synthesis . For example, the presence of phaEC gene cluster encodes a PHA synthase class III and phaJEC encodes an (R)‐enoyl‐CoA hydratase that transforms crotonyl‐CoA to (R)‐3‐hydroxybutyryl‐CoA, the precursor for P(3HB) synthesis …”

Cold adaptation of the Antarctic haloarchaea Halohasta litchfieldiae and Halorubrum lacusprofundi

“…An increased production of PHA might be linked to the demand for BCAAs, since propionyl-CoA can also be generated by degradation of BCAAs or their immediate oxoacid precursors (Steinb€ uchel and Pieper, 1992). PHA is synthesized as a carbon and energy reserve and mobilized when needed via b-oxidation; this process requires the same enzymes involved in fatty acid synthesis to operate in the reverse direction (Liu et al, 2016). The higher abundance of both hydroxyacyl-CoA synthesis (via propionyl-CoA) and b-oxidation enzymes in Hrr.…”

Current developments on polyhydroxyalkanoates synthesis by using halophiles as a promising cell factory

“…The PHA-related genes are generally organized into clusters but their arrangements are highly diversified. Mostly, the PHA gene cluster is conserved within haloarchaea and organised as maoC-phaR-phaP-phaE-phaC [100]. Compared to this, halophilic bacteria display significant differences.…”