Thirty years of metabolic engineering for biosynthesis of polyhydroxyalkanoates / 生物工程学报

Polyhydroxyalkanoate (PHA) is a family of biodegradable polyesters synthesized by microorganisms. It has various monomer structures and physical properties with broad application prospects. However, its large-scale production is still hindered by the high cost. In the past 30 years, metabolic engineering approach has been used to tune the metabolic flux, engineer and introduce pathways. The efficiency of PHA synthesis by microorganisms has been significantly improved, and the diversity of PHA monomer, structure and substrate have also been enriched. Meanwhile, by changing cell morphology and PHA particle size, more efficient downstream production process has achieved and PHA production costs have been reduced. In recent years, "Next generation industrial biotechnology" (NGIB) based on extremophiles, especially halophilic Halomonas spp., has been rapidly developed. NGIB has achieved the opening and continuous production of PHA, which simplifies the production process and saves energy and fresh water. Combined with metabolic engineering, Halomonas spp. can be transformed into low-cost production platform of numerous PHA. It is expected to improve the market competitiveness and promote the commercialization of PHA.

[Isolation of a moderately halophilic bacterium resistant to some toxic metals from Aran and Bidgol Salt Lake and its phylogenetic characterization by 16S rDNA gene]

Heavy metals are toxic for human beings, animals and even plants. For example, nickel causes contact hypersensitivity and also may have carcinogenic effects in human. There are physicochemical and biological methods for removing these elements from environment. Some bacteria are able to remove these elements. In this study, the resistance of bacteria in Aran and Bidgol Salt Lake to heavy metals has been evaluated. Seven bacterial samples of the lake were transferred to Ventosa culture medium. Isolated colonies were grown on the medium containing nickel. The resistant bacteria were transferred to media containing other heavy metal elements. Biochemical, morphological and phylogenetic studies were done based on sequencing of 16S rDNA gene in order to identify the isolated resistant bacterium. In addition, enzymatic potency of the bacteria was evaluated for determination of biotechnological value. 16s rDNA sequencing was applied only for one [out of 46] isolated halophilic bacterium. The bacterium displayed a good potency for growing up in the medium containing 2.5-10% NaCl with a considerable tolerance to nickel and other heavy metals. A bacterium with 98% homology with Salinovibrio costicola species is resistant to some toxic metals and it also has the potency of removing nickel from the contaminated environment and producing some industrial enzymes