Abstract
Polyhydroxyalkanoate (PHA) is a biodegradable polymer that is synthesized by a wide range of microorganisms. One of the derivatives of PHA, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) has flexible material properties and low melting temperature. We have previously demonstrated that PHBH is degradable in a freshwater environment via the formation of biofilm on the surface of the PHBH film. Undibacterium sp. KW1 and YM2, which were isolated from the biofilm present on the PHBH film in the freshwater sample, were shown to have PHBH-degrading activity. In this study, the complete genome sequence of KW1 and YM2 revealed that the extracellular PHA depolymerase gene, designated as phaZUD, was present in their chromosomes. Sequence analysis revealed that PhaZUD contained four domains: a signal peptide, catalytic domain, linker domain, and substrate-binding domain. Escherichia coli harboring a PhaZUD-expressing plasmid showed PHBH-degrading activity in LB medium containing 1 wt% PHBH powder. The recombinant His-tagged PhaZUD from KW1 and YM2 was purified from the culture supernatant and shown to have PHBH-degrading activity at the optimum temperature of 35 and 40°C, respectively. When the degradation product in the PHBH solution was treated with PhaZUD and assayed by LC-TOF-MS, we detected various oligomer structures, but no more than pentamers, which consist of 3-hydroxybutyrate and 3-hydroxyhexanoate. These results demonstrated that PhaZUD may have an endo-type extracellular PHA depolymerase activity.
Highlights
In modern society, plastic pollution is a serious problem with serious effects on the environment and wildlife [1]
We demonstrated that the genome sequences of the Undibacterium sp
The genus Undibacterium belongs to the family Oxalobacteraceae, which is a phylogenetically diverse aquatic bacterium family [24]
Summary
Plastic pollution is a serious problem with serious effects on the environment and wildlife [1]. The use of biodegradable plastics is one of the solutions to prevent the generation of microplastics in the aquatic environment. We have previously demonstrated that the PHBH film is degradable in both seawater and freshwater environments [8, 9]. PHBH-degrading bacteria isolated from the biofilm formed on the surface of the PHBH film were assigned to the genus Acidovorax, Undibacterium, and Chitinimonas [9]. The genus Acidovorax has been previously shown to be PHA-degrading bacteria [10, 11], there is no report of the genus Undibacterium as having this activity. We isolated two PHBH-degrading strains, Undibacterium sp., KW1 and YM2, from the Japanese lakes Kawaguchi-ko and Yamanaka-ko, respectively [9]. We investigated the enzymatic activity of the purified PHBH-degrading enzyme
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