A Novel Esterase, DacApva, from Comamonas sp. Strain NyZ500 with Deacetylation Activity for the Acetylated Polymer Polyvinyl Alcohol

摘要

As a water-soluble polymer, the widely used polyvinyl alcohol (PVA) is produced from hydrolysis of polyvinyl acetate. Microbial PVA carbon backbone cleavage via a two-step reaction of dehydrogenation and hydrolysis has been well studied. The content of the acetyl group is a pivotal factor affecting performance of PVA derivatives in industrial applications, and deacetylation is a nonnegligible part of PVA degradation. However, the genetics and biochemistry of its deacetylation remain largely elusive. Here, Comamonas sp. strain NyZ500 was isolated for its capability of growing on acetylated PVA from activated sludge. The spontaneous PVA utilization-deficient mutant strain NyZ501 was obtained when strain NyZ500 was cultured in rich media. Comparative analysis between the genomes of these two strains revealed a fragment (containing a putative hydrolase gene, dacA_(pva) ) deletion in strain NyZ501, and in the dacA_(pva)- complemented strain NyZ501 the ability to grow on PVA was restored. DacA_(pva,) which shares 21% identity with xylan esterase AxeA1 from Prevotella ruminicola 23, is a unique deacetylase catalyzing the conversion of acetylated PVA and its derivatives to deacetylated counterparts. This indicates that strain NyZ500 utilizes acetylated PVA via acetate as a carbon source to grow. DacA_(pva) also possesses the ability to deacetylate acetylated xylan and the antibiotic intermediate 7-aminocephalosporanic acid (7ACA), but the enzymes responsible for the conversion of those two compounds have no activity against PVA derivatives. This study enhanced our understanding of the diversity of microbial degradation of PVA, and DacA_(pva) characterized here is also a potential biocatalyst for the eco-friendly biotransformation of PVA derivatives and other acetylated compounds.IMPORTANCE Water-soluble PVA, which possesses a very robust ability to accumulate in the environment, has a very grave environmental impact due to its widespread use in industrial and household applications. On the other hand, chemical transformation of PVA derivatives is currently being carried out under high-energy-consumption and high-pollution conditions using hazardous chemicals (such as NaOH and methanol) under high temperatures. The DacA_(pva) reported here performs PVA deacetylation under mild conditions, so it has great potential to be developed into an eco-friendly biocatalyst for biotransformation of PVA derivatives. DacA_(pva) also has deacetylation activity for compounds other than PVA derivatives, which facilitates its development into a broad-spectrum deacetylation biocatalyst for production of certain desired compounds.