A novel esterase DacA from sp. strain NyZ500 with deacetylation activity for acetylated polymer polyvinyl alcohol.

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. Content of acetyl group is a pivotal factor affecting performance of PVA derivatives in industrial application, and deacetylation is a non-negligible part in PVA degradation. However, the genetic and biochemical studies of its deacetylation remain largely elusive. Here, sp. strain NyZ500 was isolated for its capability of growing on acetylated PVA from activated sludge. A 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 ) deletion in NyZ501 and complemented strain NyZ501 restored the ability to grow on PVA. DacA which shares 21% identity with xylan esterase AxeA1 from 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 also possessed the deacetylation ability for acetylated xylan and the antibiotic intermediate 7-aminocephalosporanic acid (7ACA) but the enzymes for the above two compounds had no activities against PVA derivatives. This study enhanced our understanding of the diversity of microbial degradation of PVA and DacA characterized here is also a potential biocatalyst for the eco-friendly biotransformation of PVA derivatives and other acetylated compounds. 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 at high energy consumption and high pollution conditions using hazardous chemicals (such as NaOH, methanol) under high temperatures. The DacA reported here performs PVA deacetylation under mild conditions, then it has a great potential to be developed into an eco-friendly biocatalyst for biotransformation of PVA derivatives. DacA 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.