bph genes of the thermophilic PCB degrader, Bacillus sp. JF8: characterization of the divergent ring-hydroxylating dioxygenase and hydrolase genes upstream of the Mn-dependent BphC

Abstract

Bacillus sp. JF8 is a thermophilic polychlorinated biphenyl (PCB) degrader, which utilizes biphenyl and naphthalene. A thermostable, Mn-dependent 2,3-dihydroxybiphenyl 1,2-dioxygenase, BphC_JF8, has been characterized previously. Upstream of bphC are five ORFs exhibiting low homology with, and a different gene order from, previously characterized bph genes. From the 5' to 3' direction the genes are: a putative regulatory gene (bphR), a hydrolase (bphD), the large and small subunits of a ring-hydroxylating dioxygenase (bphA1A2), and a cis-diol dehydrogenase (bphB). Hybridization studies indicate that the genes are located on a plasmid. Ring-hydroxylating activity of recombinant BphA1A2_JF8 towards biphenyl, PCB, naphthalene and benzene was observed in Escherichia coli cells, with complementation of non-specific ferredoxin and ferredoxin reductase by host cell proteins. PCB degradation by recombinant BphA1A2_JF8 showed that the congener specificity of the recombinant enzyme was similar to Bacillus sp. JF8. BphD_JF8, with an optimum temperature of 85 degrees C, exhibited a narrow substrate preference for 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid. The Arrhenius plot of BphD_JF8 was biphasic, with two characteristic energies of activation and a break point at 47 degrees C.