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Sal genes determining the catabolism of salicylate esters are part of a supraoperonic cluster of catabolic genes in Acinetobacter sp. strain ADP1.

ABSTRACT: A 5-kbp region upstream of the are-ben-cat genes was cloned from Acinetobacter sp. strain ADP1, extending the supraoperonic cluster of catabolic genes to 30 kbp. Four open reading frames, salA, salR, salE, and salD, were identified from the nucleotide sequence. Reverse transcription-PCR studies suggested that these open reading frames are organized into two convergent transcription units, salAR and salDE. The salE gene, encoding a protein of 239 residues, was ligated into expression vector pET5a. Its product, SalE, was shown to have esterase activity against short-chain alkyl esters of 4-nitrophenol but was also able to hydrolyze ethyl salicylate to ethanol and salicylic acid. A mutant of ADP1 with a Km(r) cassette introduced into salE had lost the ability to utilize only ethyl and methyl salicylates of the esters tested as sole carbon sources, and no esterase activity against ethyl salicylate could be detected in cell extracts. SalE was induced during growth on ethyl salicylate but not during growth on salicylate itself. salD encoded a protein of undetermined function with homologies to the Escherichia coli FadL membrane protein, which is involved in facilitating fatty acid transport, and a number of other proteins detected during aromatic catabolism, which may also function in hydrocarbon transport or uptake processes. A Km(r) cassette insertion in salD deleteriously affected cell growth and viability. The salA and salR gene products closely resemble two Pseudomonas proteins, NahG and NahR, respectively encoding salicylate hydroxylase and the LysR family regulator of both salicylate and naphthalene catabolism. salA was cloned into pUC18 together with salR and salE, and its gene product showed salicylate-inducible hydroxylase activity against a range of substituted salicylates, with the same relative specific activities as found in wild-type ADP1 grown on salicylate. Mutations involving insertion of Km(r) cassettes into salA and salR eliminated expression of salicylate hydroxylase activity and the ability to grow on either salicylate or ethyl salicylate. Studies of mutants with disruptions of genes of the beta-ketoadipate pathway with or without an additional salE mutation confirmed that ethyl salicylate and salicylate were channeled into the beta-ketoadipate pathway at the level of catechol and thence dissimilated by the cat gene products. SalR appeared to regulate expression of salA but not salE.

SUBMITTER: Jones RM

PROVIDER: S-EPMC101918 | biostudies-literature | 2000 Apr

REPOSITORIES: biostudies-literature

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sal genes determining the catabolism of salicylate esters are part of a supraoperonic cluster of catabolic genes in Acinetobacter sp. strain ADP1.

Jones R M RM Pagmantidis V V Williams P A PA

Journal of bacteriology 20000401 7

A 5-kbp region upstream of the are-ben-cat genes was cloned from Acinetobacter sp. strain ADP1, extending the supraoperonic cluster of catabolic genes to 30 kbp. Four open reading frames, salA, salR, salE, and salD, were identified from the nucleotide sequence. Reverse transcription-PCR studies suggested that these open reading frames are organized into two convergent transcription units, salAR and salDE. The salE gene, encoding a protein of 239 residues, was ligated into expression vector pET5a ...[more]

PMID: 10715011

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Project description:Hydroxycinnamates are plant products catabolized through the diphenol protocatechuate in the naturally transformable bacterium Acinetobacter sp. strain ADP1. Genes for protocatechuate catabolism are central to the dca-pca-qui-pob-hca chromosomal island, for which gene designations corresponding to catabolic function are dca (dicarboxylic acid), pca (protocatechuate), qui (quinate), pob (p-hydroxybenzoate), and hca (hydroxycinnamate). Acinetobacter hcaC had been cloned and shown to encode a hydroxycinnamate:coenzyme A (CoA) SH ligase that acts upon caffeate, p-coumarate, and ferulate, but genes for conversion of hydroxycinnamoyl-CoA to protocatechuate had not been characterized. In this investigation, DNA from pobS to an XbaI site 5.3 kb beyond hcaC was captured in the plasmid pZR8200 by a strategy that involved in vivo integration of a cloning vector near the hca region of the chromosome. pZR8200 enabled Escherichia coli to convert p-coumarate to protocatechuate in vivo. Sequence analysis of the newly cloned DNA identified five open reading frames designated hcaA, hcaB, hcaK, hcaR, and ORF1. An Acinetobacter strain with a knockout of HcaA, a homolog of hydroxycinnamoyl-CoA hydratase/lyases, was unable to grow at the expense of hydroxycinnamates, whereas a strain mutated in HcaB, homologous to aldehyde dehydrogenases, grew poorly with ferulate and caffeate but well with p-coumarate. A chromosomal fusion of lacZ to the hcaE gene was used to monitor expression of the hcaABCDE promoter. LacZ was induced over 100-fold by growth in the presence of caffeate, p-coumarate, or ferulate. The protein deduced to be encoded by hcaR shares 28% identity with the aligned E. coli repressor, MarR. A knockout of hcaR produced a constitutive phenotype, as assessed in the hcaE::lacZ-Km(r) genetic background, revealing HcaR to be a repressor as well. Expression of hcaE::lacZ in strains with knockouts in hcaA, hcaB, or hcaC revealed unambiguously that hydroxycinnamoyl-CoA thioesters relieve repression of the hcaABCDE genes by HcaR.

Project description:Hydroxycinnamates are ubiquitous in the environment because of their contributions to the structure and defense mechanisms of plants. Additional plant products, many of which are formed in response to stress, support the growth of Acinetobacter sp. strain ADP1 through pathways encoded by genes in the dca-pca-qui-pob chromosomal cluster. In an appropriate genetic background, it was possible to select for an Acinetobacter strain that had lost the ability to grow with caffeate, a commonly occurring hydroxycinnamate. The newly identified mutation was shown to be a deletion in a gene designated hcaC and encoding a ligase required for conversion of commonly occurring hydroxycinnamates (caffeate, ferulate, coumarate, and 3,4-dihydroxyphenylpropionate) to thioesters. Linkage analysis showed that hcaC is linked to pobA. Downstream from hcaC and transcribed in the direction opposite the direction of pobA transcription are open reading frames designated hcaDEFG. Functions of these genes were inferred from sequence comparisons and from the properties of knockout mutants. HcaD corresponded to an acyl coenzyme A (acyl-CoA) dehydrogenase required for conversion of 3,4-dihydroxyphenylpropionyl-CoA to caffeoyl-CoA. HcaE appears to encode a member of a family of outer membrane proteins known as porins. Knockout mutations in hcaF confer no discernible phenotype. Knockout mutations in hcaG indicate that this gene encodes a membrane-associated esterase that hydrolyzes chlorogenate to quinate, which is metabolized in the periplasm, and caffeate, which is metabolized by intracellular enzymes. The chromosomal location of hcaG, between hcaC (required for growth with caffeate) and quiA (required for growth with quinate), provided the essential clue that led to the genetic test of HcaG as the esterase that produces caffeate and quinate from chlorogenate. Thus, in this study, organization within what is now established as the dca-pca-qui-pob-hca chromosomal cluster provided essential information about the function of genes in the environment.

Dataset Information

Sal genes determining the catabolism of salicylate esters are part of a supraoperonic cluster of catabolic genes in Acinetobacter sp. strain ADP1.

Publications

sal genes determining the catabolism of salicylate esters are part of a supraoperonic cluster of catabolic genes in Acinetobacter sp. strain ADP1.

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