Diverse organization of genes of the beta-ketoadipate pathway in members of the marine Roseobacter lineage.
Members of the Roseobacter lineage, an ecologically important marine clade within the class alpha-Proteobacteria, harbor genes for the protocatechuate branch of the beta-ketoadipate pathway, a major catabolic route for lignin-related aromatic compounds. The genes of this pathway are typically clustered, although gene order varies among organisms. Here we characterize genes linked to pcaH and -G, which encode protocatechuate 3,4-dioxygenase, in eight closely related members of the Roseobacter lineage (pairwise 16S rRNA gene sequence identities, 92 to 99%). Sequence analysis of genomic fragments revealed five unique pca gene arrangements. Identical gene organization was found for isolates demonstrating species-level identity (i.e., >99% 16S rRNA gene similarity). In one isolate, six functionally related genes were clustered: pcaQ, pobA, pcaD, pcaC, pcaH, and pcaG. The remaining seven isolates lacked at least one of these genes in their clusters, although the relative order of the remaining genes was preserved. Three genes (pcaC, -H, and -G) were physically linked in all isolates. A highly conserved open reading frame (ORF) was found immediately downstream of pcaG in all eight isolates. Reverse transcription-PCR analysis of RNA from one isolate, Silicibacter pomeroyi DSS-3, provides evidence that this ORF is coexpressed with upstream pca genes. The absence of this ORF in similar bacterial pca gene clusters from diverse microbes suggests a niche-specific role for its protein product in Roseobacter group members. Collectively, these comparisons of bacterial pca gene organization illuminate a complex evolutionary history and underscore the widespread ecological importance of the encoded beta-ketoadipate pathway.
Department of Marine Sciences, University of Georgia, Athens, Georgia 30602, USA. alison.buchan@yale.edu
Alison
A
Buchan
Ellen L
EL
Neidle
Mary Ann
MA
Moran
D000272:Adipates / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D017753:Ecosystem; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D010802:Phylogeny; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D015183:Restriction Mapping; D041904:Roseobacter / Q000145:classification / Q000235:genetics* / Q000378:metabolism*; D013045:Species Specificity
D000272:Adipates; D004269:DNA, Bacterial; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; C027316:3-oxoadipic acid