Utility of a Bifunctional Tryptophan Pathway Enzyme for the Classification of the Herbicola-Agglomerans Complex of Bacteria

Abstract

Bifunctional proteins are the result of relatively infrequent genetic events that are faithfully conserved. They are reliable markers that define phylogenetic clusters. The bifunctional protein anthranilate synthase: anthranilate 5-phosphoribosylpyrophosphate phosphoribosyltransferase (AS:PRT) separates two enteric clusters. Previously published data show that this bifunctional protein is present in the lineage shared by Escherichia coli, Salmonella typhimurium, Citrobacter freundii, Klebsiella pneumoniae, Enterobacter aerogenes, and Enterobacter cloacae, but is absent in Erwinia carotovora, Serratia marcescens, Proteus vulgaris, Morganella morganii, and Hafnia alvei. It has been postulated that aerogenic and anaerogenic strains of Enterobacter agglomerons belong to different groups, which correspond to the clusters mentioned above, respectively. In confirmation of this, we found that Enterobacter agglomerons ATCC 29915 (aerogenic) possesses bifunctional AS:PRT, whereas Enterobacter agglomerons ATCC 27155T (T = type strain) (anaerogenic) lacks AS:PRT. We also found that Erwinia herbicola 33243T lacks AS:PRT. Beji et al. (Int. J. Syst. Bacteriol. 38:77-88) recently showed that the type strains of Enterobacter agglomerons (ATCC 27155) and Erwinia herbicola (ATCC 33243) belong to the same genomic species. We suggest that Enterobacter agglomerons (= Erwinia herbicola) should be excluded from the genus Enterobacter. We further suggest that strains currently designated Enterobacter agglomerons can be grouped with Erwinia herbicola or with the enteric cluster containing Enterobacter depending upon whether bifunctional AS:PRT is absent or present, respectively.