Escherichia coli genes expressed preferentially in an aquatic environment

Abstract

SummaryEnteric bacteria are frequently found in aquatic environments, where they may pose a risk to human health. Although bacterial survival and persistence in such habitats has been studied extensively, there is almost no information about bacterial adaptation to these conditions at the level of changes in gene expression. As a first exploration of this field, we have carried out a screen designed to identify Escherichia coli genes that show increased expression in an aquatic environment. The screen was performed by subtractive hybridization on a genomic library and led to the identification of several RNA species more abundant in cells inoculated in this medium than in stationaryphase cultures after growth in rich medium. The genes identified include specific tRNA operons and a gene of unknown function, gapC, with similarities to glyceraldehyde-3-phosphate dehydrogenases. E. coli K-12 strains appear to have accumulated mutations in gapC, which may impede its translation, whereas natural isolates have an intact gapC gene. Sequence comparison of gapC with related genes suggests its acquisition by horizontal gene transfer from Gram-positive bacteria.

The genetic structure of Escherichia coli populations in primary and secondary habitats

“…Savageau (1983) suggested that E. coli cells cope with the transition by possessing a dual regulation system, where genes with products in high demand are under positive control, whilst genes with products in low demand are under negative control ; the controls systems alternate depending on the specific demands imposed by the primary and secondary environments. Savageau (1983) presented numerous examples of physiological functions in enteric bacteria that are consistent with the demand theory and it has been demonstrated that, in E. coli, some genes appear to be preferentially expressed in the external environment (Espinosa-Urgel & Kolter, 1998).…”

Protein patterns of gel-entrappedEscherichia coli cells differ from those of free-floating organisms

“…The amino acid sequence of Alda displays similarities with sequences of several aldehyde dehydrogenases of eucaryotic origin but not with microbial glyceraldehyde 3-phosphate dehydrogenase [30]. Nevertheless, the overexpression of Alda may be compared with recent data obtained by EspinosaUrgel and Kolter [31]. These authors showed that E. coli cells exposed to aquatic environments overexpressed a gene of unknown function, gapC, whose product showed [32].…”

“…These authors showed that E. coli cells exposed to aquatic environments overexpressed a gene of unknown function, gapC, whose product showed [32]. In a similar way, Espinosa-Urgel and Kolter speculated that the expression of gapC in organisms exposed to an aquatic environment helps the cells to prepare for the colonization of a new host by contributing to the synthesis of curli [31]. Might Alda accumulation reflect another stress response of the cells?…”

Biodiversity and evolution of primary carbon metabolism in Aspergillus nidulans and other Aspergillus spp.

“…Such a multiplicity is well known in bacteria (in, e.g., E. coli; Hidalgo et al, 1996;Espinosa-Urgel and Kolter, 1998). In A. fumigatus strain Af293, the second gene (gpdB) [locus AFUA_5G01030] is a pseudogene due to a very recent duplication of 18 bases in the coding area which introduces an in-frame stop codon whereas the deduced amino acid sequence is otherwise identical to that of the GpdB protein from a second A. fumigatus strain, A1163.…”