Shifts from glucose to certain secondary carbon-sources result in activation of the extracytoplasmic function sigma factor σ E in Salmonella enterica serovar Typhimurium

Abstract

Salmonella enterica serovar Typhimurium (S. Typhimurium) elicits the starvation-stress response (SSR) due to starvation for an essential nutrient, e.g. a carbon/energy source (C-source). As part of the SSR, the alternative sigma factor s E is activated and induced. The authors suspect that this activation is, in part, triggered by changes in the S. Typhimurium cell envelope occurring during the adaptation from growth to carbon/energy starvation (C-starvation), and resulting in an increased need for s E -regulated factors involved in the proper folding and assembly of newly synthesized proteins destined for this extracytoplasmic compartment. This led to the hypothesis that a s E activation signal might arise during C-source shifts that cause the induction of proteins localized to the extracytoplasmic compartment, i.e. the outer membrane or periplasm, of the cell. To test this hypothesis, cultures were grown in minimal medium containing enough glucose to reach mid-exponential-phase, plus a non-limiting amount of a secondary 'less-preferred' but utilizable carbon/energy source. The s E activity was then monitored using plasmids carrying rpoEP1-and rpoEP2-lacZ transcriptional fusions, which exhibit s E -independent and -dependent lacZ expression, respectively. The secondary C-sources maltose, succinate and citrate, which have extracytoplasmic components involved in their utilization (e.g. LamB), resulted in a discernible diauxic lag period and a sustained increase in s E activity. Growth transition from glucose to other utilizable phosphotransferase (PTS) and non-PTS C-sources, such as trehalose, mannose, mannitol, fructose, glycerol, D-galactose or L-arabinose, did not cause a discernible diauxic lag period or a sustained increase in s E activity. Interestingly, a shift from glucose to melibiose, which does not use an extracytoplasmic-localized protein for uptake, did cause an observable diauxic lag period but did not result in a sustained increase in s E activity. In addition, overexpression of LamB from an arabinose-inducible promoter leads to a significant increase in s E activity in the absence of a glucose to maltose shift or C-starvation. Furthermore, a DlamB : : V-Km r mutant, lacking the LamB maltoporin, exhibited an approximately twofold reduction in the sustained s E activity observed during a glucose to maltose shift, again supporting the hypothesis. Interestingly, the LamB protein lacks the typical Y-X-F terminal tripeptide of the OmpC-like peptides that activate DegS protease activity leading to s E activation. It does, however, possess a terminal pentapeptide (Q-M-E-I-W-W) that may function as a ligand for a putative class II PDZ-binding site. The authors therefore propose that the s E regulon of S. Typhimurium not only is induced in response to deleterious environmental conditions, but also plays a role in the adaptation of cells to new growth conditions that necessitate changes in the extracytoplasmic compartment of the cell, which may involve alternative signal recognition and activation pathways t...

Resistance and survival strategies of Salmonella enterica to environmental stresses

“…Of the several Csources tested, only those whose utilization involved a periplasmic and/or outer membrane protein component (e.g., maltose, citrate, and succinate) resulted in sustained σ E activation (Kenyon et al, 2005). Furthermore, overexpression of LamB from a plasmid resulted in σ E activation even though it lacks the Y-x-F peptide shown to activate the DegS protease triggering the RIP cascade (Kenyon et al, 2005). Furthermore, LamB overexpression appears to promote σ E activation by indirectly increasing OMP (e.g., OmpC) misfolding (W.J.…”

“…inner membrane, peptidoglycan and outer membrane components [e.g., the types and amounts of fatty acids in membrane lipids or the lipopolysaccharide (LPS) of the outer membrane], and (vi) enzymes to prevent or repair cellular damage as a result of environmental stresses (Almirón, Link, Furlong, & Kolter, 1992;Dougherty & Pucci, 1994;Druilhet & Sobek, 1984;El-Khani & Stretton, 1981;Hengge-Aronis, 1999;Huisman et al, 1996;Humphreys et al, 2003;Kenyon et al, 2007;Kenyon, Humphreys, Roberts, & Spector, 2010;Kenyon, Thomas, Johnson, Pallen, & Spector, 2005;Matin, 2009;Skovierova et al, 2006;Spector, 1998;Spector & Cubitt, 1992;Spector, DiRusso, et al, 1999;. Microarray analyses comparing C-starved S. Typhimurium to growing/non-starved cells indicates that there are approximately 160, 500 and 1300 open reading frames (ORFs) exhibiting at least 10-, 5-and 2-fold induction, respectively, in response to C-starvation (M. Antonio, S. Lucchini, R. Chaudhuri, A. Thompson, J. Hinton, M. Spector & M. Pallen, unpublished data).…”

Role of cAMP receptor protein in phenotype and stress tolerance in Salmonella enterica serovar Typhimurium

“…A reduction in the zwf gene expression in the Δcrp (Figure 4a) signifies a slow glucose metabolism via the pentose phosphate pathway, a diminished NADPH formation, and a decreased synthesis of fatty acids, steroids and ribose which are important precursors for various metabolic processes [40]. Kenyon et al [13] have demonstrated an observable diauxic lag period in S. Typhimurium showed with the secondary carbon sources like D-maltose, D-succinate and D-citrate [13]. Nevertheless, all three aforementioned carbon sources did not support the growth of the Δcrp (Figure S1).…”

A Tale of 6 Sigmas: How Changing Partners Allows Salmonella to Thrive in the Best of Times and Survive the Worst of Times

“…When the bacteria face stressors, other sigma factors are involved in the expression of genes necessary to survive the stress, such as σ E , σ 24 , or RpoE which results in transcription of genes to combat envelop stress (Kenyon et al, 2005). RpoE is constitutively expressed in the bacteria, held inactive by interaction with various binding proteins.…”