A Global Metabolic Shift Is Linked to Salmonella Multicellular Development

Bacteria can elaborate complex patterns of development that are dictated by temporally ordered patterns of gene expression, typically under the control of a master regulatory pathway. For some processes, such as biofilm development, regulators that initiate the process have been identified but subsequent phenotypic changes such as stress tolerance do not seem to be under the control of these same regulators. A hallmark feature of biofilms is growth within a self-produced extracellular matrix. In this study we used metabolomics to compare Salmonella cells in rdar colony biofilms to isogenic csgD deletion mutants that do not produce an extracellular matrix. The two populations show distinct metabolite profiles. Even though CsgD controls only extracellular matrix production, metabolite signatures associated with cellular adaptations associated with stress tolerances were present in the wild type but not the mutant cells. To further explore these differences we examine the temporal gene expression of genes implicated in biofilm development and stress adaptations. In wild type cells, genes involved in a metabolic shift to gluconeogenesis and various stress-resistance pathways exhibited an ordered expression profile timed with multicellular development even though they are not CsgD regulated. In csgD mutant cells, the ordered expression was lost. We conclude that the induction of these pathways results from production of, and growth within, a self produced matrix rather than elaboration of a defined genetic program. These results predict that common physiological properties of biofilms are induced independently of regulatory pathways that initiate biofilm formation

Antibiotic resistance in swarming salmonella

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Bringing order to a complex molecular machine: The assembly of the bacterial flagella

AbstractThe bacterial flagellum is an example of elegance in molecular engineering. Flagella dependent motility is a widespread and evolutionarily ancient trait. Diverse bacterial species have evolved unique structural adaptations enabling them to migrate in their environmental niche. Variability exists in the number, location and configuration of flagella, and reflects unique adaptations of the microorganism. The most detailed analysis of flagellar morphogenesis and structure has focused on Escherichia coli and Salmonella enterica. The appendage assembles sequentially from the inner to the outer-most structures. Additionally the temporal order of gene expression correlates with the assembly order of encoded proteins into the final structure. The bacterial flagellar apparatus includes an essential basal body complex that comprises the export machinery required for assembly of the hook and flagellar filament. A review outlining the current understanding of the protein interactions that make up this remarkable structure will be presented, and the associated temporal genetic regulation will be briefly discussed

Long-Term Survival of Salmonella enterica Serovar Typhimurium Reveals an Infectious State That Is Underrepresented on Laboratory Media Containing Bile Salts▿

Cells in desiccated Salmonella enterica serovar Typhimurium rdar (red, dry, and rough) morphotype colonies were examined for culturability and infectivity after 30 months. Culturability decreased only 10-fold; however, cells were underrepresented on Salmonella selective media containing bile salts. These cells were mildly attenuated compared to the infectivity of freshly grown cells but still able to cause systemic infections in mice

Model of biofilm development dependent on cellular response to self-produced extracellular matrix.

Aggregation is initiated by the activation of the CsgD regulon; BapA is a large cell-surface protein involved in biofilm formation [84]. The metabolic demand of polysaccharide production leads to induction of gluconeogenesis and the subsequent response to the self-produced matrix activates pathways that lead to general biofilm phenotypes. These later processes represent emergent behaviors and are not under control of a “biofilm specific’ regulatory cascade.</p

Comparison of global gene expression in aggregative (wild-type) and non-aggregative (<i>csgD</i> mutant) <i>S.</i> Typhimurium cultures during growth at 28°C.

Each wild-type (A) or csgD mutant (B) reporter strain contains a plasmid-based promoter-luciferase (luxCDABE) fusion designed to measure gene expression by light production. For each reporter, shown is the ratio of lux activity at each time point divided by the maximum luminescence in the wt reporter strain. Blue and red indicate low and high expression, respectively. Gene (or operon) names are listed on the left of each panel; sig38H4 and sig70_7 are synthetic reporters designed to measure σS and σ70 activity, respectively. Genes that are essential for rdar morphotype formation are shown in red; mlrA encodes a transcriptional regulator required for csgDEFG expression [83]. Arrows in (A) signify the beginning of the aggregation process at 25 h.</p

Detailed comparison of gene expression in <i>wt</i> and Δ<i>csgD</i> strains.

Each red (wild-type) or blue (csgD mutant) curve represents the raw, non-normalized gene expression value (light counts per second; CPS) in each strain as a function of time. Expression profiles are shown for operons encoding proteins essential for rdar morphotype aggregation (A), gluconeogenesis-specific enzymes (B), glycolytic or gluconeogenic bi-directional enzymes (C), upper tricarboxylic acid cycle enzymes (D), or proteins involved in osmoprotection (E). Gene (operon) names are listed on the upper left in each panel. σS activity is represented by expression measured from the sig38H4 reporter. Vertical lines in each graph in (A) represent the beginning of the aggregation process at 25 h; these lines are shown for all other reporters to highlight the coordinated timing of gene expression. For the majority of genes, promoter activity peaks at or near the time of aggregation in wild-type cells.</p

Simplified <i>S.</i> Typhimurium metabolic map displaying the results of metabolomic analaysis.

Compounds shown were identified at statistically higher concentrations in wild-type colonies (red) or csgD mutant colonies (blue). The schematics for gluconeogenesis, the TCA cycle, and related pathways were adapted from the EcoCYC™ database (www.ecocyc.org). Genes encoding important enzymes are listed in italics; their expression was monitored using promoter luciferase fusions. Genes encoding enzymes that catalyze key reactions in gluconeogenesis are underlined.</p