Effect of glucose concentration on swimming motility in enterobacteria

The oral microbiome is associated with HPA axis response to a psychosocial stressor

Intense psychosocial stress during early life has a detrimental effect on health-disease balance in later life. Simultaneously, despite its sensitivity to stress, the developing microbiome contributes to long-term health. Following stress exposure, HPA-axis activation regulates the "fight or flight" response with the release of glucose and cortisol. Here, we investigated the interaction between the oral microbiome and the stress response. We used a cohort of 115 adults, mean age 24, who either experienced institutionalisation and adoption (n = 40) or were non-adopted controls (n = 75). Glucose and cortisol measurements were taken from participants following an extended socially evaluated cold pressor test (seCPT) at multiple time points. The cohort´s oral microbiome was profiled via 16S-V4 sequencing on microbial DNA from saliva and buccal samples. Using mixed-effect linear regressions, we identified 12 genera that exhibited an interaction with host's cortisol-glucose response to stress, strongly influencing intensity and clearance of cortisol and glucose following stress exposure. Particularly, the identified taxa influenced the glucose and cortisol release profiles and kinetics following seCPT exposure. In conclusion, our study provided evidence for the oral microbiome modifying the effect of stress on the HPA-axis and human metabolism, as shown in glucose-cortisol time series data.

Glucose-Induced Enhanced Virulence in Strains of Multidrug-Resistant Pseudomonas aeruginosa Isolated from Diabetic Patients

Pseudomonas aeruginosa is known for its metabolic versatility and uses a variety of substrates; interestingly, glucose is not the favored carbon source. Although glucose is not readily utilized by them, there is a possibility that the increased susceptibility of diabetics to infections with P. aeruginosa is related to the effect of glucose on the expression of virulence genes. The curiosity in understanding the effect of glucose on virulence gene expression in P. aeruginosa and the lacuna of studies in this field prompted us to undertake the current investigation. It included the quantification of various virulence factors and their gene expression upon supplementation with glucose in clinical MDR P. aeruginosa isolates recovered from diabetics. Interestingly, the study observed a remarkable difference in the virulence attributes in the isolates with and without glucose supplementation. External glucose was found to be modulating the QS gene expression, thus altering the elaboration of other virulence factors. Variations in the gene expressions induced by glucose partly explain the increased susceptibility of diabetic patients to P. aeruginosa infections.

Influence of glucose on swarming and quorum sensing of Dickeya solani

Dickeya solani is a pathogen most frequently responsible for infecting potato plants in Europe. As in the case of most plant pathogens, its ability to colonize and invade the host depends on chemotaxis and motility. The coordinated movement of Dickeya over solid surfaces is governed by a quorum sensing mechanism. In D. solani motility is regulated by ExpI-ExpR proteins, homologous to luxI-luxR system from Vibrio fisheri, in which N-acyl-homoserine lactones (AHLs) serve as signaling molecules. Moreover, in many Gram-negative bacteria motility is coupled with central metabolism via carbon catabolite repression. This enables them to reach more nutrient-efficient niches. The aim of this study was to analyze the swarming motility of D. solani depending on the volume of the medium in the cultivation plate and glucose content. We show that the ability of this bacterium to move is strictly dependent on both these factors. Moreover, we analyze the production of AHLs and show that the quorum sensing mechanism in D. solani is also influenced by the availability of glucose in the medium and that the distribution of these signaling molecules are different depending on the volume of the medium in the plate.

Bacterial-induced pH shifts link individual cell physiology to macroscale collective behavior

Bacteria have evolved a diverse array of signaling pathways that enable them to quickly respond to environmental changes. Understanding how these pathways reflect environmental conditions and produce an orchestrated response is an ongoing challenge. Herein, we present a role for collective modifications of environmental pH carried out by microbial colonies living on a surface. We show that by collectively adjusting the local pH value, Paenibacillus spp., specifically, regulate their swarming motility. Moreover, we show that such pH-dependent regulation can converge with the carbon repression pathway to down-regulate flagellin expression and inhibit swarming in the presence of glucose. Interestingly, our results demonstrate that the observed glucose-dependent swarming repression is not mediated by the glucose molecule per se, as commonly thought to occur in carbon repression pathways, but rather is governed by a decrease in pH due to glucose metabolism. In fact, modification of the environmental pH by neighboring bacterial species could override this glucose-dependent repression and induce swarming of Paenibacillus spp. away from a glucose-rich area. Our results suggest that bacteria can use local pH modulations to reflect nutrient availability and link individual bacterial physiology to macroscale collective behavior.

Construction of a genetic multiplexer to toggle between chemosensory pathways in Escherichia coli

Many applications require cells to switch between discrete phenotypic states. Here, we harness the FimBE inversion switch to flip a promoter, allowing expression to be toggled between two genes oriented in opposite directions. The response characteristics of the switch are characterized using two-color cytometry. This switch is used to toggle between orthogonal chemosensory pathways by controlling the expression of CheW and CheW*, which interact with the Tar (aspartate) and Tsr* (serine) chemoreceptors, respectively. CheW* and Tsr* each contain a mutation at their protein-protein interface such that they interact with each other. The complete genetic program containing an arabinose-inducible FimE controlling CheW/CheW* (and constitutively expressed tar/tsr*) is transformed into an Escherichia coli strain lacking all native chemoreceptors. This program enables bacteria to swim toward serine or aspartate in the absence or in the presence of arabinose, respectively. Thus, the program functions as a multiplexer with arabinose as the selector. This demonstrates the ability of synthetic genetic circuits to connect to a natural signaling network to switch between phenotypes.

Glucose induced fractal colony pattern of Bacillus thuringiensis

Growing colonies of bacteria on the surface of thin agar plates exhibit fractal patterns as a result of nonlinear response to environmental conditions, such as nutrients, solidity of the agar medium and temperature. Here, we examine the effect of glucose on pattern formation by growing colonies of Bacillus thuringiensis isolate KPWP1. We also present the theoretical modeling of the colony growth of KPWP1 and the associated spatio-temporal patterns. Our experimental results are in excellent agreement with simulations based on a reaction-diffusion model that describes diffusion-limited aggregation and branching, in which individual cells move actively in the periphery, but become immotile in the inner regions of the growing colony. We obtain the Hausdorff fractal dimension of the colony patterns: D(H.Expt)=1.1969 and D(H, R.D.=)1.1965, for experiment and reaction-diffusion model, respectively. Results of our experiments and modeling clearly show how glucose at higher concentration can prove to be inhibitory for motility of growing colonies of B. thuringiensis cells on semisolid support and be responsible for changes in the growth pattern.

Similar and divergent effects of ppGpp and DksA deficiencies on transcription in Escherichia coli

The concerted action of ppGpp and DksA in transcription has been widely documented. In disparity with this model, phenotypic studies showed that ppGpp and DksA might also have independent and opposing roles in gene expression in Escherichia coli. In this study we used a transcriptomic approach to compare the global transcriptional patterns of gene expression in strains deficient in ppGpp (ppGpp(0)) and/or DksA (DeltadksA). Approximately 6 and 7% of all genes were significantly affected by more than twofold in ppGpp- and DksA-deficient strains, respectively, increasing to 13% of all genes in the ppGpp(0) DeltadksA strain. Although the data indicate that most of the affected genes were copositively or conegatively regulated by ppGpp and DksA, some genes that were independently and/or differentially regulated by the two factors were found. The large functional group of chemotaxis and flagellum synthesis genes were notably differentially affected, with all genes being upregulated in the DksA-deficient strain but 60% of them being downregulated in the ppGpp-deficient strain. Revealingly, mutations in the antipausing Gre factors suppress the upregulation observed in the DksA-deficient strain, emphasizing the importance of the secondary channel of the RNA polymerase for regulation and fine-tuning of gene expression in E. coli.

Catabolite repression control of flagellum production by Serratia marcescens

Serratia marcescens is an emerging opportunistic pathogen with a remarkably broad host range. The cAMP-regulated catabolite repression system of S. marcescens has recently been identified and demonstrated to regulate biofilm formation through the production of surface adhesions. Here we report that mutations in components of the catabolite repression system (cyaA and crp) eliminate flagellum production and swimming motility. Exogenous cAMP was able to restore flagellum production to adenylate cyclase mutants, as determined by transmission electron microscopy and PAGE analysis. A transposon-generated suppressor mutation of the crp motility defect mapped to upstream of the flhDC operon. This suppressor mutation resulted in an upregulation of flhD expression and flagellum production, indicating that flhDC expression is sufficient to restore flagellum production to crp mutants. Lastly, and contrary to a previous report, we found that flhD expression is controlled by the catabolite repression system using quantitative RT-PCR. Together, these data indicate that flagellum production is regulated by the cAMP-dependent catabolite repression system. Given the role of flagella in bacterial pathogenicity, the regulatory pathway described here may assist us in better understanding the putative role of motility in dissemination and virulence of this opportunistic pathogen.

Role of flhDC in the expression of the nuclease gene nucA, cell division and flagellar synthesis in Serratia marcescens

We investigated in Serratia marcescens the functions of the flhDC operon, which controls motility and cell division in enteric bacteria. Included in our evaluations were investigation of cell division, flagellar synthesis and regulation of the expression of nuclease (encoded by the nucA(Sm) gene, one of the virulence factors). Interruption of the chromosomal flhDC operon in S. marcescens CH-1 resulted in aberrant cell division and loss of nuclease and flagella. Expression of nucA(Sm) and other mutated phenotypes was restored in the flhDC mutant by the induction of overexpression of flhDC in a multicopy plasmid. Multicopied flhDC also induced the formation of differentiated cells (polyploid aseptate cells with oversynthesis of peritrichous flagella) in broth culture using minimal growth medium. Expression of the flhDC operon showed positive autoregulation, and was growth phase dependent (upregulated in early log phase). In addition, flhDC expression was inhibited when the temperature increased from 30 to 37 degrees C, and when osmolarity was increased, but was not influenced by glucose catabolite repression. These results show that FlhD/FlhC is a multifunctional transcriptional activator involved in the process of cell differentiation, swarming and virulence factor expression.