Effect of N-acetyl-D-glucosamine on gene expression in Vibrio parahaemolyticus

Enhanced production of N-acetyl-glucosaminidase by marine Aeromonas caviae CHZ306 in bioreactor

N-Acetyl-glucosaminidases (GlcNAcases) are exoenzymes found in a wide range of living organisms, which have gained great attention in the treatment of disorders related to diabetes, Alzheimer's, Tay-Sachs', and Sandhoff's diseases; the control of phytopathogens; and the synthesis of bioactive GlcNAc-containing products. Aiming at future industrial applications, in this study, GlcNAcase production by marine Aeromonas caviae CHZ306 was enhanced first in shake flasks in terms of medium composition and then in bench-scale stirred-tank bioreactor in terms of physicochemical conditions. Stoichiometric balance between the bioavailability of carbon and nitrogen in the formulated culture medium, as well as the use of additional carbon and nitrogen sources, played a central role in improving the bioprocess, considerably increasing the enzyme productivity. The optimal cultivation medium was composed of colloidal α-chitin, corn steep liquor, peptone A, and mineral salts, in a 5.2 C:N ratio. Optimization of pH, temperature, colloidal α-chitin concentration, and kLa conditions further increased GlcNAcase productivity. Under optimized conditions in bioreactor (i.e., 34 °C, pH 8 and kLa 55.2 h-1), GlcNAcase activity achieved 173.4 U.L-1 after 12 h of cultivation, and productivity no less than 14.45 U.L-1.h-1 corresponding to a 370-fold enhancement compared to basal conditions.

Quorum sensing regulates transcription of the pilin gene mshA1 of MSHA pilus in Vibrio parahaemolyticus

Vibrio parahaemolyticus produces two types of IV pili: mannose-sensitive haemagglutinin type IV pili (MSHA) and chitin-regulated pili (ChiRP). Both of them are required for biofilm formation and the pathogen persistence in hosts. However, there are few reports on the regulation of their expression. In the present study, we showed that the master quorum sensing (QS) regulators AphA and OpaR oppositely regulated the transcription of mshA1 encoding the pilin of MSHA pilus in V. parahaemolyticus. At low cell density (LCD), AphA indirectly repressed mshA1 transcription. In contrast, at high cell density (HCD), OpaR bound to the regulatory DNA region of mshA1 to activate its transcription. Oppositely regulation of mshA1 by AphA and OpaR led to a gradual increase in the expression level of mshA1 from LCD to HCD. Thus, regulation of type IV pili production was one of the mechanisms that V. parahaemolyticus adopted to control biofilm formation.

Evidence for reciprocal evolution of the global repressor Mlc and its cognate phosphotransferase system sugar transporter

Because the bacterial phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) is involved in the regulation of various physiological processes in addition to carbohydrate transport, its expression is precisely regulated in response to the availability of PTS sugars. The PTS consists of enzyme I and histidine phosphocarrier protein, and several sugar-specific enzymes II. In Escherichia coli, genes for enzymes II specific for glucose and related sugars are co-regulated by the global repressor Mlc, and glucose induction of the Mlc regulon genes is achieved by its interaction with glucose-specific enzyme II (EII^Glc ). In this study, we revealed that, in Vibrio species, which are phylogenetically older than Enterobacteriaceae, the membrane sequestration of Mlc and thereby the induction of its regulon genes is mediated by N-acetylglucosamine (NAG)-specific EII. While Vibrio Mlc interacts only with the EIIB domain of EII^Nag , E. coli Mlc interacts with the EIIB domain of both EII^Glc and EII^Nag . The present data suggest that EII^Nag may be the primordial regulator of Mlc, and EII^Glc has evolved to interact with Mlc since an EIIA domain was fused to EII^Nag in Enterobacteriaceae. Our findings provide insight into the coevolutionary dynamics between a transcription factor and its cognate regulator according to long-term resource availability in the bacterial natural habitat.

Determination of metabolic activity in planktonic and biofilm cells of Mycoplasma fermentans and Mycoplasma pneumoniae by nuclear magnetic resonance

Mycoplasmas are fastidious microorganisms, typically characterised by their restricted metabolism and minimalist genome. Although there is reported evidence that some mycoplasmas can develop biofilms little is known about any differences in metabolism in these organisms between the growth states. A systematic metabolomics approach may help clarify differences associated between planktonic and biofilm associated mycoplasmas. In the current study, the metabolomics of two different mycoplasmas of clinical importance (Mycoplasma pneumoniae and Mycoplasma fermentans) were examined using a novel approach involving nuclear magnetic resonance spectroscopy and principle component analysis. Characterisation of metabolic changes was facilitated through the generation of high-density metabolite data and diffusion-ordered spectroscopy that provided the size and structural information of the molecules under examination. This enabled the discrimination between biofilms and planktonic states for the metabolomic profiles of both organisms. This work identified clear biofilm/planktonic differences in metabolite composition for both clinical mycoplasmas and the outcomes serve to establish a baseline understanding of the changes in metabolism observed in these pathogens in their different growth states. This may offer insight into how these organisms are capable of exploiting and persisting in different niches and so facilitate their survival in the clinical setting.

Chitin Heterodisaccharide, Released from Chitin by Chitinase and Chitin Oligosaccharide Deacetylase, Enhances the Chitin-Metabolizing Ability of Vibrio parahaemolyticus

Vibrio parahaemolyticus RIMD2210633 secretes both chitinase and chitin oligosaccharide deacetylase and produces β-N-acetyl-d-glucosaminyl-(1,4)-d-glucosamine (GlcNAc-GlcN) from chitin. Previously, we reported that GlcNAc-GlcN induces chitinase production by several strains of Vibrio harboring chitin oligosaccharide deacetylase genes (T. Hirano, K. Kadokura, T. Ikegami, Y. Shigeta, et al., Glycobiology 19:1046-1053, 2009). The metabolism of chitin by Vibrio was speculated on the basis of the findings of previous studies, and the role of chitin oligosaccharide produced from chitin has been well studied. However, the role of GlcNAc-GlcN in the Vibrio chitin degradation system, with the exception of the above-mentioned function as an inducer of chitinase production, remains unclear. N,N'-Diacetylchitobiose, a homodisaccharide produced from chitin, is known to induce the expression of genes encoding several proteins involved in chitin metabolism in Vibrio strains (K. L. Meibom, X. B. Li, A. Nielsen, C. Wu, et al., Proc Natl Acad Sci U S A 101:2524-2529, 2004). We therefore hypothesized that GlcNAc-GlcN also affects the expression of enzymes involved in chitin metabolism in the same manner. In this study, we examined the induction of protein expression by several sugars released from chitin using peptide mass fingerprinting and confirmed the expression of genes encoding enzymes involved in chitin metabolism using real-time quantitative PCR analysis. We then confirmed that GlcNAc-GlcN induces the expression of genes encoding many soluble enzymes involved in chitin degradation in Vibrio parahaemolyticus Here, we demonstrate that GlcNAc-GlcN enhances the chitin-metabolizing ability of V. parahaemolyticus IMPORTANCE We demonstrate that β-N-acetyl-d-glucosaminyl-(1,4)-d-glucosamine (GlcNAc-GlcN) enhances the chitin-metabolizing ability of V. parahaemolyticus Members of the genus Vibrio are chitin-degrading bacteria, and some species of this genus are associated with diseases affecting fish and animals, including humans (F. L. Thompson, T. Iida, and J. Swings, Microbiol Mol Biol Rev 68:403-431, 2004; M. Y. Ina-Salwany, N. Al-Saari, A. Mohamad, F.-A. Mursidi, et al., J Aquat Anim Health 31:3-22, 2019). Studies on Vibrio are considered important, as they may facilitate the development of solutions related to health, food, and aquaculture problems attributed to this genus. This report enhances the current understanding of chitin degradation by Vibrio bacteria.

Differences in carbon source utilization of Salmonella Oranienburg and Saintpaul isolated from river water

Long-term exposure to river water by non-indigenous micro-organisms such as Salmonella may affect metabolic adaptation to carbon sources. This study was conducted to determine differences in carbon source utilization of Salmonella Oranienburg and Salmonella Saintpaul (isolated from tropical river water) as well as the control strain Salmonella Typhimurium exposed to laboratory, river water, and host cells (Hep-2 cell line) growth conditions. Results showed that Salmonella Oranienburg and Salmonella Saintpaul showed better ability for carbon source utilization under the three growth conditions evaluated; however, S. Oranienburg showed the fastest and highest utilization on different carbon sources, including D-Glucosaminic acid, N-acetyl-D-Glucosamine, Glucose-1-phosphate, and D-Galactonic acid, while Salmonella Saintpaul and S. Typhimurium showed a limited utilization of carbon sources. In conclusion, this study suggests that environmental Salmonella strains show better survival and preconditioning abilities to external environments than the control strain based on their plasticity on diverse carbon sources use.

Manipulation of intestinal epithelial cell function by the cell contact-dependent type III secretion systems of Vibrio parahaemolyticus

Vibrio parahaemolyticus elicits gastroenteritis by deploying Type III Secretion Systems (TTSS) to deliver effector proteins into epithelial cells of the human intestinal tract. The bacteria must adhere to the human cells to allow colonization and operation of the TTSS translocation apparatus bridging the bacterium and the host cell. This article first reviews recent advances in identifying the molecules responsible for intercellular adherence. V. parahaemolyticus possesses two TTSS, each of which delivers an exclusive set of effectors and mediates unique effects on the host cell. TTSS effectors primarily target and alter the activation status of host cell signaling proteins, thereby bringing about changes in the regulation of cellular behavior. TTSS1 is responsible for the cytotoxicity of V. parahaemolyticus, while TTSS2 is necessary for the enterotoxicity of the pathogen. Recent publications have elucidated the function of several TTSS effectors and their importance in the virulence of the bacterium. This review will explore the ability of the TTSS to manipulate activities of human intestinal cells and how this modification of cell function favors bacterial colonization and persistence of V. parahaemolyticus in the host.

Defining the niche of Vibrio parahaemolyticus during pre- and post-monsoon seasons in the coastal Arabian Sea

The bacteria Vibrio parahaemolyticus is an important component of coastal ecosystems worldwide, and in recent years, V. parahaemolyticus has caused several cases of food-borne gastroenteritis. However, research investigating which parameters are important in regulating V. parahaemolyticus abundance in tropical areas with relatively stable temperatures and salinity are largely lacking. The objective here was to investigate which environmental forces are driving elevated abundances of V. parahaemolyticus in a tropical oligotrophic coastal area in the Arabian Sea. We analysed a large number of environmental parameters in parallel with cell densities of V. parahaemolyticus and Vibrio spp. Abundance data was obtained using real-time PCR, during two different sampling periods, representative for two distinct seasons. Water temperature and salinity were stable during and between sampling periods, but V. parahaemolyticus abundances were on average six times higher during the first sampling period in December, compared to the second period in February-March. V. parahaemolyticus abundance was found to be positively correlated to inorganic phosphate concentration and copepod abundance. We thus hypothesise that these are important factors regulating V. parahaemolyticus abundance in coastal tropical areas during these periods.

(1)H NMR-based metabolite profiling of planktonic and biofilm cells in Acinetobacter baumannii 1656-2

Acinetobacter baumannii is an aerobic and gram-negative pathogenic bacterium that is resistant to most antibiotics. Recently, A. baumannii 1656-2 exhibited the ability to form biofilms under clinical conditions. In this study, global metabolite profiling of both planktonic and biofilm forms of A. baumannii 1656-2 was performed using high-resolution nuclear magnetic resonance (NMR) spectroscopy and multivariate statistical analysis to investigate the metabolic patterns leading to biofilm formation. Principal components analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) score plots showed a distinct separation between planktonic and biofilm cells. Metabolites including acetates, pyruvate, succinate, UDP-glucose, AMP, glutamate, and lysine were increasingly involved in the energy metabolism of biofilm formation. In particular, the ratio of N-acetyl-D-glucosamine (GlcNAc) to D-glucosamine (GlcNH₂) was significantly higher during biofilm formation than under the planktonic condition. This study demonstrates that NMR-based global metabolite profiling of bacterial cells can provide valuable insight into the metabolic changes in multidrug resistant and biofilm-forming bacteria such as A. baumannii 1656-2.

The N-acetyl-D-glucosamine repressor NagC of Vibrio fischeri facilitates colonization of Euprymna scolopes

To successfully colonize and persist within a host niche, bacteria must properly regulate their gene expression profiles. The marine bacterium Vibrio fischeri establishes a mutualistic symbiosis within the light organ of the Hawaiian squid, Euprymna scolopes. Here, we show that the repressor NagC of V. fischeri directly regulates several chitin- and N-acetyl-D-glucosamine-utilization genes that are co-regulated during productive symbiosis. We also demonstrate that repression by NagC is relieved in the presence of N-acetyl-D-glucosamine-6-phosphate, the intracellular form of N-acetyl-D-glucosamine. We find that gene repression by NagC is critical for efficient colonization of E. scolopes. Further, our study shows that NagC regulates genes that affect the normal dynamics of host colonization.