Aeromonas surface glucan attached through the O-antigen ligase represents a new way to obtain UDP-glucose

Architecture, Function, Regulation, and Evolution of α-Glucans Metabolic Enzymes in Prokaryotes

Bacteria have acquired sophisticated mechanisms for assembling and disassembling polysaccharides of different chemistry. α-d-Glucose homopolysaccharides, so-called α-glucans, are the most widespread polymers in nature being key components of microorganisms. Glycogen functions as an intracellular energy storage while some bacteria also produce extracellular assorted α-glucans. The classical bacterial glycogen metabolic pathway comprises the action of ADP-glucose pyrophosphorylase and glycogen synthase, whereas extracellular α-glucans are mostly related to peripheral enzymes dependent on sucrose. An alternative pathway of glycogen biosynthesis, operating via a maltose 1-phosphate polymerizing enzyme, displays an essential wiring with the trehalose metabolism to interconvert disaccharides into polysaccharides. Furthermore, some bacteria show a connection of intracellular glycogen metabolism with the genesis of extracellular capsular α-glucans, revealing a relationship between the storage and structural function of these compounds. Altogether, the current picture shows that bacteria have evolved an intricate α-glucan metabolism that ultimately relies on the evolution of a specific enzymatic machinery. The structural landscape of these enzymes exposes a limited number of core catalytic folds handling many different chemical reactions. In this Review, we present a rationale to explain how the chemical diversity of α-glucans emerged from these systems, highlighting the underlying structural evolution of the enzymes driving α-glucan bacterial metabolism.

Influence of Polysaccharides From Polygonatum kingianum on Short-Chain Fatty Acid Production and Quorum Sensing in Lactobacillus faecis

Polysaccharide is one of the main active ingredients of Polygonatum kingianum, which has been proven to regulate the balance of gut microbiota. For the first time, this study focused on the regulation of polysaccharides from Polygonatum kingianum (PS) on Lactobacillus faecis, a specific probiotic in the intestinal tract. PS effectively promoted the biomass, biofilm and acetic acid production in L. faecis 2-84, and enhanced quorum sensing (QS) signaling. The characteristics of gene sequence were analyzed using genomics approaches, and L. faecis 2-84 was found to encode 18 genes that are closely related to QS and 10 genes related to short-chain fatty acids (SCFAs). Additionally, transcriptome and proteome analysis demonstrated that PS could promote the QS system of L. faecis by enhancing the transcription of oppA gene and expression of oppD protein. PS also regulated the production and metabolism of SCFAs of L. faecis by upregulating the expression of ldh and metE gene and adh2 protein, and downregulating the expression of mvK gene. In conclusion, it was speculated that PS could affect intestinal SCFAs production by affecting the QS system and SCFAs production in L. faecis. The present study implied that PS might have a role in promoting the growth of intestinal probiotics, where the QS system and SCFAs might be two of the important mechanisms for the probiotic activity of PS.

Surface Glucan Structures in Aeromonas spp

Aeromonas spp. are generally found in aquatic environments, although they have also been isolated from both fresh and processed food. These Gram-negative, rod-shaped bacteria are mostly infective to poikilothermic animals, although they are also considered opportunistic pathogens of both aquatic and terrestrial homeotherms, and some species have been associated with gastrointestinal and extraintestinal septicemic infections in humans. Among the different pathogenic factors associated with virulence, several cell-surface glucans have been shown to contribute to colonization and survival of Aeromonas pathogenic strains, in different hosts. Lipopolysaccharide (LPS), capsule and α-glucan structures, for instance, have been shown to play important roles in bacterial–host interactions related to pathogenesis, such as adherence, biofilm formation, or immune evasion. In addition, glycosylation of both polar and lateral flagella has been shown to be mandatory for flagella production and motility in different Aeromonas strains, and has also been associated with increased bacterial adhesion, biofilm formation, and induction of the host proinflammatory response. The main aspects of these structures are covered in this review.

The Social Life of Aeromonas through Biofilm and Quorum Sensing Systems

Bacteria of the genus Aeromonas display multicellular behaviors herein referred to as “social life”. Since the 1990s, interest has grown in cell-to-cell communication through quorum sensing signals and biofilm formation. As they are interconnected, these two self-organizing systems deserve to be considered together for a fresh perspective on the natural history and lifestyles of aeromonads. In this review, we focus on the multicellular behaviors of Aeromonas, i.e., its social life. First, we review and discuss the available knowledge at the molecular and cellular levels for biofilm and quorum sensing. We then discuss the complex, subtle, and nested interconnections between the two systems. Finally, we focus on the aeromonad multicellular coordinated behaviors involved in heterotrophy and virulence that represent technological opportunities and applied research challenges.

Comparative genomic and phylogenetic analyses of Gammaproteobacterial glg genes traced the origin of the Escherichia coli glycogen glgBXCAP operon to the last common ancestor of the sister orders Enterobacteriales and Pasteurellales

Production of branched α-glucan, glycogen-like polymers is widely spread in the Bacteria domain. The glycogen pathway of synthesis and degradation has been fairly well characterized in the model enterobacterial species Escherichia coli (order Enterobacteriales, class Gammaproteobacteria), in which the cognate genes (branching enzyme glgB, debranching enzyme glgX, ADP-glucose pyrophosphorylase glgC, glycogen synthase glgA, and glycogen phosphorylase glgP) are clustered in a glgBXCAP operon arrangement. However, the evolutionary origin of this particular arrangement and of its constituent genes is unknown. Here, by using 265 complete gammaproteobacterial genomes we have carried out a comparative analysis of the presence, copy number and arrangement of glg genes in all lineages of the Gammaproteobacteria. These analyses revealed large variations in glg gene presence, copy number and arrangements among different gammaproteobacterial lineages. However, the glgBXCAP arrangement was remarkably conserved in all glg-possessing species of the orders Enterobacteriales and Pasteurellales (the E/P group). Subsequent phylogenetic analyses of glg genes present in the Gammaproteobacteria and in other main bacterial groups indicated that glg genes have undergone a complex evolutionary history in which horizontal gene transfer may have played an important role. These analyses also revealed that the E/P glgBXCAP genes (a) share a common evolutionary origin, (b) were vertically transmitted within the E/P group, and (c) are closely related to glg genes of some phylogenetically distant betaproteobacterial species. The overall data allowed tracing the origin of the E. coli glgBXCAP operon to the last common ancestor of the E/P group, and also to uncover a likely glgBXCAP transfer event from the E/P group to particular lineages of the Betaproteobacteria.

The main Aeromonas pathogenic factors

The members of the Aeromonas genus are ubiquitous, water-borne bacteria. They have been isolated from marine waters, rivers, lakes, swamps, sediments, chlorine water, water distribution systems, drinking water and residual waters; different types of food, such as meat, fish, seafood, vegetables, and processed foods. Aeromonas strains are predominantly pathogenic to poikilothermic animals, and the mesophilic strains are emerging as important pathogens in humans, causing a variety of extraintestinal and systemic infections as well as gastrointestinal infections. The most commonly described disease caused by Aeromonas is the gastroenteritis; however, no adequate animal model is available to reproduce this illness caused by Aeromonas. The main pathogenic factors associated with Aeromonas are: surface polysaccharides (capsule, lipopolysaccharide, and glucan), S-layers, iron-binding systems, exotoxins and extracellular enzymes, secretion systems, fimbriae and other nonfilamentous adhesins, motility and flagella.