Insights into the Ropy Phenotype of the Exopolysaccharide-Producing Strain Bifidobacterium animalis subsp. lactis A1dOxR

Abstract

bThe proteome of the ropy strain Bifidobacterium animalis subsp. lactis A1dOxR, compared to that of its nonropy isogenic strain, showed an overproduction of a protein involved in rhamnose biosynthesis. Results were confirmed by gene expression analysis, and this fact agreed with the high rhamnose content of the ropy exopolysaccharide.T he ability to synthesize an extracellular layer of carbohydrates, or exopolysaccharides (EPS), is a common trait in bacteria, such as those members of the microbiota inhabiting our gut (1, 2), including Bifidobacterium and Lactobacillus (3-5). For instance, some strains of these human commensal genera are able to produce complex EPS under laboratory conditions. These polymers, built on repeating units of different monosaccharides, are also known as heteropolysaccharides (6, 7). Recently, EPS-producing bacteria have received particular attention due to the presumptive implication of the polymers in the cross talk between bacteria and host (8-11). However, there is limited information as to why only some specific EPS are able to interact with human cells (12)(13)(14). Previous results from our group, also supported by other literature data, have shown that some physicochemical characteristics of EPS could be correlated with their immune-modulating capability. Specifically, it seems that polymers with high molecular weights (HMWs) are able to act as suppressors of the immune response (15). Part of the results supporting this hypothesis were obtained with a model of three isogenic EPS-producing Bifidobacterium animalis subsp. lactis strains, A1, A1dOx, and A1dOxR, the last being able to synthesize an HMW EPS fraction with an immunosuppressive profile (13).This strain, A1dOxR, also named IPLA-R1, displays a characteristic "ropy" phenotype, denoted by the formation of a long filament when a loop is introduced into the colony. Interestingly, this ropy character was not observed in two related (isogenic) EPS-producing strains, A1 and A1dOx, which also lack the production of the HMW EPS fraction; in fact, it seems that all three strains synthesize a low-molecular-weight (LMW) EPS fraction (Table 1). Additionally, the monosaccharides building the EPS produced by the three strains are the same (glucose, galactose, and rhamnose), but they are present at different ratios (16). Furthermore, the LMW EPS from the two isogenic strains did not elicit a suppression of the immune response (13). Therefore, it seems that both the ability to suppress the immune response and the ropy phenotype in strain A1dOxR may be related to the synthesis of the HMW polymer. In this regard, it has been indicated that the ability of certain EPS-producing bacteria to confer ropiness to a fermented product is directly related to the molecular weight of its polymer. That is, ropy strains have EPS of high molecular weights, whereas nonropy strains produce polymers of smaller molecular weights (17, 18). In the current work, we have tried to gain insight into some molecular and physiological aspects of the occurrence of the ...

A Single Mutation in the Gene Responsible for the Mucoid Phenotype of Bifidobacterium animalis subsp. lactis Confers Surface and Functional Characteristics

“…lactis IPLA-R1 displayed a mucoid phenotype compared with that of the strain A1dOx. The strain IPLA-R1 is a derivative of A1dOx, which, after consecutive generations, spontaneously acquired a mucoid phenotype (20). The sequencing of the EPS clusters (32) (Fig.…”

“…lactis strain IPLA-R1 can produce an EPS that generates a mucoid (or ropy) phenotype. IPLA-R1 was spontaneously obtained, after several consecutive cultures, from the strain A1dOx, which was derived from the yogurt isolate A1 after adaptation to increasing concentrations of ox gall (20). In the present work, we aimed to further study our models of EPS-producing bifidobacteria (and their polymers), and we wanted to address whether the mucoid phenotype could be connected with a specific genetic background.…”

Genomic Overview and Biological Functions of Exopolysaccharide Biosynthesis in Bifidobacterium spp

“…lactis IPLA-R1 (Table 1), whose EPS-unit contains 50% rhamnose (39). This fact has recently been correlated with an overexpression of genes coding for rhamnose biosynthesis precursors located inside the eps cluster of this strain (28). Therefore, taking into account the limitations imposed by the low number of bifido-EPS analyzed, we propose that they share common compositional traits with LAB-EPS, especially with those synthesized by strains of human origin.…”

“…One remarkable finding that could shed light on some important traits that effector EPS might have is the case of the polymers purified from isogenic B. animalis subsp. lactis strains A1, A1dOx, and A1dOxR (also known as IPLA-R1) (28). The three polymers elicited different cytokine patterns, and the A1dOxR polymer, which has the highest molar mass, showed the lowest capability to induce the release of both pro-and antiinflammatory cytokines by PBMC (9).…”

“…The first step in the formation of the EPSunit would be catalyzed by the priming-GTF; in the case of B. animalis subsp. lactis, the two p-gtf genes seem to be functional (13,28). This enzyme would transfer a sugar-1-phosphate (not identified in EPS IPLA-R1) to the lipophilic carrier molecule anchored to the cell membrane.…”