The Gram-positive bacterium Romboutsia ilealis harbors a polysaccharide synthase that can produce (1,3;1,4)-β-d-glucans

Abstract

Abstract(1,3;1,4)-β-d-Glucans are widely distributed in the cell walls of grasses (family Poaceae) and closely related families, as well as some other vascular plants. Additionally, they have been found in other organisms, including fungi, lichens, brown algae, charophycean green algae, and the bacterium Sinorhizobium meliloti. Only three members of the Cellulose Synthase-Like (CSL) genes in the families CSLF, CSLH, and CSLJ are implicated in (1,3;1,4)-β-d-glucan biosynthesis in grasses. Little is known about the enzymes responsible for synthesizing (1,3;1,4)-β-d-glucans outside the grasses. In the present study, we report the presence of (1,3;1,4)-β-d-glucans in the exopolysaccharides of the Gram-positive bacterium Romboutsia ilealis CRIBT. We also report that RiGT2 is the candidate gene of R. ilealis that encodes (1,3;1,4)-β-d-glucan synthase. RiGT2 has conserved glycosyltransferase family 2 (GT2) motifs, including D, D, D, QXXRW, and a C-terminal PilZ domain that resembles the C-terminal domain of bacteria cellulose synthase, BcsA. Using a direct gain-of-function approach, we insert RiGT2 into Saccharomyces cerevisiae, and (1,3;1,4)-β-d-glucans are produced with structures similar to those of the (1,3;1,4)-β-d-glucans of the lichen Cetraria islandica. Phylogenetic analysis reveals that putative (1,3;1,4)-β-d-glucan synthase candidate genes in several other bacterial species support the finding of (1,3;1,4)-β-d-glucans in these species.

Variations and Interseasonal Changes in the Gut Microbial Communities of Seven Wild Fish Species in a Natural Lake with Limited Water Exchange during the Closed Fishing Season

“…Clostridium sensu stricto 1 is a common group in the gut microbial community of freshwater fish [10], but it is also frequently found in the gut of marine mammals [46][47][48], where it often appears as a potential pathogen [49,50]. Bacteria of the genus Romboutsia are Gram-positive bacteria, one of the common intestinal microorganisms, and most species of Romboutsia originate from the gut, although some isolated strains of Romboutsia have originated from diseased individuals, but recent reports have shown that this group of bacteria contains a polysaccharide-synthesizing enzyme that produces (1,3;1,4)-β-d-glucans, so the role of this group of bacteria in the human and mammalian gastrointestinal tract is less clear [51,52]. Pseudomonas is one of the most diverse genera, and in our study the most abundant ASV of Pseudomonas belonged to Pseudomonas koreensis, which is a common causative agent of freshwater fish [53,54].…”

Glycosyl transferase GT2 genes mediate the biosynthesis of an unusual (1,3;1,4)‐β‐glucan exopolysaccharide in the bacterium Sarcina ventriculi

“…However, MLGs that contain predominantly DP3 units are synthesized by the SvBmlgs2 enzyme, by the fungus Rhynchosporium secalis, by the lichen Cetraria islandica and by the bacterium Romboutsia ilealis (Figure 4; Chang et al, 2023;Pettolino et al, 2009;Stone & Clarke, 1992). In the MLG from Equisetum spp.…”

“…(2015) concluded that the evolution of (1,3;1,4)‐β‐glucan synthase genes has occurred independently on multiple occasions. The detection of MLGs in basal land plants, fungi and bacteria (Chang et al., 2023; Fry et al., 2008; Perez‐Mendoza et al., 2015; Pettolino et al., 2009; Sørensen et al., 2008) suggests that this conclusion is applicable beyond higher plants. The presence of oligosaccharides containing both (1,3)‐β‐ and (1,4)‐β‐glucosidic linkages in S. ventriculi culture media raised the possibility that this Gram‐positive bacterium might also synthesize (1,3;1,4)‐β‐glucan (Lee & Hollingsworth, 1997).…”

“…In Sinorhizobium meliloti , lichenase treatment releases predominantly laminaribiose, indicating that the polysaccharide consists of strictly alternating (1,3)‐ and (1,4)‐β‐glucosyl residues; MLG synthesis in this bacterium is also regulated by the bacterial second messenger c‐di‐GMP (Perez‐Mendoza et al., 2015). However, MLGs that contain predominantly DP3 units are synthesized by the Sv Bmlgs2 enzyme, by the fungus Rhynchosporium secalis , by the lichen Cetraria islandica and by the bacterium Romboutsia ilealis (Figure 4; Chang et al., 2023; Pettolino et al., 2009; Stone & Clarke, 1992). In the MLG from Equisetum spp.…”

“…org/ ; Drula et al, 2022] might be present in bacteria. Some of these uncertainties were addressed recently by Chang et al (2023), who presented evidence for the presence of an MLG in the Gram-positive bacterium Romboutsia ilealis; this polysaccharide is structurally similar to the MLG from the lichen Cetraria islandica (Lazaridou et al, 2004).…”