Rhamnose-Containing Compounds: Biosynthesis and Applications

Acidithiobacillia class members originating at sites within the Pacific Ring of Fire and other tectonically active locations and description of the novel genus 'Igneacidithiobacillus'

Recent studies have expanded the genomic contours of the Acidithiobacillia, highlighting important lacunae in our comprehension of the phylogenetic space occupied by certain lineages of the class. One such lineage is 'Igneacidithiobacillus', a novel genus-level taxon, represented by 'Igneacidithiobacillus copahuensis' VAN18-1T as its type species, along with two other uncultivated metagenome-assembled genomes (MAGs) originating from geothermally active sites across the Pacific Ring of Fire. In this study, we investigate the genetic and genomic diversity, and the distribution patterns of several uncharacterized Acidithiobacillia class strains and sequence clones, which are ascribed to the same 16S rRNA gene sequence clade. By digging deeper into this data and contributing to novel MAGs emerging from environmental studies in tectonically active locations, the description of this novel genus has been consolidated. Using state-of-the-art genomic taxonomy methods, we added to already recognized taxa, an additional four novel Candidate (Ca.) species, including 'Ca. Igneacidithiobacillus chanchocoensis' (mCHCt20-1TS), 'Igneacidithiobacillus siniensis' (S30A2T), 'Ca. Igneacidithiobacillus taupoensis' (TVZ-G3 TS), and 'Ca. Igneacidithiobacillus waiarikiensis' (TVZ-G4 TS). Analysis of published data on the isolation, enrichment, cultivation, and preliminary microbiological characterization of several of these unassigned or misassigned strains, along with the type species of the genus, plus the recoverable environmental data from metagenomic studies, allowed us to identify habitat preferences of these taxa. Commonalities and lineage-specific adaptations of the seven species of the genus were derived from pangenome analysis and comparative genomic metabolic reconstruction. The findings emerging from this study lay the groundwork for further research on the ecology, evolution, and biotechnological potential of the novel genus 'Igneacidithiobacillus'.

O26 Polysaccharides as Key Players in Enteropathogenic E. coli Immune Evasion and Vaccine Development

Enteropathogenic Escherichia coli (EPEC) produce a capsule of polysaccharides identical to those composing the O-antigen polysaccharide of its LPS (lipopolysaccharide) molecules. In light of this, the impact of O26 polysaccharides on the immune evasion mechanisms of capsulated O26 EPEC compared to non-capsulated enterohemorrhagic Escherichia coli (EHEC) was investigated. Our findings reveal that there was no significant difference between the levels in EPEC and EHEC of rhamnose (2.8:2.5), a molecule considered to be a PAMP (Pathogen Associated Molecular Patterns). However, the levels of glucose (10:1.69), heptose (3.6:0.89) and N-acetylglucosamine (4.5:2.10), were significantly higher in EPEC than EHEC, respectively. It was also observed that the presence of a capsule in EPEC inhibited the deposition of C3b on the bacterial surface and protected the pathogen against lysis by the complement system. In addition, the presence of a capsule also protected EPEC against phagocytosis by macrophages. However, the immune evasion provided by the capsule was overcome in the presence of anti-O26 polysaccharide antibodies, and additionally, these antibodies were able to inhibit O26 EPEC adhesion to human epithelial cells. Finally, the results indicate that O26 polysaccharides can generate an effective humoral immune response, making them promising antigens for the development of a vaccine against capsulated O26 E. coli.

Preparation of isoquercitrin and rhamnose from readily accessible rutin by a highly specific recombinant α-L-rhamnosidase (r-Rha1)

Isoquercitrin has superior in vivo bioactivities with respect to its primary glycoside rutin. Its conventional preparation was ineffective, with large chemical consumption and many by-products. Rhamnose, a high value-added monosaccharide, is usually separated from acid hydrolytes of rutin. This study aimed to establish a novel enzymatic hydrolysis-based approach for their preparation. α-L-rhamnosidase was expressed in Pichia pastoris GS115 and applied to enzymolysis of rutin. Then, one-factor-at-a-time optimisation of hydrolysis conditions was performed. Two compounds were produced in 0.02 M HAc-NaAc buffer (pH4.50) containing α-L-rhamnosidase/rutin (1:4, w/w) at 60 °C. Consequently, 20.0 g/L rutin was completely hydrolysed in 2 hrs, and isoquercitrin was obtained after purification by HPD-100 resin. Additionally, rhamnose was enriched by decolorisation and crystallisation. MD simulation analysis suggested that rutin was catalysed on the hydrophobic surface of r-Rha1 with van-der-Waals force being main driving force. This strategy is an efficient approach for preparation of isoquercitrin and rhamnose.

Analysis of phenotypic changes in high temperature and low pH extreme conditions of Alicyclobacillus sendaiensis PA2 related with the cell wall and sporulation genes

The A. sendaiensis PA2 is a polyextremophile bacterium. In this study, we analyze the A. sendaiensis PA2 genome. The genome was assembled and annotated. The A. sendaiensis PA2 genome structure consists of a 2,956,928 bp long chromosome and 62.77% of G + C content. 3056 CDSs were predicted, and 2921 genes were assigned to a putative function. The ANIm and ANIb value resulted in 97.17% and 96.65%, the DDH value was 75.5%, and the value of TETRA (Z-score) was 0.98. Comparative genomic analyses indicated that three systems are enriched in A. sendaiensis PA2. This strain has phenotypic changes in cell wall during batch culture at 65 °C, pH 5.0 and without carbon and nitrogen source. The presence of unique genes of cell wall and sporulation subsystem could be related to the adaptation of A. sendaiensis PA2 to hostile conditions.

Selective biosynthesis of a rhamnosyl nosiheptide by a novel bacterial rhamnosyltransferase

Nosiheptide (NOS) is a thiopeptide antibiotic produced by the bacterium Streptomyces actuosus. The hydroxyl group of 3-hydroxypyridine in NOS has been identified as a promising site for modification, which we therefore aimed to rhamnosylate. After screening, Streptomyces sp. 147326 was found to regioselectively attach a rhamnosyl unit to the 3-hydroxypyridine site in NOS, resulting in the formation of a derivative named NOS-R at a productivity of 24.6%. In comparison with NOS, NOS-R exhibited a 17.6-fold increase in aqueous solubility and a new protective effect against MRSA infection in mice, while maintaining a similar in vitro activity. Subsequently, SrGT822 was identified as the rhamnosyltransferase in Streptomyces sp. 147326 responsible for the biosynthesis of NOS-R using dTDP-L-rhamnose. SrGT822 demonstrated an optimal reaction pH of 10.0 and temperature of 55°C, which resulted in a NOS-R yield of 74.9%. Based on the catalytic properties and evolutionary analysis, SrGT822 is anticipated to be a potential rhamnosyltransferase for use in the modification of various complex scaffolds.

Acquired stress resilience through bacteria-to-nematode interdomain horizontal gene transfer

Natural selection drives the acquisition of organismal resilience traits to protect against adverse environments. Horizontal gene transfer (HGT) is an important evolutionary mechanism for the acquisition of novel traits, including metazoan acquisitions in immunity, metabolic, and reproduction function via interdomain HGT (iHGT) from bacteria. Here, we report that the nematode gene rml-3 has been acquired by iHGT from bacteria and that it enables exoskeleton resilience and protection against environmental toxins in Caenorhabditis elegans. Phylogenetic analysis reveals that diverse nematode RML-3 proteins form a single monophyletic clade most similar to bacterial enzymes that biosynthesize L-rhamnose, a cell-wall polysaccharide component. C. elegans rml-3 is highly expressed during larval development and upregulated in developing seam cells upon heat stress and during the stress-resistant dauer stage. rml-3 deficiency impairs cuticle integrity, barrier functions, and nematode stress resilience, phenotypes that can be rescued by exogenous L-rhamnose. We propose that interdomain HGT of an ancient bacterial rml-3 homolog has enabled L-rhamnose biosynthesis in nematodes, facilitating cuticle integrity and organismal resilience to environmental stressors during evolution. These findings highlight a remarkable contribution of iHGT on metazoan evolution conferred by the domestication of a bacterial gene.

Cytotoxic triterpenoid saponins from the root of Olax subscorpioidea Oliv. (Olacaceae)

Bioactivity-guided phytochemical fractionation of the methanol extract of Olax subscorpioidea root has led to the isolation of six triterpenes. Three of these compounds are previously undescribed triterpenoid saponins: oleanolic acid 3-O-[α-L-rhamnopyranosyl-(1→3)-β-D-glucopyranosyl-(1 → 2)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (2), oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 3)-β-D-glucopyranoside] (3), and oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-6-O-methyl-β-D-glucuronopyranoside] ester (5). Other reported known compounds include two triterpene glycosides: oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-6-O-methyl-β-D-glucuronopyranoside]-28-O-β-D-glucopyranosyl ester (1) and oleanolic acid 3-O-[β-D-glucopyranosyl-(1 → 4)-β-D-glucuronopyranoside] (4); and a triterpene acid, oleanolic acid (6). The structures of these compounds were elucidated by spectroscopic means. The isolated compounds were tested against human cervical cancer (HeLa), colorectal cancer (Caco-2) and breast cancer (MCF-7) cell lines using the in vitro 3-[4,5-dimethylthiazole-2-yl] 3,5-diphenyltetrazolium bromide (MTT) assay, with vincristine as positive control. The cytotoxicity assay showed that compounds 3 and 5 exhibited significant inhibitory effects on the HeLa cell line, with IC50 values of 7.42 ± 0.34 μM and 10.27 ± 1.26 μM; and moderate effects on MCF-7 (IC50 values, 36.67 ± 1.23 μM and 43.83 ± 0.65 μM) and Caco-2 (IC50 values, 35.83 ± 0.55 μM and 39.03 ± 4.38 μM, respectively) cell lines. They were also more selectively cytotoxic than vincristine against the cancer cell lines, when compared with cytotoxicity against the normal lung cell line MRC5.

Acquired stress resilience through bacteria-to-nematode horizontal gene transfer

Natural selection drives acquisition of organismal resilience traits to protect against adverse environments. Horizontal gene transfer (HGT) is an important evolutionary mechanism for the acquisition of novel traits, including metazoan acquisition of functions in immunity, metabolism, and reproduction via interdomain HGT (iHGT) from bacteria. We report that the nematode gene rml-3, which was acquired by iHGT from bacteria, enables exoskeleton resilience and protection against environmental toxins in C. elegans. Phylogenetic analysis reveals that diverse nematode RML-3 proteins form a single monophyletic clade most highly similar to bacterial enzymes that biosynthesize L-rhamnose to build cell wall polysaccharides. C. elegans rml-3 is regulated in developing seam cells by heat stress and stress-resistant dauer stage. Importantly, rml-3 deficiency impairs cuticle integrity, barrier functions and organismal stress resilience, phenotypes that are rescued by exogenous L-rhamnose. We propose that iHGT of an ancient bacterial rml-3 homolog enables L-rhamnose biosynthesis in nematodes that facilitates cuticle integrity and organismal resilience in adaptation to environmental stresses during evolution. These findings highlight the remarkable contribution of iHGT on metazoan evolution that is conferred by the domestication of bacterial genes.