Diversity of enzymes for exopolysaccharide synthesis in the fructophilic honeybee symbiont Apilactobacillus kunkeei

作者：Marina Mota-Merlo, Julia E Pedersen, S. Andersson · 发表于：BMC Microbiology · 年份：2026 · DOI：10.1186/s12866-025-04680-3 · 被引用次数：2 · 研究领域：Medicine

Apilactobacillus kunkeei is a fructophilic lactic acid bacterium adapted to honeybees, their food sources and products. These bacteria synthesize exopolysaccharides thought to promote host colonization and protection against toxic compounds and stressful conditions. Homopolysaccharides consisting of glucose residues are synthesized by enzymes in the glycoside hydrolase family 70 (GH70), whereas polysaccharides that contain fructose are synthesized by family 32 (GH32) enzymes. However, the mechanisms whereby these enzymes diversify are not well understood. Here, we used a comparative genomics approach to investigate the evolution of GH70 and GH32 enzymes in the A. kunkeei population. Based on phylogenetic inferences, the GH70 proteins in 38 reference A. kunkeei strains were sorted into glucan-binding enzymes, which were predicted to have glucansucrase and branching sucrase activities, and non-glucan binding enzymes of unknown enzymatic functions. Genes for the glucan sucrases and the branching sucrases are clustered in a chromosomal segment that also contains genes for GH32 enzymes. The number and combination of genes for the glucan-binding GH70 enzymes were mostly strain-specific, indicative of high rates of gene turnover. Neighboring genes often displayed a dramatic variability in synonymous and nonsynonymous substitution frequencies and have only rarely co-diverged. We identified short recombination tracts and a few long tracts that spanned across the cluster of genes for G...