Metabolic diversity of microorganisms toward atypical sugar enantiomers

Life on Earth has long been regarded as homochiral, relying almost exclusively on a single enantiomer of sugars--typically the D-form. However, recent discoveries challenge this paradigm, including the identification of L-glucose-catabolizing bacteria and microbial L-glucoside hydrolases. Despite these findings, the metabolic diversity of organisms toward a broader range of atypical sugar enantiomers and their ecological relevance remains largely unexplored. This study aimed to identify and isolate microorganisms capable of catabolizing atypical enantiomers of diverse sugars. We performed enrichment cultures with either the D- or L-forms of glucose, fructose, xylose, and sorbose, using soil and activated sludge as microbial sources. Microbial growth was observed under all tested conditions, with the dominant taxa varying depending on the sugars supplied. Six phylogenetically distinct bacterial isolates exhibited the ability to catabolize atypical sugar enantiomers, two of which exhibited growth on all tested sugars. These findings uncover a previously unrecognized diversity in microbial sugar metabolisms, providing new insights into the environmental dynamics of atypical sugar enantiomers and offering a novel perspective on the principle of biological homochirality. Furthermore, this work lays a foundation for the development of biomanufacturing processes using racemic sugar mixtures synthesized via abiotic chemical reactions.