Bioprospecting c-di-GMP-activated exopolysaccharides in bacteria: isolation of a novel atypical sphingan

The genetic and physiological diversity of bacteria are critical resources for discovering new exopolysaccharides (EPS) as raw materials with biotechnological applications. However, uncovering new EPS is limited by their lack of production in laboratory cultures, as EPS are often cryptic, and their biosynthesis only proceeds upon unknown environmental cues. The dinucleotide cyclic diguanosine monophosphate (c-di-GMP) has emerged as a universal second messenger in bacteria and a common activator of many EPS. Here, a pleD* transformation to elevate intracellular c-di-GMP levels and a carbohydrate fingerprinting analysis were combined for high-throughput screening of 330 bacterial strains (~70% exhibiting robust growth under the conditions tested) in search of c-di-GMP-activated EPS. Nearly 10% of strains were revealed as promising candidates to overproduce novel EPS composites in a c-di-GMP-dependent manner. Under these conditions, Sphingomonas sp. SphC10 massively produced an EPS with an unusual monosaccharide composition compared with known biotechnologically relevant sphingans.