One-step bioconversion of hemicellulose polymers to rhamnolipids with Cellvibrio japonicus: A proof-of-concept for a potential host strain in future bioeconomy

The purpose of this study was to evaluate Cellvibrio japonicus as a potential host strain for one-step bioconversion of hemicellulose polymers to value-added products. C. japonicus could be cultivated on all main lignocellulose monosaccharides as well as xylan polymers as a sole carbon source. This is particularly interesting as most industrially relevant bacteria are neither able to depolymerize wood polymers nor metabolize most hemicellulose monosaccharides. As a result, lignocellulose raw materials typically have to be degraded employing additional processes while the complete conversion of all lignocellulose sugars remains a challenge. Exemplary for a value-added product, a one-step conversion of xylan polymers to mono-rhamnolipid biosurfactants with C. japonicus after transformation with the plasmid pSynPro8oT carrying the genes rhlAB was demonstrated. As achieved product yields in this one-step bioconversion process are comparably low, many challenges remain to be overcome for application on an industrial scale. Nonetheless, this study provides a first step in the search for establishing a future host strain for bioeconomy, which will ideally be used for bioconversion of lignocellulose polymers with as little exhaustive pretreatment as possible.