A novel three‐component system‐based regulatory model for d ‐xylose sensing and transport in C lostridium beijerinckii

Summary d ‐Xylose is the most abundant fermentable pentose in nature and can serve as a carbon source for many bacterial species. Since d ‐xylose constitutes the major component of hemicellulose, its metabolism is important for lignocellulosic biomass utilization. Here, we report a six‐protein module for d ‐xylose signaling, uptake and regulation in solvent‐producing C lostridium beijerinckii . This module consists of a novel ‘three‐component system’ (a putative periplasmic ABC transporter substrate‐binding protein XylFII and a two‐component system LytS / YesN ) and an ABC ‐type d ‐xylose transporter XylFGH . Interestingly, we demonstrate that, although XylFII harbors a transmembrane domain, it is not involved in d ‐xylose transport. Instead, XylFII acts as a signal sensor to assist the response of LytS / YesN to extracellular d ‐xylose, thus enabling LytS / YesN to directly activate the transcription of the adjacent xylFGH genes and thereby promote the uptake of d ‐xylose. To our knowledge, XylFII is a novel single transmembrane sensor that assists two‐component system to respond to extracellular sugar molecules. Also of significance, this ‘three‐component system’ is widely distributed in F irmicutes, indicating that it may play a broad role in this bacterial phylum. The results reported here provide new insights into the regulatory mechanism of d ‐xylose sensing and transport in bacteria.