FrlP, an ABC type I importer component of Bacillus subtilis: regulation and impact in bacterial fitness

Abstract Bacillus subtilis is able to catabolize fructosamines, also known as Amadori rearrangement products. The frlBONMD-frlP operon mediates this process and is subjected to specific and global regulation. Although the degradation pathway favoring α-glycated amino acids is known, the mechanisms of substrate uptake have remained unclear. In this study, mutagenic and functional analyses revealed that FrlONM, a type I ABC importer, along with the nucleotide-binding domain (NBD) FrlP, is required for the uptake of fructosevaline. Transcriptional and translation frlP-lacZ fusions indicated that frlP is induced by fructosevaline and negatively regulated by the FrlR repressor. Furthermore, by targeting an RNA molecule (S1254) encoded upstream from frlP and overlapping the repressor flrR gene transcribed in the opposite direction, we provide evidence for the dual regulation of frlP by this anti-sense RNA and FrlR. This result adds a posttranscriptional layer to the intricate regulation of the fructosamines operon. In addition, we show that MsmX, a multitask NBD of B. subtilis, is also able to serve as energy motor of this type I ABC importer, and that its presence alongside FrlP is vital for optimal growth on fructosevaline. To address the physiological significance of this functional redundancy we assessed the distribution of ABC type I NBDs FrlP and MsmX across the Bacillaceae family. MsmX is homogeneously distributed in Bacillaceae family tree, while FrlP is restricted to the Bacillus subtilis group, suggesting that the presence of FrlP together with other components of the fructosamines operon is important for bacteria fitness in plant-associated ecological niches. Importance Bacillus subtilis is widely applied in the industry as a microbial cell factory, as a biofertilizer for sustainable agriculture, in the animal feed industry and as human probiotic. In its natural environment B. subtilis helps to shape the gut microbiome and the phytomicrobiome. Fructosamines, or Amadori rearrangement products, are ubiquitously found in nature and serve as precursors of toxic cell end-products implicated in the pathology of human diseases. This study provides a solid contribution to a deep knowledge of transport mechanisms, genetic regulation and physiological relevance of fructosamines utilization in B. subtilis. Moreover, it highlights an unusual strategy to adapt to alterations in nutrient availability by swapping the energy providing domain of ABC transporters.