A Riboflavin Transporter in <b><i>Bdellovibrio exovorous</i></b> JSS

Abstract

The ImpX transporters of the drug/metabolite transporter superfamily were first proposed to transport riboflavin (RF; vitamin B2) based on findings of a cis-regulatory RNA element responding to flavin mononucleotide (an FMN riboswitch). Bdellovibrio exovorous JSS has a homolog belonging to this superfamily. It has 10 TMSs and shows 30% identity to the previously characterized ImpX transporter from Fusobacterium nucleatum. However, the ImpX homolog is not regulated by an FMN-riboswitch. In order to test the putative function of the ImpX homolog from B. exovorous (BexImpX), we cloned and heterologously expressed its gene. We used functional complementation, growth inhibition experiments, direct uptake experiments and inhibition studies, suggesting a high degree of specificity for RF uptake. The EC50 for growth with RF was estimated to be in the range 0.5-1 µM, estimated from the half-maximal RF concentration supporting the growth of a RF auxotrophic Escherichia coli strain, but the K half for RF uptake was 20 µM. Transport experiments suggested that the energy source is the proton motive force but that NaCl stimulates uptake. Thus, members of the ImpX family members are capable of RF uptake, not only in RF prototrophic species such as F. nucleatum, but also in the B2 auxotrophic species, B. exovorous.

Phylogenomic insights into distribution and adaptation of Bdellovibrionota in marine waters

“…A total of 148 genomes of Bdellovibrionota were downloaded from GTDB database (Table S1), eight genomes were obtained from the NCBI to represent the model species that have been well studied previously (19, 20). After quality control (>70% completeness, < 10% contamination and average nucleotide identity ≽ 98.5%) (Tables S2 and S3), 82 genomes were retained for the subsequent study.…”

The Transporter Classification Database (TCDB): 2021 update

“…This has been possible in part because of novel metagenomic data; 36% of the new families in this update include proteins from metagenomes. Moreover, combined with the improvement of software tools and developments in the field, TCDB now provides excellent opportunities to (a) explore relationships between families of transporters ( 5 , 13 , 28–32 , 37 , 40–42 ), (b) characterize and perform comparative analyses of transportomes encoded within genomes and metagenomes ( 14–18 , 22 ) and (c) derive inferences of function to be followed by experimental verification ( 50 ). The characterization of transporter families in TCDB, based on shared domains (tcDoms), allows rapid evaluation of family memberships for individual proteins, identification of evolutionary relationships, and inference of substrates and molecular functions.…”