Patients with recurrent C. difficile infection harbor large numbers of microbes with antibiotic resistance genes. Fecal microbial transplantation eradicates pathogenic organisms and eliminates antibiotic-resistance genes suggesting this may be a viable treatment option to eradicate multidrug resistant bacteria from patients.

YrzC has previously been identified as a repressor controlling ytmI expression via its regulation of YtlI activator synthesis in Bacillus subtilis. We identified YrzC as a master regulator of sulfur metabolism. Gene expression profiles of B. subtilis ⌬yrzC mutant and wild-type strains grown in minimal medium with sulfate as the sole sulfur source were compared. In the mutant, increased expression was observed for 24 genes previously identified as repressed in the presence of sulfate. Since several genes involved in the pathways leading to cysteine formation were found, we propose to rename YrzC CymR, for "cysteine metabolism repressor." A CymR-dependent binding to the promoter region of the ytlI, ssuB, tcyP, yrrT, yxeK, cysK, or ydbM gene was demonstrated using gel shift experiments. A potential CymR target site, TAAWNCN 2 ANTWNAN 3 ATMGGAA TTW, was found in the promoter region of these genes. In a DNase footprint experiment, the protected region in the ytlI promoter region contained this consensus sequence. Partial deletion or introduction of point mutations in this sequence confirmed its involvement in ytlI, yrrT, and yxeK regulation. The addition of O-acetylserine in gel shift experiments prevented CymR-dependent binding to DNA for all of the targets characterized. Transcriptome analysis of a ⌬cymR mutant and the wild-type strain also brought out significant changes in the expression level of a large set of genes related to stress response or to transition toward anaerobiosis.

The symporter YhcL and two ATP binding cassette transporters, YtmJKLMN and YckKJI, were shown to mediate L-cystine uptake in Bacillus subtilis. A triple ⌬yhcL ⌬ytmJKLMN ⌬yckK mutant was unable to grow in the presence of L-cystine and to take up L-cystine. We propose that yhcL, ytmJKLMN, and yckKJI should be renamed tcyP, tcyJKLMN, and tcyABC, respectively. The L-cystine uptake by YhcL (K m ‫؍‬ 0.6 M) was strongly inhibited by seleno-DL-cystine, while the transport due to the YtmJKLMN system (K m ‫؍‬ 2.5 M) also drastically decreased in the presence of DL-cystathionine, L-djenkolic acid, or S-methyl-L-cysteine. Accordingly, a ⌬ytmJKLMN mutant did not grow in the presence of 100 M DL-cystathionine, 100 M L-djenkolic acid, or 100 M S-methyl-L-cysteine. The expression of the ytmI operon and the yhcL gene was regulated in response to sulfur availability, while the level of expression of the yckK gene remained low under all the conditions tested.