Hurdle, J. | bioRxiv Science

bioRxiv2026

Systematic analysis of the type VII secretion system in Streptococcus gallolyticus subsp. gallolyticus reveals genomic diversity and functional associations

Streptococcus gallolyticus subsp. gallolyticus (Sgg) is an opportunistic pathobiont associated with bacteremia, infective endocarditis, and colorectal cancer. However, the genomic diversity of this subspecies and the distribution of key virulence determinants, particularly the type VII secretion system (T7SS), remain poorly characterized. Here, we performed genomic analyses of 76 Sgg strains from diverse geographic and host origins. Core- and pan-genome analyses, multi locus sequence typing, and phylogenetic reconstruction revealed dominant sequence types (STs) that correlate with geographic origin or source of isolation. Furthermore, systematic characterization of the T7SS locus identified five new T7SS subtypes and demonstrated a strong association between T7SS subtype and ST. We further expanded the known repertoire of T7SS LXG domain-containing polymorphic toxins (LXG toxins) in Sgg substantially through genome-wide searches. Distinct distribution patterns were observed for the LXG toxins across the strains. Lastly, our data indicated that T7SS subtype was significantly associated with biofilm formation capacity of Sgg strains. Together, these findings advance our understanding of Sgg genomic diversity, reveal substantial lineage-associated variation in T7SS architecture and effector repertoires, and suggest a previously unrecognized connection between T7SS and biofilm formation in Sgg.

microbiology↗

bioRxiv2022

The Ferrous Iron Transporter FeoB1 is Essential for Clostridioides difficile Toxin Production and Pathogenesis in Mice

Ferrous iron is the dominant form of iron in the oxygen-limited large intestine, the site for Clostridioides difficile infection (CDI). We investigated the extent to which C. difficile requires the ferrous iron transporter 1 (FeoB1), a main permease for iron acquisition, using in vitro and in vivo approaches. Construction of feoB1 deletion mutant in C. difficile R20291 (i.e., R20291{Delta}feoB1) decreased intracellular iron content by [~]25%. This was accompanied by downregulation of tcdA and tcdB genes and reduced synthesis of TcdA and TcdB toxins, which was reflected by a [~]1000-fold reduction in cytopathy against Vero cells. Complementation with WT feoB1 restored toxin production. Transcriptional and biochemical analyses revealed {Delta}feoB1 altered metabolic pathways that negatively impact toxin production, including downregulation of the oxidative branch of the Kreb cycle and an associated cellular accumulation of pyruvate. Hence FeoB1 influences multiple bioenergetic and redox pathways, which in turn inhibits toxin biosynthesis. R20291{Delta}feoB1 was avirulent in mice with underlying colitis. In this model, mice are prone to develop severe CDI, but mice infected with the mutant lacked diarrheal symptoms, had lesser inflammatory responses, bacterial bioburdens and cecal toxin titers. These results strongly imply that ferrous iron acquisition and homeostasis is central to toxin metabolism and virulence. Hence targeting FeoB1 could be a potential therapeutic strategy to impede the colonization and pathogenesis of C. difficile, even in the setting of colitis where intestinal bleeding may occur and CDI is more severe.

microbiology↗