Wright, G. | bioRxiv Science

bioRxiv2018

Genome location dictates the transcriptional response to sub-inhibitory concentrations of PolC-inhibitors in Clostridium difficile

Clostridium difficile is a potentially lethal gut pathogen that causes nosocomial and community acquired infections. Limited treatment options and reports of reduced susceptibility to current treatment emphasize the necessity for novel antimicrobials. The DNA-polymerase of gram-positive organisms is an attractive target for the development of antimicrobials. ACX-362E (N2-(3<,4-Dichlorobenzyl)-7-(2-[1-morpholinyl]ethyl)guanine; MorE-DCBG) is a DNA polymerase inhibitor in pre-clinical development as a novel therapeutic against C. difficile infection. This synthetic purine shows preferential activity against C. difficile PolC over those of other organisms in vitro and is effective in an animal model of C. difficile infection. In this study we have determined its efficacy against a large collection of clinical isolates. At concentrations below the minimal inhibitory concentration, the presumed slowing (or stalling) of replication forks due to ACX-362E leads to a growth defect. We have determined the transcriptional response of C. difficile to replication inhibition and observed an overrepresentation of up-regulated genes near the origin of replication in the presence of PolC-inhibitors, but not when cells were subjected to sub-inhibitory concentrations of other antibiotics. This phenomenon can be explained by a gene dosage shift, as we observed a concomitant increase in the ratio between origin-proximal versus terminus-proximal gene copy number upon exposure to PolC-inhibitors. Moreover, we show that certain genes differentially regulated under PolC-inhibition are controlled by the origin-proximal general stress response regulator sigma factor B. Together, these data suggest that genome location both directly and indirectly determines the transcriptional response to replication inhibition in C. difficile.

microbiology↗

bioRxiv2017

Mesophotic Coral Ecosystems Inside and Outside a Caribbean Marine Protected Area

Recent widespread shallow coral reef loss has led to calls for more holistic approaches to coral reef management, requiring inclusion of all ecosystems interacting with coral reefs in management plans. Yet almost all current reef management is biased towards shallow reefs, and overlooks that many reef species can also be found on mesophotic coral ecosystems (MCEs; reefs 30 -150 m). This study presents the first detailed quantitative characterisation of MCEs off Cozumel, in the Mexican Caribbean and provides insights into their general state. We investigate whether MCEs within the marine park have similar ecological communities to mesophotic reefs outside protection, despite widely recognised shallow reef impacts outside the protected area. Results show some taxon specific differences in MCE benthic communities between sites within the protected area and areas outside; although overall communities are similar. Regardless of protection and location, and in contrast to shallow reefs, all observed Cozumel MCEs were continuous reefs dominated by calcareous macroalgae, sponges, octocorals, and black corals. Hard corals were present on MCEs, but at low abundance. We found that 42.5 % of fish species recorded on Cozumel could be found on both shallow reefs and MCEs, including many commercially-important fish species. This suggest that MCEs may play a role in supporting fish populations. However, regardless of protection status and depth we found that large-body fishes (>500 mm) were nearly absent at all studied sites. MCEs should be incorporated into the existing shallow-reef focused management plan in Cozumel, with well informed and implemented fisheries and harvesting regulations.

ecology↗