SummaryIdentifying how microbes are able to manipulate, survive, and thrive in complex multispecies communities has expanded our understanding of how microbial ecosystems impact human health and the environment. The ability of bacteria to negatively affect neighbors, through explicit toxin delivery systems, provides them with an opportunity to manipulate the composition of growing microbial communities. Contact-dependent inhibition (CDI) systems (a Type Vb secretion system) are a distinct subset of competition systems whose contribution to shaping the development of spatially structured bacterial communities are yet to be fully understood. Here, we compare the impact of different CDI systems, at both the single-cell and population level, to determine the key drivers of CDI-mediated competition within spatially structured bacterial populations. Through an iterative approach using both an Escherichia coli experimental system and computational modeling, we show that CDI systems have subtle and system-specific effects at the single-cell level, generating single-cell-wide boundaries between CDI-expressing inhibitor cells and their neighboring targets. Despite the subtle effects of CDI at a single-cell level, CDI systems greatly diminished the ability of susceptible targets to expand their range during colony growth. The inoculum density of the population, together with the CDI system-specific variables of the speed of inhibition after contact and biological cost of CDI, strongly affects CDI-mediated competition. In contrast, the magnitude of the toxin-induced growth retardation of target cells only weakly impacts the composition of the population. Our work reveals how distinct CDI systems can differentially affect the composition and spatial arrangement of bacterial populations.
The feasibility of a new concept of wastewater treatment by combining a membrane bioreactor (MBR) and a microalgae membrane photobioreactor (MPBR) is assessed in this study. In this system, the organic carbon present in wastewater is expected to be fully oxidized in the MBR, while the nutrients are removed via the subsequent MPBR treatment. The effluent of a lab-scale MBR was fed into a PBR and a MPBR which served as growing medium for Chlorella vulgaris. The MPBRs demonstrated their superiority by limiting the algae wash-out, thus increasing the allowable optimum dilution rate (Dopt). At these corresponding Dopt values, 3.5 and 2 times higher biomass concentrations and volumetric productivities respectively were achieved by the MPBR. It is also possible to run the MPBR at still higher biomass concentration, thus enabling a smaller footprint and higher nutrient removal efficiency. However, reduced nutrient removal efficiencies were found to be one possible drawback.
The well-studied spv operon of Salmonella typhimurium is important for causing full virulence in mice and both the regulation and function of the Spv proteins have been characterized extensively over the past several decades. Using quantitative single-cell fluorescence microscopy, we demonstrate the spv regulon to display a bimodal expression pattern that originates in the bimodal expression of the SpvR activator. The spv expression pattern is influenced by growth conditions and the specific S. typhimurium strain used, but does not require Salmonella-specific virulence regulators. By monitoring real-time promoter kinetics, we reveal that SpvA has the ability to impart negative feedback on spvABCD expression without affecting spvR expression. Together, our data suggest that the SpvA protein counteracts the positive feedback loop imposed by SpvR, and could thus be responsible for dampening spvABCD expression and coordinating virulence protein production in time. The results presented here yield new insights in the intriguing regulation of the spv operon and adds this operon to the growing list of virulence factors exhibiting marked expression heterogeneity in S. typhimurium.
In this study, we examined the intracellular whereabouts of Mrr, a cryptic type IV restriction endonuclease of Escherichia coli K12, in response to different conditions. In absence of stimuli triggering its activity, Mrr was found to be strongly associated with the nucleoid as a number of discrete foci, suggesting the presence of Mrr hotspots on the chromosome. Previously established elicitors of Mrr activity, such as exposure to high (hydrostatic) pressure (HP) or expression of the HhaII methyltransferase, both caused nucleoid condensation and an unexpected coalescence of Mrr foci. However, although the resulting Mrr/nucleoid complex was stable when triggered with HhaII, it tended to be only short-lived when elicited with HP. Moreover, HP-mediated activation of Mrr typically led to cellular blebbing, suggesting a link between chromosome and cellular integrity. Interestingly, Mrr variants could be isolated that were specifically compromised in either HhaII- or HP-dependent activation, underscoring a mechanistic difference in the way both triggers activate Mrr. In general, our results reveal that Mrr can take part in complex spatial distributions on the nucleoid and can be engaged in distinct modes of activity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.