Mms19 encodes a cytosolic iron-sulphur assembly component. We found that Drosophila Mms19 is also essential for mitotic divisions and for the proliferation of diploid cells. Reduced Mms19 activity causes severe mitotic defects in spindle dynamics and chromosome segregation, and loss of zygotic Mms19 prevents the formation of imaginal discs. The lack of mitotic tissue in Mms19P/P larvae can be rescued by overexpression of the Cdk-activating kinase (CAK) complex, an activator of mitotic Cdk1, suggesting that Mms19 functions in mitosis to allow CAK (Cdk7/Cyclin H/Mat1) to become fully active as a Cdk1-activating kinase. When bound to Xpd and TFIIH, the CAK subunit Cdk7 phosphorylates transcriptional targets and not cell cycle Cdks. In contrast, free CAK phosphorylates and activates Cdk1. Physical and genetic interaction studies between Mms19 and Xpd suggest that their interaction prevents Xpd from binding to the CAK complex. Xpd bound to Mms19 therefore frees CAK complexes, allowing them to phosphorylate Cdk1 and facilitating progression to metaphase. The structural basis for the competitive interaction with Xpd seems to be the binding of Mms19, core TFIIH and CAK to neighbouring or overlapping regions of Xpd.
The Gram‐negative bacterium Legionella pneumophila is the causative agent of Legionnaires' disease and replicates in amoebae and macrophages within a distinct compartment, the Legionella‐containing vacuole (LCV). The facultative intracellular pathogen switches between a replicative, non‐virulent and a non‐replicating, virulent/transmissive phase. Here, we show on a single‐cell level that at late stages of infection, individual motile (PflaA‐GFP‐positive) and virulent (PralF‐ and PsidC‐GFP‐positive) L. pneumophila emerge in the cluster of non‐growing bacteria within an LCV. Comparative proteomics of PflaA‐GFP‐positive and PflaA‐GFP‐negative L. pneumophila subpopulations reveals distinct proteomes with flagellar proteins or cell division proteins being preferentially produced by the former or the latter, respectively. Toward the end of an infection cycle (˜ 48 h), the PflaA‐GFP‐positive L. pneumophila subpopulation emerges at the cluster periphery, predominantly escapes the LCV, and spreads from the bursting host cell. These processes are mediated by the Legionella quorum sensing (Lqs) system. Thus, quorum sensing regulates the emergence of a subpopulation of transmissive L. pneumophila at the LCV periphery, and phenotypic heterogeneity underlies the intravacuolar bi‐phasic life cycle of L. pneumophila.
Pseudomonas aeruginosa and Staphylococcus aureus frequently occur together in polymicrobial infections, and their interactions can complicate disease progression and treatment options. While interactions between P. aeruginosa and S. aureus have been extensively described using planktonic batch cultures, little is known about whether and how individual cells interact with each other on solid substrates. This is important because both species frequently colonize surfaces to form aggregates and biofilms in infections. Here, we performed single-cell time-lapse fluorescence microscopy, combined with automated image analysis, to describe interactions between P. aeruginosa PAO1 with three different S. aureus strains (Cowan I, 6850, JE2) during microcolony growth on agarose surfaces. While P. aeruginosa is usually considered the dominant species, we found that the competitive balance tips in favor of S. aureus on surfaces. We observed that all S. aureus strains accelerated the onset of microcolony growth in competition with P. aeruginosa and significantly compromised P. aeruginosa growth prior to physical contact. Upon direct contact, JE2 was the most competitive S. aureus strain, simply usurping P. aeruginosa microcolonies, while 6850 was the weakest competitor itself suppressed by P. aeruginosa. Moreover, P. aeruginosa reacted to the assault of S. aureus by showing increased directional growth and expedited expression of quorum sensing regulators controlling the synthesis of competitive traits. Altogether, our results reveal that quantitative single-cell live imaging has the potential to uncover microbial behaviors that cannot be predicted from batch culture studies, and thereby contribute to our understanding of interactions between pathogens that co-colonize host-associated surfaces during polymicrobial infections.
Pseudomonas aeruginosa and Staphylococcus aureus frequently occur together in polymicrobial infections, and there is evidence that their interactions negatively affect disease outcome in patients. At the molecular level, interactions between the two bacterial taxa are well-described, with P. aeruginosa usually being the dominant species suppressing S. aureus through a variety of inhibitory molecules. However, in polymicrobial infections, the two species interact over prolonged periods of time, and S. aureus might evolve resistance against inhibitory molecules deployed by P. aeruginosa. Here, we used experimental evolution to test this hypothesis by exposing three different S. aureus strains (Cowan I, 6850, JE2) to the growth-inhibitory supernatant of P. aeruginosa PAO1 over 30 days. We found that all three S. aureus strains rapidly evolved resistance against inhibitory molecules and show that (i) adaptations were strain-specific; (ii) resistance evolution affected the expression of virulence traits; and (iii) mutations in membrane transporters were the most frequent evolutionary targets. Our work indicates that adaptations of S. aureus to co-infecting pathogens could increase virulence and decrease antibiotic susceptibility, because both virulence traits and membrane transporters involved in drug resistance were under selection. Thus, pathogen co-evolution could exacerbate infections and compromise treatment options.
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.