Life After Secretion—Yersinia enterocolitica Rapidly Toggles Effector Secretion and Can Resume Cell Division in Response to Changing External Conditions

Abstract

Many pathogenic bacteria use the type III secretion system (T3SS) injectisome to manipulate host cells by injecting virulence-promoting effector proteins into the host cytosol. The T3SS is activated upon host cell contact, and its activation is accompanied by an arrest of cell division; hence, many species maintain a T3SS-inactive sibling population to propagate efficiently within the host. The enteric pathogen Yersinia enterocolitica utilizes the T3SS to prevent phagocytosis and inhibit inflammatory responses. Unlike other species, almost all Y. enterocolitica are T3SS-positive at 37°C, which raises the question, how these bacteria are able to propagate within the host, that is, when and how they stop secretion and restart cell division after a burst of secretion. Using a fast and quantitative in vitro secretion assay, we have examined the initiation and termination of type III secretion. We found that effector secretion begins immediately once the activating signal is present, and instantly stops when this signal is removed. Following effector secretion, the bacteria resume division within minutes after being introduced to a non-secreting environment, and the same bacteria are able to re-initiate effector secretion at later time points. Our results indicate that Y. enterocolitica use their type III secretion system to promote their individual survival when necessary, and are able to quickly switch their behavior toward replication afterwards, possibly gaining an advantage during infection.

Dynamic relocalization of cytosolic type III secretion system components prevents premature protein secretion at low external pH

“…Maleimide based needle staining. To visualize the injectisome needles, expression of SctF S5C 46 was induced from plasmid. Protein expression was induced with 0.4-1.0% L-arabinose at the temperature shift.…”

Dynamic relocalization of the cytosolic type III secretion system components prevents premature protein secretion at low external pH

“…92 But how does Y. enterocolitica prevent secretion at low pH? To determine if the absence of secretion 93 is due to a complete disassembly of injectisomes at that pH, we visualized the needles at different pH 94 values and over time by labeling an introduced cysteine residue with a maleimide-linked dye (Milne-95 Davies et al, 2019). The needles were stable at pH 4 over continued time periods ( Fig.…”

Adaptivity and dynamics in type III secretion systems

“…While in Shigella and Yersinia , almost all bacteria assemble injectisomes at 37°C (Burgess et al, 2020; Milne‐Davies et al, 2019; Wiley et al, 2007), bimodal expression of injectisome components is observed in Salmonella and Pseudomonas , where a large subpopulation does not assemble any injectisomes (Rietsch and Mekalanos, 2006; Rundell et al, 2016; Sturm et al, 2011). Salmonella uses division of labor and bet‐hedging strategies for more efficient infection and increased survival if conditions change (Davis and Isberg, 2019; Weigel and Dersch, 2018).…”

“…In Y. enterocolitica , the T3SS is homogenously expressed and bacteria are able to survive and restart division following secretion. These observations imply that Y. enterocolitica aim to maximize individual survival chances (Milne‐Davies et al, 2019). In the case of S. flexneri and S. sonnei , the Shigella virulence plasmid (pINV), which contains the injectisome, even harbors multiple toxin–antitoxin (TA) systems that aid in maintaining the plasmid during cell division (McVicker and Tang, 2017; Sayeed et al, 2000) and suppress the rise of faster‐growing “cheaters”—an indication that like Yersinia , Shigella focuses on the survival of individual bacteria during infection, which is also indicated by the very low infectious dose (DuPont et al, 1989).…”

“…As for the flagellum, it is possible that SctQ, possibly in cooperation with other cytosolic components, increases the local concentration of cargo (e.g., chaperone‐effector complexes) at the injectisome, or directly delivers these proteins to the export gate, which would also conform to the observed interaction between SctQ and effectors and chaperones. However, the observed exchange rate of SctQ (which has a FRAP recovery half‐time of slightly above 1 min, corresponding to an average dwell time of several seconds per molecule) is too slow to explain the measured export rates of up to 60 effectors per injectisome and second (Enninga et al, 2005; Ittig et al, 2015; Mills et al, 2008; Schlumberger et al, 2005), which stay approximately constant over time in Y. enterocolitica (Milne‐Davies et al, 2019). Notably, SctQ exchange was measured in an effector‐less strain (Diepold et al, 2015), leaving the possibility that the binding of chaperones‐effector complexes induces faster exchange.…”