Pseudomonas aeruginosa Quorum-Sensing and Type VI Secretion System Can Direct Interspecific Coexistence During Evolution

Abstract

It is reported that a wide range of bacterial infections are polymicrobial, and the members in a local microcommunity can influence the growth of neighbors through physical and chemical interactions. Pseudomonas aeruginosa is an important opportunistic pathogen that normally causes a variety of acute and chronic infections, and clinical evidences suggest that P. aeruginosa can be frequently coisolated with other pathogens from the patients with chronic infections. However, the interspecific interaction and the coexisting mechanism of P. aeruginosa with coinfecting bacterial species during evolution still remain largely unclear. In this study, the relationships of P. aeruginosa with other Gram-positive (Staphylococcus aureus) and Gram-negative (Klebsiella pneumoniae) are investigated by using a series of on-plate proximity assay, in vitro coevolution assay, and RNA-sequencing. We find that although the development of a quorum-sensing system contributes P. aeruginosa a significant growth advantage to compete with S. aureus and K. pneumoniae, the quorum-sensing regulation of P. aeruginosa will be decreased during evolution and thus provides a basis for the formation of interspecific coexistence. The results of comparative transcriptomic analyses suggest that the persistent survival of S. aureus in the microcommunity has no significant effect on the intracellular transcriptional pattern of P. aeruginosa, while a more detailed competition happens between P. aeruginosa and K. pneumoniae. Specifically, the population of P. aeruginosa with decreased quorum-sensing regulation can still restrict the proportion increase of K. pneumoniae by enhancing the type VI secretion system-elicited cell aggressivity during further coevolution. These findings provide a general explanation for the formation of a dynamic stable microcommunity consisting of more than two bacterial species, and may contribute to the development of population biology and clinical therapy.

Coexistence of Microbial Species in Structured Communities by Forming a Hawk-Dove Game Like Interactive Relationship

“…Therefore, the unexpected mutual invasion relationship between P. aeruginosa and K. pneumoniae was similar with the outcome of hawk-dove game. This result was different from our previous finding that P. aeruginosa could overcome cocultured K. pneumoniae , while K. pneumoniae failed to invade P. aeruginosa in liquid culture with shaking (Zhao et al, 2018). We reasoned that this divergence could be due to the spatial distribution difference of bacterial cells between shaking and static culture conditions, since the structured population frequently led to coexistence of individuals with different relative fitness (Kerr et al, 2002; Ross-Gillespie et al, 2007; Santos et al, 2008; Pande et al, 2016).…”

“…Compared with the uniformly distributed P. aeruginosa in the communities, K. pneumoniae was excluded in the middle parts of colonies that grew from 99:1 or 1:1 mixture of P. aeruginosa and K. pneumoniae for 4 days (Supplementary Figure 2). As we had reported previously (Zhao et al, 2018), the peripheral distribution of K. pneumoniae was caused by the H1-T6SS (type VI secretion system) elicited cytotoxicity of P. aeruginosa , which could kill K. pneumoniae after 4 days of coculture. However, no inhibitory effect was observed when P. aeruginosa was cocultured with K. pneumoniae from an initial ratio of 1:99 (Supplementary Figure 2).…”

“…Moreover, we also noticed that P. aeruginosa had intrinsically stronger swimming ability than K. pneumoniae , and the mixed communities composed of both species showed remarkably enhanced swimming motility, instead of swarming, compared to the pure cultures (Supplementary Figure 3). Our previous work also found that the flagellum-encoding genes of P. aeruginosa were up-regulated during the coevolution with K. pneumoniae in liquid medium (Zhao et al, 2018). Therefore, these findings indicated that the presence of K. pneumoniae in the communities might improve the motility of P. aeruginosa .…”

“…LB is a rich medium containing abundant resources which enables the normal growth of P. aeruginosa and K. pneumoniae . Our prior work showed that no significant growth difference was detected between monocultured P. aeruginosa and K. pneumoniae on LB plates, while P. aeruginosa had a competitive advantage over K. pneumoniae under coculture condition (Zhao et al, 2018). In this study, we found that in comparison to the moderately increased proportion of P. aeruginosa in the coculture with K. pneumoniae from an initial ratio of 1:1, either P. aeruginosa or K. pneumoniae from low initial proportion (1%) in the mixture could rapidly invade each other’s population (Figure 1A,B).…”

“…Strains of mCherry-labeled wild type P. aeruginosa PAO1 (WT PAO1), mCherry-labeled P. aeruginosa PAO1 isogenic lasR mutant (in-frame knockout) and green fluorescent protein (GFP)-labeled K. pneumoniae were previously preserved in the laboratory (Zhao et al, 2018). All the strains were routinely cultured in Luria-Bertani (LB) broth from a single colony.…”