Abstract
Microorganisms evolve kinds of elaborate interaction models that can form relatively stable communities in a wide range of ecosystems. It is recognized that the spatial genetic structure of microbes in surface-attached environments lays a good foundation for the persistence of polymicrobial communities in adverse conditions. However, the interacting dynamics of microbes in facilitating the formation and stabilization of community structure still remains elusive. In this study, we identify a hawk-dove game like interspecific relationship between the two Gram-negative opportunistic pathogens Pseudomonas aeruginosa and Klebsiella pneumoniae, which naturally coexist in insect gut and can cocolonize human tissues. Specifically, although P. aeruginosa had significant competitive advantage over cocultured K. pneumoniae on solid medium with rich nutrient factors, K. pneumoniae could resist the suppression of P. aeruginosa by enhancing the expression of membrane transporters induced by the extracellular metabolites of P. aeruginosa. By contrast, under the condition that K. pneumoniae had a growth advantage but P. aeruginosa met a metabolic burden in producing quorum-sensing-controlled extracellular products, the frequency of K. pneumoniae would be slightly higher than P. aeruginosa during the coexistence because K. pneumoniae was also capable of exploiting the extracellular metabolite from P. aeruginosa. In addition, P. aeruginosa quorum-sensing variant could reap benefits from K. pneumoniae in turn and reach a relatively stable two species equilibrium. These findings provide an explanation for the formation and maintenance of polymicrobial communities in different spatially structured environments, and thus may contribute to understanding the complex interspecific interactions of microbes in local communities and shed new light on the development of social microbiology.
Highlights
Microorganisms are ubiquitous inhabitants of natural and unnatural ecosystems, and growth of them in a sessile lifestyle inevitably form communities composed of homo-/heterogeneous species with complex ecological interacting networks (Griffin et al, 2004; Adnani et al, 2017; Tshikantwa et al, 2018)
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)
The relative fitness of P. aeruginosa was always higher than K. pneumoniae under the same starting conditions after 2 days (Figure 1C), indicating that the invasion of P. aeruginosa toward K. pneumoniae was easier than the invasion of K. pneumoniae toward P. aeruginosa when they were cocultured on LB plate
Summary
Microorganisms are ubiquitous inhabitants of natural and unnatural ecosystems, and growth of them in a sessile lifestyle inevitably form communities composed of homo-/heterogeneous species with complex ecological interacting networks (Griffin et al, 2004; Adnani et al, 2017; Tshikantwa et al, 2018). Nutrient limitation as a hallmark of dense communities can result in social competition for extracellular products that significantly benefit the producers and neighboring recipients This creates selection for individuals with deficiency in producing the key factor but can reap the benefits of producers’ investment (Hansen et al, 2007; Xavier et al, 2011; Zengler and Zaramela, 2018). Such kind of exploitive competition may occur in many aspects involving extracellular digestive proteases, antibiotic resistance enzymes and iron chelate, biofilm production, virulence determinants and so on (Diggle et al, 2007a; Brockhurst et al, 2008, 2010; Gore et al, 2009; Diard et al, 2013; van Gestel et al, 2014; Kelsic et al, 2015; Luján et al, 2015; Frost et al, 2018)
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