Relationships between community composition, productivity and invasion resistance in semi-natural bacterial microcosms

Abstract

Common garden experiments that inoculate a standardised growth medium with synthetic microbial communities (i.e. constructed from individual isolates or using dilution cultures) suggest that the ability of the community to resist invasions by additional microbial taxa can be predicted by the overall community productivity (broadly defined as cumulative cell density and/or growth rate). However, to the best of our knowledge, no common garden study has yet investigated the relationship between microbial community composition and invasion resistance in microcosms whose compositional differences reflect natural, rather than laboratory-designed, variation. We conducted experimental invasions of two bacterial strains (Pseudomonas fluorescens and Pseudomonas putida) into laboratory microcosms inoculated with 680 different mixtures of bacteria derived from naturally occurring microbial communities collected in the field. Using 16S rRNA gene amplicon sequencing to characterise microcosm starting composition, and high-throughput assays of community phenotypes including productivity and invader survival, we determined that productivity is a key predictor of invasion resistance in natural microbial communities, substantially mediating the effect of composition on invasion resistance. The results suggest that similar general principles govern invasion in artificial and natural communities, and that factors affecting resident community productivity should be a focal point for future microbial invasion experiments.

Microbial invasion of a toxic medium is facilitated by a resident community but inhibited as the community co-evolves

“…Taken together, although our experimental data cannot conclusively test all the different explanations (Fig. 4 ), we find support for the role of community productivity [ 15 ], but cannot exclude increased interference competitive or niche coverage as additional factors reducing invasion success.…”

“…First, more productive communities (greater population size) are expected to be harder to invade (Fig. 4A ) [ 15 ]. Although we observed no significant differences in productivity between ancestral and co-evolved communities at the time of transfer (Fig.…”

“…While productivity is a plausible explanation for reduced invasion success in co-evolved communities, it need not be the only one [ 15 ]. Another explanation could be that communities with higher species- and strain-level diversity tend to be more robust against invasions (Fig.…”

“…What determines the ability of an invasive species to colonize an existing ecosystem depends on the characteristics of both the invading species and the resident community [ 7 , 8 ]. Many theoretical and empirical studies have established factors that influence invasion outcome, such as propagule pressure [ 9 – 14 ], resident community productivity [ 15 ], genotypic richness of invaders [ 13 , 16 ] or the resident community [ 3 , 13 , 17 – 20 ], community niche coverage [ 3 , 21 , 22 ], and abiotic conditions (e.g., the presence of antibiotics [ 23 ]).…”

Interactions between culturable bacteria are highly non-additive

“…Though positive effects were common, making up about one third of the single species effects, they became less common as the number of community members increased, making up only one quarter of the effects of species pairs. Furthermore, we found similar trends in the larger communities of 4 species (three affecting species and one focal), both that effects combined in a non additive manner, being dominated by the strongest single species effect, and that negative effects became more common in larger communities which is consistent with previous studies (Cook et al 2006;van Elsas et al 2012;Jones et al 2021;Piccardi, Vessman, and Mitri 2019;Gould et al 2018;Palmer and Foster 2022).…”