Impact of interspecific interactions on antimicrobial activity among soil bacteria

Abstract

Certain bacterial species produce antimicrobial compounds only in the presence of a competing species. However, little is known on the frequency of interaction-mediated induction of antibiotic compound production in natural communities of soil bacteria. Here we developed a high-throughput method to screen for the production of antimicrobial activity by monocultures and pair-wise combinations of 146 phylogenetically different bacteria isolated from similar soil habitats. Growth responses of two human pathogenic model organisms, Escherichia coli WA321 and Staphylococcus aureus 533R4, were used to monitor antimicrobial activity. From all isolates, 33% showed antimicrobial activity only in monoculture and 42% showed activity only when tested in interactions. More bacterial isolates were active against S. aureus than against E. coli. The frequency of interaction-mediated induction of antimicrobial activity was 6% (154 interactions out of 2798) indicating that only a limited set of species combinations showed such activity. The screening revealed also interaction-mediated suppression of antimicrobial activity for 22% of all combinations tested. Whereas all patterns of antimicrobial activity (non-induced production, induced production and suppression) were seen for various bacterial classes, interaction-mediated induction of antimicrobial activity was more frequent for combinations of Flavobacteria and alpha- Proteobacteria. The results of our study give a first indication on the frequency of interference competitive interactions in natural soil bacterial communities which may forms a basis for selection of bacterial groups that are promising for the discovery of novel, cryptic antibiotics.

Socially mediated induction and suppression of antibiosis during bacterial coexistence

“…In addition, our data reveal that the classical dichotomy between killing and resistance used to understand interference competition between microbes is insufficient to describe interactions driven by antibiotics. Cells induce facultative responses to the presence of competitors by (i) increasing their own antibiotic production, thereby decreasing costs associated with constitutive synthesis of these expensive products, and (ii) by suppressing antibiotic production in competitors, thereby reducing direct threats to themselves (26). In a community context, these facultative strategies can influence A B C D biodiversity by converting lethal interactions between neighbors to neutral interactions where neither strain excludes the other.…”

“…Equally, we predict that social growth will elicit defensive strategies to suppress or attenuate antibiotic production in competitors (18). Though this study was not aimed at identifying the mechanisms of elicitation and attenuation, both outcomes have been observed and can result from diverse mechanisms, including a response to stress caused by resource competition or antibiotic exposure (7,(24)(25)(26), or via enzymatic degradation of antibiotics or the signals regulating their production (2). Fig.…”

Volatile communication between fungi and bacteria

“…By testing their effect on bacterial traits I found that VOCs emitted by particular fungi/oomycetes strongly affect the motility of two bacterial isolates (Collimonas pratensis and Serratia plymuthica). This suggests that, similar to bacterial VOCs that have been shown to alter specific fungal/oomycetal traits (Tyc et al, 2014, De Vrieze et al, 2015, Sharifi & Ryu, 2016, VOCs produced by fungi/ oomycetes can be in turn sensed by bacteria, therefore modulating their ability to move. These results were confirmed when studying the bacterial transcriptome and proteome of S. plymuthica PRI-2C in response to fungal VOCs.…”

“…To test the triggering of antimicrobial activity by bacterial strains in response to fungal and oomycetal volatiles, an agar overlay assay was performed on day 6 (Tyc et al, 2014). The two indicator organisms E. coli WA321 and S. aureus 533R4…”

The ecological role of volatile mediated interactions belowground

“…During interspecific interactions, the production of various secondary metabolites can be triggered (e.g. Garbeva & De Boer 2009;Traxler et al 2013) and these secondary metabolites can act differently as compared to metabolites released by species in monoculture (Garbeva et al 2014a;Tyc et al 2014).…”