Taxonomy of spp. determines interactions with .

UNLABELLED

Bacilli and pseudomonads are among the most well-studied microorganisms commonly found in soil and frequently co-isolated. Isolates from these two genera are frequently used as plant beneficial microorganisms; therefore, their interaction in the plant rhizosphere is relevant for agricultural applications. Despite this, no systematic approach has been employed to assess the coexistence of members from these genera. Here, we screened 720 fluorescent soil isolates for their effects on pellicle formation in two types of media and found a predictor for interaction outcome in taxonomy. Interactions were context-dependent, and both medium composition and culture conditions strongly influenced interactions. Negative interactions were associated with , , and , and 2,4-diacetylphloroglucinol was confirmed as a strong (but not exclusive) inhibitor of . Non-inhibiting strains were closely related to and . Using such a non-inhibiting isolate, P9_31, which increased pellicle formation demonstrated that the two species were spatially segregated in cocultures. Our study is the first one to propose an overall negative outcome from pairwise interactions between and fluorescent pseudomonads; hence, cocultures comprising members from these groups are likely to require additional microorganisms for coexistence.

IMPORTANCE

There is a strong interest in the microbial ecology field to predict interaction among microorganisms, whether two microbial isolates will promote each other's growth or compete for resources. Numerous studies have been performed based on surveying the available literature or testing phylogenetically diverse sets of species in synthetic communities. Here, a high throughput screening has been performed using 720 isolates, and their impact on the biofilm formation of was tested. The aim was to determine whether a majority of will promote or inhibit the biofilms of in the co-cultures. This study reports that taxonomy is a good predictor of interaction outcome, and only a minority of isolates promote biofilm establishment.