Microbial Small Talk: Volatiles in Fungal–Bacterial Interactions

Abstract

There is increasing evidence that volatile organic compounds (VOCs) play an important role in the interactions between fungi and bacteria, two major groups of soil inhabiting microorganisms. Yet, most of the research has been focused on effects of bacterial volatiles on suppression of plant pathogenic fungi whereas little is known about the responses of bacteria to fungal volatiles. In the current study we performed a metabolomics analysis of volatiles emitted by several fungal and oomycetal soil strains under different nutrient conditions and growth stages. The metabolomics analysis of the tested fungal and oomycetal strains revealed different volatile profiles dependent on the age of the strains and nutrient conditions. Furthermore, we screened the phenotypic responses of soil bacterial strains to volatiles emitted by fungi. Two bacteria, Collimonas pratensis Ter291 and Serratia plymuthica PRI-2C, showed significant changes in their motility, in particular to volatiles emitted by Fusarium culmorum. This fungus produced a unique volatile blend, including several terpenes. Four of these terpenes were selected for further tests to investigate if they influence bacterial motility. Indeed, these terpenes induced or reduced swimming and swarming motility of S. plymuthica PRI-2C and swarming motility of C. pratensis Ter291, partly in a concentration-dependent manner. Overall the results of this work revealed that bacteria are able to sense and respond to fungal volatiles giving further evidence to the suggested importance of volatiles as signaling molecules in fungal–bacterial interactions.

The ecological role of volatile mediated interactions belowground

“…in soil under similar conditions . However, F. culmorum is also able to produce various volatile terpenes including fenchone or camphene as observed here and elsewhere (Schmidt et al 2016;Schulz-Bohm et al 2017b). …”

“…Due to the shifts in bacterial community, we observed changes in fungal pigmentation and volatile emission. In the last years, it has become evident that microbial volatiles can play major roles in long-distance interactions within soil microbial communities acting as infochemicals or antimicrobial compounds (Effmert et al 2012;Schmidt et al 2015;Schmidt et al 2016). The shifts in fungalassociated bacterial community led to shifts in volatile production of the original and the The composition and abundance of volatiles was affected by the nutrient conditions with more volatiles produced on the nutrient-rich PDA media.…”

“…The shifts in fungalassociated bacterial community led to shifts in volatile production of the original and the The composition and abundance of volatiles was affected by the nutrient conditions with more volatiles produced on the nutrient-rich PDA media. Several independent studies have reported that the volatile profiles of bacteria and fungi are strongly dependent on growth conditions, interactions and nutrient availability (Garbeva et al 2014b;Tyc et al 2015;Schmidt et al 2016;Weikl et al 2016). Hence, it is questionable whether the same volatile-mediated interactions will occur in nature under nutrient-limited conditions.…”

“…Monoxenic protist cultures (Table S4.2) were obtained from an enrichment cultivation approach as described in Geisen et al (2014). In frame deletion of the terpene synthase gene (CPter91_2617) and phytoene synthase gene (CPter91_3184) Exposure of protists to bacterial volatiles Two-compartment Petri-dishes were filled with 12 ml 1.5 % (v/v) water-agar (WA) supplied with artificial root exudates (18 ml artificial root exudates stock solution [SchulzBohm et al 2015] per liter WA [Schmidt et al 2016 …”

“…Recently, Schmidt et al (2016) screened the phenotypic responses of soil bacterial strains to volatiles emitted by several fungal and oomycetal soil strains under different nutrient conditions during different growth stages. Out of the phenotypical responses tested such as growth alteration, antimicrobial activity, biofilm formation or motility, motility of bacteria (both swimming and swarming) was significantly positively or negatively affected by fungal and oomycetal VOCs.…”