Bacillus Responses to Plant-Associated Fungal and Bacterial Communities

Abstract

Some members of root-associated Bacillus species have been developed as biocontrol agents due to their contribution to plant protection by directly interfering with the growth of pathogens or by stimulating systemic resistance in their host. As rhizosphere-dwelling bacteria, these bacilli are surrounded and constantly interacting with other microbes via different types of communications. With this review, we provide an updated vision of the molecular and phenotypic responses of Bacillus upon sensing other rhizosphere microorganisms and/or their metabolites. We illustrate how Bacillus spp. may react by modulating the production of secondary metabolites, such as cyclic lipopeptides or polyketides. On the other hand, some developmental processes, such as biofilm formation, motility, and sporulation may also be modified upon interaction, reflecting the adaptation of Bacillus multicellular communities to microbial competitors for preserving their ecological persistence. This review also points out the limited data available and a global lack of knowledge indicating that more research is needed in order to, not only better understand the ecology of bacilli in their natural soil niche, but also to better assess and improve their promising biocontrol potential.

Elicitors of Plant Immunity Triggered by Beneficial Bacteria

“…Low temperature, acidic pH or poor oxygen availability are among the rhizosphere specific abiotic parameters that affect bacterial physiology and which may also modulate the production of secondary metabolites including elicitors as reported for Bacillus lipopeptides ( Fahim et al, 2012 ; Pertot et al, 2013 ; Zhao and Kuipers, 2016 ). Biotic factors such as interactions with other microbial species of the soil microbiome or chemical cross-talk with the host plant, may also influence elicitor production under natural conditions ( Debois et al, 2015 ; Wu et al, 2015 ; Venturi and Keel, 2016 ; Andrić et al, 2020 ). A better evaluation of the impact of all these factors deserve further investigation and is necessary to better anticipate inconsistencies in PGPR efficacy observed upon application under field conditions.…”

Chelator sensing and lipopeptide interplay mediates molecular interspecies interactions between soil bacilli and pseudomonads

“…It includes interactions with other organisms sharing the niche. Some recent reports illustrate how soil bacilli may adapt their behavior upon sensing bacterial competitors but almost exclusively focusing on developmental traits (sporulation, biofilm formation, or motility) 6 . Unlike other genera such as Streptomyces, it remains largely unknown to what extent bacilli in general and B. velezensis in particular, may modulate the expression of their secondary metabolome upon interaction with other bacteria 2,8,9,27 .…”

“…This competition can involve signal interference or toxins deployed by contact-dependent delivery systems 4, 5 but is mainly mediated at distance through the emission of various molecular weapons. The molecular basis of interference interactions and their phenotypic outcomes between diverse soil bacterial species have been amply investigated in the last decade 6, 7 .…”

“…It includes interactions with other organisms sharing the niche. Some recent reports illustrate how soil bacilli may adapt their behavior upon sensing bacterial competitors but almost exclusively focusing on developmental traits (sporulation, biofilm formation, or motility) 7 .…”

“…Unlike other genera such as Streptomyces , it remains largely unknown to what extent bacilli in general and B. velezensis in particular, may modulate the expression of their secondary metabolome upon interaction with other bacteria 7, 20 . In this work, we investigated the molecular outcomes of interspecies interactions in which B. velezensis may engage.…”