Agricultural relevance of fungal mycelial growth-promoting bacteria: Mutual interaction and application

Bacterial-fungal interaction (BFI) is found ubiquitously and plays important roles in various environmental settings, thus being responsible for numerous biophysical and chemical processes in nature. In terms of BFI, the capacity of the bacterium to enhance the growth of fungal mycelia is an indication of the roles of the bacterium in mutualistic interaction, since increasing mycelial growth results in higher changes for fungal establishment. In this review, the interaction between mycelial growth-promoting bacterium (MGPB) and its fungal counterpart in agricultural settings and the promotion of mycelial growth as an outcome of mutual interactions in various environmental niches were evaluated. The beneficial relationships included endohyphal interaction, association of bacteria with mushrooms, bacteria-mycorrhizae symbiosis, and geomicrobiology. Furthermore, the mode of interaction between MGPB and their fungal counterparts was also explained. There are two fundamental modes of interaction involved, namely physical interaction and chemical interaction. The first involved endosymbiosis and bacterial attachment, while the latter comprised quorum sensing, volatile metabolites, enzymatic activity, and chemotaxis. Particularly, the growth stimulants secreted by the bacteria, which promote the growth of hyphae, are discussed thoroughly. Moreover, the chance of trade-off metabolites between fungi and their MGPBs as a consequence of mutualistic interaction will also be observed. Finally, the agricultural relevance of BFI, particularly the relation between fungi and MGPBs, will also be provided, including key technologies and future bioprospects for optimum application.