Tropentag 2023, September 20 - 22, Berlin, Germany "Competing pathways for equitable food systems transformation: trade-offs and synergies."

Inhibitory activity of bacterial lipopeptides against Fusarium oxysporum f.sp. strigae

¹University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany
²University of Hohenheim, Core Facility Hohenheim, Mass Spectrometry Unit, Germany

Abstract

This study investigated the impact of bacterial cyclic lipopeptides (LP; surfactins, iturins, fengycins) on microbial interactions in the plant endosphere. The objective was to investigate whether the presence of bacteria inhibits fungal growth and whether this inhibition is due to the release of bacterial metabolites, particularly LP. The study employed selected endophytic bacterial strains with known plant-growth promoting potential that were cultured in the presence of Fusarium oxysporum f.sp. strigae (Fos), which was applied as the model fungal organism. The extracellular metabolome of tested bacteria, with a focus on LP, was characterised, and the inhibitory effect of bacterial LP on fungal growth was investigated. The results showed that Bacillus velezensis GB03 and FZB42, as well as B. subtilis BSn5 exhibited the strongest antagonism against Fos, while Paraburkholderia phytofirmans PsJN had a slight stimulatory effect. Crude LP from strains GB03 and FZB42 had the strongest inhibitory effect on Fos, with a significant inhibition of spore germination and damage to the hyphal structure. Liquid chromatography tandem mass spectrometry revealed the production of several variants of iturin, fengycin, and surfactin LP families from strains GB03, FZB42, and BSn5, with varying intensity. Using plate cultures, bacillomycin D fractions were detected in higher abundance in strains GB03, FZB42, and BSn5 in the presence of Fos. Additionally, the presence of Fos in dual plate culture triggered an increase in bacillomycin D production from the Bacillus strains, possibly through activation of signaling molecules. It was also suggested that fungal metabolites produced by Fos in dual culture might have triggered LP production by bacteria. The study clearly demonstrated the potent antagonistic effect of certain Bacillus strains, including Bacillus sp. GB03, FZB42, and BSn5, on Fos development. Conversely, we found that P. phytofirmans PsJN promoted the development of Fos. Our findings emphasise the crucial role of microbial interactions in shaping the co-existence of microbial assemblages in plant endospheres.

Keywords: Bacillomycin D, biological control, co-inoculation, lipopeptide abundance, microbial interaction

Contact Address: Mekuria Wolde Assena, University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Garbenstr. 13, 70593 Stuttgart Stuttgart, Germany, e-mail: mekuriawolde.assenauni-hohenheim.de