Volatile-Mediated Inhibitory Activity of Rhizobacteria as a Result of Multiple Factors Interaction: The Case of Lysobacter capsici AZ78

Abstract

Plant beneficial rhizobacteria may antagonize soilborne plant pathogens by producing a vast array of volatile organic compounds (VOCs). The production of these compounds depends on the medium composition used for bacterial cell growth. Accordingly, Lysobacter capsici AZ78 (AZ78) grown on a protein-rich medium was previously found to emit volatile pyrazines with toxic activity against soilborne phypathogenic fungi and oomycetes. However, the discrepancy between the quantity of pyrazines in the gaseous phase and the minimum quantity needed to achieve inhibition of plant pathogens observed, lead us to further investigate the volatile-mediated inhibitory activity of AZ78. Here, we show that, besides VOCs, AZ78 cells produce ammonia in increased amounts when a protein-rich medium is used for bacterial growth. The production of this volatile compound caused the alkalinization of the physically separated culture medium where Rhizoctonia solani was inoculated subsequently. Results achieved in this work clearly demonstrate that VOC, ammonia and the growth medium alkalinization contribute to the overall inhibitory activity of AZ78 against R. solani. Thus, our findings suggest that the volatile-mediated inhibitory activity of rhizobacteria in protein-rich substrates can be regarded as a result of multiple factors interaction, rather than exclusively VOCs production.

Biosynthesis, regulation, and engineering of natural products from Lysobacter

“…16). 197–199 These compounds appear to be produced in nutrient-rich conditions, which is in contrast to HSAF and analogues that are produced only in conditions where nutrients are depleted. Among the 2,5-diketopiperazines, cyclo( l -Pro- l -Tyr) ( 51 ) exhibited strong in vitro and in vivo activity against Phytophthora infestans and Plasmopara viticola , and cyclo( l -Pro- l -Val) ( 52 ) showed a cytotoxic activity similar to chloramphenicol (25 μg mL −1 ) against Rhodococcus fascians , a phytopathogenic Gram-positive bacterium.…”

“…These compounds contribute to the antagonistic effects of AZ78 against plant pathogenic microorganisms, including Pythium ultimum , Rhizoctonia solani , and Sclerotinia minor . 199,202…”

Lysobacter enzymogenes prevents Phytophthora infection by inhibiting pathogen growth and eliciting plant immune responses

“…Lysobacter capsici AZ78 generates cyclo (L-Pro-L-Tyr), a 2,5-diketopiperazine that inhibits sporangia development and virulence in P. infestans ( Puopolo et al., 2014 ). VOCs from L. capsici have been reported to suppress mycelial growth of various fungi and oomycete ( Vlassi et al., 2020a ; Vlassi et al., 2020b ).…”

Genetic Basis and Expression Pattern Indicate the Biocontrol Potential and Soil Adaption of Lysobacter capsici CK09

“…Additionally, they produce various secondary metabolites, such as phenazine [ 15 ], heat-stable antifungal factor (HSAF) [ 23 ], hypeptine [ 24 ], lysocin E [ 25 ] and 2,5-diketopiperazines [ 26 ], which were identified as antimicrobial agents. Volatile compounds produced by Lysobacter species also contribute to their antimicrobial activity [ 27 ], while certain Lysobacter species may induce systemic resistance in plants [ 28 ]. Thus, Lysobacter species show potential as biocontrol agents in agriculture.…”