Volatile Organic Compounds From Lysobacter capsici AZ78 as Potential Candidates for Biological Control of Soilborne Plant Pathogens

Abstract

The genus Lysobacter includes several bacterial species which show potential for being used in biological control of plant diseases. It was shown recently that several Lysobacter type strains produce volatile organic compounds (VOCs) which controlled the growth of Phytophthora infestans in vitro when the bacteria were grown on a protein rich medium. In the present study, Lysobacter capsici AZ78 (AZ78) has been tested for its potential to produce VOCs that may contribute to the bioactivity against soilborne plant pathogens. To this end, split Petri dish assays of bacterial cultures have been combined with GC-MS measurements with the aim to reveal the identity of the VOCs which inhibit the growth of Pythium ultimum Rhizoctonia solani, and Sclerotinia minor. While AZ78 completely suppressed the growth of P. ultimum and S. minor, the growth of R. solani was still reduced significantly. The GC-MS analysis revealed 22 VOCs to be produced by AZ78, the majority of which were (putatively) identified as mono-and dialkylated methoxypyrazines. Based on additional cultivation and GC-MS experiments, 2,5-dimethylpyrazine, 2-ethyl-3-methoxypyrazine and 2-isopropyl-3-methoxypyrazine were selected as presumable bioactive compounds. Further bioassays employing indirect exposure to standard solutions (1-10 mg per Petri dish) of the synthetic compounds via the gas phase, revealed that each of these pyrazines was able to suppress the growth of the pathogens under investigation. The results of this study highlight the possible future implementation of pyrazine derivatives in the control of soilborne plant diseases and further support the biocontrol potential of L. capsici AZ78.

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

“…Sample preparation for GC-MS analysis was identical to Vlassi et al [45]. Briefly, split Petri dishes containing PDA medium in one compartment and AZ78 inoculated on NA or NAG as reported above, were sealed and incubated at 27 • C for 168 h. PDA and NA or NAG, inoculated with AZ78, were then cut into pieces and transferred into sterile headspace (HS) vials (20 mL, La-Pha-Pack, Langerwehe, Germany) having sterile metal caps with 1.3 mm silicone/PTFE septa (La-Pha-Pack).…”

“…Briefly, split Petri dishes containing PDA medium in one compartment and AZ78 inoculated on NA or NAG as reported above, were sealed and incubated at 27 • C for 168 h. PDA and NA or NAG, inoculated with AZ78, were then cut into pieces and transferred into sterile headspace (HS) vials (20 mL, La-Pha-Pack, Langerwehe, Germany) having sterile metal caps with 1.3 mm silicone/PTFE septa (La-Pha-Pack). The 168 h time point was chosen, as it was previously found that AZ78 growing on NA had the most abundant volatile profile [45]. HS vials that were empty and HS vials with PDA, NA or NAG medium from uninoculated Petri dishes were used as controls.…”

“…Analyses were carried out according to Vlassi et al [45]. In brief, the samples to be analyzed were initially introduced to the DHS where they were first incubated (27 • C for 15 min) and subsequently VOCs were dynamically collected onto a 2 cm TENAX trap (Buchem, Apeldoorn, Netherlands) at 30 • C, while an intermediate purging step to remove water from the trap was applied.…”

“…The biocontrol agent L. capsici AZ78 (AZ78) [41] can successfully suppress the growth of plant pathogenic oomycetes by implementing mycophagy [42], secretion of secondary metabolites [43] and lytic enzymes [44]. Recently, AZ78 was shown to be able to emit VOCs with inhibitory activity against plant pathogenic fungi and oomycetes [45]. However, the abundance of these metabolites in the blend of AZ78 volatiles could not fully explain the growth inhibition of plant pathogens in vitro [45].…”

“…Recently, AZ78 was shown to be able to emit VOCs with inhibitory activity against plant pathogenic fungi and oomycetes [45]. However, the abundance of these metabolites in the blend of AZ78 volatiles could not fully explain the growth inhibition of plant pathogens in vitro [45].…”