Bacterial iturins mediate biocontrol activity of Bacillus sp. against postharvest pear fruit‐rotting fungi

Abstract

A potential antagonist, Bacillus sp. LYLB4 isolated from pear fruits, was tested for its antifungal activity against postharvest pear pathogens. LYLB4 had a remarkable antifungal effect on Botryosphaeria dothidea. Although it showed a weak inhibition effect on the growth of Rhizopus stolonifer on potato dextrose agar (PDA) plates, LYLB4 almost completely destroyed R. stolonifer during direct contact in potato dextrose broth (PDB). LYLB4 treatment was able to significantly reduce disease incidence (by 68.9% and 100%, respectively) and lesion diameter (by 68.7% and 100%, respectively) of ring rot caused by B. dothidea and soft rot caused by R. stolonifer in pears. LYLB4 also suppressed several other phytopathogens in vitro, suggesting a broad‐spectrum antagonistic activity against fungal pathogens. 16S rRNA and gyrA sequence analysis indicated that LYLB4 is closely related to B. velezensis. Genome mining indicated that LYLB4 had 11 secondary metabolites encoding clusters, but that the surfactin and fengycin gene clusters may not be functional because of a large deletion. Matrix‐assisted laser desorption ionization‐time of flight mass spectra (MALDI‐TOF‐MS) demonstrated that iturins were the major lipopeptides, and that C16/C17 Bacillomycin D synthesis was stimulated when LYLB4 was co‐cultured with B. dothidea compared to the control. Overall, these results demonstrate that the main biocontrol mechanism adopted by LYLB4 could be through the production of toxic metabolites and direct contact with pathogens.

Biocontrol Ability of the Bacillus amyloliquefaciens Group, B. amyloliquefaciens, B. velezensis, B. nakamurai, and B. siamensis, for the Management of Fungal Postharvest Diseases: A Review

“…LYLB4, which was able to synthesize iturin, completely inhibited the symptoms of Rhizopus stolonifer in pears. 119 It must also be noted that, in most reports, the genes involved in the biosynthesis of the mentioned metabolites were sequenced, but there is a lack of elucidation studies to confirm the exact structures of the active metabolites. In a few cases, the identification of the compounds was carried out by mass spectrometry, which allowed the structural elucidation of the antifungal compounds.…”

“…LYLB4. 119 Iturin A consists of seven amino acids, L-aspartic acid, L-asparagine, L-glutamic acid, L-glutamine, L-serine, and L-proline, attached to a 14-or a 15-carbon chain (Figure 2B). 89,93,119 Bacillomycin D and iturin A are members of the iturin family and show several structural similarities, such as a seven-amino acid cyclic peptide.…”

Biossurfactante produzido por linhagem termo-halofílica de >i<Bacillus alveayuensis>/i<: caracterização química e avaliação da atividade tensoativa em meio poroso com óleo e sobre microrganismos

“…Tabela 5 -Aminoácidos presentes em quantidades acima de 1g/100g na amostra BSSP60 e suas proporções relativas. O intervalo m/z 1065-1067 é identificado na literatura como um representante de possíveis adutos dos lipopeptídeos bacilomicina D, [189][190][191][192][193] iturina A, 36,78,190,[194][195][196] micosubtilisina [196][197] ou surfactina. 36,[197][198][199] No presente trabalho foram identificados dois padrões para a fragmentação do pico m/z 1066; no primeiro padrão de fragmentação, foram considerados os fragmentos 250, 493, 687, 725 e 935.…”

“…Tomando como base a análise feita por Jemil e colaboradores, 197 O íon 1072, observado na Figura 28a, é descrito na literatura como C 15-16pumilacidina, C 16 -surfactina, Iturina A, C 17 -bacilomicina D 36,189,[192][193]195,199,[201][202] Asn-Gln-CO + ), assim como indicado também por Lin et al 75 O íon 1081 é descrito na literatura como sendo possíveis adutos de sódio ou potássio de C 14-iturina A, 36,78,195 C 16 -surfactina 192,205 e C 16 -bacilomicina 191,193,[196][197] e também [M+2Na] + de C 15 -surfactina 1035. 199 Também foram observados m/z na região de 1300-1630, Figura 30 e Figura 31, intervalos descritos por apresentar fengicinas.…”

“…Bacilomicina D [189][190][191][192][193] Asn Tyr Asn Pro Glu Ser Tyr ---Iturina A 36,78,[194][195][196]200 Asn Tyr Asn Gln Pro Asn Ser ---Pumilacidina 34,197,202…”