Combined mass spectrometry-guided genome mining and virtual screening for acaricidal activity in secondary metabolites of Bacillus velezensis W1

Abstract

A comprehensive analytic strategy was performed to study the acaricidal activity ingredients of Bacillus velezensis W1, a strain for biological control of Tetranychus urticae. Through genome mining, 14 biosynthetic gene clusters were identified, which encode secondary metabolites, and these were further confirmed by MALDI-TOF-MS or LC-ESI-MS/MS, including bacillomycin D C13-C17, macrolactin A, 7-O-malonyl-macrolactin A, surfactin C14, and surfactin C15. Moreover, 27 volatile compounds were identified by GC-MS, mainly including cyclodipeptides, alkanes, organic acids, and esters. Finally, 43 compounds identified from W1 were used in the virtual screening of acaricidal activity. The results showed that 16 compounds, including cyclodipeptides, bacillomycins, macrolactins, and surfactins, have acaricidal potential. This work provides a base for studying the mechanism of acaricidal action of B. velezensis W1 and a comprehensive strategy for the study of active ingredients from biocontrol strains.

Fig. 1. MALDI-TOF MS spectrum of bacillomycin D from Bacillus velezensis W1.

Fig. 2. GC-MS spectra of cyclic dipeptide from Bacillus velezensis W1 (A1, B1, C1, D1, E1, and F1). GC-MS spectrum of the reference standard compound cyclo (Gly–Pro) (A2), cyclo (Leu–Leu) (B2), cyclo (Phe–Leu) (C2), cyclo (Phe–Pro) (D2), cyclo (Pro–Pro) (E2), and cyclo (Ala–Val) (F2).

Fig. 3. (A) LC-ESI-MS full scan spectrum of the bacillomycin D C14. (B) ESI-MS/MS spectrum analysis of the precursor ion [M + H]⁺ at m/z 1031.54. (C) The theoretical b-ion and y-ion fragments dissociated from ring-opening reactions between Glu and Pro. (D) Structure of bacillomycin D C14.

Fig. 4. LC-ESI-MS/MS tandem mass spectra of surfactin C15 (A1) and surfactin C14 (B1). ESI-MS/MS spectra analysis of the precursor ion [M + H]⁺ at m/z 1058.67 (A2) and 1044.66 (B2). The theoretical b-ion and y-ion fragments of surfactin C15 (A3) and surfactin C14 (B3). (A3). Structures of surfactin C15 (A4) and surfactin C14 (B4).

Fig. 5. LC-ESI-MS/MS tandem mass spectra of macrolactin A (A1) and 7-O-malonyl-macrolactin A (B1). Structures and theoretical fragment ions of macrolactin A (A2) and 7-O-malonyl-macrolactin A (B2). ESI-MS/MS spectra analysis of macrolactin A (A3) and 7-O-malonyl-macrolactin A (B3).