Visualizing fungal metabolites during mycoparasitic interaction by MALDI mass spectrometry imaging

Abstract

Studying microbial interactions by MALDI mass spectrometry imaging (MSI) directly from growing media is a difficult task if high sensitivity is demanded. We present a quick and robust sample preparation strategy for growing fungi (Trichoderma atroviride, Rhizoctonia solani) on glass slides to establish a miniaturized confrontation assay. By this we were able to visualize metabolite distributions by MALDI MSI after matrix deposition with a home-built sublimation device and thorough recrystallization. We present for the first time MALDI MSI data for secondary metabolite release during active mycoparasitism.

Keywords: Fungal communication; MALDI MSI; Mycoparasitism; Peptaibiotics; Rhizoctonia; Trichoderma.

Figure 1

MALDI MSI of physically non‐interacting T. atroviride and R. solani hyphae. (A) Light microscopic image showing non‐interacting hyphae. (B) Distribution of selected m/z values representing characteristics for T. atroviride (m/z 1949.4 and 2006.3) and R. solani (m/z 525.5) (Supporting Information S1). (C) Mass profile for the selected ROI (outlined rectangle) exhibiting potato dextrose agar derived background signals with Δm/z 162 and signals characteristic for each fungus (green … R. solani, blue … T. atroviride). Blue and green lines in (A) and (B) mark the outer rim of hyphal growth.

Figure 2

MALDI MSI of physically interacting T. atroviride (T) and R. solani (R) hyphae. (A) Light microscopic image showing points of inoculation (green tetragons), the outer rim of hyphal growth for both species (white lines) and borders for features detected by MSI (blue lines). (B) Molecular distributions of selected secondary metabolites localized by MALDI MSI. (C) T. atroviride specific metabolites (Supporting Information S3). (D) R. solani specific metabolites (Supporting Information S4). (E) Profile mass spectrum exhibiting signals assigned to R. solani (marked in green) and T. atroviride (marked in blue).