Homogeneous Matrix Deposition on Dried Agar for MALDI Imaging Mass Spectrometry of Microbial Cultures

Abstract

Abstract. Matrix deposition on agar-based microbial colonies for MALDI imaging mass spectrometry is often complicated by the complex media on which microbes are grown. This Application Note demonstrates how consecutive short spray pulses of a matrix solution can form an evenly closed matrix layer on dried agar. Compared with sieving dry matrix onto wet agar, this method supports analyte cocrystallization, which results in significantly more signals, higher signal-to-noise ratios, and improved ionization efficiency. The even matrix layer improves spot-to-spot precision of measured m/z values when using TOF mass spectrometers. With this technique, we established reproducible imaging mass spectrometry of myxobacterial cultures on nutrient-rich cultivation media, which was not possible with the sieving technique.

Utilizing a Robotic Sprayer for High Lateral and Mass Resolution MALDI FT-ICR MSI of Microbial Cultures

“…Recently, Vergeiner reported an alternative sample preparation route that produced more homogenous matrix coverage on agar samples and expanded the type of matrices that can be utilized in microbial MALDI MSI measurements [9]. Also, Hoffmann and Dorrestein expanded on another group's work [1], detailing the benefits of using an automated nebulizing sprayer for matrix application, which lead to improved S/N and an increase in the number of analytes detected in MALDI analysis of microbial cultures [10].…”

A one‐step matrix application method for MALDI mass spectrometry imaging of bacterial colony biofilms

“…Thus, an automatic matrix deposition system was assessed, based on the aforementioned airbrush method, with the addition of a laboratory‐built robotic motion control. Three major parameters ‐ N 2 gas pressure, solvent flow rate and the distance of spray emitter to the sample stage ‐ were optimized to achieve even matrix coatings on the agar samples in a short period of time . The concentration and composition of the solvent were modified slightly in order to prevent clogging of the sprayer head.…”

“…Imprinting circumvents many of the difficulties associated with analyzing agar cultures with DESI imaging . The agar film can also be desiccated with reduced pressure or heat; a dried sample can then be treated with matrix solution for MALDI imaging . While these approaches allow MS‐based imaging of microbial colonies/biofilms grown on agar media, each has limitations.…”

“…While these approaches allow MS‐based imaging of microbial colonies/biofilms grown on agar media, each has limitations. The sieving method results in an uneven coating and matrix aggregation that may produce artifacts in the ion images obtained . In the imprinting technique, selective analyte transfer may bias the resulting images, and the overall process may lead to chemical redistribution.…”

“…[16,18] The agar film can also be desiccated with reduced pressure or heat; a dried sample can then be treated with matrix solution for MALDI imaging. [19,20] While these approaches allow MS-based imaging of microbial colonies/biofilms grown on agar media, each has limitations. The sieving method results in an uneven coating and matrix aggregation that may produce artifacts in the ion images obtained.…”