Mapping secondary metabolites of Streptomyces sp. from Caatinga rhizosphere with Desorption Electrospray Ionization Mass Spectrometry (DESI-MS)

Actinobacteria Streptomyces sp strain CAAT 1-54 isolated from Caatinga biome was studied to detect and map the secondary metabolites by ambient ionization mass spectrometry technique, by DESI-MS and DESI-MSI. The secondary metabolites, Lysolipin[1] (m/z 598) and an analogue of Lienomycin[2] (m/z 1229), released by actinobacteria CAAT 1-54 was previously isolated and characterized using conventional analytical techniques. Production of these metabolites was monitored by performing analysis with different culture period (4 and 14 days) to better understand the environmental impact on their release.It was observed an analogue of Lienomycin was only apparent at the edges for both 4 and 14 days incubation and with 4 days of incubation it was also noticed at the center (Figure 1). In contrast, Lysolipin appears at the top surface of the dried bacterial residue and is evident that it was produced after 14 days of incubation while with after 4 days of incubation the compound is relatively less produced(Figure 2). In disc-diffusion studies with DESI-IMS, reinforces that the compounds are actually responsibility for inhibition of growth of the bacteria and fungus at the zone of inhibition. The temporal and spatial study with DESI-MS and DESI-IMS presented significant and promising results, it was possible to identify the relationship of each secondary metabolite under study with the actinobacteria life cycle. The analogue of Lienomycin is a compound associated with young cells, that is, the development of actinobacteria, while the Lysolipin to older cells, that is, the process of sporulation of de microorganism. Through this knowledge it was possible to better understand the secondary metabolism of actinobacteria, as well as to observe the compounds involved in inhibition of fungi and bacteria. The benefit of using different techniques in mass spectrometry in this kind of study not is only the ability to provide the visualization of compounds but also to understand the role of each metabolite when interacting with the environment. It is a rapid technique for the complete analysis of secondary metabolites, where questions of “where” (spatial distribution), “when” (temporal distribution), “what” (identification), “why” (function of each metabolite) and “which” (compounds involved in inhibition processes) are answered and proved in details.

Figure 1. DESI-MS imaging imprint.
Figure 2. DESI-MS imaging directly.

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[2]PAWLAK, J. et al. The Structure of Lienomycin, a Pentaene Macrolide Antitumor Antibiotic. The Journal of antibiotics, v. 33, n. 9, p. 989-997, 1980. ISSN 0021-8820.