Evaluating the changes in metabolomic profiles of Streptomyces sp. in response to signaling molecules from another bacterium Michelle Marie T. Ochoa (a*,b), Hiyas A. Junio, Ph.D. (a), and Lilibeth A. Salvador, Ph.D. (b)
a) Institute of Chemistry, College of Science, University of the Philippines, Diliman, Quezon City, 1101, Philippines.
*mtochoa[at]up.edu.ph
b) Marine Science Institute, College of Science, College of Science, University of the Philippines, Diliman, Quezon City, 1101, Philippines.
Abstract
The genus Streptomyces is a source of diverse small molecules due to a high number of biosynthetic gene clusters (BGCs) in its genome. However, under normal laboratory culture conditions, these BGCs may be silenced, becoming cryptic. An untargeted coculture elicitation approach was used to evaluate changes in the secondary metabolites of Streptomyces in response to foreign signaling molecules. Streptomyces was cultured in the presence of small molecules from another bacterium to mimic potential environmental interactions between microorganisms. Streptomyces sp. was incubated at normal conditions (R2A medium), low (9:1 R2A medium: cell-free extract), and high (1:1 R2A medium:cell-free extract) ratios. Crude extracts from the three Streptomyces fermentation conditions were obtained by solvent partitioning with ethyl acetate and were profiled using ultrahigh performance liquid chromatography tandem mass spectrometry with a quadrupole time-of-flight mass analyzer (UHPLC-qTOF). MS data were analyzed using online platforms such as Global Natural Products Social Molecular Networking (GNPS) for compound identification and molecular networking, and MetaboAnalyst 6.0 for statistical evaluation between culture conditions. Relative quantitation of selected compounds was also performed using multiple reaction monitoring (MRM). Molecular networking revealed that this Streptomyces sp. strain produced three major classes of compounds: polycyclic tetramate macrolactams (PTM), cyclodepsipeptides, and macrotetrolides. Statistical analysis showed that the relative concentrations of the identified compounds in Streptomyces sp. coculture differ significantly from those in normal culture conditions. As such, varying the composition of the culture medium to incorporate signaling molecules from other bacteria may be a possible means of altering the biosynthetic ability of Streptomyces.
Keywords: Natural products, secondary metabolites, metabolomics, mass spectrometry, symbionts, bacteria
