1H NMR-Based Metabolomics Profiling of Syzygium grande and Oenanthe javanica and Relationship Between Their Metabolite Compositions and Antimicrobial Activity Against Bacillus species

The aim of the present study was to evaluate the variations in the phytochemical compositions and the antimicrobial activities of Syzygium grande and Oenanthe javanica leaf extracts against Bacillus sp. The antibacterial activity of the methanol, 70% methanol, ethyl acetate, and hexane extracts of both plant species were examined in vitro, against various Bacillus species. In addition, the 1H Nuclear Magnetic Resonance (1H NMR) spectroscopy-based metabolomics was employed to gain insights into the correlations between the chemical constituents of the bioactive extract to the biological activity. The hexane extract of S. grande leaves and methanolic extract of O. javanica leaves showed more potent anti-Bacillus activity, among the test extracts. Principal component analysis (PCA) successfully differentiated the extracts on the basis of their metabolite profiles.  The results of the Partial Least Square (PLS) analysis showed that the non-polar compounds of the hexane extract of S. grande (alanine, betulin, β-sitosterol, β-caryophyllene, acetic acid and 3-hydroxybutyric acid) were strongly correlated to its anti-Bacillus activity. On the other hand, choline, ellagic acid, and gallic acid, the metabolites present in the methanolic extract of O. javanica, were strongly correlated to its anti-Bacillus activity.  On this basis, it was therefore concluded that these conmpounds could be the potential bioactive constituents, contributing to the anti-Bacillus activity of the individual plant species.  Further in-depth investigations into the potential utilization of the two plants for useful applications in managing and control of Bacillus sp., will help pave the way towards their valorization.