Characterization of New Bioactive Enzyme Inhibitors from Endophytic Bacillus amyloliquefaciens RWL-1

Abstract

Endophytic bacteria are known to produce a wide array of bioactive secondary metabolites with beneficial effects on human health. In the current study, a novel endophytic bacterial strain, Bacillus amyloliquefaciens RWL-1, was isolated from the seeds of Oryza sativa. Initially, the crude extract of RWL-1 was assessed for potential biological effects of enzyme inhibition and cytotoxicity and was found to exhibit a broad spectrum inhibition for α-glucosidase (37 ± 0.09%) and urease (49.4 ± 0.53%). The screening results were followed by bioassay-guided isolation of secondary metabolite(s) from RWL-1. Extensive chromatographic and spectrophotometry analyses revealed the presence of compound 1 (S)-2-hydroxy-N-((S)-1-((S)-8-hydroxy-1-oxoisochroman-3-yl)-3-methylbutyl)-2-((S)-5-oxo-2,5-dihydrofuran-2-yl)acetamide. Further bioassays of compound 1 showed significant inhibition of α-glucosidase (52.98 ± 0.8%) and urease (51.27 ± 1.0%), compared with positive control values of 79.14 ± 1.9% and 88.24 ± 2.2%, and negative controls (0.08 ± 0.1% and 0.05 ± 0.01%), respectively. The current study suggests that bacterial endophytes are a rich source of novel bioactive compounds with high therapeutic value.

Keywords: biological potential; endophytes; secondary metabolites; urease; α-glucosidase.

Figure 1

Biological potential of endophytic RWL-1 crude extract. The graph values are presented as the mean of three replicates with standard error. The acarbose, thiourea, DMSO and galantamine was used as reference standard for α-Glucosidase, Urease, MTT (HCT-15 cells) and AChE inhibition respectively. Bars with different letters are significantly different at p ≤ 0.05 based on Duncan multiple range test.

Figure 2

Nuclear magnetic resonance spectroscopic analysis of compound 1 ((S)-2-hydroxy-N-((S)-1-((S)-8-hydroxy-1-oxoisochroman-3-yl)-3-methylbutyl)-2-((S)-5-oxo-2,5-dihydrofuran-2-yl)acetamide).

Figure 3

Inhibitory effects of compound 1 (100 µg mL⁻¹) and reference inhibitors (80 µg mL⁻¹) on α-glucosidase and urease. The graph values are standard error of means of three replications. The acarbose and thiourea was used as reference inhibitor for α-glucosidase and urease. Bars with different letters are significantly different at p ≤ 0.05 based on Duncan multiple range test.

Figure 4

Schematic representation of biological potential of endophytic B. amyloliquefaciens RWL-1 and bioassay guided isolation of bioactive metabolite (Compound 1) for α-glucosidase and urease inhibition.