Antimycobacterial activity of the secondary metabolite fraction derived from endophytic bacterium Bacillus velezensis strain DJ4 isolated from Archidendron pauciflorum

The discovery and development of new antituberculosis medications effective against multidrug-resistant Mycobacterium strains are necessary to reduce the mortality in tuberculosis (TB) cases. To accelerate the discovery of anti- TB drugs, Mycobacterium smegmatis was commonly used as a surrogate bacterium in the preliminary screening of antituberculosis compounds. This study aimed to fractionate the secondary metabolites of the endophytic bacterium Bacillus velezensis strain DJ4 isolated from Archidendron pauciflorum, to evaluate its antimycobacterial activity against M. smegmatis, and to identify the secondary metabolite profile of its active fraction. Fifty-six fractions were successfully obtained through thin-layer chromatography (TLC) and column chromatography techniques. Among all fractions, ten fractions showed remarkable antimycobacterial activity against M. smegmatis with minimum inhibitory concentration (MIC) values ranging from 85–1,325 μg/ml. Fraction F53 exhibited the strongest antimycobacterial activity with the lowest MIC of 85 μg/ml. This fraction also inhibited the biofilm formation of M. smegmatis at 1× MIC and ½× MIC by 62,3%, and 52,1%, respectively. Observation using a scanning electron microscope (SEM) showed that the biofilm matrix of M. smegmatis treated with fraction F53 was thinner, less compact, and separated into small pieces compared to the negative control. Furthermore, liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that this corresponding fraction contained five proposed compounds, including 2-(p-anisyl)-5-methyl-1-hexene, nigakilactone H, tetratriacontanamine, and two other unidentified compounds.