Isolation, identification and bioprospecting potential of Bacillus subtilis, endophytic bacterium from Bruguiera gymnorrhiza (L.) Lam. ex Savigny

Mangroves are crucial for supporting coastal communities, benefiting both humans and animals. Their intricate root systems grasp the soil, mitigating erosion and dampening wave impact. As a result, they shield and fortify shorelines that would otherwise erode. This study focuses on the isolation of endophytic bacteria from the stem of Bruguiera gymnorrhiza. Molecular analysis using 16S rDNA gene sequencing identified the isolate as Bacillus subtilis (BG1). Its hydrolytic enzyme production capabilities were assessed, revealing its ability to produce cellulase, amylase, protease and L-asparaginase. The isolate also demonstrated various plant growth promoting traits including ammonia production, indole 3- acetic acid (IAA) production, hydrogen cyanide (HCN) production, phosphate solubilization, and ACC deaminase activity. IAA and organic acid production were quantified using Liquid Chromatography – Mass Spectrometry (LC-MS/MS), with B. subtilis producing 86.32 ± 0.64 μg mL⁻¹ of IAA, peaking at a retention time of 6.8 min. The endophyte also produced two different organic acids during phosphate solubilization with malic acid been the most abundant (398.79 ± 2.58 μg mL⁻¹). Additionally, B. subtilis was able to form biofilm and exhibited drug resistance towards Cefixime (5 μg). Biofilm was characterized using Fourier transform infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). In vitro antagonist studies demonstrated the significant effectiveness of B. subtilis against two pathogens, Staphylococcus aureus and Streptococcus mutans. This is the first study to successfully isolate and identify endophytic bacteria from B. gymnorrhiza, highlighting its plant growth promoting traits, biofilm forming potential, and antibacterial capabilities.