Unveiling Bacterial Diversity in the Holdfast and Rhizoidal Regions of Sargassum wightii and Halimeda macroloba

Bacteria associated with marine macroalgae like Sargassum wightii and Halimeda macroloba 
play key roles in promoting host growth, producing bioactive compounds, and enhancing stress 
tolerance, making them promising candidates for use as microbial biofertilizers. The study 
focuses on the isolation and characterization of bacterial strains from the holdfast region of 
Sargassum wightii and rhizoidal region of Halimeda macroloba, collected from the coastal area 
of Thonithurai in the Mandapam region of Rameswaram, Tamil Nadu. The isolates were 
initially characterized using morphological traits, Gram staining, and biochemical assays. Two 
strains from Sargassum wightii showing notable biochemical characteristics were selected for 
species level identification through 16S rRNA gene sequencing and BLAST analysis. Bacillus 
 subtilis (isolate IB.6a.1) exhibited 95% sequence similarity with reference strains. Halobacillus 
dabanensis showed 97.8-99.4% similarity with other Halobacillus species, and phylogenetic 
analysis further confirmed the classification of both isolates within their respective genera.