Preliminary Isolation and Phenotypic Characterization of Bacillus-Like Bacteria from Marine Coastal Soil

Abstract

Marine environments constitute an underexplored source of microorganisms with potential applications in food, aquaculture, and biotechnology. This study aimed to isolate cultivable bacteria from coastal soil collected at Kanyakumari Beach, Tamil Nadu, India, and to perform preliminary phenotypic characterization. Three sample types—dry surface soil, wet soil, and soil collected between rocks—were serially diluted and cultured on solid bacterial medium. Representative colonies from each sample were purified and evaluated for colony morphology, Gram reaction, cellular morphology, arrangement, and motility. More than 80 colonies were observed from each sample type. Three representative isolates, designated D, W, and R, formed medium-sized whitish colonies with predominantly circular morphology. All isolates were Gram-positive, rod-shaped, and motile; cells occurred singly or in short chains. These characteristics support their provisional classification as Bacillus-like bacteria. However, phenotypic observations alone are insufficient for species-level identification or for establishing probiotic functionality. Molecular identification, safety testing, and functional assays—including acid and bile tolerance, antimicrobial activity, adhesion-related properties, antibiotic susceptibility, and haemolysis—are required before any probiotic claim can be made. The present work therefore provides a preliminary culture collection and a foundation for subsequent strain-level evaluation.