Objective To characterize the cultivable bacterial diversity patterns and extracellular enzyme-producing capacity in mangrove sediments from the Zhangjiang Estuary, with a particular focus on the distribution of dominant Bacillus sensu lato and the environmental factors shaping their assemblages. Methods Bacterial isolates were obtained by dilution plating. Taxonomic identification was performed by 16S rRNA gene sequencing. Plate-based assays were used to evaluate the activities of eight extracellular enzymes. Results In total, 1 392 isolates were obtained, representing 97 genera of 4 phyla. Bacillus sensu lato constituted the dominant assemblage (57.8%). Preliminary screening suggested 263 isolates (18.9%) as putative novel taxa, largely concentrated in Bacillus and allied genera such as Halobacillus. The Shannon diversity of cultivable bacteria was higher in the core mangrove zone and at the estuarine outlet than at the inlet (P<0.05), and the community composition differed among sites (P<0.05), being mainly associated with salinity and metal ions. By contrast, the community structure of Bacillus sensu lato was comparatively stable across space and was primarily associated with pH and carbon-nitrogen nutrient variables. Enzyme screening showed the highest positive rates for proteases (64.2%) and lipases (52.6%). Isolates affiliated with Bacillus sensu lato displayed higher positive rates than the overall community across multiple enzymes, indicating broad metabolic potential. Conclusion Mangrove sediments from the Zhangjiang Estuary harbor abundant cultivable bacterial resources. In addition to the dominant Bacillus-related taxa, Pseudomonadota and Bacteroidota appear to be key components underpinning overall community diversity. The high ecological stability and multi-substrate degradation capacity of Bacillus sensu lato, together with other bacterial groups, contribute to element cycling in mangrove sediments.