Bacteria in the surface sediments of a subtropical mangrove habitat were investigated using a cultivation-independent molecular approach. Phylogenetic analysis of nearly full-length 16S rRNA genes revealed a diversity of sequences that were mostly novel. Members from the five subdivisions of the Proteobacteria were detected, and they collectively represented the majority (67%) of the clone library. Sequence types affiliated with the Gammaproteobacteria constituted the largest portion (29%) of the library, and many of them were related to free-living and symbiotic sulfur-oxidizing bacteria. The Epsilonproteobacteria were the second most abundant group (16%), including only one sequence type clustering with PCR-generated bacterial clones previously recovered from deep-sea sediments. A substantial portion (8%) of the clones grouped within the Deltaproteobacteria, a subdivision with anaerobic sulfate or metal reduction as the predominant metabolic trait of its members. In addition, minor portions were affiliated with the Cytophaga-Flexibacter-Bacteroides group (9%), Actinobacteria (6%), Chloroflexi (5%), Firmicutes (4%), Fusobacteria (1%), and the Chlamydiae/Verrucomicrobia group, Fibrobacteres/Acidobacteria group and Planctomycetes (each < 1%). These results significantly expand our knowledge of the bacterial diversity of the unique mangrove environment.