Abstract

ANALYSIS OF BACTERIAL DIVERSITY IN SPONGES COLLECTED FROM HA TIEN SEA, KIEN GIANG, VIETNAM AND THE ANTIMICROBIAL ACTIVITIES OF THEIR SECONDARY METABOLITES

Prof. Dr. Cao Ngoc Diep*, Dr. Ngo Thanh Phong, MSc. Tran Vu Phuong,
MSc. Dao Thi Minh Chau

ABSTRACT

The cultivable bacterial diversity associated with sponges collected from Ha Tien Sea, Kien Giang province, Vietnam was investigated by 16S rDNA gene sequence analysis and antimicrobial potential of the bacteria was also assessed. One-hundred and one bacterial isolates were isolated on two media (51 isolates on MMA medium and 50 on SYP-SW medium), 19/101 isolates had antimicrobial activities against Edwardsiella ictaluri (fish pathogenic bacteria) and Bacillus cereus (human pathogenic bacteria). Eighteen isolates were chosen to identify with PCR-16S rDNA method, the DNA sequences were compared with GenBank database of NCBI by BLAST N software. The sequences from 17 selected bacterial isolates showed high degrees of similarity to those of the Gen Bank reference strains (between 99% and 100%). From 17 isolates, 16 belonged to Bacilli, and only one isolate was Beta-Proteobacteria, respectively. Based on Pi value (nucleotide diversity), Bacili group had the highest Theta value as Theta values (per sequence) from S of SNP for DNA polymorphism were calculated for each group and Bacili group had the highest values. These results have showed that two strains as Bacillus subtilis MD4B and Bacillus thuringiensis SL1B may be considered as promising candidates for serving potential bioactivities, either against fish bacterial pathogen as Edwardsiella ictaluri or fish and human pathogens as E. ictaluri and Bacillus cereus. As a result, the bacteria will be suggested to evaluate in full-scale studies in the future.

Keywords: Bacilli, antimicrobial activity, marine sponge, sponge-associated bacteria, Ha Tien Sea.