Screening And Phylogenetic Analysis Of Marine Bacteria With Antimicrobial Activity

As broad application of antibiotics, the resistance of microorganism gets stronger and stronger. And also, with the increased environmental pollution, as well as the variation of society and civil activities, the immunity of human is declining. The new pathogen and the increasing resistance of antibiotics has become a serious social problem. The effective way to solve this problem is to search for newer antibiotics. Marine, for its unique territory condition, has become one of the most important origins to screen the antibiotics.Seawater, marine sediment and the gill, stomach or intestine of eleven kinds of marine fish, including Priacanthus macracanthus, Anguilla eel, Psenopsis anomala and Scomberomorus niphonius etc., were collected as samples from 3 locations in East China Sea, and the antibiotics producing bacteria were screened. Based on the results of disc diffusion assay test, 34 bacteria with antimicrobial activity were separated from 366 isolates using Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Aspergillus niger and Saccharomyces cerevisiae as the indicators, and their minimal inhibitory concentration (MIC) and antimicrobial titers were detected. According to the results, 14 representative strains were selected, and their morphology and biochemical properties, as well as partial 16S rDNA sequences, were determined. The results showed, 2 strains (Brevibacterium halotolerans, Kocuria rhizophila) belong to high (G+C)% Gram positive bacteria;7 strains {Bacillus marinus, Bacillus cereus, Bacillus vietnamensis, Bacillus sphaericus, Bacillus thuringiensis, Staphylococcus kloosii, Staphylococcus saprophyticus) belong to low (G+C)% Gram positive bacteria and the other 5 (Proteus penneri, Proteus mirabilis, Citrobacter freundii, Shigella boydii, Psychrobacter faecalis) are y-proteobacteria. 13 strains had high similarities with their closest matches (>97%), while the similarity of L20 with its closest match was 96.3%, therefore the whole 16S rDNA sequence should be analyzed further. The results also showed that L20 had strong antimicrobial activity;it is therefore worthy to be studied for antibioticsscreening. Besides, it was found in this study that the Kocuria rhizophila and the 5 y-proteobacteria have antimicrobial activity, which is rarely reported in other related studies. Therefore, the strain HI {Kocuria rhizophila), the 4 Enterobacteriaceae strains and 1 Psychrobacter strain are also worth studying in the future.