Diversity of epiphytic bacteria of three species of Gracilaria and their bacteriostatic activities

ObjectiveThe present study was conducted to explore the diversity of culturable epiphytic bacteria of three species of Gracilaria and bacteriostatic activities of their metabolits in sea area around Weizhoudao Island, Beibu Gulf, Guangxi, in order to provide reference for development of these epiphytic bacteria in the sea area and new biological fungicides. MethodDilution coating method was applied to observe colonial morphology and distribution of epiphytic bac-teria of three species of Gracilaria. Diversity of the epiphytic bacteria of Gracilaria was analyzed based on 16S rRNA se-quence and their bacteriostatic activities were screened by disc diffusion method. ResultTwenty-eight strains were ex-tracted from Gracilaria verrucosa, Gracilaria textorii and Gracilaria glomerata in Beibu Gulf, Guangxi belonged to four subclasses, thirteen families and fifteen genuses(Bacillus sp.; Staphylococcus sp.; Vibrio sp.; Psychrobacter sp.; Al-teromonas sp.;Pseudoalteromonas sp.; Erythrobacter sp.; Paracoccus sp.; Kocuria sp.; Micrococcus sp.; Rhodopirellula sp.; Kytococcus sp.; Dermacoccus sp.; Maribacter sp.; Cobetia sp.). The metabolites of five strains showed obvious an-tagonistic effects against Colletrichum gloeosporiode M2 or C. gloeosporiodes Lz2. Metabolites of strains GXS0044, GXS0017 and GXS0035 showed sound inhibition effects towards C. gloeosporiodes Lz2(antibacterial circle diameters were 15.0, 14.5 and 15.5 mm, respectively). Metabolites of strains GXS0023 and GXS0031 showed obvious inhibition effects towards C. gloeosporiode M2(antibacterial circle diameters were 15.0 and 17.0 mm, respectively). ConclusionThere are resource-ful epiphytic bacteria of Gracilaria and their metabolites activities are different. Therefore, searching for pathogens that are resistant to agricultural diseases from seaweeds will become a new direction in development of new pathogen fungicides that against agricultural diseases.