Antimicrobial potentialities of Ulva rigida epiphytic bacteria

Marine epiphytic bacteria (72 strains) were isolated from green alga Ulva rigida collected in two different biotopes (Cap Zebib, rocky shore: 30 strains and Ghar El Melh lagoon: 34 strains) and alga surrounding water (eight strains). All isolates were identified based on their 16S rDNA sequences and tested for antimicrobial effect against several human and fish pathogens (18 Gram+ and Gram- bacteria and the fungus Candida albicans) using in vitro drop method.

Results obtained revealed high activities of Ulva rigida epiphytic bacteria; amongst alga isolates 36% were active with variable antimicrobial spectrum. Within active isolates, 69.5% were from the alga collected in the lagoon. High level activities were observed for six isolates identified as, Bacteroidetes bacterium, Pseudoalteromonas sp., Octadecabacter sp., Stappia marina, Stappia sp. and Ruegeria sp.. Nevertheless, all free living bacteria from surrounding water were inactive. Else, we noted variable sensitivity spectrum of indicators used, Staphylococcus aureus, Micrococcus sp., Streptococcus sp and Salmonella typhimurium were mostly inhibited by the isolates tested, while, Vibrio species (V. anguillarum, V. tapetis and V. alginolyticus) were resistant. Candida albicans was inhibited only by the two Stappia species isolated from Ulva rigida of Cap Zebib locality. Further investigations continue on the inhibition effect of Ulva rigida organic crude extracts against epiphytic bacteria isolated, in order to assess degree of affinity of epibionts to their proper host.

Keywords: Ulva rigida, Epiphytic bacteria, Antimicrobial activities

Acknowledgement: The authors thank Ms. Veronique Confurius-Guns, Department of Marine Microbiology, Netherlands Institute of Ecology, NIOO-KNAW, Yerseke, The Netherlands, for her assistance and help with PCR and DNA sequencing.