Identification of epiphytic bacterial communities associated with the brown alga Splachnidium rugosum

Marine macroalgae host diverse bacterial communities with which they share a complex array of chemical interactions based on the exchange of nutrients, minerals and secondary metabolites. The brown alga Splachnidium rugosum is a rich source of a valuable fucose-containing sulphated polysaccharide (fucoidan). It grows exclusively in the Southern Hemisphere along temperate shores. While growth and development are dependent on specific microbial interactions, the microbiome of S. rugosum has not been characterized. This study reports on the composition and uniqueness of epiphytic bacterial communities associated with S. rugosum. Sporophytes were collected during winter (July 2012) from the Western Cape (-34A degrees 18' 5.0004aEuro(3), +18A degrees 48' 59.0004aEuro(3)), South Africa. Culture-based methods relied on a range of selective marine media including marine agar, nutrient sea water agar, nutrient agar and thiosulfate-citrate-bile-salts-sucrose agar. Epiphytic isolates were identified to species level by 16S rRNA gene sequence analysis and encompassed 39 Gram-negative and 2 Gram-positive bacteria. Isolates were classified as Gamma-Proteobacteria, Alpha-Proteobacteria, Firmicutes or Bacteriodetes. Gamma-Proteobacteria were the most abundant, dominated by Vibrio and Pseudoalteromonas species. Three isolates displayed low sequence identity (E,97 %) with their closest relatives and were grouped into the genera Shewanella, Sphingomonas and Sulfitobacter. All bacterial isolates (41) were screened for anti-microbial activity against indicator strains of Bacillus cereus, Staphylococcus epidermidis, Mycobacterium smegmatis, Micrococcus luteus and Pseudomonas putida. Fifteen isolates (36 %) displayed antimicrobial activity against one or more of the indicator strains. One isolate (Pseudomonas sp.) was active against all strains tested. Splachnidium rugosum is a valuable source for the discovery of bioactive compounds of bacterial origin active against human pathogens.