Beneficial effects of 2,4-diacetylphloroglucinol- producing pseudomonads on the marine alga Saccharina latissima

Pseudomonas strains were shown to be regularly associated with the brown macroalga Saccharina latissima from the Baltic Sea, studied over several years, and were identified as producers of the antimicrobially active compound 2,4-diacetylphloroglucinol. These findings support the assumption of a stable association between the Pseudomonas spp. strains and S. latissima in the Baltic Sea. The metabolite profile of the Pseudomonas spp. comprised monoacetylphloroglucinol, 2,4-diacetylphloroglucinol, pyoluteorin and several rhizoxins, which exhibited broad-spectrum antibiotic activities against Gram-positive and Gram-negative bacteria as well as against fungi. Because the antibiotic activities included the inhibition of the 2 algal pathogens Pseudoalteromonas elyakovii and Algicola bacteriolytica, we propose a beneficial effect of these marine pseudomonads on their host S. latissima.