Chemical inhibition of bacterial colonization by the red alga Bonnemaisonia hamifera

Abstract

Attachment and growth are 2 major processes in bacterial colonization of surfaces in the sea. By inhibiting either or both of these processes, marine macroorganisms may defend themselves against bacterial infection and fouling. We tested crude extracts from 5 red seaweed species for their ability to inhibit bacterial growth and attachment. For this we used 11 strains of bacteria, representing 5 different taxonomic groups. The effects on growth and attachment were tested by a standard disc-diffusion assay and by incorporating crude extracts into phytagel blocks that served as a surface for bacterial attachment. Extracts from one of the tested algae, Bonnemaisonia hamifera, were particularly active and inhibited growth of 9 bacteria at concentrations volumetrically equivalent to whole algal tissue, or lower. The other 4 algal extracts had weak growth-inhibiting effects on only a few bacterial strains. None of the algal extracts exhibited broad-spectrum effects against bacterial attachment, but 4 of 5 algal extracts had some strain-specific effects. Surface extracts of B. hamifera tested on bacteria showed that metabolites are naturally present at sufficiently high concentrations in order to inhibit bacterial growth on the surface of the seaweed. In situ quantification of bacteria on B. hamifera also showed that this alga had significantly fewer bacteria on its surface compared to a coexisting alga. These findings suggest that B. hamifera naturally reduces its epibacterial abundance by production of broad-spectrum growth-inhibiting secondary metabolites. This is one of a few examples where ecologically relevant effects of algal metabolites on bacterial colonization have been shown.

Allelochemicals produced by Caribbean macroalgae and cyanobacteria have species-specific effects on reef coral microorganisms

“…Seaweeds further utilize physical and chemical regulatory strategies to prevent bacterial and fungal colonization (Mann 1973;Nylund et al 2005;Engel et al 2006;Lane et al 2009). The microbial diversity and abundance within the marine environment varies in response to changing environmental conditions (e.g., temperature, pH, nutrients, pollutants) (Wommack et al 1999), and bacterial symbionts may allow host organisms to respond more efficiently to these changes (Reshef et al 2006;Rosenberg et al 2007).…”

Desorption electrospray ionization mass spectrometry reveals surface-mediated antifungal chemical defense of a tropical seaweed

“…In the marine realm, numerous taxa have been suggested to use surface-associated defenses against competitors, foulers, and pathogens (5)(6)(7)(8)(9)(10). However, such defenses were often proposed based on inhibitory effects detected in experiments, using whole organism extracts (5,7), and it is unclear whether target species actually encountered these chemicals in nature.…”

Seaweed–herbivore interactions at a small scale: direct tests of feeding deterrence by filamentous algae

“…Even some species of unicellular algae have demonstrated chemical defences (Wichard et al 2005). However, there is recent evidence that filamentous eukaryote algae can produce secondary metabolites that inhibit bacterial fouling (Nylund et al 2005, Paul et al 2006. Further evidence that chemical defence in filamentous algae, including herbivore deterrence, is more widespread than previously believed is that many species have specialised cellular inclusions (Young & West 1979, Paul et al 2006.…”