Allelochemical defense against epibiosis in the macroalga Caulerpa racemosa var. turbinata

Abstract

The abundance and diversity of microorganisms on the surface of the tropical green macroalga Caulerpa racemosa var. turbinata and the effect of algal surface and waterborne compounds on fouling organisms were investigated both in laboratory and field experiments. As shown via electron microscopic enumeration, the abundance of epibiotic bacteria and diatoms on algal frond surfaces was not significantly different from the reference biofilms harvested from stones in the C. racemosa habitat. The analysis of Terminal Restriction Fragment Length Polymorphism of DNA from algal surface-associated bacterial communities revealed that despite a similar abundance of these bacteria, the community profile on algal frond surfaces differed significantly from that of inanimate, undefended substrates. These results suggest that the alga regulate the occurrence of certain bacterial ribotypes. This result was in accordance with the fact that different bacterial communities formed on the artificial substrata (i.e. Petri dishes) placed in the C. racemosa habitat and alga-free control sites. Neither C. racemosa conditioned seawater (CCW) nor hexane surface extracts affected the growth of bacterial isolates from biofilms. However, only CCW exhibited a toxic effect on the larvae of the fouling polychaete Hydroides elegans, and evoked abnormal larval development in a concentration-dependent fashion. At sublethal concentrations, the <1 kD fraction of CCW inhibited the larval settlement of H. elegans and the bryozoan Bugula neritina. Caulerpenyne, the prominent bioactive metabolite in the genus Caulerpa, was not detected in CCW by chromatographic procedures. Our data suggest that waterborne compounds other than caulerpenyne are involved in the chemical defense of the alga C. racemosa.

Ecology of antifouling resistance in the bladder wrack Fucus vesiculosus: patterns of microfouling and antimicrobial protection

“…The band patterns obtained were analyzed using the GelBuddy software (www.gelbuddy.org) and compared using the Primer software package. To this end, migration distance was assimilated to species and the sum of presences/absences of bands at given distances constituted the community composition, which was compared among samples by a Bray-Curtis similarity analysis (for more details on the RFLP and its analysis, see Dobretsov et al 2006a). In order to identify the bacterial species that were represented by different bands, the pre-cut DNA was cloned using the pCR4-Topo TA cloning kit (Invitrogen) according to the user's manual.…”

Macroalgal Chemical Defenses and Their Roles in Structuring Temperate Marine Communities

“…Therefore, capability to inhibit or modify the very first fouling stages by bacteria may be especially important, as it may prevent or reduce successive epibiotism. Macroalgae commonly contain antimicrobial metabolites (e.g., Hellio et al 2001) and the microbial community on algal frond surfaces has been found to differ from that of inanimate, undefended substrates (Dobretsov et al 2006a), indicating that macroalgae may be able to affect the formation of bacterial biofilm and thereby influencing successive fouling by macroorganisms. Oxidative bursts, i.e., rapid production of active oxygen species such as hydrogen peroxide and hydroxyl radicals from cells when they come into contact with pathogens, may be involved in encounters with epiphytic bacteria, fungi, or other organisms (reviewed in Steinberg and de Nys 2002;Potin et al 2002; see also Chap.…”

Chemical Defenses: From Compounds to Communities

“…Allelopathic activities have also been reported for extracts of Caulerpa spp. and caulerpenyne toward microalgae (Lemee et al, 1997;Smyrniotopoulos et al, 2003) and the fouling polychaete worm Hydroides elegans (Dobretsov et al, 2006).…”