SPORE RELEASE IN ACROCHAETIUM SP. (RHODOPHYTA) IS BACTERIALLY CONTROLLED¹

Abstract

The facultative red algal epiphyte Acrochaetium sp. liberated spores preferentially and recruited more successfully in laboratory cultures when its host Gracilaria chilensis C. J. Bird, McLachlan et E. C. Oliveira was present. The same effect was also induced by cell-free medium from G. chilensis, suggesting it contained a molecular signal. Antibiotics prevented spore release in Acrochaetium sp., even when G. chilensis was present, suggesting a prokaryotic origin of the signal. Simultaneous application of N-butyl-homoserine-lactone (BHL) restored the spore-release capacity, which demonstrated that spore release was not directly inhibited by the antibiotics and indicated that bacterially generated Nacyl-homoserine-lactones (AHLs) regulate spore release. An involvement of AHL was further indicated by the fact that two different halofuranone inhibitors of AHL receptors also inhibited spore release when they were applied at relatively low concentrations. Of seven different AHLs tested, only BHL induced the effect. However, BHL was only active at relatively high concentrations (100 lM), and it was not detected in spore-release-inducing medium of G. chilensis. Another water-soluble AHL or an AHL structure analog is therefore probably the active compound in G. chilensis cultures. The data presented demonstrate that life cycle completion in Acrochaetium sp. strongly depends on bacteria, which are not always present in sufficient numbers on the alga itself. Exogenous bacteria that are associated with G. chilensis or with other potential substrates may therefore trigger timely spore liberation in Acrochaetium sp., provided that the necessary concentration of AHL is reached. This first finding of AHL perception in a red alga confirms that AHL signalling is more widespread among eukaryotes than was thought until recently. However, spore release of a second red alga, Sahlingia subintegra (Rosenv.) Kornmann, was unaffected by AHL, and the reaction observed is therefore not universal.Algal spore release is known to be controlled by numerous factors, including light and temperature

Effect of quorum sensing signals produced by seaweed-associated bacteria on carpospore liberation from Gracilaria dura

“…Weinberger et al (2007) reported that C 4 -HSL potentially influenced the carpospore liberation capacity in Acrochaetium sp. While, the present study found that both C 4 - and C 6 -HSL equally contributed to carpospore liberation from G. dura .…”

Composition, uniqueness and variability of the epiphytic bacterial community of the green alga Ulva australis

“…A notable example of such an interaction is the dependence of several green algae on the presence of particular bacteria to develop a normal morphology (Provasoli and Pintner, 1980;Nakanishi et al, 1996;Matsuo et al, 2003;Marshall et al, 2006). Algal-associated bacteria have also been shown to induce the release and settlement of algal spores (Joint et al, 2007;Weinberger et al, 2007), to positively influence algal growth and provide essential nutrients (KeshtacherLiebson et al, 1995;Croft et al, 2006), and to induce settlement of sea urchin and other larvae (Johnson and Sutton, 1994;Huggett et al, 2006Huggett et al, , 2008. Examples such as these indicate that an epiphytic bacterial community is important to the algal host's normal function and, by extension, the ecology of the habitats in which they exist.…”

How endo- is endo-? Surface sterilization of delicate samples: a Bryopsis (Bryopsidales, Chlorophyta) case study

“…After all, many seaweeds live in close association with numerous epiphytic bacteria, which control morphological development (Fries and Iwasaki 1976;Marshall et. al 2006;Provasoli and Pintner 1980;Tatewaki et al 1983) or are linked with various metabolic functions (Chisholm et al 1996;Croft et al 2005;Head and Carpenter 1975;Staufenberger et al 2008;Weinberger 2007), and Bryopsis seems no exception (Kan et al 1999). Whereas the usage of axenic cultures is quite common for micro-algae, for the study of marine macro-algae this is limited.…”