Algae Microbe Interactions
Marine microorganisms are regularly, and as it turned out over the past years, quite specifically associated with marine algae and animals. They are associated with outer and inner surfaces and in many cases involved in true symbiotic interrelationships. We have studied bacteria associated with marine sponges and macroalgae and analysed the biodiversity of the associated microbes and to the specificity of the association by metagenomic approaches using 16S rRNA genes as well as functional genes. We have realised that associations of bacteria are specific for algal and sponge species but also with different types of cells of sponges and different parts of the agal thallus. Since molecular studies show only parts of the total diversity, we combine molecular studies and culture-based diversity analyses, which enables studies on the organismic level (such as physiological, proteomic, metabolomic and regulation studies). Moreover, isolation of strains from marine habitats enables the description of new species, genera or ever higher taxa and allows in depth comparison at a systematic level. A comprehensive study of new species isolated form marine algae demonstrated that worldwide a large number of new bacterial species and genera have been isolated from algae, suggesting that algae are a distinct source for new bacterial taxa and quite a number of bacterial species are specifically associated with algae. A phylogenetic study was performed based on 16S rRNA gene sequences available in GenBank of 101 bacterial species which have been previously described as valid new species (with deposited type strains) and were isolated from eukaryotic macro- and micro-algal sources (Goecke et al., 2013). Although such associations can be random or specific, they could be explained by evolutionary adaptations through metabolic pathways, niche specificity or mutualistic relationships. This assumption was supported by information provided with the descriptions of these species. On one hand, 32% of all new bacterial species isolated from macroalgae, were able to decompose macroalgal polysaccharides. On the other hand, most of the bacteria described from microalgae grouped into the Roseobacter clade (Alphaproteobacteria), indicating that some members of this group are well adapted to living in close association with phytoplancton
New bacterial species associated with macroalgae. Bacteroidetes corresponded with 42 newly described bacterial species to the major lineage, followed by Proteobacteria with 36 species. Firmicutes, Actinobacteria, Verrucomicrobia and Planctomycetes contributed to a lesser extent.
Marine microbes associated with macroorganisms are an excellent source for secondary metabolites. These metabolites are thought to have specific functions in the interspecies communication between microbes and host and are evolved for specific interactions to protect the host and/or the producer against competitors and/or diseases. We are studying the chemical basis of microbial interactions with pure culture isolates and characterize the substances produced by these microorganisms. From a biotechnological point of view, many compounds have pharmaceutical properties, often antibiotic or cytotoxic, creating opportunities to use these compounds as anti-cancer agents (see under Marine microbial resources below). In addition, bioactive compounds may be important for the health of marine macrobiota and can be used for the prevention of marine diseases and as mediators in aquacultures.
As an example, we studied the bacterial communities associated with the brown macroalga Saccharina latissima (synonym Laminaria saccharina), which comprised a large number of antimicrobial active bacteria, including several Pseudomonas species (Wiese et al., 2009). These were regularly associated with Saccharina latissima over the years and were identified as producers of several antimicrobial active compounds. Their metabolite profile comprised monoacetylphloroglucinol (MAPG), 2,4-diacetyl-phloroglucinol (DAPG), pyoluteorin (PLT) and several rhizoxins, which exhibited broad-spectrum antibiotic activities against Gram-positive and Gram-negative bacteria as well as against fungi (Nagel et al., 2012). Because DAPG, MAPG and PLT are inhihitory to Pseudoalteromonas elyakovii and Algicola bacteriolytica, causing disease of Saccharina japonica, it is anticipated that the marine pseudomonads may prevent diseases of the macroalgal host.
Head of the Research Unit:
Prof. Dr. Johannes F. Imhoff
GEOMAR | Helmholtz Centre for Ocean Research Kiel
Düsternbrooker Weg 20
Phone: ++49-431 600-4450
Fax: ++49-431 600-4482
Personal Assistant / Office Management:
Phone: ++49-431 600-4481
Fax: ++49-431 600-4482