MINIREVIEW What we can learn from sushi: a review on seaweed–bacterial associations Joke Hollants1,2, Frederik Leliaert2, Olivier De Clerck2 & Anne Willems1 1Laboratory of Microbiology, Department of Biochemistry and Microbiology, Ghent University, Ghent, Belgium; and 2Phycology Research Group, Department of Biology, Ghent University, Ghent, Belgium Correspondence: Joke Hollants, Ghent Abstract University, Department of Biochemistry and Microbiology (WE10), Laboratory of Many eukaryotes are closely associated with bacteria which enable them to Microbiology, K.L. Ledeganckstraat 35, expand their physiological capacities. Associations between algae (photosyn- B-9000 Ghent, Belgium. thetic eukaryotes) and bacteria have been described for over a hundred years. Tel.: +32 9 264 5140; fax: +32 9 264 5092; A wide range of beneficial and detrimental interactions exists between macroal- e-mail: [email protected] gae (seaweeds) and epi- and endosymbiotic bacteria that reside either on the surface or within the algal cells. While it has been shown that these chemically Received 6 April 2012; revised 27 June 2012; accepted 3 July 2012. mediated interactions are based on the exchange of nutrients, minerals, and secondary metabolites, the diversity and specificity of macroalgal–bacterial rela- DOI: 10.1111/j.1574-6941.2012.01446.x tionships have not been thoroughly investigated. Some of these alliances have been found to be algal or bacterial species-specific, whereas others are wide- Editor: Lily Young spread among different symbiotic partners. Reviewing 161 macroalgal–bacterial studies from the last 55 years, a definite bacterial core community, consisting Keywords of Gammaproteobacteria, CFB group, Alphaproteobacteria, Firmicutes, and bacteria; diversity; interaction; macroalgae; Actinobacteria species, seems to exist which is specifically (functionally) symbiosis. adapted to an algal host–associated lifestyle. Because seaweed–bacterial associa- tions are appealing from evolutionary and applied perspectives, future studies should integrate the aspects of diverse biological fields. If there is one thing we can learn from sushi, it is that needed some delimitation and is restricted to the studies seaweed-associated bacteria can have unexpected benefi- of bacteria associated with marine macroalgae (seaweed) cial effects. The carbohydrate active enzyme porphyranase belonging to the Chlorophyta (green algae), Rhodophyta from the marine Bacteroidetes bacterium Zobellia galacta- (red algae), and Phaeophyceae (brown algae). Seaweed nivorans breaks down the sulphated polysaccharide por- and bacteria have come a long way because algal plastids phyran from the red alga Porphyra (nori) traditionally originated from endosymbiotic cyanobacteria (Margulis, used to prepare sushi. Moreover, the genes coding for 1998). Like their unicellular ancestors, marine macroalgae this porphyranase have been horizontally transferred form the modern-day playground for a wide diversity of through dietary seaweed from Z. galactanivorans to the bacterial associations ranging from beneficial (mutualis- gut microbe Bacteroides plebeius from particularly Japa- tic), harmful (parasitic), and neutral (commensal), over nese people, allowing them to digest the algae that wrap obligate and facultative, to endo- and ectophytic interac- sushi rolls and other delicacies (Hehemann et al., 2010). tions (Relman, 2008). This, along with applied aspects of This not only indicates that the human gut microbiota current algal–bacterial symbioses, makes their associations may become proficient at using dietary polysaccharides appealing for evolutionary, ecological, and biochemical by horizontal gene transfer; it also highlights the signifi- studies. Nevertheless, investigations of macroalgal–bacte- cance of macroalgal–bacterial associations. rial associations lag behind these of other marine eukary- MICROBIOLOGY ECOLOGY MICROBIOLOGY Like sushi, algae come in many forms and flavors rang- otes (Goecke et al., 2010). Whereas the full cycle 16S ing from microscopic unicells to gigantic kelps inhabiting rRNA approach (Olsen et al., 1986) is well established to oceans, freshwater habitats, soils, rocks, and even trees characterize the microbial associates of unicellular algae, (van den Hoek et al., 1995). Consequently, this review corals, and sponges (Geng & Belas, 2010; Olson & FEMS Microbiol Ecol && (2012) 1–16 ª 2012 Federation of European Microbiological Societies Published by Blackwell Publishing Ltd. All rights reserved 2 J. Hollants et al. Kellogg, 2010), these molecular techniques are just begin- who was the first to suggest a true symbiotic marcoalgal– ning to be applied to macroalgae (Goecke et al., 2010 and bacterial partnership. The occurrence of Azotobacter as an references therein). epiphyte on marine algae led him to propose that a sym- biosis may exist in which the algae supply Azotobacter with carbohydrates and use the nitrogen fixed by the bac- From a kitchen secret to molecular teria (Waksman et al., 1933; ZoBell, 1946). Also Edgar microbiology: a historical overview Johnson Allen (1910), Director of the Marine Biological Association of the United Kingdom, and his collaborator Foundations E.W. Nelson recognized a symbiotic aspect in xenic mar- The first report of a seaweed–bacterium alliance – coalgal cultures (Andersen, 2006). As they laid the foun- although artificial – is one that altered bacteriology for- dations for seaweed culture, they noticed good growth of ever. In 1881, Walther Hesse, a German physician, joined algae only when small quantities of natural seawater were Robert Koch’s laboratory to study the bacteria responsible added to the artificial culture media. Allen remarked that for his patients’ illnesses. But, like his colleagues, Hesse these effects may be caused by products of the metabo- encountered major technical problems attaining pure bac- lism of bacteria (Andersen, 2006). terial cultures on solid gelatin-based media. The gelatin often liquefied because of bacterial enzymes or because of First cultivation and microscopy studies the incubation temperature. When he vented his frustra- tions to his wife Fanny, she suggested using a seaweed It took until after World War II for Luigi Provasoli and extract, agar–agar, which she had used to thicken her jel- colleagues to establish the first bacteria-free cultures of lies and puddings for years (Hesse & Gro¨schel, 1992). the green foliaceous seaweed Ulva using newly discovered The practical application of this kitchen secret accelerated antibiotics (Andersen, 2006). Provasoli, however, observed bacteriological research greatly, opening the way also for that the typical foliose morphology of Ulva lactuca was real-life macroalgal–bacterial studies. In fact, it was Wal- lost in the absence of bacteria and – even more interest- ther Hesse himself who developed agar plate techniques ing – that the normal thallus morphology was restored to count bacteria in water samples. Techniques the ship’s when certain bacteria previously isolated from the algal physician Bernard Fischer (1889) used to great success in surface were re-added to the culture medium (Provasoli, the tropical waters of the Sargasso Sea during the Plank- 1958; Provasoli & Pintner, 1980). In 1955, Harold and ton Expedition of the Humboldt Foundation across the Stanier were the first to exhaustively describe the bacte- Atlantic Ocean (ZoBell, 1946). Throughout that trip, Fi- rium Leucothrix mucor that was found consistently as an scher noted that the greatest abundance of culturable algal epiphyte, showing macroalgae not only to interact marine bacteria was associated with planktonic organisms with bacteria but also to represent a distinct source of and seaweeds. Hans Gazert (1906) who was in charge of new microbial taxa. With the introduction of electron the bacteriological investigations of the German South microscopy to study the macroalgal ultrastructure in the Polar Expedition made similar observations in the South 1970s, an intriguing new form of seaweed–bacterial inter- Atlantic and Antarctic Ocean where some of the largest actions was discovered. In addition to epiphytic bacteria, bacterial populations were found in the vicinity of sea- various siphonous seaweeds such as Bryopsis, Caulerpa, weeds (ZoBell, 1946). Although these observations are Chlorodesmis, Halimeda, Penicillus, and Udotea were also mainly founded on a high influx of organic matter from shown to harbor intracellular bacteria within their cyto- the remains of dead seaweeds (ZoBell, 1946), also symbi- plasm and/or vacuolar systems (Burr & West, 1970; Burr otic (here defined as mutualistic) associations with living & Evert, 1972; Turner & Friedmann, 1974; Colombo, macroalgae might have contributed. Simultaneously with 1978; Dawes & Lohr, 1978; Menzel, 1987). Simultaneously these initial notes of seaweed–bacterial alliances at sea, with these early microscopic observations, the first culti- scientists in the laboratory deduced similar conclusions vation studies aiming to examine the total diversity of from their preliminary late 19th century macroalgal cul- bacteria associated with macroalgae arose. Although the ture work. The German botanist Georg Klebs (1896) was bacteria were initially identified only by morphological aware of the presence of bacteria in his seaweed cultures and biochemical tests, the epiphytic flora on seaweeds and tried to set up pure, axenic cultures of filamentous was clearly very diverse, covering numerous bacterial taxa and siphonous algae. While he was successful in