title: Selective growth promotion of bloom-forming raphidophyte Heterosigma akashiwo by a marine bacterial strain.
abstract: Algal bloom is typically caused by aberrant propagation of a single species, resulting in its predomination in the local population. While environmental factors including temperature and eutrophication are linked to bloom, the precise mechanism of its formation process is still obscure. Here, we isolated a bacterial strain that promotes growth of Heterosigma akashiwo, a Raphidophyceae that causes harmful algal blooms. Based on 16S rRNA gene sequence, the strain was identified as Altererythrobacter ishigakiensis, a member of the class Alphaproteobacteria. When added to culture, this strain facilitated growth of H. akashiwo and increased its cell culture yield significantly. Importantly, this strain did not affect the growth of other raphidophytes, Chattonella ovate and C. antiqua, indicating that it promotes growth of H. akashiwo in a species-specific manner. We also found that, in co-culture, H. akashiwo suppressed the growth of C. ovate. When A. ishigakiensis was added to the mixed culture, H. akashiwo growth was facilitated while C. ovate propagation was markedly suppressed, indicating that the presence of the bacterium enhances the dominance of H. akashiwo over C. ovate. This is the first example of selective growth promotion of H. akashiwo by a marine bacterium, and may exemplify importance of symbiotic bacterium on algal bloom forming process in general.
authors.affiliation: Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Higashi
authors.affiliation: Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Fujitani
authors.affiliation: National Research and Development Agency, Japan Fisheries Research and Education Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Nakayama
authors.affiliation: Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Tani
authors.affiliation: Institute of Plant Science and Resources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan. Electronic address: shokoueki@okayama-u.ac.jp.
authors.forename: Shoko
authors.initials: S
authors.lastname: Ueki
mesh_terms: D059001:Aquatic Organisms / Q000502:physiology*; D001419:Bacteria / Q000378:metabolism; D018407:Bacterial Physiological Phenomena; D057097:Harmful Algal Bloom; D056265:Microbial Interactions; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012623:Seawater / Q000382:microbiology; D058009:Stramenopiles / Q000254:growth & development* / Q000382:microbiology*
chemical_list: D012336:RNA, Ribosomal, 16S
keywords: Heterosigma akashiwo; Marine bacterium; Mutualism; Selective growth promotion