A Novel Algicidal Bacterium, Microbulbifer sp. YX04, Triggered Oxidative Damage and Autophagic Cell Death in Phaeocystis globosa , Which Causes Harmful Algal Blooms

P. globosa is one of the most notorious harmful algal bloom (HAB)-causing species, which can secrete hemolytic toxins, frequently cause serious ecological pollution, and pose a health hazard to animals and humans. Hence, screening for bacteria with high algicidal activity against P. globosa and studies on the algicidal characteristics and mechanism will contribute to providing an ecofriendly microorganism-controlling agent for preventing the occurrence of algal blooms and reducing the harm of algal blooms to the environment.

Biochemical and Physiological Responses of Harmful Karenia mikimotoi to Algicidal Bacterium Paracoccus homiensis O-4

Harmful algal blooms caused by Karenia mikimotoi frequently occur worldwide and severely threaten the marine environment. In this study, the biochemical and physiological responses of K. mikimotoi to the algicidal bacterium Paracoccus homiensis O-4 were investigated, and the effects on the levels of reactive oxygen species (ROS), malondialdehyde content, multiple antioxidant systems and metabolites, photosynthetic pigments, and photosynthetic index were examined. The cell-free supernatant in strain O-4 significantly inhibited K. mikimotoi cell growth. The bacterium caused the K. mikimotoi cells to activate their antioxidant defenses to mitigate ROS, and this effect was accompanied by the upregulation of intracellular antioxidant enzymes and non-enzyme systems. However, the overproduction of ROS induced lipid peroxidation and oxidative damage within K. mikimotoi cells, ultimately leading to algal death. In addition, the photosynthetic efficiency of the algal cells was significantly inhibited by O-4 and was accompanied by a reduction in photosynthetic pigments. This study indicates that O-4 inhibits K. mikimotoi through excessive oxidative stress and impaired photosynthesis. This research into the biochemical and physiological responses of K. mikimotoi to algicidal bacteria provides insights into the prophylaxis and control of harmful algal blooms via interactions between harmful algae and algicidal bacteria.

Cochlodiniinecator piscidefendens gen. nov., sp. nov., an algicidal bacterium against the ichthyotoxic dinoflagellate Cochlodinium polykrikoides

Harmful algal blooms caused by Cochlodinium polykrikoides result in enormous economic damage to the aquaculture industry. Biological control methods have attracted wide attention due to their environmental-friendliness. In this study, a novel algicidal bacterium, designated strain M26A2MT, was determined for its taxonomic position and was evaluated for its potential to mitigate C. polykrikoides blooms. Strain M26A2MT exhibited the highest 16S rRNA gene sequence similarity to the type strains of Planktotalea lamellibrachiae (97.3%), Halocynthiibacter namhaensis (97.2%), Pseudohalocynthiibacter aestuariivivens (96.8%) and Halocynthiibacter arcticus (96.4%) in the family Rhodobacteraceae . The predominant fatty acids were C10 : 0 3-OH and summed feature 8 (comprising C18 : 1 ω7c and/or C18 : 1 ω6c). The major polar lipids were phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, one unidentified aminolipid and three unidentified lipids. Q-10 was the respiratory quinone. Strain M26A2MT exerted significant algicidal activity against C. polykrikoides cells by destroying the membrane integrity and the photosynthetic system. Our findings suggest that strain M26A2MT shows a high potential to control outbreaks of C. polykrikoides. Based on the polyphasic characterization, strain M26A2MT is considered to represent a novel species within a novel genus of the family Rhodobacteraceae , for which the name Cochlodiniinecator piscidefendens gen. nov., sp. nov. is proposed. The type strain is M26A2MT (=KCTC 82083T=JCM 34119T).

Biocontrol of Toxin Producing Cyanobacterium Microcystis aeruginosa by Algicidal Bacterium Exiguobacterium acetylicum Strain TM2 Isolated from Mid-Altitudinal Himalayan Lake of Northern India

Microcystis aeruginosa is a hepatotoxin producing cyanobacteria, found globally in freshwaters. In the present study, an algicidal bacterium against M. aeruginosa was isolated from Bhimtal Lake (29°20’39”N; 79°33’32”E) of Himalayan region of Uttarakhand, India. The isolated bacterium Exiguobacterium acetylicum strainTM2was identified by morphological characteristics, biochemical characteristics and partial 16S ribosomal DNA (rDNA) gene amplification (GenBank accession number: KX155561). Efficacy of E. acetylicum TM2, and its mode of algicidal activity was evaluated against M. aeruginosa. E. acetylicum TM2 showed intense anti-cyanobacterial effect against M. aeruginosa, and approximately 90.0 % death of M. aeruginosa cells were observed after 10 days of incubation. The bacterium attacked the M. aeruginosa cells directly by physically coming in contact and caused damaged to its membrane and internal organelles. Cell free filtrate of E. acetylicum TM2 did not exhibited algicidal activity, which indicates that mode of algicidal mechanism, is cell to cell contact, and not chemically mediated damage by algicidal compounds released from E. acetylicum TM2. Furthermore, in vitro and in vivo pathogenicity test confirm the non-virulence of E. acetylicum TM2 and so it could be potentially useful in mitigation of M. aeruginosa blooms in water.

Fibrivirga Algicola Gen. Nov., Sp. Nov., An Algicidal Bacterium Isolated from a Freshwater River

An aerobic, gram-negative, pink-colored, non-motile, rod-shaped algicidal bacterium, designated JA-25T was isolated from the freshwater of the Geumgang River, Republic of Korea. It grew at 15–30°C, 6.0–9.0 pH, and in the presence of 0–1% (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain JA-25T belongs to the Family ‘Spirosomaceae’ and is most closely related to Fibrella aestuarina BUZ 2T (93.6%). The strain JA-25T showed < 90% sequence similarity to other members of the Family ‘Spirosomaceae’. The average nucleotide identity(ANI), in silico DNA-DNA hybridization and the average amino acid identity(AAI) values based on the genomic sequences of JA-25T and F. aestuarina BUZ 2T were 74.4, 20.5 and 73.6 %, respectively. The genomic DNA G + C content was 52.5mol %. The major cellular fatty acids were Summed feature 3 (C16:1 ω6c/C16:1 ω7c), C16:1 ω5c, C16:0 (> 10%). The genomic DNA G + C content was 52.5 mol %. The major respiratory quinone was MK-7 and the polar lipids were phosphatidylethanolamine, two unidentified aminolipids, two phospholipids and five unidentified lipids. Considering the phylogenetic inference, phenotypic and chemotaxonomic data, strain JA-25T should be classified as a novel species of the novel genus Fibrivirga, with the proposed name Fibrivirga algicola sp. nov. The type strain is JA-25T (= KCCM 43334T = NBRC 114259T).

Nutrient deficiency and an algicidal bacterium improved the lipid profiles of a novel promising oleaginous dinoflagellate, Prorocentrum donghaiense, for biodiesel production

The lipid production potential of 8 microalgae species was investigated. Among these eight species, the best strain was a dominant bloom-causing dinoflagellate, Prorocentrum donghaiense ; this species had a lipid content of 49.32±1.99% and exhibited a lipid productivity of 95.47±0.99 mg L −1 d −1 , which was 2-fold higher than the corresponding values obtained for the oleaginous microalgae Nannochloropsis gaditana and Phaeodactylum tricornutum . P. donghaiense, which is enriched in C16:0 and C22:6, is appropriate for commercial DHA production. Nitrogen or phosphorus stress markedly induced lipid accumulation to levels surpassing 75% of the dry weight, increased the C18:0 and C17:1 contents, and decreased the C18:5 and C22:6 contents, and these effects resulted in decreases in the unsaturated fatty-acid levels and changes in the lipid properties of P. donghaiense such that the species met the biodiesel specification standards. Compared with the results obtained under N-deficient conditions, the enhancement in the activity of alkaline phosphatase of P. donghaiense observed under P-deficient conditions could partly alleviate the adverse effects on the photosynthetic system exerted by P deficiency to induce the production of more carbohydrates for lipogenesis. The supernatant of the algicidal bacterium Paracoccus sp. Y42 culture lysed P. donghaiense without decreasing its lipid content, which resulted in facilitation of the downstream oil extraction process and energy savings through the lysis of algal cells. The Y42 supernatant treatment improved the lipid profiles of algal cells by increasing their C16:0, C18:0 and C18:1 contents and decreasing their C18:5 and C22:6 contents, which is favourable for biodiesel production. IMPORTANCE This study demonstrates the high potential of P. donghaiense , a dominant bloom-causing dinoflagellate, for lipid production. Compared with previously studied oleaginous microalgae, P. donghaiense exhibit greater potential for practical application due to its higher biomass and lipid contents. Nutrient deficiency and the algicidal bacterium Paracoccus sp. Y42 could improve the suitability of the lipid profile of P. donghaiense for biodiesel production. Furthermore, Paracoccus sp. Y42 effectively lyse algal cells, which facilitates the downstream oil extraction process for biodiesel production and results in energy savings through the lysing of algal cells. This study provides a more promising candidate for the production of DHA for human nutritional products and of microalgal biofuel, as well as a more cost-effective method for breaking algal cells. The high lipid productivity of P. donghaiense and algal cell lysis by algicidal bacteria contribute to reductions in the production cost of microalgal oil.

Encapsulation and Algicidal Properties of Fermentation Products From Vibrio brasiliensis H115

Algicidal bacteria offer an eco-friendly and promising approach for controlling harmful algae blooms (HABs). In this study, repeated batch fermentation of immobilized algicidal bacterium Vibrio brasiliensis H115 was preformed to enhance the productivity of the algicidal compounds. The highest algicidal efficiency of the fermentation products against Akashiwo sanguinea (100%) was achieved when the fermentation time was decreased from 24 to 14 h. The cell-free fermentation broth was then spray-dried and floating microcapsules were prepared from the dried powder. The optimum preparation conditions for floating microcapsules were: sodium alginate (SA), 3%; CaCO3: SA (mass ratio), 3:4; CaCl2, 3%; citric acid, 4%; ethylcellulose, 2%; crosslinking time, 30 min. Under the optimal conditions, the floating microcapsules displayed efficient A. sanguinea cell lysis ability and the algicidal efficiency increased from 10.62% (4 h) to 100% (24 h). These results suggest that the floating microcapsules could potentially be practically used for controlling the outbreaks of A. sanguinea.

Complete Genome Sequence of Shewanella sp. Strain Lzh-2, an Algicidal Bacterial Strain Isolated from Lake Taihu, People’s Republic of China

ABSTRACT Shewanella sp. strain Lzh-2 is an algicidal bacterium isolated from surface water samples collected from Meiliang Bay of Lake Taihu in China. Here, we present the complete genome sequence of Shewanella sp. Lzh-2. Some functional genes and secondary metabolite gene clusters were predicted.

Complete genome sequence of Stenotrophomonas rhizophila KC1, a quorum sensing-producing algicidal bacterium, isolated from mangrove Kandelia candel

This paper describes the isolation of an algicidal strain, Stenotrophomonas rhizophila KC1, from mangrove (Kandelia candel), and its genome, which was sequenced using next-generation sequencing technology. The genome is 5.93 Mb with a G+C content of 63.17%. A total of 3,352 functional proteins were assigned according to KEGG categories. A total of 11,586 protein coding genes, 73 tRNA genes, and 17 rRNA genes were obtained. In silico genome annotation protocols identified 83 putative quorum sensing (QS) genes, and the algicidal potential of KC1 was related with the QS genes (for example LuxI-LuxR genes). Collectively, these data suggest that KC1 may be an antialgal bacterium whose behavior can be modulated by QS signaling. The annotated genome sequence of this strain may represent a valuable tool for studying algae–bacteria interactions and developing microbe-based methods for controlling harmful algae.