In recent years, Microcystis aeruginosa blooms have occurred throughout the world, causing huge economic losses and destroying aquatic ecosystems. It is necessary to develop effective and ecofriendly methods to control M. aeruginosa blooms. Here, we report a high algicidal activity of prodigiosin (PG) against M. aeruginosa as well as the algicidal mechanism. PG showed high algicidal activity against M. aeruginosa, with a 50% lethal dose (LD50) of 5.87 μg/mL in 72 h. A combination of methods, including propidium iodide and Annexin V-fluorescein staining assays and light and electron microscopy indicated the existence of two modes of cell death with features similar to those in eukaryotic programmed cell death: necrotic-like and apoptotic-like. Biochemical and physiological analyses showed that PG generates reactive oxygen species (ROS), which induce lipid peroxidation, damage the membrane system and destroy the function of the photosystem. A proteomics analysis revealed that many proteins were differentially expressed in response to PG stress and that most of these proteins were involved in important metabolic processes, which may trigger necrotic-like or apoptotic-like cell death. The present study sheds light on the multiple toxicity mechanisms of PG on M. aeruginosa and its potential for controlling the occurrence of M. aeruginosa blooms in lakes.

Chitinase producing bacteria can involve extensively in nutrient cycling and energy flow in the aquatic environment through degradation and utilization of chitin. It is well known that diatoms cells are encased by box-like frustules composed of chitin. Thus the chitin containing of diatoms shall be a natural target of chitinase producing bacteria, however, the interaction between these two organismic groups has not been studied thus far. Therefore, in this study, the algicidal mechanism of one chitinase producing bacterium (strain LY03) on Thalassiosira pseudonana was investigated. The algicidal range and algicidal mode of strain LY03 were first studied, and then bacterial viability, chemotactic ability and direct interaction characteristic between bacteria and diatom were also confirmed. Finally, the characteristic of the intracellular algicidal substance was identified and the algicidal mechanism was determined whereby algicidal bacterial cells showed chemotaxis to algal cells, fastened themselves on algal cells with their flagella, and then produced chitinase to degrade algal cell walls, and eventually caused algal lysis and death. It is the first time to investigate the interaction between chitinase producing bacteria and diatoms, and this novel special interaction mode was confirmed in this study, which will be helpful in protection and utilization of diatoms resources.

A novel Gram-staining-negative, aerobic, rod-shaped, non-motile, reddish-orange and chemoheterotrophic bacteria, designated strain KD52T, was isolated from a culture of the alga Phaeodactylum tricornutum from Xiamen, Fujian Province, China. 16S rRNA gene sequence comparison showed that strain KD52T was a member of the family Saprospiraceae , forming a distinct lineage with ‘Portibacter lacus’ KCTC 23747. The 16S rRNA gene sequence similarity between strain KD52T and the type strains of species of the family Saprospiraceae ranged from 86 % to 89 %. Growth occurred at 20–37 °C (optimum, 28 °C), in the presence of 1–9 % (w/v) NaCl (optimum, 2.5 %) and at pH 5–8.5 (optimum, pH 6.0). The dominant fatty acids (>10 %) of strain KD52T were iso-C15 : 0 (33.1 %), iso-C15 : 1 G (14.8 %) and summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c, 13.8 %). The major polar lipids were diphosphatidylglycerol, three unidentified phospholipids, four unknown lipids and one unidentified aminolipid. The DNA G+C content was 51 mol% and the major respiratory quinone was menaquinone-7 (MK-7). On the basis of phenotypic data and phylogenetic inference, strain KD52T represents a novel species of a new genus, for which the name Phaeodactylibacter xiamenensis gen. nov., sp. nov., is proposed. The type strain is KD52T ( = MCCC 1F01213T = KCTC 32575T).

No abstract

Alexandrium tamarense is a notorious harmful algal bloom species, which is associated with the largest number of paralytic shellfish poisoning cases, causing devastating economic losses and health hazards. The marine bacterium Mangrovimonas yunxiaonensis strain LY01 showed high algicidal effects on A. tamarense. A. tamarense was also susceptible to the supernatant of LY01 as revealed by algicidal activity assay, but washed bacterial cells did not show algicidal activity towards A. tamarense. In this study, we investigated the algicidal effect of the supernatant on growth, photosynthesis and the antioxidative response of A. tamarense. The results indicated that under the algicidal effect of the supernatant, the contents of cellular pigments including chlorophyll a and carotenoids were significantly decreased, and the decline of the maximum quantum yield and relative electron transport rate values suggested that photosynthetic inhibition occurred in the photosystem II system. The content of reactive oxygen species (ROS) increased after 0.5 h exposure, and the surplus ROS induced lipid peroxidation, the destruction of cellular membrane integrity and decreased cellular protein and carbohydrate contents in the algal cells. At the same time, the supernatant also induced the responses of antioxidant enzymes and non-enzymatic antioxidant. The transcription of photosynthesis- and respiration-related genes were significantly inhibited during the exposure procedure, which obstructed photosynthetic efficiency and capacity and disturbed the respiratory system, thereby increasing ROS production again. All these results elaborate clearly the entire procedure by which cellular physiological levels respond to the algicidal bacterium and may contribute to a better understanding of the bacterial control of A. tamarense.

Harmful algal blooms caused by Phaeocystis globosa have resulted in staggering losses to coastal countries because of their world-wide distribution. Bacteria have been studied for years to control the blooms of harmful alga, however, the action mechanism of them against harmful algal cells is still not well defined. Here, a previously isolated algicidal bacterium Bacillus sp. LP-10 was used to elucidate the potential mechanism involved in the dysfunction of P. globosa algal cells at physiological and molecular levels. Our results showed Bacillus sp. LP-10 induced an obvious rise of reactive oxygen species (ROS), which was supposed to be major reason for algal cell death. Meanwhile, the results revealed a significant decrease of photosynthetic physiological indexes and apparent down-regulated of photosynthesis-related genes (psbA and rbcS) and protein (PSII reaction center protein D1), after treated by Bacillus sp. LP-10 filtrates, suggesting photoinhibition occurred in the algal cells. Furthermore, our results indicated that light played important roles in the algal cell death. Our work demonstrated that the major lethal reason of P. globosa cells treated by the algicidal bacterium was the photoinhibition resulted from oxidative stress induced by Bacillus sp. LP-10.

No abstract

Phytoplankton blooms are a worldwide problem and can greatly affect ecological processes in aquatic systems, but its impacts on the functional potential of microbial communities are limited. In this study, a high-throughput microarray-based technology (GeoChip) was used to profile the functional potential of free-living microbes from the Xiamen Sea Area in response to a 2011 Akashiwo sanguinea bloom. The bloom altered the overall community functional structure. Genes that were significantly (p < 0.05) increased during the bloom included carbon degradation genes and genes involved in nitrogen (N) and/or phosphorus (P) limitation stress. Such significantly changed genes were well explained by chosen environmental factors (COD, nitrite-N, nitrate-N, dissolved inorganic phosphorus, chlorophyll-a and algal density). Overall results suggested that this bloom might enhance the microbial converting of nitrate to N2 and ammonia nitrogen, decrease P removal from seawater, activate the glyoxylate cycle, and reduce infection activity of bacteriophage. This study presents new information on the relationship of algae to other microbes in aquatic systems, and provides new insights into our understanding of ecological impacts of phytoplankton blooms.