Xueqian Lei

The first evidence of deinoxanthin from Deinococcus sp. Y35 with strong algicidal effect on the toxic dinoflagellate Alexandrium tamarense

Harmful algal blooms (HABs) could be deemed hazardous materials in aquatic environment. Alexandrium tamarense is a toxic HAB causing alga, which causes serious economic losses and health problems. In this study, the bacterium Deinococcus xianganensis Y35 produced a new algicide, showing a high algicidal effect on A. tamarense. The algicidal compound was identified as deinoxanthin, a red pigment, based on high resolution mass spectrometry and NMR after the active compound was isolated and purified. Deinoxanthin exhibited an obvious inhibitory effect on algal growth, and showed algicidal activity against A. tamarense with an EC50 of 5.636 μg/mL with 12h treatment time. Based on the unique structure and characteristics of deinoxanthin, the content of reactive oxygen species (ROS) increased after 0.5h exposure, the structure of organelles including chloroplasts and mitochondria were seriously damaged. All these results firstly confirmed that deinoxanthin as the efficient and eco-environmental algicidal compound has potential to be used for controlling harmful algal blooms through overproduction of ROS.

Altererythrobacter xiamenensis sp. nov., an algicidal bacterium isolated from red tide seawater

A Gram-stain-negative, yellow-pigmented, aerobic bacterial strain, designated LY02(T), was isolated from red tide seawater in Xiamen, Fujian Province, China. Growth was observed at temperatures from 4 to 44 °C, at salinities from 0 to 9% and at pH from 6 to 10. Phylogenetic analysis based on 16S rRNA gene sequencing revealed that the isolate was a member of the genus Altererythrobacter, which belongs to the family Erythrobacteraceae. Strain LY02(T) was related most closely to Altererythrobacter marensis MSW-14(T) (97.2% 16S rRNA gene sequence similarity), followed by Altererythrobacter ishigakiensis JPCCMB0017(T) (97.1%), Altererythrobacter epoxidivorans JCS350(T) (97.1%) and Altererythrobacter luteolus SW-109(T) (97.0%). The dominant fatty acids were C(18 : 1)ω7c, C(17 : 1)ω6c and summed feature 3 (comprising C(16 : 1)ω7c and/or C(16 : 1)ω6c). DNA-DNA hybridization showed that strain LY02(T) possessed low DNA-DNA relatedness to A. marensis MSW-14(T), A. ishigakiensis JPCCMB0017(T), A. epoxidivorans JCS350(T) and A. luteolus SW-109(T) (mean ± SD of 33.2 ± 1.3, 32.1 ± 1.0, 26.7 ± 0.7 and 25.2 ± 1.1 %, respectively). The G+C content of the chromosomal DNA was 61.2 mol%. The predominant respiratory quinone was ubiquinone-10 (Q-10). According to its morphology, physiology, fatty acid composition and 16S rRNA gene sequence data, the novel strain most appropriately belongs to the genus Altererythrobacter, but can readily be distinguished from recognized species. The name Altererythrobacter xiamenensis sp. nov. is proposed (type strain LY02(T) = CGMCC 1.12494(T) = KCTC 32398(T) = NBRC 109638(T)).

Chitinase producing bacteria with direct algicidal activity on marine diatoms.

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.

Lysing bloom-causing alga Phaeocystis globosa with microbial algicide: An efficient process that decreases the toxicity of algal exudates

Algicidal microbes could effectively remove the harmful algae from the waters. In this study, we were concerned with the ecological influence of an algicide extracted from Streptomyces alboflavus RPS, which could completely lyse the Phaeocystis globosa cells within two days. In microcosms, 4 μg/mL of the microbial algicide could efficiently remove P. globosa cells without suppressing other aquatic organisms. Bioluminescent assays confirmed that the toxicity of microbial algicide at this concentration was negligible. Interestingly, the toxicity of P. globosa exudates was also significantly reduced after being treated with the algicide. Further experiments revealed that the microbial algicide could instantly increase the permeability of the plasma membrane and disturb the photosynthetic system, followed by the deformation of organelles, vacuolization and increasing oxidative stress. The pre-incubation of N-acetyl cysteine (NAC) verified that the rapid damages to the plasma membrane and photosynthetic system caused the algal death in the early phase, and the increasing oxidative stress killed the rest. The late accumulation and possible release of CAT also explained the decreasing toxicity of the algal culture. These results indicated that this microbial algicide has great potential in controlling the growth of P. globosa on site.

Photoinhibition of Phaeocystis globosa resulting from oxidative stress induced by a marine algicidal bacterium Bacillus sp. LP-10

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.

Comprehensive insights into the response of Alexandrium tamarense to algicidal component secreted by a marine bacterium.

Harmful algal blooms occur throughout the world, threatening human health, and destroying marine ecosystems. Alexandrium tamarense is a globally distributed and notoriously toxic dinoflagellate that is responsible for most paralytic shellfish poisoning incidents. The culture supernatant of the marine algicidal bacterium BS02 showed potent algicidal effects on A. tamarense ATGD98-006. In this study, we investigated the effects of this supernatant on A. tamarense at physiological and biochemical levels to elucidate the mechanism involved in the inhibition of algal growth by the supernatant of the strain BS02. Reactive oxygen species (ROS) levels increased following exposure to the BS02 supernatant, indicating that the algal cells had suffered from oxidative damage. The levels of cellular pigments, including chlorophyll a and carotenoids, were significantly decreased, which indicated that the accumulation of ROS destroyed pigment synthesis. The decline of the maximum photochemical quantum yield (Fv/Fm) and relative electron transport rate (rETR) suggested that the photosynthesis systems of algal cells were attacked by the BS02 supernatant. To eliminate the ROS, the activities of antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT), increased significantly within a short period of time. Real-time PCR revealed changes in the transcript abundances of two target photosynthesis-related genes (psbA and psbD) and two target respiration-related genes (cob and cox). The transcription of the respiration-related genes was significantly inhibited by the treatments, which indicated that the respiratory system was disturbed. Our results demonstrate that the BS02 supernatant can affect the photosynthesis process and might block the PS II electron transport chain, leading to the production of excessive ROS. The increased ROS can further destroy membrane integrity and pigments, ultimately inducing algal cell death.

The death mechanism of the harmful algal bloom species Alexandrium tamarense induced by algicidal bacterium Deinococcus sp. Y35

Harmful algal blooms (HABs) cause a variety of deleterious effects on aquatic ecosystems, especially the toxic dinoflagellate Alexandrium tamarense, which poses a serious threat to marine economic and human health based on releasing paralytic shellfish poison into the environment. The algicidal bacterium Deinococcus sp. Y35 which can induce growth inhibition on A. tamarense was used to investigate the functional mechanism. The growth status, reactive oxygen species (ROS) content, photosynthetic system and the nuclear system of algal cells were determined under algicidal activity. A culture of strain Y35 not only induced overproduction of ROS in algal cells within only 0.5 h of treatment, also decrease the total protein content as well as the response of the antioxidant enzyme. Meanwhile, lipid peroxidation was induced and cell membrane integrity was lost. Photosynthetic pigments including chlorophyll a and carotenoid decreased along with the photosynthetic efficiency being significantly inhibited. At the same time, photosynthesis-related gene expression showed down-regulation. More than, the destruction of cell nuclear structure and inhibition of proliferating cell nuclear antigen (PCNA) related gene expression were confirmed. The potential functional mechanism of the algicidal bacterium on A. tamarense was investigated and provided a novel viewpoint which could be used in HABs control.

A comprehensive insight into functional profiles of free-living microbial community responses to a toxic Akashiwo sanguinea bloom

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.

The algicidal mechanism of prodigiosin from Hahella sp. KA22 against Microcystis aeruginosa

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.