Zhangran Chen

A Novel Algicide: Evidence of the Effect of a Fatty Acid Compound from the Marine Bacterium, Vibrio sp. BS02 on the Harmful Dinoflagellate, Alexandrium tamarense

Alexandrium tamarense is a notorious bloom-forming dinoflagellate, which adversely impacts water quality and human health. In this study we present a new algicide against A. tamarense, which was isolated from the marine bacterium Vibrio sp. BS02. MALDI-TOF-MS, NMR and algicidal activity analysis reveal that this compound corresponds to palmitoleic acid, which shows algicidal activity against A. tamarense with an EC50 of 40 μg/mL. The effects of palmitoleic acid on the growth of other algal species were also studied. The results indicate that palmitoleic acid has potential for selective control of the Harmful algal blooms (HABs). Over extended periods of contact, transmission electron microscopy shows severe ultrastructural damage to the algae at 40 μg/mL concentrations of palmitoleic acid. All of these results indicate potential for controlling HABs by using the special algicidal bacterium and its active agent.

Toxicity of algicidal extracts from Mangrovimonas yunxiaonensis strain LY01 on a HAB causing Alexandrium tamarense

Toxicity of algicidal extracts from Mangrovimonas yunxiaonensis strain LY01 on Alexandrium tamarense were measured through studying the algicidal procedure, nuclear damage and transcription of related genes. Medium components were optimized to improve algicidal activity, and characteristics of algicidal extracts were determined. Transmission electron microscope analysis revealed that the cell structure was broken. Cell membrane integrity destruction and nuclear structure degradation were monitored using confocal laser scanning microscope, and the rbcS, hsp and proliferating cell nuclear antigen (PCNA) gene expressions were studied. Results showed that 1.0% tryptone, 0.4% glucose and 0.8% MgCl2 were the optimal nutrient sources. The algicidal extracts were heat and pH stable, non-protein and less than 1kD. Cell membrane and nuclear structure integrity were lost, and the transcription of the rbcS and PCNA genes were significantly inhibited and there was up-regulation of hsp gene expression during the exposure procedure. The algicidal extracts destroyed the cell membrane and nuclear structure integrity, inhibited related gene expression and, eventually, lead to the inhibition of algal growth. All the results may elaborate firstly the cell death process and nuclear damage in A. tamarense which was induced by algicidal extracts, and the algicidal extracts could be potentially used as bacterial control of HABs in future.

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)).

First Report of Pseudobodo sp, a New Pathogen for a Potential Energy-Producing Algae: Chlorella vulgaris Cultures

Chlorella vulgaris, is a kind of single-celled green algae, which could serve as a potential source of food and energy because of its photosynthetic efficiency. In our study, a pathogenic organism targeting C. vulgaris was discovered. The algae-lytic activity relates to a fraction from lysates of infected C. vulgaris that was blocked upon filtration through a 3 µm filter. 18S rRNA gene sequence analysis revealed that it shared 99.0% homology with the protist Pseudobodo tremulans. Scanning electron microscope analysis showed that Pseudobodo sp. KD51 cells were approximately 4–5 µm long, biflagellate with an anterior collar around the anterior part of the cell in unstressed feeding cells. Besides the initial host, Pseudobodo sp. KD51 could also kill other algae, indicating its relatively wide predatory spectrum. Heat stability, pH and salinity tolerance experiments were conducted to understand their effects on its predatory activities, and the results showed that Pseudobodo sp. KD51 was heat-sensitive, and pH and salinity tolerant.

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.

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.

Influence of plaque-forming bacterium, Rhodobacteraceae sp: On the growth of Chlorella vulgaris

Experiments were conducted to find out the molecular features, infection process of a special alga plaque-forming microorganism and its potential influence on the biomass of Chlorella vulgaris during the infection process. Direct contact between the algal cell and the bacterium may be the primary steps needed for the bacterium to lyse the alga. Addition of C. vulgaris cells into f/2 medium allowed us obtain the object bacterium. The 16S rRNA gene sequence comparisons results showed that the plaque-forming bacterium kept the closest relationship with Labrenzia aggregata IAM 12614(T) at 98.90%. The existence of the bacterium could influence both the dry weight and lipid content of C. vulgaris. This study demonstrated that direct cell wall disruption of C. vulgaris by the bacterium would be a potentially effective method to utilize the biomass of microalgae.

Phaeodactylibacter luteus sp. nov., isolated from the oleaginous microalga Picochlorum sp.

A Gram-staining-negative, orange-pigmented, non-motile, aerobic bacterial strain, designated GYP20T, was isolated from a culture of the alga Picochlorum sp., a promising feedstock for biodiesel production, which was isolated from the India Ocean. Growth was observed at temperatures from 20 to 37 °C, salinities from 0 to 3% and pH from 5 to 9.Mg2+ and Ca2+ ions were required for growth. Phylogenetic analysis based on 16S rRNA gene sequencing revealed that the strain was a member of the genus Phaeodactylibacter, which belongs to the family Saprospiraceae. Strain GYP20T was most closely related to Phaeodactylibacter xiamenensis KD52T (95.5% sequence similarity). The major fatty acids were iso-C15 : 1 G, iso-C15 : 0, iso-C17 : 0 3-OH and summed feature 3. The predominant respiratory quinone was menaquinone-7 (MK-7). The polar lipids of strain GYP20T were found to consist of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, four unidentified glycolipids, two unidentified phospholipids and three unidentified aminolipids. According to its morphology, physiology, fatty acid composition and 16S rRNA sequence data, the novel strain most appropriately belongs to the genus Phaeodactylibacter, but can readily be distinguished from Phaeodactylibacter xiamenensis GYP20T. The name Phaeodactylibacter luteus sp. nov. is proposed with the type strain GYP20T ( = MCCC 1F01222T = KCTC 42180T).