Characterization of cell viability in Phaeocystis globosa cultures exposed to marine algicidal bacteria

The bloom of Phaeocystis globosa has occurred frequently in the southern coastal areas of China in recent years, which has led to substantial economic losses. This study investigated the effects of culture broth of strains Y1 and Y4 isolated from algal blooms in Zhuhai, China on physiological characteristics and cell viability of P. globosa. The increase in the levels of reactive oxygen species (ROS) in P. globosa cells exposed to strains Y1 and Y4 culture broth were detected, indicating that the algal cells suffered from oxidative damage. The surplus ROS induced the increase of malondialdehyde (MDA) contents and the activities of antioxidant enzymes, including superoxide dismutase (SOD) and catalase (CAT). The decrease in protein content indicated that strains Y1 and Y4 culture broth inhibited cell growth. The contents of pigments decreased after 96 h treatment, indicated that oxidative stress destroyed pigment synthesis. Furthermore, flow cytometry coupled with the propidium iodide stain and chlorophyll auto-fluorescence was used to investigate cell viability. Results showed that chlorophyll fluorescence intensities and cell integrity decreased with time of exposure, which demonstrated that strains Y1 and Y4 culture broth could change membrane permeability and resulted in the loss of these photosynthetic pigments. The isolated strains were identified as Bacillus sp. by culture morphology, biochemical reactions, and homology research based on 16S rDNA. Overall, these findings suggested that oxidative stress caused from Bacillus sp. potentially destroyed pigment synthesis and cell membrane integrity, and ultimately led to the lysis of the algal cells

Exploration in antioxidant and photosynthetic system of a marine algicidal Bacillus on four HABs species

A novel marine bacterium strain B1, initially showed 96.4% of algicidal activity on Phaeocystis globosa. Under this, three other harmful algal species (Skeletonema costatum, Heterosigma akashiwo and Prorocentrum donghaiense) were chosen to study the algicidal effects of strain B1, and the algicidal activities were 91.4 %, 90.7 % and 90.6 %, respectively. In order to explore the algicidal mechanism of strain B1 on these four harmful algal species, the characteristic of antioxidant and photosynthetic system were studied. Sensitivity to strain B1 supernatant, enzyme activity and gene expression varied with algal species, while the algicidal patterns were similar. Strain B1 supernatant increased malondialdehyde contents, decreased chlorophyll a contents as well as changed total antioxidant and superoxide dismutase activity, restrained psbA, psbD and rbcL genes expression which eventually results in the algal cells death. The algicidal procedure was observed using field emission scanning electron microscopy, which indicated that algal cells were lysed and cellular substances were released. These findings suggested that antioxidant and photosynthetic system of these four algal species was destroyed under strain B1 supernatant stress. This is the first report to explore and compare the mechanism of a marine Bacillus against harmful algal bloom species of covered four phyla.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Spatial and seasonal variations of total petroleum hydrocarbon in surface water and sediment in Pearl River Delta

Abstract A field study in the Pearl River Delta of China was conducted in order to describe to the spatial and seasonal variation of occurrence and concentrations of total petroleum hydrocarbon (TPH) in surface water and sediments. Petroleum hydrocarbons and isoprenoid alkanes were quantified by UV spectroscopy and gas chromatography with a mass selective detector. The concentrations of TPH ranged from 4.3 to 68.7 μg L-1 in surface water, and from 66.6 to 1445 μg g-1 in surface sediments. The ratios of pristine to phytane suggested that the main sources of TPH in the sediment were petroleum importation. The highest concentrations of TPH were present in the spring season. When compared with results from previous studies, it can be concluded that the Pearl River Delta was moderately polluted by TPH. No statistically significant correlations were observed between the concentrations of TPH in surface water and sediments

Effects of bacterial supernatant on algal cell densities.

<p>(a) <i>C. vulgaris</i>, (b) <i>C. muelleri</i>, and (c) <i>I. galbana</i>. Data represent mean ± standard deviation. Error bars represent standard deviation of triplicate samples. The asterisk (*) indicates a significant difference of p < 0.05 when compared to the control.</p

Predicted formula, theoretical mass, experimental mass and mass errors of the molecular ions of the two purified compounds.

<p>Predicted formula, theoretical mass, experimental mass and mass errors of the molecular ions of the two purified compounds.</p

Effects of algicidal compounds on (a) SOD activity, (b) CAT activity and (c) MDA content of <i>P. globosa</i>.

<p>Data represent mean ± standard deviation. Error bars represent standard deviation of triplicate samples. The asterisk (*) indicates a significant difference of p < 0.05, (**) indicates a significant difference of p < 0.01 when compared to the control </p

Mortalities of <i>M. mongolica</i> treated with different concentrations of purified compounds for 24 h.

<p>Mortalities of <i>M. mongolica</i> treated with different concentrations of purified compounds for 24 h.</p

Phylogenetic tree based on 16S rDNA gene of strain B1.

<p>The tree was inferred using the neighbor-joining method. Bootstrap values were evaluated from 1000 replications.</p

Toxic Effect of a Marine Bacterium on Aquatic Organisms and Its Algicidal Substances against <i>Phaeocystis globosa</i>

<div><p>Harmful algal blooms have caused enormous damage to the marine ecosystem and the coastal economy in China. In this paper, a bacterial strain B1, which had strong algicidal activity against <i>Phaeocystis globosa</i>, was isolated from the coastal waters of Zhuhai in China. The strain B1 was identified as <i>Bacillus</i> sp. on the basis of 16S rDNA gene sequence and morphological characteristics. To evaluate the ecological safety of the algicidal substances produced by strain B1, their toxic effects on marine organisms were tested. Results showed that there were no adverse effects observed in the growth of <i>Chlorella vulgaris</i>, <i>Chaetoceros muelleri</i>, and <i>Isochrystis galbana</i> after exposure to the algicidal substances at a concentration of 1.0% (v/v) for 96 h. The 48h LC₅₀ values for <i>Brachionus plicatilis</i>, <i>Moina mongolica</i> Daday and <i>Paralichthys olivaceus</i> were 5.7, 9.0 and 12.1% (v/v), respectively. Subsequently, the algicidal substances from strain B1 culture were isolated and purified by silica gel column, Sephadex G-15 column and high-performance liquid chromatography. Based on quadrupole time-of-flight mass spectrometry and PeakView Software, the purified substances were identified as prolyl-methionine and hypoxanthine. Algicidal mechanism indicated that prolyl-methionine and hypoxanthine inhibited the growth of <i>P. globosa</i> by disrupting the antioxidant systems. In the acute toxicity assessment using <i>M. mongolica</i>, 24h LC₅₀ values of prolyl-methionine and hypoxanthine were 7.0 and 13.8 g/L, respectively. The active substances produced by strain B1 can be considered as ecologically and environmentally biological agents for controlling harmful algal blooms.</p></div