Biochar application on paddy and purple soils in southern China: soil carbon and biotic activity.

Soil carbon reserves are the largest terrestrial carbon pools. Common agricultural practices, such as high fertilization rates and intensive crop rotation, have led to global-scale environmental changes, including decreased soil organic matter, lower carbon/nitrogen ratios and disruption of soil carbon pools. These changes have resulted in a decrease in soil microbial activity, severe reduction in soil fertility and transformation of soil nutrients, thereby causing soil nutrient imbalance, which seriously affects crop production. In this study, 16S rDNA-based analysis and static chamber-gas chromatography were used to elucidate the effects of continuous application of straw biochar on soil carbon pools and the soil microbial environments of two typical soil types (purple and paddy soils) in southern China. Application of biochar (1) improved the soil carbon pool and its activity, (2) significantly promoted the release of soil CO2 and (3) improved the soil carbon environment. Soil carbon content was closely correlated with the abundance of organisms belonging to two orders, Lactobacillales and Bacteroidales, and, more specifically, to the genus Lactococcus. These results suggest that biochar affects the soil carbon environment and soil microorganism abundance, which in turn may improve the soil carbon pool.

First Evidence of Altererythrobacter sp. LY02 with Indirect Algicidal Activity on the Toxic Dinoflagellate, Alexandrium tamarense.

Alexandrium tamarense is a toxic harmful algal blooms (HABs) causing species, which poses great threat to human health and marine economy. In this study, we isolated an algicidal bacterium Altererythrobacter sp. LY02 towards to A. tamarense and later investigated the algicidal activity, algicidal mode, characteristics of algicidal active substance and algicidal procedure. The results indicated that the cell-free filtrate of strain LY02 showed high algicidal effect on algal growth, however, bacterial cells almost lost algicidal activity. The algicidal active substance was temperature- and pH-stability, and its molecular weight was less than 1000 Da, and was a non-proteinaceous material or non-polysaccharide, mid-polar substance. Under the algicidal effect of active substance, the morphology and structure of A. tamarense cells were seriously damaged as well as organelles. Our study confirmed that the algicidal active substance could be used as an excellent bio-agent for controlling HABs caused by A. tamarense.

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.

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.

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.

Towards molecular, physiological, and biochemical understanding of photosynthetic inhibition and oxidative stress in the toxic Alexandrium tamarense induced by a marine bacterium.

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.

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)).