Effect of inclusion of blue-green algae meal on growth and accumulation of microcystins in gibel carp (Carassius auratus gibelio)

Six isonitrogenous (crude protein content: 38%) and isoenergetic (gross energy content: 17 kJ g(-1)) diets were formulated to investigate the effects of inclusion of blue-green algae meal on gibel carp (Carassius auratus gibelio). In each diet, 15% of the protein was supplied by fishmeal; the remainder was supplied by soybean meal and blue-green algae meal. Diet 1 was used as control with no blue-green algae meal whereas the content in diets 2-6 was 15.15, 29.79, 44.69, 59.58 and 74.48%, respectively. Each diet was fed to five groups of gibel carp for 12 weeks in a flow-through system. Final body weight and specific growth rate (SGR) of fish fed diet 5 were significantly lower than the control diet (P < 0.05). Mortality of gibel carp increased with increase in algae meal inclusion (P < 0.05), but there was no significant difference between fish fed diets 3-6 (P > 0.05). Feed conversion efficiency (FCE) decreased with the increase in algae meal inclusion (P < 0.05). Fish-fed diet 6 showed the highest feeding rate (P < 0.05), while there were no significant differences among the other groups (P > 0.05). Apparent digestibility coefficient of dry matter, protein, and energy decreased with increasing algae meal inclusion in the diets (P < 0.05). Aspartate aminotransferase (GOT) activity in the liver was not significantly different among groups (P > 0.05). Liver alanine aminotransferase (GPT) activity of fish-fed diets 4, 5 and 6 was significantly lower than the control diet (diet 1; P < 0.05). Microcystins in the muscle, liver, gallbladder, and spleen increased with increasing algae inclusion (P < 0.05).

Investigation on intake, accumulation and toxicity of microcystins to silver carp

Daily intake and accumulation of microcystins (MCYSTs, MCs) in silver carp (Hypophthalmichthys molitrix) were investigated under lab conditions by feeding the fish exclusively with fresh toxic Microcystis bloom at a density of 6 x 10(9) algal cells L-1. The medial lethal dose (LD50) of microcystin-LR to silver carp was estimated to be 270 mu g kg(-1) body-weight, underlining its strong resistance to toxic Microcystis bloom. It can survive after being ingested with high doses of microcystins (about 10 mg kg(-1)) during the 28-days feeding experiment. Enzyme-linked immuno-sorbent assay results show that microcystin concentrations in muscle and liver are 1.57 +/- 0.31 mu g kg(-1) and 4.28 +/- 1.64 mg kg(-1) fresh weight. The former is much lower than the World Health Organization limit recommended for human consumption. These results suggest that silver carps can be widely used in cyanobacterial bloom control, and consumption of fish muscles is safe for human beings.

The algae-lytic ability of bacterium DC10 and the influence of environmental factors on the ability

A lysing-bacterium DC10, isolated from Dianchi Lake of Yunnan Province, was characterized to be Pseudomonas sp. It was able to lyse some algae well, such as Microcystis viridis, Selenastrum capricomutum, and so on. In this study, it was shown that the bacterium lysed the algae by releasing a substance; the best lytic effects were achieved at low temperatures and in the dark. Different concentrations of CaCl2 and NaNO3 influenced the lytic effects; the ability to lyse algae decreased in the following order: pH 4 > pH 9 > pH 7 > pH 5.5. It was significant to develop a special technology with this kind of bacterium for controlling the bloom-forming planktonic microalgae.

Physiological and biochemical microcystin-RR toxicity to the Synechococcus elongatus

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 mug (.) L-1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F-v/F-m) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. (C) 2004 Wiley Periodicals, Inc.

Dynamics of microcystins-LR and -RR in the phytoplanktivorous silver carp in a sub-chronic toxicity experiment

A sub-chronic toxicity experiment was conducted to examine tissue distribution and depuration of two microcystins (microcystin-LR and microcystin -RR) in the phytoplanktivorous filter-feeding silver carp during a course of 80 days. Two large tanks (A, B) were used, and in Tank A, the fish were fed naturally with fresh Microcystis viridis cells (collected from a eutrophic pond) throughout the experiment, while in Tank B, the food of the fish were M. viridis cells for the first 40 days and then changed to artificial carp feed. High Performance Liquid Chromatography (HPLC) was used to measure MC-LR and MC-RR in the M. viridis cells, the seston, and the intestine, blood, liver and muscle tissue of silver carp at an interval of 20 days. MC-RR and MC-LR in the collected Microcystis cells varied between 268-580 and 110-292 mug g(-1) DW, respectively. In Tank A, MC-RR and MC-LR varied between 41.5-99.5 and 6.9-15.8 mug g(-1) DW in the seston, respectively. The maximum MC-RR in the blood, liver and muscle of the fish was 49.7, 17.8 and 1.77 mug g(-1) DW, respectively. No MC-LR was detectable in the muscle and blood samples of the silver carp in spite of the abundant presence of this toxin in the intestines (for the liver, there was only one case when a relatively minor quantity was detected). These findings contrast with previous experimental results on rainbow trout. Perhaps silver carp has a mechanism to degrade MC-LR actively and to inhibit MC-LR transportation across the intestines. The depuration of MC-RR concentrations occurred slowly than uptakes in blood, liver and muscle, and the depuration rate was in the order of blood > liver > muscle. The grazing ability of silver carp on toxic cyanobacteria suggests an applicability of using phytoplanktivorous fish to counteract cyanotoxin contamination in eutrophic waters. (C) 2003 Elsevier Ltd. All rights reserved.

Bioaccumulation of polychlorinated dibenzo-p-dioxins and dibenzofurans in the foodweb of Ya-Er Lake area, China

Bioaccumulation of PCDD/F in the foodweb was investigated in the Ya-Er Lake area, which was heavily polluted by PCDD/F. The high concentrations of PCDD/F in sediment can be transferred and bioaccumulated by aquatic organisms and humans through various pathways. Benthonic invertebrate animals and aquatic plants with a lot of fibers in the root can accumulate PCDD/F from sediment and water. Snail (Bellamya aeruginosa), shrimp (Macrobranchium sp.) and freshwater mussel (Acuticosta chinensis (Lea)) took up PCDD/F from the water and maintained the emission patterns, whereas fish tended to selectively accumulate 2,3,7,8-substituted isomers. The tissues of fish-eating bird and duck (Anas platyrhynchos) were very highly contaminated by PCDD/F due to ingestion of fish and other aquatic organisms from sediment. The residual concentration in breast milk depended on the original concentration of PCDD/F in the food. A resident in Ya-Er Lake area showed a daily intake of PCDD/ F of about 9.14 pg TEQ/kg body weight/day. This is higher than the tolerable daily intake (TDI) for PCDD/F (1 pg TEQ/kg body weight/day), which was recommended by the World Health Organization (WHO). (C) 2001 Elsevier Science Ltd. All rights reserved.

Establishment and characterization of dual-species biofilms formed between a 3,5-dinitrobenzoic-degrading strain and bacteria with high biofilm-forming capabilities

In this study, the possibility of establishing a dual-species biofilm from a bacterium with a high biofilm-forming capability and a 3,5-dinitrobenzoic acid (3,5-DNBA)-degrading bacterium, Comamonas testosteroni A3, was investigated. Our results showed that the combinations of strain A3 with each of five strains with a high biofilm-forming capability (Pseudomonas sp. M8, Pseudomonas putida M9, Bacillus cereus M19, Pseudomonas plecoglossicida M21 and Aeromonas hydrophila M22) presented different levels of enhancement regarding biofilm-forming capability. Among these culture combinations, the 24-h dual-species biofilms established by C. testosteroni A3 with P. putida M9 and A. hydrophila M22 showed the strongest resistance to 3,5-DNBA shock loading, as demonstrated by six successive replacements with DMM2 synthetic wastewater. The degradation rates of 3,5-DNBA by these two culture combinations reached 63.3-91.6% and 70.7-89.4%, respectively, within 6 h of every replacement. Using the gfp-tagged strain M22 and confocal laser scanning microscopy, the immobilization of A3 cells in the dual-species biofilm was confirmed. We thus demonstrated that, during wastewater treatment processes, it is possible to immobilize degrader bacteria with bacteria with a high biofilm-forming capability and to enable them to develop into the mixed microbial flora. This may be a simple and economical method that represents a novel strategy for effective bioaugmentation.

污灌和农药对农田土壤假单胞菌种群的影响

随着环境污染问题的日益严重，微生物修复起到越来越重要的作用。假单胞菌是土壤微生物中最重要、研究最多的细菌之一，能降解简单和复杂的有机物，它们因此而广泛的存在于土壤和水体。但有关于石油、重金属及农药污染物对农田土壤假单胞菌多样性及种群结构的影响却缺乏全面和系统的认识。 本论文首次采用传统微生物培养方法与PCR-DGGE等现代微生物分子生态学研究方法相结合的手段，系统评价了长期含石油和重金属污水灌溉对中国最大的石油、重金属污灌区——沈抚、张士灌区农田土壤中的假单胞菌多样性及其种群结构的影响。同时，本论文也研究了乙草胺、甲胺磷对黑土假单胞菌多样性及种群结构的影响。得出以下结果： 石油污灌区土壤中总的假单胞菌多样性显著高于重金属污灌区；石油污灌区旱田土壤假单胞菌多样性接近于对照清洁土壤,同时低于相似污染程度的石油污灌区水田土壤。进一步测序发现，Pseudomonas mendocina、Pseudomonas stutzeri、Pseudomonas aeruginosa是所分析石油和重金属污灌区土壤中的优势类群，说明在长期污染胁迫下这3种假单胞菌分别得到了不同程度的富集。DGGE 结果显示石油和重金属污染土壤样品的可培养假单胞菌多样性没有显著差异，但均低于对照清洁土壤样品。对各个土壤样品可培养假单胞菌菌株进行REP-PCR基因分型，结果表明这些假单胞菌之间有显著的遗传差异。进一步测序表明，土壤样品中可培养假单胞菌优势类群中含有Pseudomonas. fluorescens 和Pseudomonas. Putida两种。 黑土农田土壤中使用乙草胺会严重降低总的及可培养假单胞菌群落的多样性，而且在5周内不能恢复。而甲胺磷处理土壤与对照相比则差异不显著，并且经过一段时间的适应，土壤中的总的及可培养假单胞菌种群不仅得到恢复而且超过对照。对各处理土壤总的及可培养假单胞菌DGGE谱带类型聚类分析，发现乙草胺、甲胺磷处理土壤样品均各自聚为一簇，说明农药污染类型是影响土壤中假单胞菌种群结构的重要因素。

一株嗜杂醇油细菌的分离、鉴定和特性研究

为结合一般白酒存在的杂醇油含量偏高或超标问题，作者试图寻找能嗜高醇类(含杂醇油)的有效菌株加以开发利用。本文研究了一株从富集分离、定向诱导得到的嗜异戊醇的W-2菌，该菌能以异戊醇或其它某些多碳醇作为唯一的碳源和能源进行生长。该菌在PH8.5的环境条件下，异戊醇的利用率可高达84.4%。此外，该菌还能广泛利用糖类、醇、有机酸、酯、盐等有机物作为唯一的碳源和能源。一般不利用—碳化合物。该菌具单极生鞭毛，呈杆状，适宜生长温度范围4℃—43℃。最适生长温度36℃，在PH4.0—11.0均能生长，最适生长PH为8.5—9.0，在培养基产生蓝绿色色素。W-2菌经形态，生理生化鉴定为假单胞菌属中的铜绿假单胞菌的一个变种。初步定名为Pseudomonas aeruginosa W-2。本文最后讨论了该菌的开发应用前景。

Biosorption of uranium by chemically modified Rhodotorula glutinis

The present paper reports the biosorption of uranium onto chemically modified yeast cells, Rhodotorula glutinis, in order to study the role played by various functional groups in the cell wall. Esterification of the carboxyl groups and methylation of the amino groups present in the cells were carried out by methanol and formaldehyde treatment, respectively. The uranium sorption capacity increased 31% for the methanol-treated biomass and 11% for the formaldehyde-treated biomass at an initial uranium concentration of 140 mg/L The enhancement of uranium sorption capacity was investigated by Fourier transform infrared (FTIR) spectroscopy analysis, with amino and carboxyl groups were determined to be the important functional groups involved in uranium binding. The biosorption isotherms of uranium onto the raw and chemically modified biomass were also investigated with varying uranium concentrations. Langmuir and Freundlich models were well able to explain the sorption equilibrium data with satisfactory correlation coefficients higher than 0.9. (C) 2010 Elsevier Ltd. All rights reserved.

Investigation of EscA as a chaperone for the Edwardsiella tarda type III secretion system putative translocon component EseC

Edwardsiella tarda is an important Gram-negative enteric pathogen affecting both animals and humans. It possesses a type III secretion system (T3SS) essential for pathogenesis. EseB, EseC and EseD have been shown to form a translocon complex after secretion, while EscC functions as a T3SS chaperone for EseB and EseD. In this paper we identify EscA, a protein required for accumulation and proper secretion of another translocon component, EseC. The escA gene is located upstream of eseC and the EscA protein has the characteristics of T3SS chaperones. Cell fractionation experiments indicated that EscA is located in the cytoplasm and on the cytoplasmic membrane. Mutation with in-frame deletion of escA greatly decreased the secretion of EseC, while complementation of escA restored the wild-type secretion phenotype. The stabilization and accumulation of EseC in the cytoplasm were also affected in the absence of EscA. Mutation of escA did not affect the transcription of eseC but reduced the accumulation level of EseC as measured by using an EseC-LacZ fusion protein in Ed. tarda. Co-purification and co-immunoprecipitation studies demonstrated a specific interaction between EscA and EseC. Further analysis showed that residues 31-137 of EseC are required for EseC-EscA interaction, Mutation of EseC residues 31-137 reduced the secretion and accumulation of EseC in Ed. tarda. Finally, infection experiments showed that mutations of EscA and residues 31-137 of EseC increased the LD50 by approximately 10-fold in blue gourami fish. These results indicated that EscA functions as a specific chaperone for EseC and contributes to the virulence of Ed. tarda.

Attenuation of Edwardsiella tarda Virulence by Small Peptides That Interfere with LuxS/Autoinducer Type 2 Quorum Sensing

Edwardsiella tarda is a gram-negative pathogen with a broad host range that includes humans, animals, and fish. Recent studies have shown that the LuxS/autoinducer type 2 (AI-2) quorum sensing system is involved in the virulence of E. tarda. In the present study, it was found that the E. tarda LuxS mutants bearing deletions of the catalytic site (C site) and the tyrosine kinase phosphorylation site, respectively, are functionally inactive and that these dysfunctional mutants can interfere with the activity of the wild-type LuxS. Two small peptides, 5411 and 5906, which share sequence identities with the C site of LuxS, were identified. 5411 and 5906 proved to be inhibitors of AI-2 activity and could vitiate the infectivity of the pathogenic E. tarda strain TX1. The inhibitory effect of 5411 and 5906 on AI-2 activity is exerted on LuxS, with which these peptides specifically interact. The expression of 5411 and 5906 in TX1 has multiple effects (altering biofilm production and the expression of certain virulence-associated genes), which are similar to those caused by interruption of luxS expression. Further study found that it is very likely that 5411 and 5906 can be released from the strains expressing them and, should TX1 be in the vicinity, captured by TX1. Based on this observation, a constitutive 5411 producer (Pseudomonas sp. strain FP3/pT5411) was constructed in the form of a fish commensal isolate that expresses 5411 from a plasmid source. The presence of FP3/pT5411 in fish attenuates the virulence of TX1. Finally, it was demonstrated that fish expressing 5411 directly from tissues exhibit enhanced resistance against TX1 infection.

Attenuation of Edwardsiella tarda Virulence by Small Peptides That Interfere with LuxS/Autoinducer Type 2 Quorum Sensing

Edwardsiella tarda is a gram-negative pathogen with a broad host range that includes humans, animals, and fish. Recent studies have shown that the LuxS/autoinducer type 2 (AI-2) quorum sensing system is involved in the virulence of E. tarda. In the present study, it was found that the E. tarda LuxS mutants bearing deletions of the catalytic site (C site) and the tyrosine kinase phosphorylation site, respectively, are functionally inactive and that these dysfunctional mutants can interfere with the activity of the wild-type LuxS. Two small peptides, 5411 and 5906, which share sequence identities with the C site of LuxS, were identified. 5411 and 5906 proved to be inhibitors of AI-2 activity and could vitiate the infectivity of the pathogenic E. tarda strain TX1. The inhibitory effect of 5411 and 5906 on AI-2 activity is exerted on LuxS, with which these peptides specifically interact. The expression of 5411 and 5906 in TX1 has multiple effects (altering biofilm production and the expression of certain virulence-associated genes), which are similar to those caused by interruption of luxS expression. Further study found that it is very likely that 5411 and 5906 can be released from the strains expressing them and, should TX1 be in the vicinity, captured by TX1. Based on this observation, a constitutive 5411 producer (Pseudomonas sp. strain FP3/pT5411) was constructed in the form of a fish commensal isolate that expresses 5411 from a plasmid source. The presence of FP3/pT5411 in fish attenuates the virulence of TX1. Finally, it was demonstrated that fish expressing 5411 directly from tissues exhibit enhanced resistance against TX1 infection.

Intra-habitat heterogeneity of microbial food web structure under the regime of eutrophication and sediment resuspension in the large subtropical shallow Lake Taihu, China

Planktonic microbial community structure and classical food web were investigated in the large shallow eutrophic Lake Taihu (2338 km(2), mean depth 1.9 m) located in subtropical Southeast China. The water column of the lake was sampled biweekly at two sites located 22 km apart over a period of twelve month. Site 1 is under the regime of heavy eutrophication while Site 2 is governed by wind-driven sediment resuspension. Within-lake comparison indicates that phosphorus enrichment resulted in increased abundance of microbial components. However, the coupling between total phosphorus and abundance of microbial components was different between the two sites. Much stronger coupling was observed at Site 1 than at Site 2. The weak coupling at Site 2 was mainly caused by strong sediment resuspension, which limited growth of phytoplankton and, consequently, growth of bacterioplankton and other microbial components. High percentages of attached bacteria, which were strongly correlated with the biomass of phytoplankton, especially Microcystis spp., were found at Site 1 during summer and early autumn, but no such correlation was observed at Site 2. This potentially leads to differences in carbon flow through microbial food web at different locations. Overall, significant heterogeneity of microbial food web structure between the two sites was observed. Site-specific differences in nutrient enrichment (i.e. nitrogen and phosphorus) and sediment resuspension were identified as driving forces of the observed intra-habitat differences in food web structure.