磁场对螺旋藻营养成分的影响及机理分析

对磁场作用下钝顶螺旋藻中蛋白质、氨基酸以及矿物质含量的变化进行研究,同时从水溶液性质改变和离子结合的角度对电磁场效应的机理进行了分析,研究发现：B＝0．25T的电磁场处理虽然对蛋白质和氨基酸总含量影响不大,却使必需氨基酸总含量明显提高;此外还可显著增加螺旋藻中矿物质,尤其是微量元素的含量。电磁场的生物效应可能来源于磁化水性质和离子吸收过程的改变,磁处理培养是进一步提高螺旋藻营养价值的一种较有效手段。     

Bioeffects of selenite on the growth of Spirulina platensis and its biotransformation

The bioeffects of selenium on the growth of Spirulina platensis and the selenium distribution were investigated. S. platensis was batch cultured in Zarrouk medium containing increasing concentrations of sodium selenite. The biotransformation characteristic of selenium was analysed by the determination of the detailed selenium distribution forms. At 35 degrees C, 315.2 microEm(-2) x s(-1), sodium selenite concentrations below 400 mg x l(-1) were found to stimulate algal growth, especially in the range of 0.5-40 mg x l(-1). However, above 500 mg x l(-1) sodium selenite was toxic to this alga with the toxicity being related to the sulfite level in the medium. S. platensis was found to resist higher selenite by reducing toxic Se(IV) to nonsoluble Se(0). Selenium was accumulated efficiently in S. platensis during cultivation with accumulated selenium increasing with selenite concentration in the medium. It was demonstrated that inorganic selenite could be transformed into organic forms through binding with protein, lipids and polysaccharides and other cell components. The organic selenium accounted for 85.1% of the total accumulated selenium and was comprised of 25.2% water-soluble protein-bound, 10.6% lipids-bound and 2.1% polysaccharides-bound selenium. Among the organic fractions lipid possessed the strongest ability to accumulate Se (6.47 mg x kg(-1)). The 14.9% inorganic selenium in S. platensis was composed of Se(IV) (13.7%) and Se(VI) (1.2%).     

Harvesting of Spirulina platensis by cellular flotation and growth stage determination

AIM: To investigate an effective harvesting method for Spirulina platensis. METHODS AND RESULTS: Eighty per cent of S. platensis cells in the logarithmic growth phase were harvested by flotation when the cells were set in a static condition for 2 h. The optimum harvesting time was about day 6 of cultivation. The flotation activity of S. platensis cells was enhanced by the addition of NaCl. CONCLUSIONS: The harvesting of S. platensis by flotation is a cost-effective and straightforward method that can retain the algal quality. The optimum harvesting time of S. platensis can be predicted by the cellular protein to carbon ratio. SIGNIFICANCE AND IMPACT OF THE STUDY: Flotation harvesting is also applicable to other cyanobacteria with gas vesicles.     

钝顶螺旋藻生物富集Cr(Ⅲ)影响因素的研究

对钝顶螺旋藻生物富集Cr(Ⅲ)的影响因素进行了研究。发现螺旋藻对Cr(Ⅲ)的生物富集主要经历了快速的吸附和缓慢的吸收两个步骤;化学键较弱的Cr(Ⅲ)化合物具有较高的富集效率;藻细胞浓度一定时,随着Cr(Ⅲ)浓度的增加,单位重量螺旋藻对Cr(Ⅲ)的富集量不断增加,最后趋于饱和;当Cr(Ⅲ)浓度一定时,随着藻细胞浓度的增加,螺旋藻对Cr(Ⅲ)的总富集量逐渐增加而单位重量藻体的富集量减少。研究还证实,螺旋藻干粉比新鲜藻能富集更多的Cr(Ⅲ);pH值是影响Cr(Ⅲ)生物富集的一个重要影响因素,最佳pH在7左右;温度升高和加强光强均可加强Cr(Ⅲ)的富集;阳离子对Cr(Ⅲ)的富集存在一定的促进或抑制作用。     

Effects of dissolved organic matter and ultraviolet radiation on the accrual, stoichiometry and algal taxonomy of stream periphyton

1. We investigated the effects of dissolved organic matter (DOM) and ultraviolet‐B (UVB) radiation on periphyton during a 30‐day experiment in grazer‐free, outdoor artificial streams. We established high [10–12 mg carbon (C) L⁻¹] and low (3–5 mg C L⁻¹) concentrations of DOM in artificial streams exposed to or shielded from ambient UVB radiation. Periphyton was sampled weekly for ash‐free dry mass (AFDM), chlorophyll (chl) a , algal biovolume, elemental composition [C, nitrogen (N) and phosphorus (P)], and algal taxonomic composition. 2. Regardless of the UVB environment, increased DOM concentration caused greater periphyton AFDM, chl a and total C content during the experiment. Increased DOM also significantly increased periphyton C : P and N : P (but not C : N) ratios throughout the experiment. Algal taxonomic composition was strongly affected by elevated stream DOM concentrations; some algal taxa increased and some decreased in biomass and prevalence in artificial streams receiving DOM additions. UVB removal, on the other hand, did not strongly affect periphyton biomass, elemental composition or algal taxonomic composition for most of the experiment. 3. Our results show strong effects of DOM concentration but few, if any, effects of UVB radiation on periphyton biomass, elemental composition and algal taxonomic composition. The effects of DOM may have resulted from its absorption of UVA radiation, or more likely, its provision of organic C and nutrients to microbial communities. The strong effects of DOM on periphyton biomass and elemental composition indicate that they potentially play a key role in food web dynamics and ecosystem processes in forested streams.     

Simultaneous cultivation of Spirulina platensis and the toxigenic cyanobacteria Microcystis aeruginosa

Mangueira Lagoon, located in the extreme south of Brazil, has water with physicochemical characteristics such as alkaline pH and carbonate levels propitious for the growth of the cyanobacterium Spirulina platensis. Previously published studies have shown that Mangueira Lagoon water supplemented with small quantities of carbon and nitrogen is suitable for S. platensis cultivation and can significantly reduce production costs. We studied mixed cultures of Spirulina platensis and the toxic cyanobacterium Microcystis aeruginosa using a 2(3) factorial design in which the three factors were the initial biomass concentration of S. platensis and M. aeruginosa and the type of culture medium (100% Zarrouk's medium or 80% Mangueira Lagoon water plus 20% Zarrouk's medium). The highest S. platensis maximum specific growth rate (mu(max)) occurred in the culture with the highest M. aeruginosa biomass concentration and when undiluted culture medium was used (micro(max) = 0.283 d(-1)). The highest M. aeruginosa specific death rate (k) was obtained in the presence of S. platensis (k = 0.555 d(-1)) and was independent of the initial M. aeruginosa biomass concentration and culture medium, demonstrating that S. platensis cultures are not susceptible to contamination by M. aeruginosa. The culture medium had no significant influence (p > 0.05) on S. platensis micro(max) values, indicating that production costs could be reduced by using a medium consisting of 80% Mangueira Lagoon water plus 20% Zarrouk's medium.     

Accumulation of selenium in mixotrophic culture of Spirulina platensis on glucose

Accumulation of Se in mixotrophic culture of Spirulina platensis was investigated in this study. Results indicated that glucose was better than acetate as an organic carbon source for mixotrophic culture of S. platensis. Supplementation of glucose (2 gL(-1)) significantly enhanced the biomass concentration (2.57 gL(-1)) and the production of phycocyanin (0.279 gL(-1)) and allophycocyanin (0.126 gL(-1)) in S. platensis, which were much higher than those of photoautotrophic culture (1.08 gL(-1), 0.119 gL(-1) and 0.042 gL(-1), respectively). Stepwise addition of Se during the growth phase avoided the inhibitory effect of high Se concentration on the growth of S. platensis. The Se enrichment favored the production of phycocyanin and allophycocyanin in the algal cells. The highest Se yield (1033 microgL(-1)) was obtained at an accumulative Se concentration of 250 mgL(-1), with organic Se percentage, biomass concentration, phycocyanin and allophycocyanin yields of 92.3%, 2.55 gL(-1), 0.295 gL(-1) and 0.153 gL(-1), respectively. These results indicated that the application of mixotrophic culture S. platensis with stepwise addition of Se to the medium could offer an effective and economical way for the production of high Se-enriched algal products.     

Effects of light and nutrients on the net accumulation and elemental composition of epilithon in boreal lakes

1. Two experiments in the Experimental Lakes Area (ELA) in north-western Ontario, Canada examined the effects of light and two key elements on the net accumulation and elemental composition of epilithon. In Lake (L) 224, benthic algae were grown under different light intensity and phosphorus supply, while in L302S we provided three levels of two different carbon sources (bicarbonate and glucose) to algae colonizing nutrient-diffusing substrata. After 1 month of accumulation, we sampled biofilms for chlorophyll (chl), carbon (C), phosphorus (P) and algal C.
2. Increased C supply did not significantly affect algal growth (C or chl) or elemental composition (C/P ratios) in L302S. However, P enrichment increased chl and algal C, dramatically reduced the C/P ratio of epilithon, and did not affect total organic C in L224. Phosphorus enrichment also increased the proportion of algal material in the total particulate organic matter and altered the taxonomic composition of algae in L224 biofilms. Shading had no significant effect on the C/P ratio and total organic C in epilithon from the L224 experiment.
3. Our results demonstrate that P supply affects the elemental composition of organic matter that collects on rock substrata. It thus appears that low availability of P relative to C and light drives the formation and retention of high C/P organic matter on rock surfaces in oligotrophic boreal lakes.     

Effects of increased atmospheric CO2 and N supply on photosynthesis, growth and cell composition of the cyanobacterium Spirulina platensis (Arthrospira)

The consequences of the addition of CO2 (1%) in cultures of S. platensis are examined in terms of biomass yield, cell composition and external medium composition. CO2 enrichment was tested under nitrogen saturating and nitrogen limiting conditions. Increasing CO2 levels did not cause any change in maximum growth rate while it decreased maximum biomass yield. Protein and pigments were decreased and carbohydrate increased by high CO2, but the capability to store carbohydrates was saturated. C:N ratio remained unchanged while organic carbon released to the external medium was enhanced, suggesting that organic carbon release in S. platensis is an efficient mechanism for the maintenance of the metabolic integrity, balancing the cell C:N ratio in response to environmental CO2 changes. CO2 affected the pigment content: Phycocyanin, chlorophyll and carotenoids were reduced in around 50%, but the photosynthetic parameters were slightly changed. We propose that in S. platensis CO2 could act promoting degradation of pigments synthetised in excess in normal CO2 conditions, that are not necessary for light harvesting. Nitrogen assimilation was significantly not affected by CO2, and it is proposed that the inability to stimulate N assimilation by CO2 enrichment determined the lack of response in maximum growth rate. This revised version was published online in June 2006 with corrections to the Cover Date.     

Production of biomass and nutraceutical compounds by Spirulina platensis under different temperature and nitrogen regimes

The cyanobacterium Spirulina platensis has been used by humans because of its nutritional and possibly medicinal effects. Our study evaluated the influence of temperature and nitrogen concentration in the medium on the production of biomass by this cyanobacterium and the biomass composition in protein, lipid and phenolic compounds. We found that at 35 degrees C there was a negative effect on biomass production but a positive effect on the production of protein, lipids and phenolics, the highest levels of these compounds being obtained in Zarrouk's medium containing 1.875 or 2.500 g l(-1) sodium nitrate. Higher biomass densities and productivity were obtained at 30 degrees C than at 35 degrees C, but nitrogen concentration appeared to have no effect on the amount of protein, lipid or phenolics, indicating that at 30 degrees C the concentration of sodium nitrate in Zarrouk's medium (2.50 g l(-1)) can be reduced without loss of productivity, an important cost-saving factor in large-scale cultivation.     

Dynamics of C,N, P and S in grassland soils: a model

We have developed a model to simulate the dynamics of C, N, P, and S in cultivated and uncultivated grassland soils. The model uses a monthly time step and can simulate the dynamics of soil organic matter over long time periods (100 to 10,000 years). It was used to simulate the impact of cultivation (100 years) on soil organic matter dynamics, nutrient mineralization, and plant production and to simulate soil formation during a 10,000 year run. The model was validated by comparing the simulated impact of cultivation on soil organic matter C, N, P, and S dynamics with observed data from sites in the northern Great Plains. The model correctly predicted that N and P are the primary limiting nutrients for plant production and simulated the response of the system to inorganic N, P, and S fertilizer. Simulation results indicate that controlling the C:P and C:S ratios of soil organic matter fractions as functions of the labile P and S levels respectively, allows the model to correctly simulate the observed changes in C:P and C:S ratios in the soil and to simulate the impact of varying the labile P and S levels on soil P and S net mineralization rates.     

Inhibitory effects of microalgae on the activation of hyaluronidase

The inhibitory effects of seven microalgae, Nostoc flagelliforme, Spirulina platensis, Porphyridium purpureum, Rhodosorus marinus,Chlorella pyrenoidosa, Dunaliella salina and Pleurochrysiscarterae on the activation of hyaluronidase were evaluated. Theinhibitory effect of the ethanol-insoluble fraction of each water extract frommicroalgae was stronger than that of the ethanol-soluble fraction. The50% inhibitory concentration (IC₅₀) of the ethanol-insolublefraction of S. platensis, P. purpureum, R. marinus, C.pyrenoidosa, D. salina and P. carterae was 0.15, 0.18, 0.26,0.94, 0.15 and 0.41 mg mL^-1, respectively. The IC₅₀ ofN .flagelliforme was not calculated, because there was no detectableinhibitory effect of this alga. The IC₅₀ of disodium cromoglycate(DSCG) used as the anti-allergic medicine was 0.14 mg mL^-1. The IC₅₀ of S. platensis, P. purpureum and D. salinawere almost the same as that of DSCG. This suggests that theethanol-insoluble fraction of S. platensis, P. purpureum and D. salina might be an anti-allergic substance. The ethanol-insoluble fractionof S. platensis and D. salina was ultrafiltered through a membranehaving a molecular exclusion limit of 20 kDa. The IC₅₀ of theresidue was stronger than that of the filtrate. These results suggest that theanti-allergic substance(s) of these microalgae may be polysaccharides.     

Kinetic and growth parameters of Arthrospira (Spirulina) platensis cultivated in tubular photobioreactor under different cell circulation systems

Arthrospira platensis was cultivated in tubular photobioreactor in order to evaluate growth and biomass production at variable photosynthetic photon flux density (PPFD = 60, 120, and 240 μmol photons m(-2)s(-1)) and employing three different systems for cell circulation, specifically an airlift, a motor-driven pumping and a pressurized system. The influence of these two independents variables on the maximum cell concentration (X(m)), cell productivity (P(x)), nitrogen-to-cell conversion factor (Y(X/N) ), photosynthetic efficiency (PE), and biomass composition (total lipids and proteins), taken as responses, was evaluated by analysis of variance. The statistical analysis revealed that the best combination of responses' mean values (X(m) = 4,055 mg L(-1), P(x) = 406 mg L(-1)day(-1), Y(X/N) = 5.07 mg mg(-1), total lipids = 8.94%, total proteins = 30.3%, PE = 2.04%) was obtained at PPFD = 120 μmol photons m(-2)s(-1); therefore, this light intensity should be considered as the most well-suited for A. platensis cultivation in this photobioreactor configuration. The airlift system did not exert any significant positive statistical influence on the responses, which suggests that this traditional cell circulation system could successfully be substituted by the others tested in this work.     

Kinetic and equilibrium modeling of chromium (VI) biosorption on fresh and spent Spirulina platensis/Chlorella vulgaris biomass

Biosorption of chromium (VI) was studied using both fresh and spent algal biomass of Spirulina platensis and Chlorella vulgaris. Both showed comparable behavior suggesting that biosorption is primarily a surface phenomenon. Biosorption rate was very fast during the first five minutes, in which almost 50% of the chromium (VI) was adsorbed. Two step kinetic model was proposed for biosorption. Equilibrium data obeyed Freundlich and Langmuir adsorption isotherms. Fresh algal biomass of S. platensis gave maximum of 73.6% biosorption of chromium (VI) in 100 ppm solution at 1 g l(-1) cell loading. For improved economics, beta-carotene was extracted from S. platensis and the spent biomass was used for chromium (VI) biosorption. The maximum biosorption by spent biomass was increased to 86.2%. Thus, this two step process not only showed improved efficiency in biosorption ( approximately 17% increase) but also gave valuable byproduct, namely beta-carotene.     

Effect of nutrient loading and retention time on performance of high rate algal ponds

Small pilot ponds in a glasshouse at the Scottish Agricultural College (Auchincruive) were used to investigate the effects of changing C:N:P loading rate and retention time on pond performance as measured by nutrient removal and dry matter biomass. One experiment investigated ponds operated at two C:N:P ratios: low (9:7:1) and high (104:10:1) and two retention times (4 and 7 days θ. Increasing retention time from 4 to 7 days increased the concentration of total (dry matter) and algal (chlorophyll a) biomass and the degree of nitrification. It also increased removal of phosphorus, but had no effect on nitrogen or COD removal. Cyanobacteria predominated in ponds operated at both 4 and 7 days, and the density of cyanobacteria increased with increased retention time. Nitrogen removal was independent of C:N:P ratio; indeed the lower C:N:P ratio favoured increased nitrification. A high C:N:P ratio increased phosphorus and COD removal and increased the concentration of algal biomass (chlorophyll a), but had little effect on total biomass (dry matter). A second experiment varied COD loading rate (600, 350 and 100 kg COD ha-¹ d-¹) while maintaining a constant retention time (either 5 or 7 days θ). Species composition was independent of retention time. The longer retention time increased both total and algal biomass concentration and also percentage of nitrogen removed. Nitrification was independent of retention time. Increasing loading rate increased dry matter production and resulted in a predominance of cyanobacteria over Chlorophyceae. Increased loading rate was related to increase in nitrogen removal, however more complete nitrification occurred at low COD loading rates. Phosphorus removal in the pond with 5-day (θ) remained constant independent of loading rate, but in the pond with 7-day θ phosphorus removal increased with increased COD loading. COD removal was independent of both retention time and loading rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

模拟氮沉降和接种外生菌根真菌对马尾松(Pinus massoniana)幼苗营养元素的影响

量化植物地上部和地下部元素含量对于理解和预测植物养分平衡如何响应大气氮沉降的变化至关重要。通过盆栽试验研究了氮沉降增加背景下外生菌根真菌对马尾松幼苗营养元素的影响。对马尾松幼苗进行了接种两种外生菌根真菌：（彩色豆马勃（Pisolithus tinctorius,Pt）与厚环乳牛肝菌（Suillus grevillei,Sg））以及4种氮素浓度添加：0 kg N hm^-2a^-1（N0）、正常氮沉降30 kg N hm^-2a^-1（N30）、中度氮沉降60 kg N hm^-2a^-1（N60）、重度氮沉降90 kg N hm^-2a^-1（N90）,共12个处理,测定了马尾松地上部和地下部大量元素和微量元素的含量。结果表明：施氮改变了营养元素在马尾松幼苗地上部和地下部的含量,马尾松幼苗磷（P）、钙（Ca）、铁（Fe）、锰（Mn）等元素均在N60时达到临界值,而当输入的量超过了马尾松对氮的需求时,氮沉降会使马尾松营养元素含量较最适浓度时降低,地上部碳（C）随施氮浓度的升高先升高后降低,N随施氮浓度的升高而升高,根系和叶片钾（K）、Ca、镁（Mg）均随施氮浓度的升高而降低,施氮也降低了根系C及微量元素的含量。但在同一施氮浓度下,接种外生菌根真菌（EMF）后能够提高大多数元素的含量,N90时接种厚环乳牛肝菌（Sg）和彩色豆马勃（Pt）的叶片N含量与对照相比分别提高112.6%和138.6%,根系N含量分别提高73.1%、71.6%;N60时接种Sg和Pt的植株叶片P含量比不施氮未接种对照分别提高了166.3%、132.9%,根系P含量分别提高了40.8%、38.5%。EMF能够维持植物养分平衡,从而降低高施氮量对植物的影响效果。这为未来气候变化情景中氮沉降增加下接种EMF可以调节植物元素含量,从而达到更适应环境的元素平衡来促进生长提供理论依据。     

两步培养法测定真菌产孢营养需求

生防真菌产孢条件的测定一般都是通过连续培养方法,即在同一种限定培养基上完成其生长和产孢过程。文中我们提出分离真菌的生长和产孢阶段,测定产孢营养需求的两步培养新方法。6种生防真菌首先在平板上进行营养生长,然后转移至营养成分和浓度确定的新鲜培养基中继续产孢过程来测定菌株产孢阶段实际营养需求。通过与连续培养方法比较,发现只有淡紫拟青霉Paecilomyces lilacinus、金龟子绿僵菌Metarhizium anisopliae二者产孢条件一致,而厚孢轮枝菌Pochonia chlamydosporia、球孢白僵菌Beauveria bassiana、蜡蚧轮枝菌Lecanicillium lecanii、绿色木霉Trichoderma viride菌株产孢的营养条件存在显著的差异。基于这一方法,确定了绿色木霉最佳产孢条件,即起始碳浓度2g C/L,碳氮比10:1,最佳碳氮源组合纤维二糖和酵母浸膏,为真菌生防制剂生产调控提供了依据。     

Nutritional role of two algal symbionts in the temperate sea anemone Anthopleura elegantissima brandt

The intertidal sea anemone Anthopleura elegantissima in the Pacific Northwest may host a single type of algal symbiont or two different algal symbionts simultaneously: zooxanthellae (Symbiodinium muscatinei) and zoochlorellae (green algae; Trebouxiophyceae, Chlorophyta). A seasonal comparison of zooxanthellate and zoochlorellate anemones showed stable symbiont population densities in summer and winter, with densities of zoochlorellae about 4 times those of zooxanthellae. Photosynthesis-irradiance curves of freshly isolated symbionts show that the productivity (P(max) cell) of freshly isolated zooxanthellae was about 2.5 times that of zoochlorellae during July; comparable rates were obtained in other months. Models of algal carbon flux show that zoochlorellae may supply the host with more photosynthetic carbon per unit anemone biomass than zooxanthellae supply. Zooxanthellate anemone tissue was 2 per thousand ((13)C) and 5 per thousand ((15)N) enriched and zoochlorellate anemone tissue was 6 per thousand ((13)C) and 8 per thousand ((15)N) enriched over their respective symbionts, suggesting that zoochlorellate anemones receive less nutrition from their symbionts than do zooxanthellate individuals. The disparity between predicted contributions from the algal carbon budgets and the stable isotopic composition suggests that short-term measures of algal contributions may not reflect actual nutritional inputs to the host. Isotopic data support the hypothesis of substantial reliance on external food sources. This additional nutrition may allow both algae to persist in this temperate intertidal anemone in spite of differences in seasonal photosynthetic carbon contributions.     

Ectomycorrhizal community composition and function in a spruce forest transitioning between nitrogen and phosphorus limitation

Nitrogen is the main limiting nutrient in boreal ecosystems, but studies in southwest Sweden suggest that certain forests approach phosphorus (P) limitation driven by nitrogen (N) deposition. We added N, P or N + P to a Norway spruce forest in this region, to push the system to N or P limitation. Tree growth and needle nutrient concentrations indicated that the trees are P limited. EMF biomass was reduced only by N + P additions. Soil EMF communities responded more strongly to P than to N. Addition of apatite to ingrowth meshbags altered EMF community composition and enhanced the abundance of Imleria badia in the control and N plots, but not when P was added. The ecological significance of this species is discussed. Effects on tree growth, needle chemistry, and EMF communities indicate a dynamic interaction between EMF fungi and the nutrient status of trees and soils.     

Bacterial infection changes the elemental composition of Daphnia magna

1. An animal's elemental composition can be an important indicator of its physiological state and role in ecosystem nutrient cycling. We examined the interactive effects of bacterial (Pasteuria ramosa) infection and phosphorus (P)-poor food on the body stoichiometry of Daphnia magna. Daphnia were exposed to or held free of a bacterial parasite and fed algal food of different C:P ratios (100-500) over a 28-day period. 2. To assess the effects of exposure and infection on Daphnia stoichiometry, we measured their whole body content of carbon (C), nitrogen (N), and P on four different days (4, 8, 15, and 28) during the experiment. 3. We found strong effects of infection, food quality, and/or their interactions on the C, N, and P content of Daphnia, especially as the infectious disease progressed. At the end of the experiment, infected animals had significantly more C and less P in their bodies than uninfected conspecifics. Body N content of Daphnia consuming P-rich food was reduced by bacterial infection whereas Daphnia consuming P-poor algae showed increased body N content from infection. 4. Using a mass-balance model, we found that changes in N and P content of host bodies were largely accountable by disease-induced alterations to Daphnia reproduction (i.e. bacterial induced sterility) and the accumulation of Pasteuria spores in the body cavity. Our calculations also show that the observed increase in host C content could not be accounted for by loss of eggs or accumulation of bacterial spores. This instead must result from unidentified changes to underlying daphnid tissue C content. 5. These results demonstrate that intraspecific variation in zooplankton body stoichiometry can be caused by exposure to and infection by bacterial parasites. In addition, these effects were found to depend both upon the stage of the disease and upon the food quality consumed by the host.