Response surface methodology to optimize the nutritional parameters for enhanced production of jasmonic acid by Lasiodiplodia theobromae

Aims:  To find out the cumulative effect of the nutritional parameters and to enhance the production of jasmonic acid (JA) in static fermentation by Lasiodiplodia theobromae using response surface methodology (RSM).
Method and Results:  Malt extract, sucrose, NaNO₃ and MgSO₄.7H₂O were analysed by a 30-trial central composite design using RSM for optimizing their concentrations in the medium and the effect of their mutual interaction on JA production. Sucrose and NaNO₃ were found highly significant in influencing the JA production. Malt extract and MgSO₄.7H₂O showed an effect on the JA production in interaction with other variables. When the optimum values of the parameters obtained through RSM (19·95 g l⁻¹ malt extract, 50 g l⁻¹ sucrose, 7·5 g l⁻¹ NaNO₃ and 3·51 g l⁻¹ MgSO₄.7H₂O) were applied, 32% increase in JA production (299 mg l⁻¹) was observed in comparison with 225 mg l⁻¹ of JA produced with same media components not analysed by RSM and subsequently validated the statistical model.
Conclusions:  Increase in JA production was achieved by optimizing the nutritional parameters.
Significance and Impact of the Study:  This is the first report of using RSM for optimizing a medium for JA production. It resulted in an increase in JA production without augmentation of costly additives.     

Mg2+-free buffer elevates transformation efficiency of Vibrio parahaemolyticus by electroporation

Aims:  The ability to transform Vibrio spp. is limited by the extracellular nuclease that their cells secrete. The reported transformation efficiency of this organism is 10²–10⁵ transformants per microgram DNA. We tried different buffers and conditions, aiming to elevate its transformation efficiency.
Methods and Results:  MgCl₂ and sucrose are often included in the washing and/or electroporation buffers to stabilize the cell membrane. However, Mg²⁺ is required for production and activity of the extracellular nuclease. A simple electroporation buffer lacking Mg²⁺ was found to increase transformation efficiency dramatically, to levels 50-fold more than the buffers containing Mg²⁺. To maintain the stability of the cell membranes, Mg²⁺ was replaced with high concentrations of sucrose, from 272 to 408 mmol l⁻¹. With the new buffers, the transformation efficiency of Vibrio parahaemolyticus was increased to 2·2 × 10⁶ transformants per microgram DNA.
Conclusions:  Mg²⁺ in the buffer adversely affected transformation of V. parahaemolyticus by electroporation. The cell membranes of vibrio can be stabilized by high concentration of sucrose when Mg²⁺ is absent.
Significance and Impact of the Study:  A greater transformation efficiency can facilitate the genetic analysis of an organism and its pathogenicity. Buffers lacking Mg²⁺ can be used for other nuclease-producing organisms.     

Growth and volatile compound production by Brettanomyces/Dekkera bruxellensis in red wine

Aims:  Brettanomyces / Dekkera bruxellensis is a particularly troublesome wine spoilage yeast. This work was aimed at characterizing its behaviour in terms of growth and volatile compound production in red wine.
Methods and Results:  Sterile red wines were inoculated with 5 × 10³ viable cells ml⁻¹ of three B. bruxellensis strains and growth and volatile phenol production were followed for 1 month by means of plate counts and gas chromatography-mass spectrometry (GC-MS) respectively. Maximum population levels generally attained 10⁶–10⁷ colony forming units (CFU) ml⁻¹ and volatile phenol concentrations ranged from 500 to 4000 μg l⁻¹. Brettanomyces bruxellensis multiplication was also accompanied by the production of organic acids (from C₂ to C₁₀), short chain acid ethyl-esters and the 'mousy off-flavour' component 2-acetyl-tetrahydropyridine.
Conclusions:  Different kinds of 'Brett character' characterized by distinct metabolic and sensory profiles can arise in wine depending on the contaminating strain, wine pH and sugar content and the winemaking stage at which contamination occurs.
Significance and Impact of the Study:  We identified new chemical markers that indicate wine defects caused by B. bruxellensis. Further insight was provided into the role of some environmental conditions in promoting wine spoilage.     

Denitrification in river sediments: relationship between process rate and properties of water and sediment

1. A survey was made of denitrification and nitrous oxide (N₂O) production in river sediments at fifty sites in north‐east England during one season in order to investigate the relationship between rates and environmental factors likely to influence these processes. The sites were chosen to represent a wide range of physical and chemical conditions. Denitrification rate and N₂O production were measured within 5 h of sampling using the slurry acetylene blockage technique.
2. Denitrification rate ranged from less than 0.005–260 nmol N g^–1 DW h^–1, tending to increase in a downstream direction. N₂O production ranged from negative values (net consumption) to 13 nmol N₂O‐N g^–1 DW h^–1 and accounted for 0–115% of the N gases produced.
3. Denitrification rate and N₂O concentration in the sediment were correlated positively with nitrate concentration in the water column, water content of the sediment and percentage of fine (< 100 μm) particles in the sediment.
4. The variation in denitrification rate was satisfactorily explained (64% total variance) by a model employing measurements of water nitrate and water content of sediments. No simple or multiple relationship was found for N₂O production.     

Long-term effects of successive Ca(OH)2 and CaCO3 treatments on the water quality of two eutrophic hardwater lakes

1. Whole-lake experiments were conducted in two hardwater lakes (Halfmoon and Figure Eight) in Alberta, Canada, to investigate the effectiveness of repeated lime (slaked lime: Ca(OH)₂ and/or calcite: CaCO₃) treatments (5–78 mg L^–1) for up to 7 years.
2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic total phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments.
3. After the second lime application to Halfmoon Lake, mean winter total phosphorus release rates (TPRR) decreased to < 1 mg m^–2 day^–1 compared with 3.6 mg m^–2 day^–1 during the winter after initial treatment. In the final year of lime application, mean summer TPRR decreased to 4.5 mg m^–2 day^–1 compared with 7.6 mg m^–2 day^–1 in the pre-treatment year.
4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Figure Eight Lake during lime application. Over the first 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the last year of the study, macrophyte biomass at 2 m reached initial treatment concentrations, which coincided with the greatest water transparency. Over the treatment period, macrophyte species shifted from floating to rooted plants.
5. Multiple lime applications can improve water quality in eutrophic hardwater lakes for periods of up to 7 years.     

In situ responses to elevated CO2 in tropical forest understorey plants

1. Plants growing in deep shade and high temperature, such as in the understorey of humid tropical forests, have been predicted to be particularly sensitive to rising atmospheric CO₂. We tested this hypothesis in five species whose microhabitat quantum flux density (QFD) was documented as a covariable. After 7 (tree seedlings of Tachigalia versicolor and Beilschmiedia pendula ) and 18 months (shrubs Piper cordulatum and Psychotria limonensis, and grass Pharus latifolius ) of elevated CO₂ treatment ( c. 700 μl litre^–1) under mean QFD of less than 11 μmol m^–2 s^–1, all species produced more biomass (25–76%) under elevated CO₂.
2. Total plant biomass tended to increase with microhabitat QFD (daytime means varying from 5 to 11μmol m^–2 s^–1) but the relative stimulation by elevated CO₂ was higher at low QFD except in Pharus .
3. Non-structural carbohydrate concentrations in leaves increased significantly in Pharus (+ 27%) and Tachigalia (+ 40%).
4. The data support the hypothesis that tropical plants growing near the photosynthetic light compensation point are responsive to elevated CO₂. An improved plant carbon balance in deep shade is likely to influence understorey plant recruitment and competition as atmospheric CO₂ continues to rise.     

The effect of lubricant contamination on ThinPrep® (Cytyc) cervical cytology liquid-based preparations

Objectives:  To assess the extent of lubricant use by smear-takers and the effect of lubricant contamination of ThinPrep^® processed cervical cytology samples.
Methods:  All primary care smear-takers were sent a questionnaire on lubricant type and frequency of use. Fifty cervical cytology samples were then contaminated with incremental amounts of K-Y^® jelly, 50 samples contaminated with incremental amounts of Aquagel^® and ten non-contaminated vials were processed using the ThinPrep^® T2000 processor followed by Papanicolaou staining. The morphological appearances of lubricant contamination were described microscopically and formal cell counts performed on all slides.
Results:  Seventy of 94 (74.5%) primary care smear-takers indicated lubricant use of whom 9/70 (12.8%) used Aquagel^® and 61/70 (87.2%) used K-Y^® jelly. K-Y^® jelly appeared as mucoid blue deposits in the slide background whereas Aquagel^® appeared as pink stringy background material. Cell counting showed a significant difference between Aquagel^® and K-Y^® jelly contaminated slides compared to the original non-contaminated preparations for all fields and the average fields ( P  < 0.001) with a significantly higher count for the original non-contaminated slides than the lubricant contaminated groups.
Conclusion:  Lubricant contamination of ThinPrep^® cervical cytology samples may result in reduced cellularity of the subsequent slide. This study provides evidence-based data to support British Society for Clinical Cytology recommendations for no lubricant use when taking cervical samples.     

Effects of feeding and induction strategy on the production of BmR1 antigen in recombinant E. coli

Aim:  To investigate the effects of feeding and induction strategies on the production of Bm R1 recombinant antigen.
Methods and Results:  Fed-batch fermentation was studied with respect to the specific growth rate and mode of induction to assess the growth potential of the bacteria in a bioreactor and to produce high yield of Bm R1 recombinant antigen. Cells were grown at a controlled specific growth rate (μ_set) during pre-induction, followed by constant feeding postinduction. The highest biomass (24·3 g l⁻¹) was obtained during fed-batch process operated at μ_set of 0·15 h⁻¹, whereby lower μ_set (0·075 h⁻¹) gave the highest protein production (9·82 mg l⁻¹). The yield of Bm R1 was increased by 1·2-fold upon induction with 1 mmol l⁻¹ IPTG (isopropyl-β- d -thiogalactoside) compared to using 5 mmol l⁻¹ and showed a further 3·5-fold increase when the culture was induced twice at the late log phase.
Conclusions:  Combination of feeding at a lower μ_set and twice induction with 1 mmol l⁻¹ IPTG yielded the best result of all variables tested, promising an improved method for Bm R1 production .
Significance and Impact of the Study:  This method can be used to increase the production scale of the Bm R1 recombinant antigen to meet the increasing demand for Brugia Rapid^™, a commercial diagnostic test for detection of brugian filariasis.     

Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire

1 In a glasshouse experiment we studied the effect of raised CO₂ concentration (720 p.p.m.) on CH₄ emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH₄ production and oxidation was measured at the end of the emission experiment.
2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores (' Sphagnum ') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH ₄ from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures.
3 In both Sedge and Sphagnum samples, CO₂ treatment doubled the potential CH₄ production but had no effect on the potential CH₄ oxidation. A raised concentration of CO₂ increased CH₄ efflux weakly and only at the highest peat temperatures (17–20 °C).
4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO₂ concentrations, and would thus retard any consequent increase in CH₄ emission.     

Combined effect of organic acids and supercritical carbon dioxide treatments against nonpathogenic Escherichia coli, Listeria monocytogenes, Salmonella typhimurium and E. coli O157:H7 in fresh pork

Aims:  To evaluate the effectiveness of organic acids and supercritical carbon dioxide (SC-CO₂) treatments as well as their combined effect for the reduction of nonpathogenic Escherichia coli and three pathogenic bacteria in fresh pork.
Methods and Results:  The different treatment conditions were as follows: (i) treatment with acetic (1%, 2% or 3%) or lactic acid (1%, 2% or 3%) only, (ii) treatment with SC-CO₂ at 12 MPa and 35°C for 30 min only and (iii) treatment with 3% acetic or lactic acid followed by treatment with SC-CO₂. Within the same organic acid concentration, the lactic and acetic acid treatments had similar reductions. For the combined treatment of lactic acid and SC-CO₂, micro-organism levels were maximally reduced, ranging from 2·10 to 2·60 log CFU cm⁻² ( E. coli , 2·58 log CFU cm⁻²; Listeria monocytogenes , 2·60 log CFU cm⁻²; Salmonella typhimurium , 2·33 log CFU cm⁻²; E. coli O157:H7, 2·10 log CFU cm⁻²).
Conclusions:  The results of this study indicate that the combined treatments of SC-CO₂ and organic acids were more effective at destroying foodborne pathogens than the treatments of SC-CO₂ or organic acids alone.
Significance and Impact of the Study:  The combination treatment of SC-CO₂ and organic acids may be useful in the meat industry to help increase microbial safety.     

Vaccination with SIVmac239Δnef activates CD4+ T cells in the absence of CD4+ T-cell loss

Background  Pathogenic HIV and SIV infections characteristically deplete central memory CD4⁺ T cells and induce chronic immune activation, but it is controversial whether this also occurs after vaccination with attenuated SIVs and whether depletion or activation of CD4⁺ T-cell play roles in protection against wild-type virus challenge.
Methods  Rhesus macaques were vaccinated with SIVmac239Δnef and quantitative and phenotypic polychromatic flow cytometry analyses were performed on mononuclear cells from blood, lymph nodes and rectal biopsies.
Results  Animals vaccinated with SIVmac239Δnef demonstrated no loss of CD4⁺ T cells in any tissue, and in fact CCR5⁺ and CD28⁺CD95⁺ central memory CD4⁺ T cells were significantly increased. In contrast, CD4⁺ T-cell numbers and CCR5 expression significantly declined in unvaccinated controls challenged with SIVmac239. Also, intracellular Ki67 increased acutely as much as 3-fold over baseline in all tissues after SIVmac239Δnef vaccination then declined following primary infection.
Conclusion  We demonstrated in this study that SIVmac239Δnef vaccination did not deplete CD4⁺ T cells but transiently activated and expanded the memory cell population. However, increases in numbers and activation of memory CD4⁺ T cells did not appear to influence protective immunity.     

An alternative explanation for the post-disturbance NO3– flush in some forest ecosystems

The appearance of soil NO₃^– after forest disturbance is commonly ascribed to a higher availability of NH₄⁺ to autotrophic nitrifiers, or to a reduction in available-C resulting in lower microbial assimilation of NO₃^–. Alternatively, it has been proposed that increasing NH₄⁺ pools following disturbance could increase net nitrification by reducing microbial assimilation of NO₃^–. Forest floor material was collected from shelterwood harvest plots which displayed both low available-C and low NH₄⁺ pools, and where previous experiments had suggested the prevalence of heterotrophic nitrification. Subsamples were amended with incremental rates of glucose-C or NH₄⁺, and gross NO₃^– transformation rates were measured by isotope dilution. Glucose-C additions had little effect on the net difference between gross NO₃^– production and consumption rates. On the other hand, NH₄⁺ additions caused gross NO₃^– consumption processes to decrease sharply, while gross NO₃^– production processes remained constant. The results suggest that NH₄⁺ can have an immediate positive effect on net nitrification rates by suppressing NO₃^– assimilation and uptake systems.     

Effect of culturing processes and copper addition on laccase production by the white-rot fungus Fomes fomentarius MUCL 35117

Aim:  To produce high laccase activities from the white-rot fungus Fomes fomentarius .
Methods and Results:  Different culturing methods, viz, cell immobilization on stainless steel sponges and plastic material and solid-state fermentation (SSF) using wheat bran as substrate were used for laccase production by the white-rot fungus F. fomentarius . The SSF study expresses the highest laccase activities, nearly to 6400 U l⁻¹ after 13 days of laboratory flasks cultivation. When the wheat bran medium was supplemented with 2 mmol l⁻¹ copper sulfate, laccase activity increased by threefold in comparison to control cultures, reaching 27 864 U l⁻¹. With the medium thus optimized, further experiments were performed in a 3 l fixed-bed bioreactor (working volume 1·5 l) leading to a laccase activity of about 6230 U l⁻¹ on day 13.
Conclusions:  The results obtained clearly showed the superiority of wheat bran for laccase production over stainless steel sponges and plastic material. Supplementing the wheat bran solid medium with 2 mmol l⁻¹ copper sulfate allowed obtaining high activities at flask scale. The system was scaled to fixed-bed laboratory reactor.
Significance and Impact of the Study:  The high enzyme production along with the low-cost of the substrate, showed the suitability of the system F. fomentarius – SSF for industrial purposes.     

An estimate of the sustainable rate of shell extraction from the Dutch Wadden Sea

1. Shell production by cockles Cerastoderma edule was studied to examine whether or not the present licensed rate of shell extraction in the Dutch Wadden Sea exceeds the current rate of shell addition to the exploitable stocks.
2. Long-term data on numbers of cockles and weights of their shells were used to estimate their annual production on Balgzand, a 50-km² tidal flat area in the western-most part of the Wadden Sea. During the 1969–97 period, it amounted to an average of 125 g m^–2, including 107 g m^–2 of shells large enough to be exploitable for shell-lime fishery.
3. The very irregular annual recruitment of cockles was the main cause of the wide 95% confidence limits (74 and 140 g m^–2 year^–1) of this 28-year estimate. Moreover, high mortality rates in severe winters substantially reduced production per recruit in some year classes.
4. About one-third of the estimated production does not reach exploitable stocks, because it is fragmented by birds (particularly eider ducks), permanently buried in the sediment, or removed by the fishery for live cockles.
5. During the last few decades, the estimated mean amount added annually to the exploitable stocks was 88 million kg or 132 000 m³ of large cockle shells. This amount compares favourably with the current annual level of removal of 134 000 m³ of shells, three-quarters of which are cockles.
6. Even at temporarily lower production rates, the exploitation of shell stocks at its present rate is not expected to lead to a rapid exhaustion of the existing stocks in the tidal inlets of the Dutch Wadden Sea, as these stocks will be in the order of a few million m³.     

A single ThinPrep® slide may not be representative in all head and neck fine needle aspirate specimens

Objectives:  Ideally, head and neck aspiration should be performed by trained aspirators within the setting of a one-stop clinic, where smeared material is available for immediate assessment. However, this may not always be possible for practical reasons and the use of liquid-based techniques in head and neck cytology is increasing. Although liquid-based cytology has been extensively validated for use in gynaecological cytology, no studies have investigated whether or not a single ThinPrep ^® slide is representative for head and neck aspirate specimens. We performed a prospective audit of head and neck fine needle aspiration specimens processed by the ThinPrep ^® method to investigate whether a single ThinPrep ^® slide was representative.
Methods:  A prospective audit of 115 consecutive head and neck aspirates was carried out. A single ThinPrep ^® slide was prepared and a diagnosis recorded. The remainder of the specimen was then spun down and prepared as a cell block. The ThinPrep ^® and cell block diagnoses were compared.
Results:  In 36 cases (31%), the cell block provided additional information that contributed to the diagnosis. In 14 (12%), the cell block was regarded as essential to the diagnosis.
Conclusions:  A single ThinPrep^® slide may not provide representative diagnostic material in all head and neck aspirates. This should be taken into consideration when contemplating the use of liquid-based methods for non-gynaecological cytology.     

Multidrug resistance gene deficient (mdr1a–/–) mice have an altered caecal microbiota that precedes the onset of intestinal inflammation

Aim:  To compare caecal microbiota from mdr1a ^–/– and wild type (FVB) mice to identify differences in the bacterial community that could influence the intestinal inflammation.
Methods and Results:  Caecal microbiota of mdr1a ^–/– and FVB mice were evaluated at 12 and 25 weeks of age using denaturing gradient gel electrophoresis (DGGE) and quantitative real-time PCR. DGGE fingerprints of FVB and mdr1a ^–/– mice (with no intestinal inflammation) at 12 weeks revealed differences in the presence of DNA fragments identified as Bacteroides fragilis , B. thetaiotaomicron , B. vulgatus and an uncultured alphaproteobacterium. Escherichia coli and Acinetobacter sp. were only identified in DGGE profiles of mdr1a ^–/– mice at 25 weeks (with severe intestinal inflammation), which also had a lower number of total bacteria in the caecum compared with FVB mice at same age.
Conclusions:  Differences found in the caecal microbiota of FVB and mdr1a ^–/– mice (12 weeks) suggest that the lack of Abcb1 transporters in intestinal cells due to the disruption of the mdr1a gene might lead to changes in the caecal microbiota. The altered microbiota along with the genetic defect could contribute to the development of intestinal inflammation in mdr1a ^–/– mice.
Significance and Impact of the Study:  Differences in caecal microbiota of mdr1a ^–/– and FVB mice (12 weeks) suggest genotype specific colonization. The results provide evidence that Abcb1 transporters may regulate host interactions with commensal bacteria. Future work is needed to identify the mechanisms involved in this possible cross-talk between the host intestinal cells and microbiota.     

Heterotrophic bacterioplankton production and grazing mortality rates in an Ethiopian rift-valley lake (Awassa)

SUMMARY. 1. Heterotrophic bacterioplankton growth and production rates were estimated in a tropical lake by various methods. Mean growth rates, determined by tritiated thymidine incoporation into DNA, frequency of dividing cells and increase in cell density varied between 0.013 and 0.014 (with a range of 0.006–0.026) h⁻¹ corresponding to bacterial production of 1.16–1.22 (0.34–3.63) mg C m⁻³ h⁻¹.
2. Heterotrophic bacterial production estimated from oxygen and inorganic carbon consumption in the dark were compared with these values. The oxygen method gave similar results, while values from dark carbon uptake were as much as 2.5 times higher.
3. Although the different estimates of rates of bacterial production showed different patterns, the existence of spatial (vertical) and temporal (diel and seasonal) variation was demonstrated. Bacterial production was 13–41% of the net primary production and 10–30% of gross primary production.
4. Bacterial grazing mortality rate was estimated from size-fractionation and metablic inhibitor experiments. Average grazing rates were between 0.34 and 3.77 mg C m⁻³ h⁻¹ corresponding to 76–120% of the mean bacterial production rate. Organisms 1–12 μm in size, possibly mainly ciliates. were implicated as important bacterial grazers.     

Formation and microbial community analysis of chloroanilines-degrading aerobic granules in the sequencing airlift bioreactor

Aims:  This paper investigates a selection-based acclimation strategy for improving the performance and stability of aerobic granules at a high chloroanilines loading.
Methods and Results:  The experiments were conducted in a sequencing airlift bioreactor (SABR) to develop aerobic granules fed with chloroanilines (ClA). The evolution of aerobic granulation was monitored using image analysis and scanning electron microscopy, and PCR–DGGE analysis of microbial community was performed. The sludge granulation was apparently developed by decreased settling time and gradual increased ClA loading to 0·8 kg m⁻³ day⁻¹. A steady-state performance of the granular SABR was reached at last, as evidenced by biomass concentration of 6·3 g l⁻¹ and constant ClA removal efficiency of 99·9%. The mature granules had a mean size of 1·55 mm, minimal settling velocity of 68·4 m h⁻¹, specific ClA degradation rate of 0·181 g gVSS⁻¹ day⁻¹. Phylogenetic analysis of aerobic ClA-degrading granules confirmed the dominance of β - , γ -Proteobacteria and Flavobacteria.
Conclusions:  The chosen operating strategy involving step increase in ClA loading and enhancement of major selection pressures was successful in cultivating the aerobic ClA-degrading granules.
Significance and Impact of the Study:  This research could be helpful for improving the stability of aerobic granules via optimizing operating conditions and developing economic feasible full-scale granular bioreactor.     

Population dynamics and production of the pelagic amphipod Hyalella montezuma in a thermally constant system

SUMMARY. 1. The population dynamics and annual production of the multivoltine. pelagic amphipod Hyalella montezuma were studied over a 3-year period in the thermally constant environment of Montezuma Well. Arizona.
2. H. montezuma showed two maxima which coincided with spring and autumn phytoplankton maxima. Juveniles comprised over 85% of the population in the pelagic zone compared to 37% in the littoral vegetation and there were significantly more females in the littoral vegetation. It appears that juvenile and adult H. montezuma show different habitat preferences.
3. Total annual mean production for H. montezuma calculated by the size frequency method and adjusted for multiple generations, was 357 kg ha⁻¹ yr⁻¹, which is higher than single-species production estimates reported for most zoobenthic amphipods and multivoltine planktonic crustaceans. Average energy production for H. montezuma was 4640 kJ ha⁻¹ yr⁻¹ in the pelagic zone and 1072 kJ ha⁻¹ yr⁻¹ in the littoral vegetation.
4. Average cohort P / ratios for H. montezuma were higher in the pelagic zone (5.5) than in the litttoral vegetation (3.7). Juveniles had higher cohort P ratios than adults in the pelagic zone, while the reverse relationship was true in the littoral vegetation. We propose that different size-selective predators may contribute to the differences in P ratios for juveniles and adults in these two habitats.     

Response of plankton communities to whole-lake Ca(OH)2 and CaCO3 additions in eutrophic hardwater lakes

1. The impact of whole-lake lime (slaked lime, Ca(OH)₂, and/or calcite, CaCO₃) addition on plankton communities was evaluated in eutrophic hardwater lakes on the North American Boreal Plain.
2. Two lakes received a single treatment of lime (Ca(OH)₂ at 74 or 107 mg L^–1), two lakes received multiple treatments with Ca(OH)₂ and/or CaCO₃ (5–78 mg L^–1), and four lakes were untreated and served as reference systems.
3. Over the long-term (> 1 year), phytoplankton biomass was reduced in multiple-dose lakes, but not in single-dose lakes. Cyanobacteria typically dominated the algal community in the years before, during and after lime treatment in both single- and multiple-dose lakes.
4. In the single-dose lakes, randomized intervention analysis showed no significant change in the biomass of zooplankton after lime addition.