Interacting effects of ocean acidification and warming on growth and DMS‐production in the haptophyte coccolithophore Emiliania huxleyi

The production of the marine trace gas dimethyl sulfide (DMS) provides 90% of the marine biogenic sulfur in the atmosphere where it affects cloud formation and climate. The effects of increasing anthropogenic CO₂ and the resulting warming and ocean acidification on trace gas production in the oceans are poorly understood. Here we report the first measurements of DMS‐production and data on growth, DMSP and DMS concentrations in pH‐stated cultures of the phytoplankton haptophyte Emiliania huxleyi. Four different environmental conditions were tested: ambient, elevated CO₂ (+CO₂), elevated temperature (+T) and elevated temperature and CO₂ (+TCO₂). In comparison to the ambient treatment, average DMS production was about 50% lower in the +CO₂ treatment. Importantly, temperature had a strong effect on DMS production and the impacts outweighed the effects of a decrease in pH. As a result, the +T and +TCO₂ treatments showed significantly higher DMS production of 36.2 ± 2.58 and 31.5 ± 4.66 μmol L^?1 cell volume (CV) h^?1 in comparison with the +CO₂ treatment (14.9 ± 4.20 μmol L^?1 CV h^?1). As the cultures were aerated with an air/CO₂ mixture, DMS was effectively removed from the incubation bottles so that concentration remained relatively low (3.6–6.1 mmol L^?1 CV). Intracellular DMSP has been shown to increase in E. huxleyi as a result of elevated temperature and/or elevated CO₂ and our results are in agreement with this finding: the ambient and +CO₂ treatments showed 125 ± 20.4 and 162 ± 27.7 mmol L^?1 CV, whereas +T and +TCO₂ showed significantly increased intracellular DMSP concentrations of 195 ± 15.8 and 211 ± 28.2 mmol L^?1 CV respectively. Growth was unaffected by the treatments, but cell diameter decreased significantly under elevated temperature. These results indicate that DMS production is sensitive to CO₂ and temperature in E. huxleyi. Hence, global environmental change that manifests in ocean acidification and warming may not result in decreased DMS as suggested by earlier studies investigating the effect of elevated CO₂ in isolation.     

Effect of PAR irradiance intensity on Phaeocystis antarctica (Prymnesiophyceae) growth and DMSP,DMSO, and acrylate concentrations

Phaeocystis antarctica forms extensive spring blooms in the Southern Ocean that coincide with high concentrations of dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), dimethylsulfide (DMS), and acrylate. We determined how concentrations of these compounds changed during the growth of axenic P. antarctica cultures exposed to light-limiting, sub-saturating, and saturating PAR irradiances. Cellular DMSP concentrations per liter cell volume (CV) ranged between 199 and 403 mmol · L_CV⁻¹, with the highest concentrations observed under light-limiting PAR. Cellular acrylate concentrations did not change appreciably with a change in irradiance level or growth, ranging between 18 and 45 mmol · L_CV⁻¹, constituting an estimated 0.2%–2.8% of cellular carbon. Both dissolved acrylate and DMSO increased substantially with irradiance during exponential growth on a per-cell basis, ranging from 0.91 to 3.15 and 0.24 to 1.39 fmol · cell⁻¹, respectively, indicating substantial export of these compounds into the dissolved phase. Average cellular DMSO:DMSP ratios increased 7.6-fold between exponential and stationary phases of batch growth, with a 3- to 13-fold increase in cellular DMSO likely formed from abiotic reactions of DMSP and DMS with reactive oxygen species (ROS). At mM levels, cellular DMSP and acrylate are proposed to serve as de facto antioxidants in P. antarctica not regulated by oxidative stress or changes in ROS. Instead, cellular DMSP concentrations are likely controlled by other physiological processes including an overflow mechanism to remove excess carbon via acrylate, DMS, and DMSO during times of unbalanced growth brought on by physical stress or nutrient limitation. Together, these compounds should aid P. antarctica in adapting to a range of PAR irradiances by maintaining cellular functions and reducing oxidative stress.     

The quantitative role of microzooplankton grazing in dimethylsulfide (DMS) production in the NW Mediterranean

The ubiquitous, biogenic trace gas dimethylsulfide (DMS) represents the largest natural source of atmospheric sulfur. Given DMS involvement in cloud formation and climate, understanding and parameterizing the oceanic DMS source and cycling processes is a necessary challenge. We report DMS cycling rates from microzooplankton dilution grazing experiments conducted monthly during 1 year in coastal northwestern Mediterranean waters. Concentrations of DMS, its algal precursor dimethylsulfoniopropionate (DMSPt) and chlorophyll a (Chla) ranged 0.9–11 nmol L^?1, 10–71 nmol L^?1, and 0.2–1.5 µg L^?1, respectively. By comparing the growth and stock production rates of the DMSP-producing algae to those of total phytoplankton, we estimated that 3?±?4% (range 0.4–12%) of the carbon primary production was invested in DMSP biosynthesis. Microzooplankton grazing rates on DMSP-producing phytoplankton (0.46–1.45 day^?1) were generally higher than those on the bulk assemblage (0.08–0.99 day^?1), except in midsummer months. This could have been due to the smaller size of most DMSP producers. There was no indication of micrograzer selection against DMSP-containing phytoplankton, since they were not grazed at lower rates than the bulk phytoplankton assemblage. A proportion of 6–20% of the grazed DMSP was converted into DMS, and this grazing-derived production accounted for 32–96% of dark gross DMS production by the total community. Bacteria consumed daily?≤?14–100% of the gross DMS production, which resulted in biological DMS turnover times of 1 to?≥?10 days. Throughout the year, grazing-mediated DMS production explained 73% of the variance in the DMS concentration, implying that microzooplankton grazing plays a major role in controlling DMS concentration in surface waters across a broad range of environmental and productivity conditions in the Mediterranean Sea. These findings should help improve the representation of herbivore grazing in prognostic models to predict the distribution and dynamics of the global DMS emission and its feedback response to changing climate.     

DIFFERENTIAL IMPACTS OF PHOTOACCLIMATION AND THERMAL STRESS ON THE PHOTOBIOLOGY OF FOUR DIFFERENT PHYLOTYPES OF SYMBIODINIUM (PYRRHOPHYTA)1

The capacity for photoacclimation to light at 100 or 600 μmol photons·m^?2·s^?1 and the subsequent response to thermal stress was examined in four genetically distinct cultures of symbiotic dinoflagellates in the genus Symbiodinium with the ITS2 designations A1, A1.1, B1, and F2. While all algal types showed typical signs of photoacclimation to high light via a reduction in chl a, there was a differential response in cellular growth, photosystem II (PSII) activity, and the chl a‐specific absorption coefficient between cultures. When maintained at 32°C for up to 10 days, significant variation in the susceptibility to thermal stress was observed in the rate of loss in PSII activity and electron transport, PSII reaction center degradation, and cellular growth. The order of thermal tolerance did not change between the two light levels. However, as expected, loss in photosynthetic function was exacerbated in the thermally sensitive phylotypes (B1 and A1.1) when acclimated to the higher light intensity. There was no consistent relationship between thermal tolerance and changes in light energy dissipation via non‐photochemical pathways. Phylotypes F2 and A1 showed a high degree of thermal tolerance, yet the cellular responses to light and temperature were markedly different between these algae. The F2 isolate showed the greatest capacity for photoacclimation and growth at high light and temperature, while the A1 isolate appeared to adjust to thermal stress by a slight decline in PSII activity and a significant decline in growth, possibly at the expense of increased photosystem and cellular repair rates.     

Microbial controls on DMSP degradation and DMS formation in the Sargasso Sea

Bacterial degradation of dimethylsulfoniopropionate (DMSP) represents one of the main sources of the climatically–active trace gas dimethylsulfide (DMS) in the upper ocean. Short-term enrichment studies to stimulate specific pathways of DMSP degradation in oligotrophic waters from the Sargasso Sea were used to explore regulatory connections between the different bacterial DMSP degradation steps and determine potential biological controls on DMS formation in the open ocean. Experiments were conducted with surface water at the BATS station in the western North Atlantic Ocean. We added selected organic substrates (25 nmol L^?1 final concentration) to induce different steps of DMSP degradation in the microbial community, and then measured DMSP dynamics (assimilation and turnover rates), DMS yields (using ³⁵sulfur-DMSP tracer), and bacterial production rates. In most treatments, the main fate of consumed S-DMSP was excretion as a non-volatile S product. ³⁵S-DMSP tracer turnover rates (accumulation + assimilation + excretion of transformed products as DMS or others) increased upon addition of DMSP and glucose, but not acrylate, methymercaptopropionate (MMPA), methanethiol, DMS or glycine betaine. DMS yields from ³⁵S-DMSP never exceeded 16 % except in a short term DMSP enrichment, for which the yield reached 45 % (±17 %). Results show that availability of non-sulfur containing labile C sources (glucose, acrylate) decreased bacterial DMS production while stimulating bacterial heterotrophic production, and suggest an influence of bacterial sulfur demand in controlling DMS-yielding pathways. However, regulatory effects on ³⁵S-DMSP fate were not consistent across all reduced sulfur compounds (i.e., methanethiol or MMPA), and may reflect alternate roles of DMSP as a bacterial energy source and osmolyte.     

Use of bacteriophage endolysin EL188 and outer membrane permeabilizers against Pseudomonas aeruginosa

Aims: To select and evaluate an appropriate outer membrane (OM) permeabilizer to use in combination with the highly muralytic bacteriophage endolysin EL188 to inactivate (multi‐resistant) Pseudomonas aeruginosa. Methods and Results: We tested the combination of endolysin EL188 and several OM permeabilizing compounds on three selected Ps. aeruginosa strains with varying antibiotic resistance. We analysed OM permeabilization using the hydrophobic probe N‐phenylnaphtylamine and a recombinant fusion protein of a peptidoglycan binding domain and green fluorescent protein on the one hand and cell lysis assays on the other hand. Antibacterial assays showed that incubation of 10⁶Ps. aeruginosa cells ml^?1 in presence of 10 mmol l^?1 ethylene diamine tetraacetic acid disodium salt dihydrate (EDTA) and 50 μg ml^?1 endolysin EL188 led to a strain‐dependent inactivation between 3·01 ± 0·17 and 4·27 ± 0·11 log units in 30 min. Increasing the EL188 concentration to 250 μg ml^?1 further increased the inactivation of the most antibiotic resistant strain Br667 (4·07 ± 0·09 log units). Conclusions: Ethylene diamine tetraacetic acid disodium salt dihydrate was selected as the most suitable component to combine with EL188 in order to reduce Ps. aeruginosa with up to 4 log units in a time interval of 30 min. Significance and Impact of the Study: This in vitro study demonstrates that the application range of bacteriophage encoded endolysins as ‘enzybiotics’ must not be limited to gram‐positive pathogens.     

Blood lactate loads of redthroat emperor Lethrinus miniatus associated with angling stress and exhaustive exercise

Baseline, post‐angling and maximum attainable blood lactate concentrations were measured for the fishery species redthroat emperor Lethrinus miniatus to gain insight into the condition of fish released following c. 30 s angling and <45 s air exposure. Mean ± s.d . baseline blood lactate was 1·5 ± 0·6 mmol l^?1, which increased and plateaued around 6 mmol l^?1 at 15–30 min post‐angling. These values were significantly lower than those obtained from fish maximally exhausted with a prolonged chase and air exposure protocol following capture (10·9 ± 1·8 mmol l^?1), suggesting that L. miniatus is not maximally exhausted during standard angling practices.     

Mitigating stress effects during transportation of matrinxã (Brycon amazonicus Günther, 1869; Characidae) through the application of calcium sulfate

This study verified the effects of CaSO₄ on physiological responses of the tropical fish matrinxãBrycon amazonicus (200.2 ± 51.1 g) in water containing CaSO₄ after a 4‐h transportation at concentrations of: 0, 75, 150, and 300 mg L^?1. Blood samples were collected prior to transportation (initial levels), immediately after packaging, at arrival, and 24 h and 96 h after transportation (recovery). Cortisol levels increased after packaging (118.2 ± 14.2 ng ml^?1), and decreased slightly after transportation in water containing CaSO₄ (106.8 ± 14.1), but remained higher than initial levels (21.0 ± 2.6 ng ml^?1). Fish kept at 150 mg L^?1 CaSO₄ reached the pre‐transportation levels at 24 h of recovery. Blood glucose increased after transportation in all treatments (8.2 ± 0.2 mmol L^?1) and declined after full recovery to values below initial levels (4.8 ± 0.1 mmol L^?1). Chloride levels did not change in CaSO₄ treatments; serum sodium concentrations decreased after packaging and after transportation. Serum calcium levels did not differ among treatments, but decreased after packaging and increased at 96 h of recovery. Hematocrit and the number of red blood cells were higher in all treatments after packaging and arrival, except in fish exposed to 300 mg L^?1 CaSO₄. Mean corpuscular volume increased in 75 mg L^?1 CaSO₄, which reached the higher VCM after transportation. Hemoglobin levels increased only after transportation, regardless of calcium sulfate levels. Handling before transportation and transportation itself were both stressful to fish; calcium sulfate at concentrations tested in the present work had a moderate influence in the reduction of stress responses.     

Study of laccase production by Pleurotus ostreatus in a 5 l bioreactor and application of the enzyme to determine the antioxidant concentration of human plasma

Aims: To achieve high laccase production from Pleurotus ostreatus in a bench top bioreactor and to utilize the enzyme for determination of the total antioxidant concentration (TAC) of human plasma. Methods and Results: Laccase production by P. ostreatus studied in a benchtop bioreactor was as high as, 874·0 U ml^?1 in presence of copper sulfate. The enzyme was used to replace metmyoglobin and hydrogen peroxide for the estimation of TAC in human plasma. The trolox equivalent antioxidant concentrations determined by the laccase‐based method and metmyoglobin method ranged from 1·63 ± 0·011 to 1·80 ± 0·006 mmol l^?1 and from 1·41 ± 0·004 to 1·51 ± 0·008 mmol l^?1 plasma, respectively. Conclusions: Pleurotus ostreatus produced high amount of extracellular laccase in a benchtop bioreactor. The enzyme can be used to assay TAC of blood plasma without the interference encountered with the hydrogen peroxide and metmyoglobin mediated assay method. Significance and Impact of the Study: Laccase production by P. ostreatus obtained in this study was the highest among all reported laccase producing white‐rot fungi. Moreover, an accurate laccase‐based assay method was developed for detection of TAC in human plasma.     

Production rate estimation of mycosporine‐like amino acids in two Arctic melt ponds by stable isotope probing with NAH13CO3

The net carbon uptake rate and net production rate of mycosporine‐like amino acids (MAAs) were measured in phytoplankton from 2 different melt ponds (MPs; closed and open type pond) in the western Arctic Ocean using a ¹³C stable isotope tracer technique. The Research Vessel Araon visited ice‐covered western‐central basins situated at 82°N and 173°E in the summer of 2012, when Arctic sea ice declined to a record minimum. The average net carbon uptake rate of the phytoplankton in polycarbonate (PC) bottles in the closed MP was 3.24 mg C · m^?3 · h^?1 (SD = ±1.12 mg C · m^?3 · h^?1), while that in the open MP was 1.3 mg C · m^?3 · h^?1 (SD = ±0.05 mg C · m^?3 · h^?1). The net production rate of total MAAs in incubated PC bottles was highest (1.44 (SD = ±0.24) ng C · L^?1 · h^?1) in the open MP and lowest (0.05 (SD = ±0.003) ng C · L^?1 · h^?1) in the closed MP. The net production rate of shinorine and palythine in incubated PC bottles at the open MP presented significantly high values 0.76 (SD = ±0.12) ng C · L^?1 · h^?1and 0.53 (SD = ±0.06) ng C · L^?1 · h^?1. Our results showed that high net production rate of MAAs in the open MP was enhanced by a combination of osmotic and UVR stress and that in situ net production rates of individual MAA can be determined using ¹³C tracer in MPs in Arctic sea ice.     

Aerobic turnover of dimethyl sulfide by the anoxygenic phototrophic bacterium Thiocapsa roseopersicina

This is the first report describing the complete oxidation of dimethyl sulfide (DMS) to sulfate by an anoxygenic, phototrophic purple sulfur bacterium. Complete DMS oxidation was observed in cultures of Thiocapsa roseopersicina M11 incubated under oxic/light conditions, resulting in a yield of 30.1 mg protein mmol^–1. No oxidation of DMS occurred under anoxic/light conditions. Chloroform, methyl butyl ether, and 3-amino-1,2,4-triazole, which are specific inhibitors of aerobic DMS oxidation in thiobacilli and hyphomicrobia, did not affect DMS oxidation in strain M11. This could be due to limited transport of the inhibitors through the cell membrane. The growth yield on sulfide as sole electron donor was 22.2 mg protein mmol^–1 under anoxic/light conditions. Since aerobic respiration of sulfide would have resulted in yields lower than 22 mg protein mmol^–1, the higher yield on DMS under oxic/light conditions suggests that the methyl groups of DMS have served as an additional carbon source or as an electron donor in addition to the sulfide moiety. The kinetic parameters V _max and K _m for DMS oxidation under oxic/light conditions were 12.4 ± 1.3 nmol (mg protein)^–1 min^–1 and 2 μM, respectively. T. roseopersicina M11 also produced DMS by cleavage of dimethylsulfoniopropionate (DMSP). Specific DMSP cleavage rates increased with increasing initial substrate concentrations, suggesting that DMSP lyase was only partly induced at lower initial DMSP concentrations. A comparison of T. roseopersicina strains revealed that only strain M11 was able to oxidize DMS and cleave DMSP. Both strain M11 and strain 5811 accumulated DMSP intracellularly during growth, while strain 1711 showed neither of these characteristics. Phylogenetic comparison based on 16S rRNA gene sequence revealed a similarity of 99.0% between strain M11 and strain 5811, and 97.6% between strain M11 and strain 1711. DMS and DMSP utilization thus appear to be strain-specific. Received: 26 March 1999 / Accepted: 18 June 1999     

Differences in biochemical profiles among spawners of eight common carp breeds

Eight breeds of common carp (Cyprinus carpio L.) spawners reared under identical conditions and sampled in spring after over‐wintering were examined in order to compare their basic biochemical blood profiles. The breeds compared were: Amur wild carp (AS), Ropsha scaly carp (ROP), Ukraine scaly carp (US), Northern mirror carp (M72), South Bohemian mirror carp (BV), Israeli mirror carp (Dor 70), Hungarian mirror carp (M2) and Tata scaly carp (TAT). Significant differences were found among breeds in glucose concentration (GLU), total protein concentration (TP), triacylglycerols concentration (TAG), and calcium (Ca) and phosphorus (P_i) concentration. No differences were observed in aspartate transaminase activity (AST) or alanine aminotransferase activity (ALT). The highest glucose, total protein, and calcium (Ca) concentrations were found in AS (GLU 8.3 ± 1.2 mmol L^?1, TP 32 ± 3 g L^?1, Ca 2.42 ± 0.22 mmol L^?1). High values of triacylglycerol concentration (TAG) were found in ROP (1.94 ± 0.52 mmol L^?1). Phosphorus (P_i) concentration was highest in M2 (3.82 ± 1.34 mmol L^?1). Amur wild carp and breeds originating therefrom (ROP, US, and M72) had significantly higher values of TP (P < 0.05), TAG (P < 0.05), and Ca (P < 0.01) and significantly lower values of P_i (P < 0.05) than did the other breeds. Scaly breeds had higher values of glucose (P < 0.01), TP (P < 0.01), ALT (P < 0.01), and Ca (P < 0.01) and significantly lower values of P_i (P < 0.01) than did mirror carp. Significant (P < 0.01) sex‐related differences were found in GLU, TAG and Ca concentrations.     

Concentrations of dimethylsulphoniopropionate and activities of dimethylsulphide-producing enzymes in batch cultures of nine dinoflagellate species

Dinoflagellates are recognised as one of the major phytoplankton groups that produce dimethylsulphoniopropionate (DMSP), the precursor of the marine trace gas dimethylsulphide (DMS) which has climate-cooling potential. To improve the prospects for including dinoflagellates in global climate models that include DMSP-related processes, we increased the data base for this group by measuring DMSP, DMS-producing enzyme activity (DPEA), carbon, nitrogen and Chl a in nine clonal dinoflagellate cultures (1 heterotrophic and 8 phototrophic strains). Growth rates ranged from 0.11 to 1.92?day^?1 with the highest value being for the heterotroph Crypthecodinium cohnii. Overall, we observed two orders of magnitude variability in DMSP content (11–364?mM) and detected DPEA in five of the nine strains (0.61–59.73?fmol?cell^?1?h^?1). Cell volume varied between 454 and 18,439?μm³ and whilst C and N content were proportional to the cell volume, DMSP content was not. The first DMSP measurements for a dinoflagellate from Antarctic waters and a species with diatom-like plastids are included. Lower DMSP concentrations were found in three small athecate species and a dinoflagellate with haptophyte-like plastids. The highest concentrations and production rates tended to be in globally distributed dinoflagellates and the heterotroph. Photosynthetic species that are distributed in temperate to tropical waters showed low DMSP concentrations and production rates and the polar representative showed moderate concentration and a low production rate. Estuarine species had the lowest concentrations and production rates. These data should help refine the inclusion of dinoflagellates as a functional group in future global climate models.     

Metabolism of DMSP, DMS and DMSO by the cultivable bacterial community associated with the DMSP-producing dinoflagellate Scrippsiella trochoidea

Bacterial species associated with the dimethylsulfoniopropionate (DMSP)-producing phytoplankton Scrippsiella trochoidea were cultured and identified, with the aim of establishing their ability to metabolise DMSP, dimethylsulfide (DMS) and dimethylsulfoxide (DMSO). Results demonstrate that of the cultivable bacteria only α-Proteobacteria were capable of producing DMS from DMSP. The concentration of DMSP was shown to affect the amount of DMS produced. Lower DMSP concentrations (1.5?μmol?dm^?3) were completely assimilated, whereas higher concentrations (10?μmol?dm^?3) resulted in increasing amounts of DMS being produced. By contrast to the restricted set of bacteria that metabolised DMSP,?~?70% of the bacterial isolates were able to ‘consume’ DMS. However, 98-100% of the DMS removed was accounted for as DMSO. Notably, a number of these bacteria would only oxidise DMS in the presence of glucose, including members of the γ-Proteobacteria and Bacteroidetes. The observations from this study, coupled with published field data, identify DMS oxidation to DMSO as a major transformation pathway for DMS, and we speculate that the fate of DMS and DMSP in the field are tightly coupled to the available carbon produced by phytoplankton.     

Metal-ion susceptibility of oral bacterial species

Aims: This study aimed to evaluate the effect of lead (Pb) on growth of bacterial species related to dental diseases in vitro. Methods and Results: The effects of lead acetate on representative species of the oral flora were examined at 0·1–10 mmol l^?1 and compared with the effect of silver nitrate and ferrous sulfate. The minimal inhibitory concentration of lead acetate was between 0·15 and 5 mmol l^?1 for the bacterial strains tested. The minimal bactericidal concentration of lead acetate for most oral species was detected in the range of 5–10 mmol l^?1. Silver nitrate at a concentration of 1·25 mmol l^?1 was sufficient to exhibit antibacterial activity against almost all bacteria tested. Ferrous sulfate had the lowest effect. Conclusions: The study indicated a general antimicrobial effect of lead on oral bacterial species in the range of 0·15–10 mmol l^?1. The toxicity of silver nitrate was the highest, whereas that of ferrous sulfate was the lowest. Gram‐positive species had a tendency to be less susceptible for metals than Gram‐negatives. Significance and Impact of the Study: The study shows that it is possible that microbiological changes may occur in the dental plaque in children because of toxic exposure of environmental lead.     

Arthrospira platensis biomass with high protein content cultivated in continuous process using urea as nitrogen source

Aims: Arthrospira platensis has been studied for single‐cell protein production because of its biomass composition and its ability of growing in alternative media. This work evaluated the effects of different dilution rates (D) and urea concentrations (N₀) on A. platensis continuous culture, in terms of growth, kinetic parameters, biomass composition and nitrogen removal. Methods and results: Arthrospira platensis was continuously cultivated in a glass‐made vertical column photobioreactor agitated with Rushton turbines. There were used different dilution rates (0·04–0·44 day^?1) and urea concentrations (0·5 and 5 mmol l^?1). With N₀ = 5 mmol l^?1, the maximum steady‐state biomass concentration was1415 mg l^?1, achieved with D = 0·04 day^?1, but the highest protein content (71·9%) was obtained by applying D = 0·12 day^?1, attaining a protein productivity of 106·41 mg l^?1 day^?1. Nitrogen removal reached 99% on steady‐state conditions. Conclusions: The best results were achieved by applying N₀ = 5 mmol l^?1; however, urea led to inhibitory conditions at D ≥ 0·16 day^?1, inducing the system wash‐out. The agitation afforded satisfactory mixture and did not harm the trichomes structure. Significance and Impact of the Study: These results can enhance the basis for the continuous removal of nitrogenous wastewater pollutants using cyanobacteria, with an easily assembled photobioreactor.     

SHIFT FROM CHLOROPHYTES TO CYANOBACTERIA IN BENTHIC MACROALGAE ALONG A GRADIENT OF NITRATE DEPLETION1

A survey of the spatial distribution of benthic macroalgae in a fluvial lake of the St. Lawrence River (Lake Saint‐Pierre, Quebec, Canada) revealed a shift in composition from chlorophytes to cyanobacteria along the flow path of nutrient‐rich waters originating from tributaries draining farmlands. The link between this shift and changes in water quality characteristics was investigated by sampling at 10 sites along a 15 km transect. Conductivity, current, light extinction, total phosphorus (TP; >25 μg P · L^?1), and ammonium (8–21 μg N · L^?1) remained fairly constant along the transect in contrast to nitrate concentrations, which fell sharply. Filamentous and colonial chlorophytes [Cladophora sp. and Hydrodictyon reticulatum (L.) Bory] dominated in the first 5 km where nitrate concentrations were >240 μg N · L^?1. A mixed assemblage of chlorophytes and cyanobacteria characterized a 1 km transition zone where nitrate decreased to 40–80 μg N · L^?1. In the last section of the transect, nitrate concentrations dropped below 10 μg N · L^?1, and cyanobacteria (benthic filamentous mats of Lyngbya wollei Farl. ex Gomont and epiphytic colonies of Gloeotrichia) dominated the benthic community. The predominance of nitrogen‐fixing, potentially toxic cyanobacteria likely resulted from excessive nutrient loads and may affect nutrient and trophic dynamics in the river.     

Haematological and serum biochemical characterization and comparison of wild and cultured northern snakehead (Channa argus Cantor, 1842)

The objective of this study was to compare haematological and serum biochemical parameters of cultured and wild specimens of the northern snakehead, Channa argus, to establish baseline values. Thirty sexually immature and disease‐free wild fish (37.70 ± 13.68 cm total length, 555.3 ± 449.0 g weight) and 30 cultured fish (36.82 ± 1.72 cm total length, 450.5 ± 58.8 g weight) were examined. In cultured northern snakehead, the average values of alanine aminotransferases (370.1 IU L^?1), aspartate amino transferases (1145.3 IU L^?1), albumin (15.84 g L^?1), direct billuribin (6.15 μmol L^?1), urea (1.40 mmol L^?1), glucose (21.54 mmol L^?1) and cholesterol levels (6.60 mmol L^?1) were significantly higher (P < 0.05) than in the wild fish. In wild specimens the corresponding values were 9.81 IU L^?1, 394.1 U L^?1, 12.90 g L^?1, 2.57 μmol L^?1, 0.97, 2.36 and 4.38 mmol L^?1, respectively. No significant difference (P > 0.05) was found for total protein, globulin, total bilirubin, chromium, sodium, chloride or triglyceride levels between wild and cultured populations. The mean values of the red blood cell (RBC) counts, hematocrit, haemoglobin, and mean corpuscular volume (MCV) were significantly higher (P < 0.05) in the cultured population, while the values of the white blood cell (WBC) counts, erythrocyte sedimentation rate (ESR), mean corpuscular haemoglobin (MCH), and mean corpuscular haemoglobin concentration (MCHC) were significantly higher (P < 0.05) in the wild population. The study showed that the environmental conditions significantly impacted the status of the fish. It is suggested that these physiological parameters can be conveniently employed as health monitoring tools in fish culture practices.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

The membraneless bioelectrochemical reactor stimulates hydrogen fermentation by inhibiting methanogenic archaea

The membraneless bioelectrochemical reactor (Ml-BER) is useful for dark hydrogen fermentation. The effect of the electrochemical reaction on microorganisms in the Ml-BER was investigated using glucose as the substrate and compared with organisms in a membraneless non-bioelectrochemical reactor (Ml-NBER) and bioelectrochemical reactor (BER) with a proton exchange membrane. The potentials on the working electrode of the Ml-BER and BER with membrane were regulated to ?0.9 V (versus Ag/AgCl) to avoid water electrolysis with a carbon electrode. The Ml-BER showed suppressed methane production (19.8?±?9.1 mg-C·L^?1·day^?1) and increased hydrogen production (12.6?±?3.1 mg-H·L^?1·day^?1) at pH_out 6.2?±?0.1, and the major intermediate was butyrate (24.9?±?2.4 mM), suggesting efficient hydrogen fermentation. In contrast, the Ml-NBER showed high methane production (239.3?±?17.9 mg-C·L^?1·day^?1) and low hydrogen production (0.2?±?0.0 mg-H·L^?1·day^?1) at pH_out 6.3?±?0.1. In the cathodic chamber of the BER with membrane, methane production was high (276.3?±?20.4 mg-C·L^?1·day^?1) (pH_out, 7.2?±?0.1). In the anodic chamber of the BER with membrane (anode-BER), gas production was low because of high lactate production (43.6?±?1.7 mM) at pH_out 5.0?±?0.1. Methanogenic archaea were not detected in the Ml-BER and anode-BER. However, Methanosarcina sp. and Methanobacterium sp. were found in Ml-NBER. Prokaryotic copy numbers in the Ml-BER and Ml-NBER were similar, as were the bacterial community structures. Thus, the electrochemical reaction in the Ml-BER affected hydrogenotrophic and acetoclastic methanogens, but not the bacterial community.