Kinetic comparisons of mesophilic and thermophilic aerobic biomass

Kinetic parameters describing growth and decay of mesophilic (30°C) and thermophilic (55°C) aerobic biomass were determined in continuous and batch experiments by using oxygen uptake rate measurements. Biomass was cultivated on a single soluble substrate (acetate) in a mineral medium. The intrinsic maximum growth rate (μ _max) at 55°C was 0.71±0.09 h⁻¹, which is 1.5 times higher than the μ _max at 30°C (0.48±0.11 h⁻¹). The biomass decay rates increased from 0.004 h⁻¹ at 30°C to 0.017 h⁻¹ at 55°C. Monod constants were very low for both types of biomass: 9±2 mg chemical oxygen demand (COD) l⁻¹at 30°C and 3±2 mg COD l⁻¹at 55°C. Theoretical biomass yields were similar at 30 and 55°C: 0.5 g biomass COD (g acetate COD)⁻¹. The observed biomass yields decreased under both temperature conditions as a function of the cell residence time. Under thermophilic conditions, this effect was more pronounced due to the higher decay rates, resulting in lower biomass production at 55°C compared to 30°C. Electronic Publication     

Performance of an UASB reactor treating synthetic wastewater at low-temperature using cold-adapted seed slurry

The present study is an attempt to investigate if a long-term acclimation of digester contents to low-temperatures would improve wastewater treatment at low-temperatures similar to mesophilic ranges. The feasibility of low-temperature (15 °C) anaerobic treatment of synthetic wastewater in an upflow anaerobic sludge blanket reactor was studied using inoculum from a cattle manure digester adapted to 15 °C. The effect of varying hydraulic retention time was studied by decreasing the retention time from 7 days to 1 day. Under a constant temperature of 15 °C with a hydraulic retention time of 1 day and a corresponding loading rate of 7.2 g-chemical oxygen demand (COD)/l/day, 90–95% removal efficiency was achieved. The methane production of 250 l/kg-COD removed at standard temperature pressure (STP) is a major highlight of the study complementing the high treatment efficiency achieved. Loading rates >5 g-COD/l/day was accompanied by increase in effluent volatile fatty acids (VFA) concentrations. Due to the presence of a high concentration of active granular sludge in the lower compartment of the reactor, 80% reduction of COD occurred within the granular bed of the reactor. Treatment of low strength wastewater for a short period showed 70–75% removal efficiencies with methane yield of 300 l/kg-COD removed. Specific methanogenic activity profiles of the anaerobic biomass revealed low-temperature (15 °C) optima, indicating selection of cold-active microorganisms during the acclimation process. The SMA assays also indicate the development of a putatively psychrophilic acetoclastic methanogenic community and biogas analysis showed 75% efficiency in energy recovery as methane.     

Assessment of a UASB reactor with high ammonia concentrations: Effect of zeolite addition on process performance

The UASB process for wastewater treatment has been extensively studied, but the use of zeolite to improve UASB reactor performance has rarely been explored. In this study, a UASB reactor modified with natural zeolite operating at high nitrogen concentrations (0.5, 0.7 and 1 g/L) was evaluated. Two laboratory bioreactors, one with zeolite and one without, were operated at ambient temperatures ranging between 18 °C and 21 °C. The experimental phase had a start-up period of 21 days. In the reactor with zeolite, the pH was found to be between 7.9 and 9.1, with a COD removal efficiency of about 60% after 80 days of operation at ammonia concentrations of between 0.229 and 0.429 g/L in the effluent. In the reactor without zeolite, the pH was between 8.3 and 9.3, and the COD removal efficiency was about 40% at ammonia concentrations between 0.244 and 0.535 g/L in the effluent. The addition of zeolite also decreased the volatile suspended solids (VSS) concentration in the effluent, generating a biomass with larger granules and higher settling rates as compared to a UASB reactor without zeolite. Taking the lower ammonia concentration, the higher COD removal and the improved granulation into account, it can be concluded that natural zeolite positively influenced the behavior and performance of the UASB reactor operating with high nitrogen concentrations.     

Anaerobic treatment of synthetic medium-strength wastewater using a multistage biofilm reactor

A laboratory-scale multistage anaerobic biofilm reactor of three compartments with a working volume of 54-L was used for treating a synthetic medium-strength wastewater containing molasses as a carbon source at different influent conditions. The start-up period, stability and performance of this reactor were assessed at mesophilic temperature (35 °C). During the start-up period, pH fluctuations were observed because there was no microbial selection or zoning, but as the experiment progressed, results showed that phase separation had occurred inside the reactor. COD removal percentages of 91.6, 91.6, 90.0 and 88.3 were achieved at organic loading rates of 3.0, 4.5, 6.75 and 9.0 kg COD/m³ day, respectively. A decrease in HRT from 24 to 16 h had no effect on COD removal efficiency. When HRT decreased to 8 h, COD removal efficiency was still 84.9%. Recirculation ratios of 0.5 and 1.0 had no effect on COD removal but other factors such as the volatile fatty acid (VFA) content were affected. The effect of toxic shock was also investigated and results showed that the main advantage of using this bioreactor lies in its compartmentalized structure.     

Effect of operational conditions on the degradation of organic matter and development of microalgae-bacteria consortia when treating swine slurry

There is great controversy regarding the best substrate (fresh or anaerobically digested swine slurry) for the development of microalgae–bacteria consortia. This study aims to elucidate the best substrate by assessing biomass productivity, microorganism predominance, and their ability for organic matter removal. In addition to the different substrates, different operational conditions and influent strengths were evaluated. Increasing organic matter content when favourable temperature and illumination conditions were present improved biomass production. However, these conditions were not favourable for microalgal growth, but they were favourable for bacteria. Regardless of the operational conditions, reactors fed with fresh slurry not only resulted in the highest biomass productivity, but also the greatest removal of total and soluble chemical oxygen demand (COD). On the other hand, reactors fed with digested slurry showed biomass productivity and COD removal values lower than those obtained for reactors fed with fresh slurry, most probably due to the recalcitrant nature of the former. Nevertheless, digested slurry was the substrate more appropriate for microalgae growth under harsh operational conditions (16 °C and 9-h illumination) at low influent strength and optimum operational conditions (30 °C and 24-h illumination) at higher influent strength.     

Effects of temperature on simultaneous nitrification and denitrification via nitrite in a sequencing batch biofilm reactor

A laboratory scale experiment was described in this paper to enhance biological nitrogen removal by simultaneous nitrification and denitrification (SND) via nitrite with a sequencing batch biofilm reactor (SBBR). Under conditions of total nitrogen (TN) about 30 mg/L and pH ranged 7.15–7.62, synthetic wastewater was cyclically operated within the reactor for 110 days. Optimal operation conditions were established to obtain consistently high TN removal rate and nitrite accumulation ratio, which included an optimal temperature of 31 °C and an aeration time of 5 h under the air flow of 50 L/h. Stable nitrite accumulation could be realized under different temperatures and the nitrite accumulation ratio increased with an increase of temperature from 15 to 35 °C. The highest TN removal rate (91.9%) was at 31 °C with DO ranged 3–4 mg/L. Process control could be achieved by observing changes in DO and pH to judge the end-point of oxidation of ammonia and SND.     

Simultaneous single-cell protein production and COD removal with characterization of residual protein and intermediate metabolites during whey fermentation by K. marxianus

Cheese whey fermentation with Kluyveromyces marxianus was carried out at 40 °C and pH 3.5 to examine simultaneous single-cell protein production and chemical oxygen demand (COD) removal, determine the fate of soluble whey protein and characterize intermediate metabolites. After 36 h of batch fermentation, the biomass concentration increased from 2.0 to 6.0 g/L with 55 % COD reduction (including protein), whereas soluble whey protein concentration decreased from 5.6 to 4.1 g/L. It was confirmed through electrophoresis (SDS-PAGE) that the fermented whey protein was different from native whey protein. HPLC and GC–MS analysis revealed a change in composition of organic compounds post-fermentation. High inoculum concentration in batch fermentation resulted in an increase in biomass concentration from 10.3 to 15.9 g/L with 80 % COD reduction (including protein) within 36 h with residual protein concentration of 4.5 g/L. In third batch fermentation, the biomass concentration increased from 7.3 to 12.4 g/L with 71 % of COD removal and residual protein concentration of 4.3 g/L after 22 h. After 22 h, the batch process was shifted to a continuous process with cell recycle, and the steady state was achieved after another 60 h with biomass yield of 0.19 g biomass/g lactose and productivity of 0.26 g/L h. COD removal efficiency was 78–79 % with residual protein concentration of 3.8–4.2 g/L. The aerobic continuous fermentation process with cell recycle could be applied to single-cell protein production with substantial COD removal at low pH and high temperature from cheese whey.     

Anaerobic treatment of starch-containing wastewater using a plate-column reactor

An anaerobic plate-column reactor, developed to retain a high concentration of biomass, was studied using starch-containing synthetic wastewaters with regard to its start-up profile and the effects of TOC-loading rate, hydraulic retention time (HRT), and temperature in a steasy state. Each operation was started up at an initial biomass concentration of ca. 0.5 mg-N/ml (ca. 5 mg-VSS/ml), 20°C, an HRT of 30 h, and a TOC-loading rate of 0.8 g/l/d. The removal defficiency of dissolved organic carbon exceeded 90% after 29 d. The efficiency reached a steady state at 98% removal after 116 d. The biomass concentration in the reactor was 2.3 mg-N/ml after 154 d. Circulation of effluent at a ratio of 1 gave a lower removal efficiency and a lower biomass concentration than the same reactor without circulation. The effect of TOC-loading rate was studied at an HRT of 30 h, 20°C, and removal efficiencies were found 91% at 1.6 g/l/d and 77% at 3.2 g/l/d. The effect of HRT was studied at a TOC-loading rate of 0.8 g/l/d, 20°C, and removal efficiencies 91% at an HRT of 12 h and 72% at an HRT of 6 h.     

Real evidence about zeolite as microorganisms immobilizer in anaerobic fluidized bed reactors

Using the scanning electronic microscopy, it was observed that natural zeolite possesses excellent physical characteristics as a support medium in anaerobic fluidized bed reactors (AFBR). Samples for biomass analysis were taken from two identical laboratory-scale AFBR (R-1 and R-2), which were operated with 25% of fluidization. These reactors treated distillery wastewaters (vinasses) at mesophilic temperature (30 ± 2 °C). The experiments were carried out with 0.25–0.50 and 0.50–0.80 mm zeolite particle diameter in reactors R-1 and R-2, respectively. The biomass concentration attached to zeolite in both reactors was found to be in the range of 40–45 g volatile solids/l. COD removal efficiencies as high as 90% were achieved at organic loading rate (OLRs) of up to 20 g COD/l day. The volatile fatty acid (VFA) levels were always lower that the suggested limits for digester failure. The yield coefficient of methane production was 0.29 l CH₄(at STP)/g COD consumed and was virtually independent of the OLR applied. A hybridization technique (fluorescence in situ hybridization, FISH) helped determine the predominant anaerobic microorganisms that colonized the natural zeolite, which were found to be Methanosaeta and Methanosarcinaceae, observing a reduced number of sulphate reducing bacteria. The results obtained for reactors R-1 and R-2 were very similar, showing that the particle size did not significantly influence the microbial community immobilized on zeolite.     

Identification of bacteria coexisting with anammox bacteria in an upflow column type reactor

Anammox process has attracted considerable attention in the recent years as an alternative to conventional nitrogen removal technologies. In this study, a column type reactor using a novel net type acrylic fiber (Biofix) support material was used for anammox treatment. The Biofix reactor was operated at a temperature of 25°C (peak summer temperature, 31.5°C). During more than 340 days of operation for synthetic wastewater treatment, the nitrogen loading rates of the reactor were increased to 3.6 kg-N/m³/d with TN removal efficiencies reaching 81.3%. When the reactor was used for raw anaerobic sludge digester liquor treatment, an average TN removal efficiency of 72% was obtained with highest removal efficiency of 81.6% at a nitrogen loading rate of 2.2 kg-N/m³/d. Results of extracellular polymeric substances (EPS) quantification revealed that protein was the most abundant component in the granular sludge and was found to be almost twice than that in the sludge attached to the biomass carriers. The anammox granules in the Biofix reactor illustrated a dense morphology substantiated by scanning electron microscopy and EPS results. The results of DNA analyses indicated that the anammox strain KSU-1 might prefer relatively low nutrient levels, while the anammox strain KU2 strain might be better suited at high nutrient concentration. Other types of bacteria were also identified with the potential of consuming dissolved oxygen in the influent and facilitating survival of anammox bacteria under aerobic conditions.     

Effect of COD to sulphate ratio and temperature in expanded-granular-sludge-blanket reactors for sulphate reduction

In an ethanol-fed expanded-granular-sludge-blanket (EGSB) reactor at 33°C, 80–90% of the sulphate load was removed at a rate of 4 g S/l d, provided that at least 6 g chemical oxygen demand (COD) per g sulphate-sulphur was supplied. The reactor started up in a matter of days. Gradually decreasing the ethanol to sulphate ratio (R) to about stoichiometry, resulted in 60–70% sulphate removal at rates of 7 g S/l d. Similar tendencies were observed with ethylene glycol as sole carbon and energy source. Total COD removal never reached more than 70–75%. This was related to a rather high biomass washout. The sulphate removal efficiency decrease when R was set at levels below 6, apparently because sulphate reducing bacteria (SRB) could not compete with methane producing bacteria (MPB) for acetate produced from the substrate dosed. Thermophilic operation at 55°C, after a stepwise increase in the reactor temperature over a period of 23 days, did not favour acetotrophic sulphate reduction. Yet, operation at 48°C and subsequently returning the temperature to 33°C clearly enhanced acetate conversion by SRB. In the case of an electron donor price of 0.035–0.075 USD/kg COD, the cost for operation at R=6 was found to be competitive to that at stoichiometry, i.e. R=2, provided the biogas produced was effectively used.     

Yeast screening from avermectins wastewater and investigation on the ability of its fermentation

Wastewater from avermectin production is refractory with high output, high chemical oxygen demand (COD) concentration and high cost further. The current wastewater treatment technology, with little reuse of the organic material, needs high dilution ratio during treatment. Yeast single cell protein was produced from the wastewater of avermectins fermentation in this research. First, the yeast strain (H-1) which show enough tolerance to avermectins residue was screened from the wastewater, and it was identified as being most closely related to Candida tropicalis (100%, EF120592.1) using 18S rDNA gene sequence analysis. Second, its growth characteristics in the avermectins wastewater were studied. The dry biomass reached the maximal point of 10 g/L, the COD removal was up to 66.67%, and avermectins removal in the wastewater was 99.48% at the optimal condition that it was liquid volume 50 ml (250 ml flask), pH 4.0, temperature 30°C, inoculum volume 10% (V/V) and fermentation period 20 h. Third, the nutritional contents of dry yeast powder were determined, in which the water content was 8.12%, ash content was 5.18% and the crude protein was 40.02%. The dry yeast powder from avermectin waste liquor was promising to be used as a raw material or nitrogen source for commercial production of avermectins. The project was economically feasible by primary cost accounting.     

Lipidomic analysis of psychrophilic yeasts cultivated at different temperatures

Analysis of polar lipids from eight psychrophilic yeasts (Cryptococcus victoriae, Cystofilobasidium capitatum, Holtermaniella wattica, Mrakiella aquatica, M. cryoconiti, Rhodotorula lignophila, Kondoa malvinella and Trichosporon aggtelekiense) grown at 4–28 °C by hydrophilic interaction liquid chromatography/high resolution electrospray ionization tandem mass spectrometry determined 17 classes of lipids and identified dozens of molecular species of phospholipids including their regioisomers. Most of the yeasts were able to grow over the whole temperature range, reaching the highest biomass at 4 or 10 °C. On temperature drop to 4 °C, all eight strains showed a significant decrease of MUFA and a simultaneous increase of PUFA such as α-linolenic acid, the content of which in the biomass reached up to 20%. We also found alterations in the proportions of individual phospholipids (PI, PE and PC), the PC/PE-ratio decreasing with decreasing temperature. With increasing temperature the content of PoO-PC rose while that of LL-PC decreased, the drop in the content of LL-PC being nearly 100-fold while the content of PoO-PC increased more than twice.A change in temperature brought about changes in molecular species of PC (molecular species PO-PC versus OP-PC) as well as PE, i.e. PO-PE and OP-PE. The phase transition temperature of PO-PC differs from OP-PC by 7 °C and the difference between PO-PE and OP-PE is some 10 °C; we thus assume that the cell compensates for the adverse temperature effect by changing the fatty acids in the sn-1 and sn-2 positions.     

Performance and molecular evaluation of an anaerobic system with suspended biomass for treating wastewater with high fat content after enzymatic hydrolysis

The effect of a lipase-rich fungal enzymatic preparation, produced by a Penicillium sp. during solid-state fermentation, was evaluated in an anaerobic digester treating dairy wastewater with 1200 mg of oil and grease/L. The oil and grease hydrolysis step was carried out with 0.1% (w/v) of solid enzymatic preparation at 30 °C for 24 h, and resulted in a final free acid concentration eight times higher than the initial value. The digester operated in sequential batches of 48 h at 30 °C for 245 days, and had high chemical oxygen demand (COD) removal efficiencies (around 90%) when fed with pre-hydrolyzed wastewater. However, when the pre-hydrolysis step was removed, the anaerobic digester performed poorly (with an average COD removal of 32%), as the oil and grease accumulated in the biomass and effluent oil and grease concentration increased throughout the operational period. PCR-DGGE analysis of the Bacteria and Archaea domains revealed remarkable differences in the microbial profiles in trials conducted with and without the pre-hydrolysis step, indicating that differences observed in overall parameters were intrinsically related to the microbial diversity of the anaerobic sludge.     

High midday temperature stress has stronger effects on biomass than on photosynthesis: A mesocosm experiment on four tropical seagrass species

The effect of repeated midday temperature stress on the photosynthetic performance and biomass production of seagrass was studied in a mesocosm setup with four common tropical species, including Thalassia hemprichii, Cymodocea serrulata, Enhalus acoroides, and Thalassodendron ciliatum. To mimic natural conditions during low tides, the plants were exposed to temperature spikes of different maximal temperatures, that is, ambient (29–33°C), 34, 36, 40, and 45°C, during three midday hours for seven consecutive days. At temperatures of up to 36°C, all species could maintain full photosynthetic rates (measured as the electron transport rate, ETR) throughout the experiment without displaying any obvious photosynthetic stress responses (measured as declining maximal quantum yield, Fv/Fm). All species except T. ciliatum could also withstand 40°C, and only at 45°C did all species display significantly lower photosynthetic rates and declining Fv/Fm. Biomass estimation, however, revealed a different pattern, where significant losses of both above‐ and belowground seagrass biomass occurred in all species at both 40 and 45°C (except for C. serrulata in the 40°C treatment). Biomass losses were clearly higher in the shoots than in the belowground root–rhizome complex. The findings indicate that, although tropical seagrasses presently can cope with high midday temperature stress, a few degrees increase in maximum daily temperature could cause significant losses in seagrass biomass and productivity.     

Simulated acid azo dye (Acid black 210) wastewater treatment by periodic discontinuous batch mode operation under anoxic–aerobic–anoxic microenvironment conditions

Treatment of simulated acid azo dye (C.I. Acid black 210) wastewater was studied in periodic discontinuous batch mode operation employing sequencing batch reactor (SBR) with suspended growth configuration under anoxic–aerobic–anoxic microenvironment. The performance of the reactor was evaluated at two organic loading rates (0.56 kg COD/m³-day and 0.75 kg COD/m³-day) with a total cycle period of 24 h [fill phase: 30 min; react phase: 23 h; settle phase: 15 min; decant phase: 15 min] at room temperature. The performance of SBR was assessed by monitoring both COD and colour (OD-617 nm) concentrations. Periodic discontinuous batch mode operation feasibility for dye colour removal along with simultaneous substrate (COD) removal. The performance efficiency of the system was found to depend on the operating organic loading rate. Induced anoxic microenvironment during cycle operation and persistent anoxic microenvironment in the internal layer of suspended biomass may be probable reasons for dye mineralization/reduction. Rapid startup period and non-inhibited performance at higher loading rate are some of the advantages observed in the SBR operation.     

Temperature-induced changes in treatment efficiency and microbial structure of aerobic granules treating landfill leachate

This paper investigates the effect of temperature on nitrogen and carbon removal by aerobic granules from landfill leachate with a high ammonium concentration and low concentration of biodegradable organics. The study was conducted in three stages; firstly the operating temperature of the batch reactor with aerobic granules was maintained at 29 °C, then at 25 °C, and finally at 20 °C. It was found that a gradual decrease in operational temperature allowed the nitrogen-converting community in the granules to acclimate, ensuring efficient nitrification even at ambient temperature (20 °C). Ammonium was fully removed from leachate regardless of the temperature, but higher operational temperatures resulted in higher ammonium removal rates [up to 44.2 mg/(L h) at 29 °C]. Lowering the operational temperature from 29 to 20 °C decreased nitrite accumulation in the GSBR cycle. The highest efficiency of total nitrogen removal was achieved at 25 °C (36.8 ± 10.9 %). The COD removal efficiency did not exceed 50 %. Granules constituted 77, 80 and 83 % of the biomass at 29, 25 and 20 °C, respectively. Ammonium was oxidized by both aerobic and anaerobic ammonium-oxidizing bacteria. Accumulibacter sp., Thauera sp., cultured Tetrasphaera PAO and Azoarcus–Thauera cluster occurred in granules independent of the temperature. Lower temperatures favored the occurrence of denitrifiers of Zooglea lineage (not Z. resiniphila), bacteria related to Comamonadaceae, Curvibacter sp., Azoarcus cluster, Rhodobacter sp., Roseobacter sp. and Acidovorax spp. At lower temperatures, the increased abundance of denitrifiers compensated for the lowered enzymatic activity of the biomass and ensured that nitrogen removal at 20 °C was similar to that at 25 °C and significantly higher than removal at 29 °C.     

Temperature response of C4 species big bluestem (Andropogon gerardii) is modified by growing carbon dioxide concentration

Climate change factors interact to modify plant growth and development. The objective of this study was to evaluate the response to temperature of big bluestem (Andropogon gerardii Vitman) development, growth, reproduction and biomass partitioning under low and high carbon dioxide concentrations ([CO₂]) grown in controlled environmental conditions. Ten sunlit soil–plant–atmosphere-research (SPAR) chambers were used to study the effects of two [CO₂] of low (360 μL L⁻¹) and high (720 μL L⁻¹), and five different day/night temperatures of 20/12, 25/17, 30/22, 35/27 and 40/32 °C. Big bluestem cv. Bonelli seeds were sown in pure, fine sand, in 11 rows at equal spacing and after emergence were thinned to 10 plants per row. At maturity, individual plants were harvested and divided into leaves, stems, panicles and roots. Biomass decreased either above or below the optimum temperature of 30/22 °C. The effect of high [CO₂] on biomass accumulation (12–30% increase) was visible at less than optimum temperature (30/22 °C) and absent at two high temperatures. With increase in temperature, irrespective of the [CO₂], biomass partitioned to leaves increased (35%) where as that to stems decreased (33%). Panicle weight was 6–7% of biomass at 25/17 °C and fell to 1.6% at 40/32 °C. The biomass partitioned to roots, across the temperatures, was constant for plants grown at low [CO₂] but decreased by 7% for those grown at high [CO₂]_. The decrease in panicle/seed production at two high temperatures (>30/22 °C) might reduce this species population and dominance in tallgrass prairies. The temperature response functions at different [CO₂] will be useful to improve the predictive capabilities of dynamic global vegetation models in simulating dynamics of rangelands, where big bluestem is the dominant species.     

Effects of elevated temperature on bacterial community structure and function in bioreactors treating a synthetic wastewater

The impact of elevated temperature on bacterial community structure and function during aerobic biological wastewater treatment was investigated. Continuous cultures, fed a complex growth medium containing gelatin and α-lactose as the principal carbon and energy sources, supported mixed bacterial consortia at temperatures ranging from 25–65°C. These temperature- and substrate-acclimated organisms were then used as inocula for batch growth experiments in which the kinetics of microbial growth and substrate utilization, efficiency of substrate removal, and mechanism of substrate removal were compared as functions of temperature. Bacterial community analysis by denaturing gradient gel electrophoresis (DGGE) revealed that distinct bacterial consortia were supported at each temperature. The efficiency of substrate removal declined at elevated temperatures. Maximum specific growth rates and the growth yield increased with temperature from 25–45°C, but then decreased with further elevations in temperature. Thus, maximum specific substrate utilization rates did not vary significantly over the 40°C temperature range (0.64 ± 0.04 mg COD mg⁻¹ dry cell mass h⁻¹). A comparison of the degradation of the protein and carbohydrate portions of the feed medium revealed a lag in α-lactose uptake at 55°C, whereas both components were utilized simultaneously at 25°C. Journal of Industrial Microbiology & Biotechnology (2000) 24, 140–145. Received 09 August 1999/ Accepted in revised form 12 November 1999     

Investigating thermal acclimation effects before and after a cold shock in Drosophila melanogaster using behavioural assays

Acclimation to environmental change can impose both costs and benefits to organisms. In this study we explored to what extent locomotor behaviour of Drosophila melanogaster is influenced by developmental temperature and adult temperature in both the laboratory and the field. Following development at 15, 25, or 31 °C, adult flies were tested for locomotor activity at all developmental temperatures in the laboratory before and after exposure to a cold shock and in the field for their ability to locate resources after a cold shock. Both test (15, 25, and 31 °C) and developmental temperatures strongly affected locomoter activity, with flies developed at 25 °C having the highest activity at all three test temperatures before the cold shock. After the cold shock flies developed at 15 °C had higher activity compared with flies developed at 25 and 31 °C when tested at 15 and 25 °C, and flies developed at 25 °C had the highest activity when tested at 31 °C. Furthermore, flies developed at 31 °C showed longer recovery times following the cold shock at test temperatures of 15 and 25 °C. However, flies acclimated at 15 °C during development did not recover faster at 15 and 25 °C compared with flies developed at 25 °C. There were no significant correlations between recovery time and locomotor activity at any of the test temperatures. Flies developed at 15 °C and exposed to a cold shock before release in the field were much more successful in locating a resource at low field temperatures compared with flies developed at 25 and 31 °C. Our results provide support for both the beneficial acclimation hypothesis and the optimal developmental temperature hypothesis, but the results are highly context dependent and change with the temperature experienced by the individual during its lifetime.