Longitudinal distribution of macroinvertebrates in two glacier-fed New Zealand rivers

1. Environmental variables, benthic algal biomass and macroinvertebrate fauna were examined from September 1999 to January 2000 (austral summer) along two glacier-fed rivers in South Island, New Zealand.
2. The rivers were characterized by high flow variability, high turbidity and physically disturbed beds. Water temperature ranged from <1 °C near the glacier margin to 10 °C further downstream.
3. Epilithic algal biomass was very low (<0.1 mg m^–2) in months characterized by heavy rainfall, but ranged from 1.1 to 14.4 mg m^–2 following an extended period with negligible precipitation.
4. Abundance and diversity of invertebrates in both rivers was low. Dominant taxa were Chironomidae (Orthocladiinae, Podonominae, Diamesinae), although mayfly species ( Deleatidium : Leptophlebiidae) also occurred at most sites. A species of Eukiefferiella (Orthocladiinae) was collected at all sites and was the most abundant invertebrate close to the glacier margins. No meiofauna were found in either river.
5. Faunal diversity increased at the lowermost stations where species of Plecoptera, Trichoptera, Coleoptera and non-chironomid Diptera also occurred.
6. The faunas of the two New Zealand rivers conformed to the conceptual model of Milner & Petts (1994) in that taxon richness increased downstream with water temperature. However, invertebrate abundance increased downstream in only one of the two rivers. Also in contrast to the model predictions, Leptophlebiidae and Orthocladiinae, rather than Diamesinae, dominated the fauna at the coldest sites.     

Modelling the growth of Weissella cibaria as a function of fermentation conditions

Aims:  To investigate the effect of pH, water activity ( a _w) and temperature on the growth of Weissella cibaria DBPZ1006, a lactic acid bacterium isolated from sourdoughs.
Methods and Results:  The kinetics of growth of W. cibaria DBPZ1006 was investigated during batch fermentations as a function of pH (4·0–8·0), a _w (0·935–0·994) and temperature (10–45°C) in a rich medium. The growth curve parameters (lag time, growth rate and asymptote) were estimated using the dynamic model of Baranyi and Roberts (1994. A dynamic approach to predicting bacterial growth in food. Int J Food Microbiol 23, 277–294). The effect of pH, a _w and temperature on maximum specific growth rate (μ_max) were estimated by fitting a cardinal model. μ_max under optimal conditions (pH = 6·6, a _w = 0·994, T  = 36·3°C) was estimated to be 0·93 h⁻¹. Minimum and maximum estimated pH and temperature for growth were 3·6 and 8·15, and 9·0°C and 47·8°C, respectively, while minimum a _w was 0·918 (equivalent to 12·2% w/v NaCl).
Conclusions:  Weissella cibaria DBPZ1006 is a fast-growing heterofermentative strain, which could be used in a mixed starter culture for making bread.
Significance and Impact of the Study:  This is the first study reporting the modelling of the growth of W. cibaria , a species that is increasingly being used as a starter in sourdough and vegetable fermentations.     

Acclimation is beneficial at extreme test temperatures in the Danube crested newt, Triturus dobrogicus (Caudata, Salamandridae)

Despite many studies demonstrating the effect of acclimation on behavioural or physiological traits, considerable debate still exists about the evolutionary significance of this phenomenon. One of the unresolved issues is whether acclimation to warmer temperature is beneficial at treatment or at more extreme test temperatures. To answer this question, we assessed the effect of thermal acclimation on preferred body temperatures ( T _ps), maximum swimming and running speed, and critical thermal maximum ( CT _max) in the Danube crested newt ( Triturus dobrogicus ). Adult newts were kept at 15 °C (control) and 25 °C (treatment) for 8 weeks prior to measurements. We measured T _ps in an aquatic thermal gradient over 24 h, maximum speeds in a linear racetrack at six temperatures (5–33 °C), and CT _max in a continuously heated water bath. T _ps were higher in newts kept at 15 °C than in those kept at 25 °C. The maximum swimming speed did not acclimate. The maximum running speed at 30–33 °C was substantially higher in newts kept at 25 °C than in those kept at 15 °C. CT _max increased with the treatment temperature. Hence, we conclude that the acclimation response to warm temperature is beneficial not at treatment but at more extreme temperatures in newts.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 627–636.     

Thermal acclimation of photosynthesis in black spruce [Picea mariana (Mill.) B.S.P.

We investigated the thermal acclimation of photosynthesis and respiration in black spruce seedlings [ Picea mariana (Mill.) B.S.P.] grown at 22/14 °C [low temperature (LT)] or 30/22 °C [high temperature (HT)] day/night temperatures. Net CO₂ assimilation rates ( A _net) were greater in LT than in HT seedlings below 30 °C, but were greater in HT seedlings above 30 °C. Dark and day respiration rates were similar between treatments at the respective growth temperatures. When respiration was factored out of the photosynthesis response to temperature, the resulting gross CO₂ assimilation rates ( A _gross) was lower in HT than in LT seedlings below 30 °C, but was similar above 30 °C. The reduced A _gross of HT seedlings was associated with lower needle nitrogen content, lower ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) maximum carboxylation rates ( V _cmax) and lower maximum electron transport rates ( J _max). Growth treatment did not affect V _cmax :  J _max. Modelling of the CO₂ response of photosynthesis indicated that LT seedlings at 40 °C might have been limited by heat lability of Rubisco activase, but that in HT seedlings, Rubisco capacity was limiting. In sum, thermal acclimation of A _net was largely caused by reduced respiration and lower nitrogen investments in needles from HT seedlings. At 40 °C, photosynthesis in LT seedlings might be limited by Rubisco activase capacity, while in HT seedlings, acclimation removed this limitation.     

Macroinvertebrate community structure in relation to environmental variables in a Swiss glacial stream

1. Benthic macroinvertebrate distribution was examined in relation to channel characteristics (including stability), substratum, hydraulic variables, primary production (chlorophyll a ) and coarse particular organic matter (CPOM) in an alpine glacial stream, the Mutt (Upper Rhône valley, Switzerland). Co-inertia analysis and canonical correspondence analysis were used to identify the major environmental gradients influencing community variations.
2. The Mutt (length: 3.6 km, altitudinal range: 1800–3099 m a.s.l.) exhibited typical characteristics of a kryal stream. Average summer temperature remained below 2 °C immediately downstream from the snout but was on average 5 °C higher 1700 m downstream. Seasonal variations in water sources were evidenced by the high late-summer (September) contribution of groundwater with increased conductivity.
3. Sixty-six taxa were recorded from the five reaches sampled at three periods (snowmelt, ice melt and low water in late summer) in 1996 and 1997, of which 29 were Chironomidae. Three taxa of Diamesinae were the first colonizers of the stream below the glacier, but 16 taxa, including Ephemeroptera, Plecoptera and Trichoptera, were already recorded 200 m downstream. Water depth, channel slope and Pfankuch's Index of channel stability were strongly correlated with the longitudinal faunal gradient. Maximum temperature, current velocity and water conductivity were also correlated, but to a lesser extent.
4. The rapid incorporation of non-chironomid taxa into the stream community represented a departure from Milner & Petts's (1994) conceptual model of invertebrate succession downstream of glacial margins. The results confirmed that glacial stream communities are primarily driven by physical determinants.     

The growth of brown trout (Salmo trutta) in mild winters and summer droughts in upland Wales

SUMMARY. 1. We compared the observed annual growth of 0- and I-group trout in nine Welsh upland streams, with growth predicted from temperature assuming that this was the only limiting factor.
2. Autumn weights of second year fish were 51–67% of predicted ( G _max) values in 1988, but only 30–40% in 1989 and 1990 when drought occurred. Though initial weights of fry were unknown, simulations suggested that first year growth was also less than G _max, but with no obvious effect of drought.
3. To evaluate the possible effects of future climate change, we simulated stream temperature regimes 1.5–4.5°C above those of a recent year with temperatures similar to the long-term average. Growth was set at 60% G _max for both 0- and I-group, or at 40% for I-group to represent the effect of drought. As winter temperature increased, time to hatching and emergence decreased, for example by 56 and 49 days respectively for a rise of 3°C. 0-group growth was slightly enhanced at up to + 3°C but retarded at + 4.5°C. Simulations of I-group growth suggested that warmer winters could enhance trout growth while warmer summers would only increase growth if there were no adverse effects of drought.
4. We discuss many uncertainties in these simulations, which nevertheless suggest the magnitude of possible effects of climate change.     

The distribution of macroinvertebrate communities in two Portuguese rivers

SUMMARY. 1. The distribution of macroinvertebrates in two chemically different rivers of Central Portugal (Soure and Alva) was analysed.
2. In the Soure, a lowland, alkaline river (mean values for alkalinity, conductivity and pH, 101 mg I⁻¹ CaCO₃, 255 μS cm⁻¹ and 7.8, respectively), a relatively high number of individuals and low diversity (mean H '= 2.27) was found. There was considerable temporal variation in the number of individuals present.
3. In the Alva, a highland, acidic river (mean values for alkalinity, conductivity and pH. 4.8 mg 1⁻¹ CaCO₃, 22 μ S cm⁻¹ and 5.7, respectively), diversity was higher (mean H '=3.41). There were large temporal changes in the number of species present, but not in the number of individuals.
4. Similarity indices and cluster analysis identified six site-types and seventeen groups of co-occurring taxa. Some of the taxonomic groups were characteristic of one or more sites, hut others had no strong association with a particular site. Although the rivers differed considerably in terms of physico-chemistry, communities in the upper sections of the two rivers were more similar to each other, than to other communities in the same river. The way the samples of both rivers were clustered seems to indicate that community structure was influenced by factors associated with (1) within river longitudinal variation (e.g. substrate grain size), (2) water chemistry, and (3) seasonal variations (e.g. temperature, flow).     

The survival of Salmonella enterica serovar Typhimurium DT104 and total viable counts on beef surfaces at different relative humidities and temperatures

Aims:  The aim of this study was to investigate changes in Salmonella and total viable count (TVC) survival on beef carcass surfaces stored for 72 h under different combinations of relative humidity (i.e. RH 75% or 96%) and temperature (5°C or 10°C).
Methods and Results:  The influence of low water activity ( a _w) and temperature on the survival and growth of Salmonella enterica serovar Typhimurium DT104 and the aerobic mesophilic flora on meat pieces from different sites on beef carcasses was investigated, under controlled conditions (75% or 96% RH; 5 or 10°C) in an environmental cabinet. Salmonella counts declined during storage at low a _w (75% RH) conditions at 5°C or 10°C. Salmonella counts increased during storage at high a _w (96% RH) at 10°C only. At 5°C, TVCs increased during storage at high a _w, but not at low a _w. TVCs increased on all samples from carcasses stored at high or low a _w at 10°C, except those samples taken from areas of surface fat.
Conclusions:  This suggests that substrate composition dictates growth rates under low a _w conditions. The results are discussed in terms of the possible protective effects of substrate osmolyte accumulation in bacterial survival and/or growth.
Significance and Impact of the Study:  The data obtained in this study provides useful insights on the influence of a _w and temperature on pathogen survival on meat surfaces at chill temperature.     

Effect of temperature and water activity on in vitro germination of Monilinia spp.

Aims:  This study evaluated the effect of temperature (0–38°C) and water activity ( a _w: 0·87–0·99) on the lag phase prior to germination and the percentage of germination over time for Monilinia laxa , Monilinia fructicola and Monilinia fructigena .
Methods and Results:  More than 80% of viable conidia germinated at 25°C and 0·99 a _w within 2 h for M. fructicola and M. fructigena and 4 h for M. laxa . There was no germination at 38°C, and all three Monilinia spp. germinated at 0°C. At the lowest a _w (0·87), none of the Monilinia spp. was able to germinate at any of the incubation temperatures studied. Whereas at 0·90 a _w, conidia were only able to germinate at 15, 25 and 30°C for the three species studied, except for M. fructicola at 15°C. In contrast, at 0·95, 0·97 and 0·99 a _w, germination occurred at all studied temperatures less 38°C. Generally, the lag phase was longer at low levels of a _w (0·90–095), and differences were more evident as temperatures were far from the optimum (0–5°C).
Conclusions:  Germination and lag phase period were markedly influenced by temperature and a _w, and in general when conditions of temperature and a _w were suboptimal, the lag phase was longer and the percentage of germination was lower.
Significance and Impact of the Study:  Knowledge of the germination requirements of this fungus is important in order to understand their behaviour in natural situations and to provide baseline data required for the construction of new prediction models. Our study might be used to develop a predictive model to understand and control the disease caused by Monilinia spp.     

Macrobenthic invertebrate richness and composition along a latitudinal gradient of European glacier-fed streams

1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier-fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near-pristine reaches were studied on each stream in 1996–97.
2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non-insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa).
3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell-shaped with an optimum at an intermediate level of stability.
4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross-validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated.
5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier-fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier-fed streams under climate or hydrological change scenarios.     

Roles of endothermy in niche differentiation for ball-rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient

Abstract.  1. An analysis of whether niche differentiation in ball-rolling dung beetles can be explained by the way in which they regulate their body temperature was conducted.
2.  A priori assumptions were: (i) if thermoregulation affects niche partitioning, sympatric species must have different endothermic strategies that minimise encounters; or, alternatively (ii) if two co-occurring species show the same thermoregulation pattern and their flight periods overlap, they might be avoiding competition by exhibiting different resource preferences or different food relocation behaviour.
3. The ball-rolling dung beetles studied showed a hierarchical structure based on the species' endothermic capacity, measured as temperature excess [ T _ex= difference between body temperature ( T _b) and ambient temperature ( T _a)]. Those with a high T _ex (10–15 °C) were located exclusively at altitudes >1000 m a.s.l. On the coastal plains, species with a high T _ex were restricted to flying at night when the T _a was lower. Species with a lower T _ex (less than 10 °C higher than T _a) were found in the coastal plains zone.
4. Where there was sympatry with similar trophic habits, the species involved showed very different thermal niches, and where there was significant overlap of thermal niches between sympatric species, trophic habits of species were very different.
5. The results suggest that it is possible to use the concept of the thermal niche as a tool to explain interspecific interactions and the spatial distribution of species.     

Impact of temperature on food intake and growth in juvenile burbot

The effect of temperature on food consumption, food conversion and somatic growth was investigated with juvenile burbot Lota lota (age 0 years). Juvenile burbot showed a significant dome shaped relationship between relative daily food consumption ( C _R) and temperature ( T ) with C _R = − 0·00044 T ² + 0·01583 T  − 0·06010; ( n  = 90, r ² = 0·61). Maximum C _R was at 17·9° C (95% CL 17·2–18·6° C). The temperature related instantaneous growth rate ( G ) also followed a dome shaped function with G  = − 0·000063 T ² + 0·002010 T  − 0·007462; ( n  = 95, r ² = 0·57), with maximum growth rate at 16·0° C (95% CL 15·3–16·6° C). A significant linear relationship was found between the water temperature and the conversion coefficient ( C _C) with C _C = − 1·63 T  + 59·04; ( n  = 80, r ² = 0·74). The results indicate that juvenile burbot in large lakes benefit from higher water temperatures in the littoral zone, by increased food uptake and growth, especially during the warm summer months. Because profundal water temperatures do not reflect the optimal temperature for food consumption in large burbot, temperature is unlikely to be the main proximate factor for the obligate littoral‐profundal migration of juvenile burbot observed in many lake populations.     

The macroinvertebrate communities of two contrasting Norwegian glacial rivers in relation to environmental variables

1. Macroinvertebrate communities in two Norwegian glacial rivers, one in the western fjords (Dalelva) and one in the eastern mountains (Leirungsåi), were investigated during three time periods in 1996 and 1997.
2. Channel stability variables (substratum heterogeneity/Pfankuch index/hydraulic stress) and water temperature accounted for 54% of the total inertia in the principal components analysis (PCA) ordination of environmental variables. The importance of these variables was confirmed by cluster analysis.
3. The two rivers were well separated in the ordinations, with Leirungsåi showing much greater heterogeneity. This is explained by differences in altitudinal range, terrestrial vegetation and the importance and nature of tributary inputs.
4. Channel stability and temperature were also important in determining faunal communities in the two glacial rivers, supporting the main determining variables in the conceptual model of glacial streams ( Milner & Petts, 1994 ). However, clear temporal differences were apparent in the data, the two rivers being more similar during the summer period of high discharge dominated by glacial meltwater. During spring and especially during autumn environmental conditions and the macroinvertebrate fauna differed both within and between rivers.
5. Diamesinae dominated in the upper reaches of both rivers, with Orthocladiinae becoming more common downstream. The dominance of Diamesinae persisted further down Dalelva because of the continued influence of glacial tributaries, whereas in Leirungsåi the influence of non-glacial tributaries led to a change towards a greater proportion of Orthocladiinae. Lakes modified macroinvertebrate communities in both river systems.     

Can filter‐feeding fishes improve water quality in lakes?

1.  In this paper we examine the potential of a cichlid fish species ( Sarotherodon galilaeus ) to both maintain positive growth rates through filter-feeding on phytoplankton and improve water quality in Lake Kinneret through suppression of dinoflagellate ( Peridinium gatunense ) blooms.
2.  Seasonal plankton consumption by S. galilaeus from Lake Kinneret was examined experimentally by monitoring changes in plankton assemblages during 24 h in 5-m³ mesocosms containing varying densities of fish. Taxon-specific grazing rates ranged from 0 to 17 mg g_fish day^–1, with mean total consumption of 1.6% fish body weight per day. During the spring bloom of P. gatunense , S. galilaeus consumed mostly (94%) netphytoplankton (≥20 μm). The remaining 6% consisted mostly of nanophytoplankton (<20 μm). During the summer and fall, net- and nanophytoplankton accounted for 54 and 42%, respectively, of the diet of S. galilaeus . Zooplankton and flagellated and ciliated protozoans made up the remaining 4%.
3.  Simulations using a fish bioenergetics model indicated that consumption rates ( C ) were near maximum in spring (90% C _max), while consumption was reduced in summer-fall (59% C _max). Sarotherodon galilaeus obtains sufficient energy through filter-feeding year-round, although most growth (≥60%) occurs during the spring P. gatunense bloom.
4.  Despite efficient feeding on P. gatunense and nanophytoplankton by S. galilaeus , estimates of instantaneous plankton mortality caused by ingestion were two orders of magnitude lower than maximum potential plankton growth rates. Thus the potential for the S. galilaeus population in Lake Kinneret to positively affect water quality through algal suppression is low.     

Escherichia coli O157 can grow in natural freshwater at low carbon concentrations

Whereas much information on the die-off of Escherichia coli in the aquatic environment is available, only few data support its growth under such conditions. We therefore investigated batch growth in microcosms containing different types of sterile freshwater. The water samples were inoculated with low starting cell concentrations of E. coli O157 (3 × 10³ cells ml⁻¹) and growth was followed using nucleic acid staining combined with flow cytometry. We demonstrated that E. coli O157 is able to grow in sterile freshwater at low carbon concentrations, which is against the common view that cell numbers decline over time when added to freshwater samples. A correlation between apparent assimilable organic carbon (AOC_app) concentration and the final cell concentration reached by E. coli O157 was established ( P  <  0.01). A considerable fraction of the AOC_app (34 ± 13%) was used by E. coli O157 but the numerical cell yield was about five-times lower in comparison with the bacterial AOC-test community, which originated from natural freshwater. On average, the maximum specific growth rate ( μ _max) of E. coli O157 growing in sterile freshwater at 30°C was 0.19 ± 0.07 h⁻¹. Batch growth assays at five different temperatures revealed a positive influence of temperature on μ _max of E. coli O157. The results give new information on the behaviour of this common pathogen in the aquatic environment and contribute to microbial risk assessment in order to prevent spreading of water-borne diseases.     

Changes in Escherichia coli O157:H7 numbers during holding on excised lean, fascia and fat beef surfaces at different temperatures

Aim:  To investigate changes in Escherichia coli O157:H7 numbers on excised beef carcass surfaces over 72 h at different temperatures.
Methods and Results:  Excised lean meat, fascia and fat were inoculated with E. coli O157:H7 and held in an environmental chamber for 72 h, at air speed 0·5 m s⁻¹, relative humidity (RH) 90%, and temperatures 4, 8 and 12°C. On lean, pathogen counts increased significantly at 12°C. On fascia, significant reductions in counts occurred at 4 and 8°C. Pathogen numbers were significantly reduced on fat at 4, 8 and 12°C (64 h). Counts on fat were significantly less at all temperatures, compared to lean or fascia and surface water activity, a_w, decreased significantly over time on fat at 4°C. Significant decreases in surface pH values were recorded on all meat substrates.
Conclusions:  The survival of E. coli O157:H7 varied in relation to the meat substrate and the holding temperature. Reductions in counts on fat surfaces appeared to be related to low surface a_w values. No relationship between pathogen survival and surface pH was established.
Significance and Impact of the Study:  The use of excised meat pieces in an environmental cabinet offers a more flexible approach to determining the use of different chilling regimes in the production of safe meat.     

Disruption of a longitudinal pattern in environmental factors and benthic fauna by a glacial tributary

SUMMARY 1. In the upper Rhône catchment (Swiss Alps), modifications in the longitudinal pattern of environmental conditions and the benthic macroinvertebrate fauna were investigated in a glacier-fed stream (Rhône) at its confluence with a smaller glacier-fed tributary (Mutt) in June, August and September 1998. The distance to the source glacier was greater for the Mutt than for the Rhône.
2. Environmental conditions were harsher for the biota in the main stream upstream of the confluence than in the tributary. The tributary upstream of the confluence was characterised by higher taxonomic richness and abundance of the zoobenthos than the Rhône upstream.
3. Although environmental conditions in the main stream were little modified by the tributary, the fauna was richer and more diverse below the confluence. During the period of ice melt, colonisation from the Mutt led to the occurrence of faunal elements atypical of glacial streams in the main glacial stream upstream of the confluence, where water temperature remains below 4 °C.
4. Although contributing an average of only 10% to the Rhône discharge, the Mutt tributary is suggested to be the faunal driver of the system.     

Mixotrophic ciliates in an Andean lake: dependence on light and prey of an Ophrydium naumanni population

1. Planktonic ciliates were examined during a spring–summer period (November 1998–April 1999) in the ultraoligotrophic Lake Moreno Oeste (41°5' S and 71°33' W, 758 m a.s.l), which belongs to the Nahuel Huapi System (Patagonia, Argentina). The lake is deep ( Z _max=90 m) and warm monomictic.
2. Sampling was performed at a mid-lake station, where vertical profiles of temperature and light were measured in situ , and samples for bacteria and ciliates enumeration were taken throughout the water column.
3. The peritrich Ophrydium naumanni , a freshwater pelagic ciliate with endosymbiotic Chlorella , was the dominant ciliate in the lake.
4.  Ophrydium naumanni and autotrophic picoplankton exhibit a clear coincidence in their vertical distribution ( P  < 0.05), preferring levels at or near the 1% of surface photosynthetically active radiation (PAR) irradiance. Both may have the same light requirements, or the coincidence may reflect a trophic relationship.
5. Dependence on light and prey by O. naumanni were studied using field experiments, in which we analysed ciliate grazing on bacteria, and in laboratory experiments, in which we compared particle uptake under dark and light conditions.
6.  Ophrydium naumanni was able to ingest particles [latex microspheres and fluorescently labelled bacteria (FLB)] in field and laboratory experiment, indicating that it has the potential to affect bacteria population of Lake Moreno Oeste.
7. Ciliate particle ingestion was observed to be dependent on light availability because under dark conditions, the ingestion was lowered ( P  < 0.05).     

Determination of optimal growth parameters for the bioincising fungus Physisporinus vitreus by means of response surface methodology

Aim:  To evaluate the influence of water activity ( a _w), temperature and pH on the radial growth and lag phase of Physisporinus vitreus (E-642), a basidiomycete was used in the biotechnological process of bioincising.
Methods and Results:  Radial growth was monitored for 20 days on malt extract agar medium. Five levels of a _w (0·998, 0·982, 0·955, 0·928, 0·892) were combined with three incubation temperatures (10, 15, 20°C) and three pH values (4, 5, 6). Data analyses showed a highly significant effect of a _w and temperature ( P <  0·0001) and a significant effect of pH ( P <  0·05). The radial growth rate and lag phase of P. vitreus were very sensitive to a _w reduction. Although P. vitreus was able to grow at all the selected temperatures and pH values, the lag phase increased with decreasing a _w and growth became inhibited at a _w = 0·955. Optimal conditions for growth of P. vitreus were a _w = 0·998, 20°C and pH 5. The response surface model provided reliable estimates of these growth parameters and confirmed a greater dependence on a _w than on temperature or pH under in vitro conditions.
Conclusions:  Low levels of a _w can prevent growth of P. vitreus , so wood moisture content should be adjusted accordingly.
Significance and Impact of the Study:  Implementation of these results should contribute towards the optimization and efficiency of bioincising.