Some effects of heat shocks on bacterial growth

Summary In large industrial scale bioreactors process cultures are frequently exposed to supperoptimal temperatures for short intervals of time. Data concerning the physiologica effects of such exposures are scant. Here, experiments involving short term heat shocks on two bacteria, Klebsiella pneumoniae, a non-fastidious mesophile growing on glucose and Bacillus sp. NCIB 12522, a fastidious thermotolerant methylotroph growing on methanol, are described. Markedly different response patterns for the two bacteria are evident, clearly indicating not only the dangers of making generalizations with respect to the effects of superoptimal temperatures on growing bacterial cultures but also, the significance of scale related segregation phenomena such as wall growth.     

Evaluation ofChaoborus predation on natural populations of herbivorous zooplankton in a eutrophic lake

Hydrobiologia - The effect ofChaoborus predation on natural zooplankton communities was tested in enclosure experiments during June, July and August in the eutrophic Frederiksborg Slotssø,...     

Kinetics of glucose stimulatory effect on silica deposition and growth of natural populations of Fragilaria crotonensis

Diatoms are known to exploit organic substrates for growth; however, convincing evidence that they can utilize dissolved organic carbon under natural conditions is not available. In 2008–2009, we performed in situ experiments examining the effect of glucose addition on silica deposition kinetics and growth rates of Fragilaria crotonensis in the eutrophic ?ímov Reservoir (Czech Republic). Silica deposition kinetics was measured at 4‐h intervals over a 24‐h incubation with PDMPO [2‐(4‐pyridyl)‐5{[4‐dimethylaminoethyl‐aminocarbamyl)‐methoxy] phenyl}oxazole] fluorescence probe. A significant stimulatory effect of glucose supplemented at the concentration of 10^?4 M on Fragilaria silification was observed at 20 and 24 h. Fragilaria growth rates almost doubled upon glucose enrichment compared with the untreated control at 24 h. In addition, we conducted a dose‐response experiment testing the glucose additions from 10^?8 to 10^?3 M in a 24‐h incubation. Glucose stimulated both Fragilaria silification and growth at concentrations >10^–7 M, which might occasionally occur in a reservoir as a result of accidental contamination of water by organic pollution.     

The effect of biomanipulation of the zooplankton on the growth, feeding and survival of pikeperch (Stizostedion lucioperca) in nursing ponds

The following treatments were evaluated for use in rearing pikeperch larvae (Stizostedion lucioperca L.) in nursing ponds: treatment with Dipterex (Bayer); concurrent stocking with common carp (Cyprinus carpio L.); short flooding periods and prefeeding fish larvae. Treatment with Dipterex (active ingredient trichloorfon, i.e. 00-dimethyl-2,2,2, trichlorohydroxyethyl phosphonate) gave zooplankton populations dominated by rotatoria and nauplii at the onset of exogenous feeding and dominated by copepods later on. Cladocerans dominated the plankton in untreated ponds but were never prominent in treated ones. Stomach analysis revealed a fast changing feeding preference in pikeperch from nauplii and copepodites towards cladocerans and chironomids. The excellent food conditions for first feeding pikeperch larvae in Dipterex treated ponds resulted in a significant higher number of harvested fingerlings. In spite of the more favourable food conditions in untreated ponds during the second half of the culture period, a significant growth difference was not found. Concurrent carp stocking did not affect significantly the survival and growth of the pikeperch, although it decreased the accessability of chironomids for pikeperch. Short flooding periods and prefeeding pikeperch larvae failed as useful management strategies for pikeperch nursing. Pikeperch fingerlings cultured in ponds are larger than those found in natural populations at the same time, giving them a high chance to become piscivorous and to increase the year class strength when stocked in natural waters.     

Carbohydrate dynamics and growth rate of natural phytoplankton populations

Diurnal changes in carbohydrate content of natural phytoplankton populations differed from those found for cyanobacteria grown in continuous cultures. The carbohydrate accumulation rate was not constant during the light period. Also in contrast to results obtained using continuous cultures the photosynthetic characteristics changed during the light period. A close correlation was observed between changes in carbohydrate accumulation rate and the efficiency of photosynthesis over 24 hours. Seasonal changes in carbohydrate consumption rate over the dark period were proportional to changes in growth rate.     

Simulated eutrophication and browning alters zooplankton nutritional quality and determines juvenile fish growth and survival

The first few months of life is the most vulnerable period for fish and their optimal hatching time with zooplankton prey is favored by natural selection. Traditionally, however, prey abundance (i.e., zooplankton density) has been considered important, whereas prey nutritional composition has been largely neglected in natural settings. High‐quality zooplankton, rich in both essential amino acids (EAAs) and fatty acids (FAs), are required as starting prey to initiate development and fast juvenile growth. Prey quality is dependent on environmental conditions, and, for example, eutrophication and browning are two major factors defining primary producer community structures that will directly determine the nutritional quality of the basal food sources (algae, bacteria, terrestrial matter) for zooplankton. We experimentally tested how eutrophication and browning affect the growth and survival of juvenile rainbow trout (Oncorhynchus mykiss) by changing the quality of basal resources. We fed the fish on herbivorous zooplankton (Daphnia) grown with foods of different nutritional quality (algae, bacteria, terrestrial matter), and used GC‐MS, stable isotope labeling as well as bulk and compound‐specific stable isotope analyses for detecting the effects of different diets on the nutritional status of fish. The content of EAAs and omega‐3 (ω‐3) polyunsaturated FAs (PUFAs) in basal foods and zooplankton decreased in both eutrophication and browning treatments. The decrease in ω‐3 PUFA and especially docosahexaenoic acid (DHA) was reflected to fish juveniles, but they were able to compensate for low availability of EAAs in their food. Therefore, the reduced growth and survival of the juvenile fish was linked to the low availability of DHA. Fish showed very low ability to convert alpha‐linolenic acid (ALA) to DHA. We conclude that eutrophication and browning decrease the availability of the originally phytoplankton‐derived DHA for zooplankton and juvenile fish, suggesting bottom‐up regulation of food web quality.     

Pigments and species composition of natural phytoplankton populations: effect on the absorption spectra

Data from three cruises (Arabesque 1 and 2 cruises in the ArabianSea and the Vancouver Island cruise) were examined to assessthe importance of species composition and accessory pigmentsin modifying specific absorption coefficients. The three cruisesdiffered widely in their phytoplankton assemblages with smallcells dominating the Arabesque 2 cruise and large diatoms theVancouver Island cruise. Absorption spectra from each cruisewere decomposed into 13 Gaussian bands representing absorptionby the major chlorophylls and accessory pigments. The maximumspecific peak height     

Probability of ultimate survival of a newly occurred inversion in natural populations

Summary An expression was derived that gave necessary and sufficient conditions for the ultimate probability of survival of a newly occurred inversion to be positive. The assumptions included a large population with a Poisson progeny distribution per parent and a time-heterogeneous average number of inversion heterozygote progeny ( _t ) for one inversion heterozygote parent. It was shown that an inversion, not possessing a unique or constant selective advantage, could have a positive ultimate probability of survival.

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Zusammenfassung Es wurde ein Ausdruck abgeleitet, der notwendige und hinreichende Bedingungen dafür ergab, daß die endgültige Überlebenswahrscheinlichkeit einer neu aufgetretenen Inversion positiv ist. Die Annahmen schließen eine große Population mit einer Poisson-Verteilung der Nachkommen je Elter und eine zeit-heterogene durchschnittliche Anzahl von inversions-heterozygoten Nachkommen (_t) eines inversions-heterozygoten Elters ein. Es wird gezeigt, daß eine Inversion, die keinen konstanten oder einzigartigen Selektionsvorteil hat, eine positive endgültige Über-lebenswahrscheinlichkeit haben kann.

     

Application of heat shock protein expression for detecting natural adaptation and exposure to stress in natural populations

Heat-shock proteins (HSPs) play an undisputed role for maintaining cellular functioning under environmental challenges and protein denaturing conditions. Compelling evidence points to an evolutionary important role of HSPs and a strict evolutionary control of these proteins as a balance between benefits and costs. While there is a great potential for using HSP expression for detecting natural adaptation and exposure to stress in natural populations, some obstacles and key issues await investigation. From an...     

Optimal reproductive strategies in age-structured populations of zooplankton

SUMMARY. We describe a model of zooplankton population dynamics that accounts for differences in mortality and physiology among animals of different ages or sizes. The model follows changes in numbers of individuals and changes in individual and egg biomass through time and it expresses mortality and net assimilation as functions of animal size.
We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non-primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.
The model analysis shows how to assess age-dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality.     

Impacts of chlorination and heat shocks on growth, pigments and photosynthesis of Phaeodactylum tricornutum (Bacillariophyceae)

The main impacts of cooling water from thermal (nuclear) power plants on aquatic organisms were caused by chlorination and temperature increase. In this study, we investigated the impacts of residual chlorine and short-term heat shocks on growth, pigment contents and photosynthesis of Phaeodactylum tricornutum. Growth of P. tricornutum was completely inhibited; Chlorophyll a and carotenoids contents deceased about 63.3% and 61.4% in 24 h treated with 0.2 mg L^− 1 chlorine. The negative effects of chlorination increased with enhanced concentration and prolonged exposure time. Relative electrode transfer rate (rETR) of P. tricornutum was significantly suppressed when treated with 0.2 mg L^− 1 residual chlorine for 24 h. Furthermore, the effective quantum yield (F_v'/F_m') decreased first but then recovered with prolonged exposure when residual chlorine ranged between 0.1 and 0.2 mg L^− 1. The cells were less sensitive to heat shocks compared with chlorination: the rETR and F_v'/F_m' was suppressed only when the temperature exceeded 35 °C for 1 h. When P. tricornutum was exposed to chlorination combined with heat shocks, the rETR was further inhibited at 35 °C. It indicated that both chlorination and heat shocks had negative impacts on the primary producers living in discharging coastal waters; furthermore, there were synergistic effects of heat shocks on chlorination toxicity.     

Selective feeding of four zooplankton species on natural lake phytoplankton

Grazing experiments evaluated by microscopical counting were conducted with different size classes of Daphnia hyalina, D. galeata, Eudiaptomus gracilis, and Cyclops sp., all from Lake Constance, using natural lake phytoplankton as food. Species-specific grazing selectivity coefficients were calculated for the dominant phytoplankton species from weekly experiments. Specific selectivities were found to be largely invariant through the growing season. All zooplankters grazed more efficiently on phytoflagellates such as Rhodomonas and Cryptomonas than on coccales such as Chlorella and Scenedesmus, regardless of their relative abundance in the phytoplankton assemblage. Filtering rates did not decrease in the presence of filamentous algae. Certain filamentous species were grazed efficiently, but only by D. hyalina: Anabaena planktonica, Oscillatoria amphigranulata, and Stephanodiscus binderanus. Large diatom colonies like Asterionella formosa and Fragilaria crotonensis were grazed well only by Cyclops sp. Some algal species were consistently selected against: Mougeotia thylespora and Dinobryon sp. The species-specific selectivity coefficients can be used as weighting factors to assess the effective food concentration relative to Rhodomonas minuta, a reference species for optimal food.     

Effects of ultraviolet radiation and dissolved organic carbon on the survival of subarctic zooplankton

High intensities of ultraviolet radiation are known to be harmful to aquatic biota, especially for species living in shallow, clear water bodies. Zooplankton species from such habitats are good model organisms to study the effect of changes in UV radiation, and how animals deal with this. We tested experimentally the effect of natural UV radiation, which was controlled by different filters and varying concentrations of UV-screening dissolved organic carbon (DOC), on the survival of the cladocerans, Daphnia longispina and D. pulex, and a calanoid copepod, Eudiaptomus graciloides. All species originated from subarctic Fennoscandia where underwater UV intensity is influenced by ozone depletion, changes in DOC and timing of ice break-up. Measured as mortality, all species were affected by both UVB and UVA radiation. Survival was highest and similar between species in the dark controls and photosynthetically active radiation exposures. Under each UV filter, the highest DOC concentration provided significant and best shelter from UV radiation and led to best survival. Variation in survival was observed between species. E. graciloides responded more readily to changes in UV radiation than did the daphnids. In natural environments, species' previous exposure to light and different protection strategies (pigmentation, vertical migration) are probably as important factors controlling the survival of zooplankton as radiation intensity and optical properties of water.     

A field technique for the determination of zooplankton grazing on natural bacterioplankton

SUMMARY. 1. A method for the determination of zooplankton community grazing rates on natural populations of bacteria is described.
2. Undisturbed zooplankton samples were incubated with ³H-thymidine-labelled bac teriioplankton, and animals and their food subsequently separated by size.
3. Prehandling of zooplankton by concentration before incubation reduce the grazing rates by a factor ranging from three to four.
4. Time series experiments showed that appropriate incubation periods ranged from 40 min at 14°C to 60 min at 10°C.
5. Spatial variability in the zooplankton was the main source of the overall standard error. This was considerably reduced by using composite samples.     

The implication of survival rates in natural populations of Drosophila: capture-recapture experiments on domestic species

Adult survival rates were estimated in field populations of domestic Drosophila species by means of multiple capture-recapture experiments. Micronized fluorescent dusts were used as marking agents and analysis used the Fisher-Ford model: the assumptions of this model are justified using evidence from this study and the literature. Survival rates were commonly 0.45-0.85 per day, suggesting that mean life expectancy for adult flies is from 1.3 to 6.2 days in natural populations. No consistent differences in survival between sexes or seasons were demonstrated. The implications of low natural survival rates are discussed.