Survival of Campylobacter jejuni in water: effect of grazing by the freshwater crustacean Daphnia carinata (Cladocera)

Environmental studies of the human-pathogenic bacterium Campylobacter jejuni have focused on linking distributions with potential sources. However, in aquatic ecosystems, the abundance of C. jejuni may also be regulated by predation. We examine the potential for grazing by the freshwater planktonic crustacean Daphnia carinata to reduce the survival of C. jejuni. We use a system for measuring grazing and clearance rates of D. carinata on bacteria and demonstrate that D. carinata can graze C. jejuni cells at a rate of 7% individual(-1) h(-1) under simulated natural conditions in the presence of an algal food source. We show that passage of C. jejuni through the Daphnia gut and incorporation into fecal material effectively reduces survival of C. jejuni. This is the first evidence to suggest that grazing by planktonic organisms can reduce the abundance of C. jejuni in natural waters. Biomanipulation of planktonic food webs to enhance Daphnia densities offers potential for reducing microbial pathogen densities in drinking water reservoirs and recreational water bodies, thereby reducing the risk of contracting water-borne disease.     

The systematics of Australian Daphnia (Cladocera: Daphniidae). Electrophoretic analyses of the Daphnia carinata complex

Genetic variation at eleven allozyme loci was scored in approximately 1600 individual Daphnia. The samples included representatives of all nine taxa described from the D. carinata complex in Australia. Principal coordinates and cluster analyses revealed only three groups of genotypes within the complex, corresponding to the taxa D. cephalata, D. nivalis, and a conglomerate of all other taxa described from the complex, D. carinata (sensu lato). These results are consistent with recent multivariate morphological analyses of the complex.     

Other environmental factors affect the size of crests developed by Daphnia carinata (Cladocera: Daphniidae) in response to notonectid predators

SUMMARY. 1. Crest size and body size was measured in Daphnia carinata King sampled from field enclosures in which environmental conditions and notonectid predator ( Anisops Hyperion Kirkaldy) levels had been manipulated, and from control treatments which had predator levels and other environmental factors equivalent to those in the natural environment.
2. Individuals of D. carinata developed larger crests in treatments with predators than in treatments without predators.
3. The environmentally manipulated treatment was considered to have lower levels of food but was also likely to have undergone other changes in physicochemistry and resource variability that may have affected crest size. The effect of the manipulation cannot be confirmed, therefore, as the result of variation in food levels. Animals in the treatments considered to have lower amounts of food had smaller crests than in the control treatment irrespective of whether predators were present. The effects of environmental manipulation and predators were additive.
4. Enclosures without predators, but in which water from the natural, predator-rich, environment was exchanged through the enclosure walls, showed no evidence of a chemical induction effect. Chemical induction effects may have been countered by a reduced food supply resulting from the higher D. carinata population densities that developed in these enclosures.
5. This work provides a second example of an alteration of the morphological response of daphnid prey to predators by environmental factors, probably food, and suggests this phenomenon may be general in cladoceran species displaying predator-induced changes in morphology.     

Field and laboratory studies on Daphnia carinata King (Cladocera: Daphnidae) from a seasonal tropical pond

The life history and seasonal variation in egg production of Daphnia carinata King, with reference to the seasonal variation in physico-chemical as well as biological factors of a tropical temporary pond, were studied. Laboratory observations on the life history of D. carinata were also made. The seasonal events of D. carinata are discussed in relation to recent studies on Cladocerans.     

Survival of Campylobacter jejuni in Waterborne Protozoa

The failure to reduce the Campylobacter contamination of intensively reared poultry may be partially due to Campylobacter resisting disinfection in water after their internalization by waterborne protozoa. Campylobacter jejuni and a variety of waterborne protozoa, including ciliates, flagellates, and alveolates, were detected in the drinking water of intensively reared poultry by a combination of culture and molecular techniques. An in vitro assay showed that C. jejuni remained viable when internalized by Tetrahymena pyriformis and Acanthamoeba castellanii for significantly longer (up to 36 h) than when they were in purely a planktonic state. The internalized Campylobacter were also significantly more resistant to disinfection than planktonic organisms. Collectively, our results strongly suggest that protozoa in broiler drinking water systems can delay the decline of Campylobacter viability and increase Campylobacter disinfection resistance, thus increasing the potential of Campylobacter to colonize broilers.     

Survival of Campylobacter jejuni in waterborne protozoa

The failure to reduce the Campylobacter contamination of intensively reared poultry may be partially due to Campylobacter resisting disinfection in water after their internalization by waterborne protozoa. Campylobacter jejuni and a variety of waterborne protozoa, including ciliates, flagellates, and alveolates, were detected in the drinking water of intensively reared poultry by a combination of culture and molecular techniques. An in vitro assay showed that C. jejuni remained viable when internalized by Tetrahymena pyriformis and Acanthamoeba castellanii for significantly longer (up to 36 h) than when they were in purely a planktonic state. The internalized Campylobacter were also significantly more resistant to disinfection than planktonic organisms. Collectively, our results strongly suggest that protozoa in broiler drinking water systems can delay the decline of Campylobacter viability and increase Campylobacter disinfection resistance, thus increasing the potential of Campylobacter to colonize broilers.     

Survival of Campylobacter jejuni in different gas mixtures

Campylobacter jejuni in fresh chilled chicken meat is known to be a major risk factor for human gastrointestinal disease. In the present study, the survival under chilled conditions of different C. jejuni strains exposed to different gas mixtures usually used for gas packaging of food was examined. Bolton broth and fresh, skinless chicken fillets were inoculated with six and four strains, respectively, and exposed to the gas mixtures 70/30% O(2)/CO(2), 70/30% N(2)/CO(2), and 100% N(2) (the latter only investigated in broth) at refrigeration temperature (4-5 degrees C). In broth culture, the strains survived significantly longer when exposed to 100% N(2) and 70/30% N(2)/CO(2) than in the oxygen-containing gas mixture, 70/30% O(2)/CO(2) (P<0.0001). For the two anaerobic gas mixtures, the reductions only reached 0.3-0.8 log(10) CFU mL(-1) within the same period. In the presence of oxygen, the numbers of C. jejuni were reduced by a minimum of 4.6 log(10) CFU mL(-1) over 21 days. When inoculated onto chicken fillets, the C. jejuni strains also died significantly faster in the oxygen-containing gas mixture, 70/30% O(2)/CO(2) (P<0.0001), reaching reductions of 2.0-2.6 log(10) CFU g(-1) after 8 days. In the gas mixture without oxygen (70/30% N(2)/CO(2)), no reductions were observed.     

Effect of previous feeding conditions on survival in Daphnia pulicaria (Crustacea: Cladocera)

Survival of natural Daphnia populations without previous acclimatization in filtered water under laboratory conditions (starvation) was used as a parameter describing the actual competitive ability of populations in periods of food limitation. Two populations (1 and 2) of Daphnia pulicaria Forbes coming from two enclosures with a low (< 1 mgC l^–1) and a high (about 3 mgC l^–1) seston level were examined in their resistance to starvation. Juveniles of both populations survived better than adult females in the conditions without seston as well as in the control experiment, despite their much lower biomass. Animals from population 1 had lower mortality than those from population 2 in all variants of the experiment. The results confirm the hypothesis that the ability of daphnids to starve depends also on adaptation to previous feeding conditions.     

隆线溞精子发生及成熟精子的超微结构

用透射电镜和扫描电镜观察隆线精子的发生过程及成熟精子的超微结构。隆线精子发生经历精原细胞、精母细胞、精子细胞和成熟精子四个时期。精原细胞核染色质凝集成团,细胞质内有线粒体、粗面内质网分布。精母细胞核染色质分散,不均匀地分布于核中,细胞质内粗面内质网聚集。在精子细胞分化形成精子的早期,细胞纵向拉伸,核物质开始浓缩;中期精子细胞呈明显的长条形,精子细胞逐渐移入精巢管腔中央,外围包裹一厚层精子鞘;后期精子细胞已进入管腔中,核物质呈高度浓缩状,细胞质层较少,精子细胞间通过外围精子鞘相互粘连成片。成熟精子分散在精巢管腔中央,外形呈棒状,一端稍钝,一端稍尖,无鞭毛、棘突等附属物;核内染色质解聚,均匀分布在核中,具双层核膜,细胞质层很少,精子鞘为单层,无法确认顶体端。隆线雄性生殖细胞的结构及其发生过程均较高等甲壳动物简单和原始,但在功能上表现出相对的适应性,使以隆线为代表的枝角类能适应复杂多变的生活环境     

Filtering rates of Daphnia carinata King (Crustacea: Cladocera) on the blue-green algae Microcystis aeruginosa Kütz. and Anabaena cylindrica (Lemm.)

Abstract Non-toxic strains (by mouse toxin assay test) of unicellular Microcystis aeruginosa and short filamentous Anabaena cylindrica were fed to Daphnia carinata in the laboratory at an algal volume concentration of 4.0 mm³ L^?1 at 24 ± 1°C. The filtering rates (FR, mL animal^?1 hr^?1) of D. carinata on M. aeruginosa and A. cylindrica increased with increasing body length (L, mm), and were expressed as a power curve: FR = 0.061L²⁰⁹. and FR = 0.232L^2.09, respectively. The potential for control of natural blue-green algal populations by D. carinata grazing is discussed briefly.     

A test for the production of sexual pheromones by Daphnia magna (Crustacea: Cladocera)

SUMMARY. (1) Swarming in the Cladocera has often been associated with periods of sexual reproduction and this has led to the suggestion that members of opposite sex are attracted to one another. The most plausible mechanism by which this could occur is through the production of pheromones. The present experiments aimed to determine if Daphnia magna Straus produce such chemicals.
(2) No evidence was found for the presence of sexual pheromones. The behaviour of both males and females was unaffected by the presence of sexually receptive animals of the opposite sex.
(3) It is suggested that the cited relationship between sexual reproduction and swarming may be due to the fact that sexual reproduction occurs during periods of high population density. It is during such periods that swarming behaviour would be most apparent.     

Pokey,a New DNA Transposon in Daphnia (Cladocera: Crustacea)

We report the complete sequence of two representatives of the transposable element, Pokey, isolated from the ribosomal DNA of the cladoceran, Daphnia pulicaria. We describe the general features of this element, which confirms its classification as a DNA transposon. We show that Pokey is similar to piggyBac and, as such, is a member of the TTAA-specific family of elements. Pokey is putatively autonomous, possessing an open reading frame that encodes a putative protein with similarity to piggyBac's transposase, in addition to putative proteins from Drosophila and human LOOPER elements, and several human proteins of unknown function. We show that these proteins all contain amino acid motifs that are perhaps conserved for similar functions. We demonstrate that Pokey is carrying several regions of similarity to Daphnia pulex IGS sequences, likely the result of some sort of recombination event with the host genome. Pokey inserts into a conserved region of the large subunit ribosomal RNA gene known to contain other arthropod elements, suggesting that this location is a hot spot for insertional activity. However, Pokey is unique in that it is the only DNA transposon yet known to insert into this region, as other such insertions are non-LTR retrotransposons. It is now clear that this "ecological niche" has been effectively exploited by both retrotransposons and DNA transposons.     

Daphnia curvirostris Eylmann in Japanese high mountain waters (Cladocera: Daphniidae)

A species of Daphnia, Daphnia curvirostris Eylmann, found in high mountain lakes and ponds in central Japan is described. Although there were some differences in the shape of the male rostrum and the chromosome number between European populations as described by Johnson (1952) and Trentini (1980), and Japanese ones collected from high mountain waters, Japanese specimens had many characteristics similar to the taxon D. curvirostris of Europe.     

上海滴水湖两种枝角类对浮游植物群落牧食的模拟研究

于2012年9月通过浮游动物添加实验,研究了大型溞(Daphnia magna)和隆腺溞(Daphnia carinata)对上海滴水湖浮游植物群落结构的影响。结果表明,实验组氨氮和可溶性活性磷浓度与空白组相比显著增加,大型溞组浮游植物密度较空白组降低了70.3%,隆腺溞组浮游植物密度较空白组降低了80.0%,叶绿素a浓度分别下降了80.4%和75.2%,叶绿素a与氨氮、可溶性活性磷呈显著相关性。浮游植物的群落结构较空白组也发生较大变化,硅藻、蓝藻和绿藻密度比例明显降低,隐藻、裸藻和甲藻在实验结束时没有检出,说明大型溞和隆线溞能有效控制水体中浮游植物密度,并能够对浮游植物群落结构产生影响。同时,附着藻类密度较空白组也有明显减少,说明大型溞和隆线溞对附着藻类也有一定的牧食作用。     

A comparison of populations from the Daphnia similis group (Cladocera: Daphniidae)

European populations of Daphnia similis Claus have been compared with populations from tropical Asia. Daphnia similoides n. sp. from tropical Asia was described as the sibling species of D. similis. The female has characteristic neonate, postabdomen, head, and ephippium. The male has characteristic rostrum, antennules, and the distalmost part of the postabdomen. The D. similis group was compared with D. carinata s. str. Australian populations.     

Genome size evolution and polyploidy in the Daphnia pulex complex (Cladocera: Daphniidae)

Genome size was estimated in 49 clones of the Daphnia pulex complex from temperate and subarctic locations using flow cytometry and microsatellite DNA analyses. Significant genome size differences were found in diploid species belonging to the two genetically distinct groups (the pulicaria and the tenebrosa groups), with clones from the tenebrosa group having genome sizes 22% larger than those in the pulicaria group. Combined flow cytometry and microsatellite DNA analyses revealed that nearly all polyploid clones in the D. pulex complex are triploid and not tetraploid, as was previously suggested. Sequencing analyses of the ND5 gene to position clones in their respective clades within the D. pulex complex have uncovered three triploid clones of Daphnia middendorffiana with a D. pulex maternal parent. This result was unexpected because Daphnia pulicaria has always been identified as the maternal parent of these hybrid polyploid clones. Triploid clones likely owe their origins to interactions between sexual and asexual populations. Further interactions in the tenebrosa group have generated tetraploid clones but these events have been rare.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 68–79.     

Estimating the size at maturity in field populations of Daphnia (Cladocera)

• 1 Two methods for estimating the average body size at the onset of reproduction were applied to populations of Daphnia hyalina. The first, ‘average maturation size’, assesses maturity by the relative length of abdominal processes of Daphnia; the second, ‘size at first reproduction’ (SFR), calculates the size class in which 50% of the maximum proportion of egg-bearing females is reached.
• 2 The influence of environmental factors on the expression of the difference in length between the first and the second abdominal process was tested in the laboratory. Neither temperature nor chemical cues from predators affected the difference in length, but the processes were indistinguishable at very low food concentrations.
• 3 During one season, D. hyalina exhibited pronounced changes in fecundity, proportion of egg-bearing adults and SFR. The pattern obtained by the two methods was similar in many cases, although maturation size estimated by the first method was slightly smaller than SFR obtained by the second method. Neither method gave reliable results during times of starvation (clear-water phase).

     

隆线溞孤雌溞生殖系统的组织学

隆线孤雌的生殖系统由一对卵巢、一对输卵管和一对雌性生殖孔组成。卵巢长管状 ,管壁由结缔组织膜和单层上皮细胞构成 ,末端渐细为一短小的输卵管 ,输卵管末端为雌性生殖孔。卵子的发生是由生发区细胞向卵巢内增殖分化 ,不同成熟度的生殖细胞在管腔内排列成生殖带。根据卵母细胞细胞核的大小及卵黄的累积情况等 ,将卵子的发生划分为三个时期 :卵原细胞、卵母细胞和成熟卵子 ,其中卵母细胞的发生又可细分为三个时期 :前期、中期和后期。后期的卵母细胞含较多的卵黄颗粒 ,最后成为成熟卵子 ,排入孵育囊内形成夏卵。隆线孤雌的卵巢发育要经历五个幼龄期 ,不同的龄期 ,卵巢的形态结构不同。至第五幼龄 ,卵巢已基本发育成熟 ,准备排卵进入第一成龄