Chemotaxis ofAeromonas hydrophila to the surface mucus of fish

Isolates ofAeromonas hydrophila from various sources show different chemotactic responses to mucus from the surface of freshwater fish. Some isolates were nonchemotactic to fish surface mucus. Isolates ofA. hydrophila from fish lesions had a significantly higher chemotactic index than isolates ofA. hydrophila from water. Maximum chemotactic responses occurred more often to diluted fish mucus than to undiluted samples. Fish which were experimentally stressed did not produce mucus that was more or less chemotactic than that of unstressed fish. Fish with red-sore lesions produced surface mucus which was not chemotactic toA. hydrophila. Differences between fish, for any isolate, were also not significant. The chemotactic substance(s) in fish mucus has a molecular weight of approximately 100,000 and did not appear to be labile when heated to 56°C.     

A model for the density ofAeromonas hydrophila in Albemarle Sound,North Carolina

The abundance ofAeromonas hydrophila was measured monthly at 29 sites in Albemarle Sound, North Carolina and its tributaries from April 1977 through July 1979. Simultaneous measurements included heterotrophic plate count bacteria, fecal coliform bacteria, and 18 physical and chemical parameters. Using only 6 water quality parameters, multiple correlation and regression analysis of the data produced a best-fit regression which explained 38% of the variation observed inA. hydrophila density. The 6 water quality parameters included dissolved oxygen, temperature, orthophosphate, chlorophyll A trichromatic, total Kjeldahl nitrogen, and ammonia. Heterotrophic plate count bacteria and fecal coliform densities were highly correlated withA. hydrophila density, but made the model very unstable. The model was successfully tested against similar data collected for 2 other North Carolina reservoirs, Lake Norman and Badin Lake. Data from 10 sites in Badin Lake over 18 months and from 7 sites on Lake Norman over 5 months were not significantly different from the Albemarle Sound model. Conditions of water quality that may give rise to “blooms” ofA. hydrophila will simultaneously contribute to the probability of increased epizootics in fish in the southeastern United States.     

Use of plasmid pULB113 (RP4::Mini-Mu) to construct a genomic map ofAeromonas hydrophila

Plasmid pULB113 (RP4::Mini-Mu) promoted homologous gene transfer inAeromonas hydrophila; transfer of chromosomal markers occurred at frequencies of between 10^–3 and 10^–4 per donor cell regardless of the marker selected; this indicated chromosome transfer from multiple origins. With a variety of amino acid biosynthetic markers, a single circular map of this bacterium was constructed.     

Comparison of lethalities in mouse versus goldfish for clinical and food isolates ofAeromonas hydrophila

Summary The lethality of 16 clinical or food isolates ofAeromonas hydrophila was assessed by determination of LD₅₀ (i.p.) in mice and goldfish. In mice LD₅₀ values for the variousA. hydrophila strains were similar, ranging from 1.2–21.0×10⁸ cells/animal. A wider range of LD₅₀ values, 0.03–11.8×10⁸ cells/animal, was observed with goldfish. Lethality was not correlated between the two test animals. Further, cytotoxic response in Y-1 adrenal cells did not correlate with lethality in either test animal. It appears that lethality is not a good measure of potential enterotoxigenicity, but may be useful in assessing the invasive character of isolates causing systemic infections in immunocompromised hosts.     

Effect of cultural conditions on the presence of a cholera-toxin cross-reactive factor in culture filtrates ofAeromonas hydrophila

Culture filtrates ofAeromonas hydrophila isolate SSU were shown to contain an extracellular product that antigenically cross-reacts with cholera enterotoxin as determined by the enzyme-linked immunosorbent assay (ELISA). We have termed this extracellular product cholera-toxin cross-reactive (CTC) factor until further characterization is accomplished. Various cultural conditions were examined to determine maximum CTC factor production. The results indicate that optimal conditions for the highest levels of extracellular CTC factor produced byA. hydrophila grown in CYE broth occurred when cultures were incubated at 37°C with shaking at 100 rpm. CYE culture filtrates caused fluid accumulation in rabbit ligated intestinal loops. Heating the culture filtrates at 56°C for 10 min resulted in the loss of biological activity and antigenic integrity of the CTC factor as determined by the rabbit ligated intestinal loop assay and theELISA, respectively. The data presented in this study suggest that culture filtrate containing this molecule, or aggregate of molecules, may play a role in the pathogenesis ofA. hydrophila-mediated disease. Further studies including the purification of this factor(s) presently are being conducted in our laboratory.     

Addressing the trophic status in urban ponds: An evaluation of current trophic state indexes

Ponds are generally understudied. Quality problems in urban freshwaters can arise from eutrophication, and trophic status classification gives information related to their ecological situation. Ponds may strongly differ from larger lakes for which most current trophic status classification methods have been developed. This paper seeks to compare and contrast the suitability of six trophic status indexes (TSI) and OECD trophic classifications system currently used to evaluate the eutrophication level of urban ponds in the Subtropical region. The trophic status was evaluated based on total phosphorus (TP), soluble reactive phosphorus (SRP), total nitrogen (TN) and phytoplankton chlorophyll a (Chl a) in 12 ponds placed in different cities from the Pampean region (Argentina), in the warm and cold seasons. Our results demonstrate that there was no relationship between pond size (0.08–2.45 ha) and trophic status. TSIs estimated with Chl a showed significant differences between seasons and the range oligotrophic-hypertrophic of trophism was encountered. Conversely, TSIs estimated with nutrient concentrations (TP, SRP, TN) did not. The pond's classification in trophic levels fell in the eutrophic-hypertrophic extreme, and only considering TN/TP broadened the trophic range. No relationship was encountered between Chl a and P; however, Chl a and TN/TP were positively correlated during the warm season. Lower trophic levels regarding TSI (Chl a) were generally associated with a dense floating-macrophyte cover. We suggest that the TSI considered should correspond to the latitudinal region in which the ponds are located. Our results indicate that it appears restrictive to consider only P contents in ponds to assess eutrophication. Under the proposed framework, the key issues for the study of pond trophic classification will be to include not only P but N concentrations and TN/TP. Also, phytoplankton Chl a concentration jointly with floating macrophytes biomass/coverage should be considered as diagnosis parameters.     

Collagen transformation in organism: modern state of the problem

Collagens, which compose 1/3 of total proteins in the organism, have unique chemical structure and biological role. Current state of the investigation of these proteins biosynthesis and catabolism, role of shaperones, prolyl- and lysiloxydases, glycosyltransferases, metalloproteinases and other enzymes in collagens metabolism, as well as biological activities of collagens and their fragments have been considered in the review.     

Fed-batch culture ofAeromonas hydrophila for the production of poly(3-hydroxubutyrate-co-3-hydroxyhexanoate) using two carbon sources

To produce polyhydroxyalkanoate (PHA) copolymer which consists of 3-hydroxy-butyrate (3HB) and 3-hydroxyhexanoate (3HHx) by cultivation ofAeromonas hydrophila, fed-batch cultures were done under several nutrient limiting conditions. With the results from flask cultures, fed-batch cultures were carried out to produce large amounts of PHA. In the fed-batch culture, firstly glucose was fed to grow cell, and then, oleic acid fed to stimulate PHA in the cell. The final cell concentration, PHA content, PHA concentration, and 3-hydroxy-hexanoate fraction in 38 hr were 48.9 g/L, 15.05 wt%, 7.36 g/L and 12.2 wt%, respectively, resulting in the productivity of 0.19 g/L-h under phosphate-limiting condition.     

Feeding ecology of Kelp Gulls (Larus dominicanus) in marine and limnetic environments

The diet of the Kelp Gull (Larus dominicanus) was investigated at the northern limit of its distribution along the South American Atlantic coast. We used two complementary methods, pellet analysis and stable isotope analysis (SIA), to describe and compare Kelp Gull feeding ecology in freshwater and marine environments. The assimilated diet over two different time scales was investigated via SIA of plasma and red blood cells, blood components with different turnover rates. Fish composed the bulk of the diet of Kelp Gulls in both marine (White Croaker Micropogonias furnieri and Banded Croaker Paralonchurus brasiliensis) and limnetic areas (Armoured Catfish Loricariidae and La Plata Croaker Pachyurus bonariensis), despite the importance of benthic prey from the intertidal zone in samples collected from the marine environment (Wedge Clam Donax hanleyanus and the Yellow Clam Mesodesma mactroides). The fish consumed by the gulls were common discards from fisheries in both environments, and marine bivalves were found at a high density at the marine beach. Diet varied between the different time scales analysed. Conventional diet data generally agreed with stable isotope model estimates, emphasising the importance of using complementary approaches in dietary studies.     

Relationship between trophic state and plankton community structure in 21 Sicilian dam reservoirs

The relationship between the trophic state of 21 Sicilian dam reservoirs and their taxonomic community structure of phytoplankton (87 taxa) as well as zooplankton (45 taxa) have been examined by means of cluster analysis performed using annual average biomass values. The phytoplankton community structure was closely connected with the trophic state of the reservoirs, whereas the zooplankton community structure was related to hydrological regimes peculiar to the individual water bodies and not to the trophic state.     

Sedimentation of phosphorus in limnetic and estuarine environments in the River Öre system,northern Sweden

Sedimentation of phosphorus was studied during the spring flood in April and May 1991 in Lake Örträsket and the Öre Estuary, northern Sweden. Lake Örträsket has an area of 7.3 km² and a mean depth of 22 m and is located 100 km from the coast halfways along the course of the River Öre. The river ends in a semi-closed low salinity estuary with an area of ca. 50 km² and a mean depth of 16 m. Sedimentation of phosphorus, iron and organic carbon were measured with sediment traps in Lake Örträsket and in the Öre Estuary. Characterization of particulate phosphorus in river water, sediment trap material and sediments were performed by the sequential extraction procedure proposed by Hieltjes & Lijklema (1980). Apart from being an efficient trap for suspended particles including particulate phosphorus, Lake Örträsket was shown to serve as a source for particulate material during spring 1991. The Öre Estuary, on the other hand, constitutes an efficient trap for the total supply of river-borne phosphorus during the spring flood period. Phosphorus was shown to be closely related to iron in particulate material in both the lake and the estuary. Adsorption of phosphorus on settling inorganic particles seems to be an important process, which is particularly pronounced in the estuary.     

Plankton secondary productivity and biomass: Their relation to lake trophic state

The biomass and production of the most important zooplankton species were followed for two years in three lakes of varying trophic status in the Lake Washington watershed. Cladocerans and copepods were of equal importance in the biomass of lakes Findley and Chester Morse (both oligotrophic), whereas, copepods were the main biomass component in Lake Sammamish (mesotrophic). Cladocerans dominated production in lakes Sammamish and Chester Morse, while in Findley Lake their productive role, like that of biomass, was equal to that of the copepods. Rotifers contributed a relatively small biomass and production.Data from this study supported Hillbricht-Ilkowska's postulate that the energy transfer efficiency between the primary and secondary trophic levels decreases with increasing trophic state. Energy transfer efficiencies for the lakes of this study expressed as a two year mean of the ratio-secondary: primary production, were as follows: Findley Lake-0.13; Chester Morse Lake-0.08; and Lake Sammanish-0.04.On the other hand, the hypothesis of Patalas that the secondary productivity: biomass ratio (P/B) tended to increase in proportion to the productivity of a lake, could not be supported. Lake Sammamish, the most productive of the lakes studied, had a P/B ratio of 0.03 while lakes Findley and Chester Morse had P/B ratios of 0.04.     

Occurrence of Flavobacterium psychrophilum in fish-farming environments

Occurrence of Flavobacterium psychrophilum in fish farms and fish-farming environments was studied using agar plate cultivation, the immunoflourescence antibody technique (IFAT) and nested PCR. Characteristics of 64 F. psychrophilum isolates from rainbow trout Oncorhynchus mykiss, fish farm rearing water, ovarian fluid and wild fish were serotyped, ribotyped and compared biochemically. Virulence of F. psychrophilum isolates from different sources was compared by injection into rainbow trout. Additionally, the number of F. psychrophilum cells shed by naturally infected rainbow trout was determined. F. psychrophilum was detected and isolated from skin mucus, skin lesions and internal organs of diseased rainbow trout and from fish without clinical disease. The pathogen was also present in wild perch Perca fluviatilis, roach Rutilus rutilus, and ovarian fluids of farmed rainbow trout brood fish. Isolates were biochemically homogenous, excluding the capability to degrade elastin. Five different agglutination patterns with different antisera against F. psychrophilum were found among the isolates studied. Although several different ribopatterns were found (ClaI: 12 ribopatterns and HaeIII: 9 ribopatterns), ribotype A was the most dominant. Farmed rainbow trout brood fish carried a broad-spectrum of serologically and genetically different F. psychrophilum in ovarian fluids. Virulence of the tested isolates in rainbow trout varied and naturally infected rainbow trout shed 10(4) to 10(8) cells fish(-1) h(-1) of F. psychrophilum into the surrounding water.     

Chromatin structure and the state of human organism

The state of chromatin in human buccal epithelium cell nuclei upon the influence of sport trainings was investigated. Chromatin state was evaluated in interphase buccal cell nuclei after orcein staining. The heterochromatin granule quantity (HGQ) was estimated in 30 nuclei per sample, and for every donor the mean HGQ value per 30 cells was determined. Donors of masculine sex, aged from 18 to 48 years performed training walks and samples of buccal epithelium were collected. Sportive charges induced the process of chromatin condensation in cell nuclei. After the period of repose (24-48 h) the HGQ decreased to control level therefore the process of chromatin decondensation was observed. The state of chromatin changes in connection with circadian rhythm. Chromatin became more condensed at nighttime and less condensed in the morning. Hormones such as adrenaline, noradrenaline, and hydrocortisone in vitro induced the increase of HGQ.     

Resilience to changes in lake trophic state: Nutrient allocation into Daphnia resting eggs

During past decades, many lakes underwent drastic human‐caused changes in trophic state with strong implications for population dynamics and food web processes. We investigated the influence of trophic state on nutrient allocation into Daphnia resting eggs. The production of resting eggs is an important survival strategy, allowing Daphnia to cope with unfavorable environmental conditions. Allocation of essential nutrients into resting eggs may crucially influence embryonic development and offspring survival and thus is of great ecological and evolutionary interest. The capacity of Daphnia to adjust the allocation of nutrients into resting eggs may depend on the dietary nutrient supply, which may vary with trophic state‐related changes in the phytoplankton community composition. Resting eggs were isolated from sediment cores taken from Lake Constance, a large prealpine lake with a distinct eutrophication and reoligotrophication history, and analyzed for elemental (carbon, nitrogen, and phosphorus) and biochemical (sterols and fatty acids) nutrients. Carbon allocation into Daphnia resting eggs continuously decreased over time, irrespective of changes in trophic state. The allocation of nitrogen into Daphnia resting eggs followed the changes in trophic state, that is, nitrogen concentrations in resting eggs increased with eutrophication and decreased again with reoligotrophication. The allocation of phosphorus, sterols and long‐chain polyunsaturated fatty acids, such as eicosapentaenoic acid, into Daphnia resting eggs did not change significantly over time. Changes in trophic state strikingly influenced all trophic levels in Lake Constance. However, nutrient allocation into Daphnia resting eggs was mostly resilient to changes in lake trophic state.     

Temporal Occurrence of Vibrio Species and Aeromonas hydrophila in Estuarine Sediments

Marine sediments were assayed for their concentration of Vibrio spp. and Aeromonas hydrophila over 1 year. A temporal variation was observed in which A. hydrophila, and to a lesser degree V. fluvialis, were found in the winter months, V. parahaemolyticus and V. vulnificus predominated in the spring and summer, with non-O-1 V. cholerae and V. alginolyticus detected in the late summer and fall. These organisms were found in greatest numbers in the top 5 cm of sediment, but were detectable down to 15 cm. Epidemiological data revealed a predominance of non-O-1 V. cholerae infections at the time the organisms were observed to flourish in the sediments.     

Productivity, organism size, and the trophic structure of the major terrestrial biomes

I present a hypothesis suggesting that terrestrial biomes' productivity determines the size of the major organisms and plant physiognomy in them and consequently determines their trophic structure. I suggest a more comprehensive set of patterns over current hypotheses, which consider productivity alone. Based on my hypothesis, I predict that the number of trophic levels decreases with increasing productivity from four in hot deserts to two in productive grasslands and that there are three to four trophic levels in all types of forested biomes. I also suggest that productivity is the limiting factor for the number of trophic levels at the lower end of the terrestrial productivity gradient, herbivore size is the limiting factor at intermediate productivities, and plant physiognomy is the limiting factor in the high productivity range. This contradicts existing hypotheses that predict either an increase (Am Nat 118:240–261, 1981; Am Nat 155:703–723, 2000) or no change (Am Nat 142:379–411, 1993) in the number of trophic levels with the increase in biome productivity.     

Coexisting small fish species in lotic neotropical environments: evidence of trophic niche differentiation

Differences among species and their ecological requirements are considered fundamental in determining the outcome of species interactions as well as in coexistence. Thus, species that co-occurs tends to differ in the use of resources as a way to mitigate the effects of interspecific competition, facilitating interactions between pairs of species. So, this study used a set of seven small-sized characid species with similar morphology and feeding strategies, in order to investigate the hypothesis that the coexistence these species is facilitated by the differential use of food resources. Samplings were conducted in the rivers Verde and São Domingos, Upper Paraná River basin, Brazil, in hydrological periods rainy and dry. The analysis of 1055 stomach contents, by the volumetric method, indicated that the species consumed mainly allochthonous items, such as seeds, terrestrial plants and insects. In addition, they showed inter- and intraspecific differences in the diet composition between hydrological periods, which allowed the identification of items that particularise each species and contribute to the trophic segregation between them. Despite the wide variety of food items used, it was not possible to observe a consistent pattern of widening or narrowing of the food spectrum between hydrological periods, as expected. The trophic niche overlap showed intermediate and low values in both periods. In this sense, resource partitioning among species of small characids, facilitated by exploitation of different preferential resources as well as the intraspecific variation in response to seasonal availability of resources, became evident. The alternation of items and proportions of items in the diet as well as changes in feeding behaviour in opportune moments was probably the key for the coexistence of these species.