Complex Dynamics of Adaptation in a Nonaxenic Microcystis Culture: 2. Computer Simulation of Dinitrophenol Effects

A hypothesis was modeled to account for complex 20-day dynamics in a culture of blue-green algae Microcystis and heterotrophic bacteria exposed to 2,4-dinitrophenol (DNP). In trials with little or no added DNP, a limiting factor (light or CO₂) may cause algal density to fluctuate after 14 days of increase. Such factors may be unimportant at levels of DNP that restrict photosynthesis. Bacterial growth may be limited by organic substrate, and bacteria may be more resistant to DNP than blue-green algae. Hence, at intermediate levels of DNP, substrate provided by increased algal death stimulates bacterial growth more than DNP retards it, causing a bacterial peak. Sorption of DNP to cells may cause the DNP decline. Greater growth and slower DNP decline in experiments with preexposed organisms indicate lower DNP sorption affinity in preexposed cells. Bacterial assimilation of DNP-containing substrate may cause the reappearance of DNP. The model reproduced the fluctuation in algal density after growth was limited and better growth and lower DNP decline with preexposed organisms. Reappearance of DNP occurred, but was not obvious. Bacterial dynamics were least well reproduced. Changes in bacterial constants most affected output. Despite model inadequacies, probable aspects of toxicant action in nature have been revealed. Ecological relationships among populations of different species and genetic differences among individuals may have led to lower than expected toxicity, adaptation, and even growth stimulation. Responses of single species tested in isolation may be inadequate to predict toxicant impact.     

Complex dynamics of adaptation in a nonaxenic microcystis culture. 1. Effects of dinitrophenol on population growth

Chronic exposure to toxicants is a selective pressure affecting populations and also the interactions between populations. Nonaxenic cultures of the blue-green alga Microcystis aeruginosa were used to investigate the ecological dynamics and the effect of preexposure to 2,4-dinitrophenol (DNP) on the tolerance toward subsequent DNP inputs. It was predicted that preexposure would induce an increased tolerance to further inputs. This should cause a higher population growth rate under a given DNP exposure, a broader tolerance range (the range of concentrations over which population growth can be sustained), a higher EC(50), and a lesser variability in growth rates, over the range of experimental exposure concentrations. DNP reduced Microcystis growth proportionally to exposure concentration. Light, inorganic carbon, and DNP were likely limiting factors for algal growth. Heterotrophic bacteria presumably used the dead cells and the exudate of living algae as substrates. Some unexpected effects occurred, such as an apparent increase in dissolved DNP in the medium following its initial decline and fluctuations of the bacterial population. The hypotheses were verified as concerns the effect of preexposure on tolerance. Changes were apparent in the EC(50) and in the breadth of the tolerance range. Moreover, the variability of preexposed populations, in terms of algal growth rate, over the range of exposure concentrations, was smaller than that of non-preexposed populations. Such a decrease in variability may reduce the potential of a population to resist further stresses.     

Effect of declining toxicant concentrations on algal bioassay endpoints

Sorption, degradation, volatilization, and uptake by test organisms cause concentrations of many toxicants to decline during toxicity testing. Despite the recognition of this occurring, nominal, measured initial or time-averaged concentrations are commonly used for the calculation of inhibitory or effect concentrations from toxicity test data. Because a premise of constant exposure is assumed but not met in these calculations, the toxicity of the test water may be significantly underestimated. Laboratory experiments using a 72-h algal growth inhibition bioassay and copper as a toxicant are used to demonstrate that calculated inhibitory concentrations will often be underestimated twofold if losses of copper occurring over the 72-h test duration are not considered. A simple model is presented for toxicant concentration decline and for the relationship between algal growth rate and toxicant concentration. This model is used to demonstrate the magnitude that calculated inhibitory concentrations may be underestimated if concentration declines are not considered for a series of different concentration decline scenarios. For a toxicant whose concentration declines exponentially to less than 5% of its original value within 36 h of a 72-h test, the inhibitory concentration is shown to be underestimated by a factor of 50.     

Impact of pentachlorophenol on growth and community structure of Nile River water microalgae

Pentachlorophenol (PCP) was found to induce significant changes in the chlorophyll (a) content, growth rate and community structure of Nile River water microalgae. The bulk of algae was represented by green algae (Chlorophyta), blue-green algae (Cyanophyta) and diatoms (Bacillariophyta). Chlorophyll (a) content of algal cultures decreased by increasing the applied PCP concentration. The specific growth rates of green and blue-green algae, and diatoms reflected the variation in the sensitivity of the algal groups to PCP. Such variations were also manifested in the change in algal counts, diversity and dominance of algal groups.     

Problems associated with the presence of cyanobacteria in recreational and drinking waters

Eutrophication of waters can lead to the development of blooms of cyanobacteria (blue-green algae) and consequent health and environmental problems. The presence of these organisms in recreational and drinking waters is generally undesirable or even hazardous, although nitrogen fixing blue-green algae can be beneficially used as biofertilisers for plantation crops. This paper reviews the characteristics of cyanobacteria and particularly their toxins. The mechanisms of toxic algal blooms are discussed, as are the factors influencing toxin production. The nuisance and health hazards associated with freshwater bluegreen algae are discussed and the options for public health control are evaluated. The problems associated with statutory control of toxic algae problems is also considered.     

The Development of Marine Toxicity Identification Evaluation (TIE) Procedures Using the Unicellular Alga Nitzschia closterium

Unicellular algae are highly sensitive to a wide range of toxicants and have been used extensively in ecotoxicological testing. This, along with their ability to grow in very small test volumes over short test durations, make them ideal test organisms for use in Toxicity Identification Evaluations (TIEs). Despite this, microalgae have not previously been used in marine TIE studies. In this study, the marine diatom Nitzschia closterium was shown to be a highly suitable test organism after modification of the standard test protocol to reduce test volumes to 6 mL and test duration to 48 h. The alga was tolerant to the chemicals used in phase I of the standard USEPA TIE protocol, and physical TIE manipulations had no effect on algal growth. The cation exchange procedure, however, inhibited algal growth, while the anion exchange procedure stimulated growth, making these two procedures unsuitable for use with this species. Of the buffers trialed for the graduated pH procedure, 0.01 M PIPES buffer was found to be suitable for buffering at pH 7 because it maintained the required pH over the duration of the test and did not affect the growth or sensitivity of the algae to one reference toxicant (copper). A trial TIE on a secondary-treated sewage effluent for discharge into coastal waters showed that the developed protocols could successfully be used to identify ammonia as the major toxicant in the effluent.     

Induced Metal Tolerance in Microbenthic Communities from Three Lowland Rivers with Different Metal Loads

The response of microbenthic communities to sustained metal stress was studied in three lowland rivers with different levels of pollution. Tolerance against zinc and cadmium was determined in short-term toxicity tests with microbenthic assemblages colonizing glass discs. Photosynthetic activity served as an endpoint in tests for algae, whereas for bacteria thymidine incorporation was determined. For bacterial assemblages from unpolluted locations, EC₅₀ values in short-term tests ranged between 6.7 and 56.2 μM zinc, and 8.7 and 25.5 μM cadmium, respectively. Bacterial assemblages from the two most polluted sites were significantly more tolerant for zinc (EC₅₀: 994 μM and >1,000 μM) and cadmium (EC₅₀: 218 μM and 154 μM). Results indicated a shift in community composition toward pollution-adapted organisms when a threshold concentration of 1 μM zinc is exceeded. Although an increasing community tolerance was also indicated for algae, EC₅₀ values for microbenthic algae from all sites exceeded in most cases the highest metal concentrations tested (Zn: 1,000 μM; Cd: 320 μM). Since species composition of algal assemblages was found to change at much lower metal levels, it is concluded that short-term toxicity tests measuring photosynthesis inhibition do not reflect well the long-term effects of these metals. Toxic effects of metals on both algal and bacterial assemblages are attenuated by precipitation and complexing capacities of the biofilm. Received: 9 June 1998/Accepted: 6 December 1998     

METIER (modular ecotoxicity tests incorporating ecological relevance). II. Ecotoxicity of poorly water-soluble compounds: Concentration versus dose

A significant binding of a toxicant to algal cells would reduce effective toxicant concentration, bringing changes in NOEC (non-observed effect concentration) values. Furthermore, if the algal cells are ingested, this may increase the significance of feeding as a route of contaminant uptake. Therefore, particularly when dealing with poorly water-soluble compounds, the amount of food ingested could become a relevant ecotoxicological parameter to be assessed. The OECD guideline for the Daphnia, reproduction test indicates that the concentration of test substances must remain within 20% of the nominal concentration. The aim of this work was to look for any change in a compound concentration due to the presence of algae (the food of Daphnia magna). During the 48-h interval between medium renewal in chronic tests with D. magna, there is a loss of the effective 3,4-dichloroaniline concentration which is greater with increasing algae densities and decreasing nominal concentrations.     

Absorption and elimination of14C-alpha- andgamma-chlordane by a freshwater alga,daphnid, and goldfish

The bioconcentration of chlordanes by fresh water food chain organisms gave values of 5,560 for algae, 24,000 for daphnids, and 162 for goldfish. The transfer of preexposed daphnids and goldfish to insecticide-free water resulted in up to 90% elimination of the absorbed/adsorbed dose in 7 and 11 days, respectively. Tissue distribution of chlordane suggests that the biliary pathway of excretion, along with elimination through the gill, kidney, and feces, may be important in the elimination of lipophilic hydrocarbons by fish.     

机械通气患者气管内导管生物被膜的观察

目的研究机械通气患者气管内导管生物被膜的形成情况以及生物被膜的形态和病原学分布特征及耐药性. 方法前瞻性研究了27例施行人工气道(气管插管和气管切开)并机械通气的患者拔除的气管内导管,分别进行扫描电镜观察生物被膜的形成,并进行细菌培养及耐药性检测. 结果 27例气管导管中培养阳性25例,占92.6%,以粪肠球菌、金黄色葡萄球菌及铜绿假单胞菌最常见,均呈高度耐药,但与痰培养结果差异无明显性;扫描电镜观察26例均可见膜状物,并可见细菌团状聚集,其间可见纤维样物质交联,膜状物中可见网状裂纹,其上附着大量细菌. 结论机械通气时气管内导管表面易黏附细菌,形成生物被膜,生物被膜的形成可能与VAP的发生有关,并常常导致难治性感染.     

Responses of marine unicellular algae to brominated organic compounds in six growth media

Marine unicellular algae, Skeletonema costatum, Thalassiosira pseudonana, and Chlorella sp. were exposed to the industrial brominated compounds tetrabromobisphenol A, decabromobiphenyloxide (DBBO), hexabromocyclododecane (HBCD), pentabromomethylbenzene (PBMB), pentabromoethylbenzene (PBEB), and the herbicide bromoxynil (BROM), in six algal growth media. High concentrations of DBBO (1 mg liter-1), PBMB (1 mg liter-1), and PBEB (0.5 mg liter-1) reduced growth by less than 50%. EC50s of the other compounds varied with growth medium, with high EC50/low EC50 ratios between 1.3 and 9.9. Lowest EC50s, 9.3 to 12.0 micrograms liter-1, were obtained with S. costatum and HBCD. It is concluded that responses to toxicants in different media are the results of interactions among algae, growth medium, toxicant, and solvent carrier.     

Inhibition of growth of freshwater microalgae by long-chained aliphatic amines employed in solvent extraction processes

The influence on algal growth by six long-chained aliphatic amines, used in industrial solvent extraction processes, was investigated by a conventional algal assay and, in addition, a simple assay where algae were grown in liquid medium in 250 l cultures on microtitration plates. Loss of solvent extractants from processes to ambient water represent a potential environmental problem. The primary, secondary, tertiary and quaternary amines (with one exception) had EC50-values based on growth rate (ECr) or algal biomass (ECb) at 0.01–0.3 mg/L (20–800 nM). This makes long-chained aliphatic amines about a thousand times more toxic than short-chained amines—on a molar basis. The difference in toxicity was interpreted as being due to different modes of action between the two groups of amines. The diatomAsterionella formosa and the blue-green algaAnabaena flos-aquae were more sensitive to the amines than the green-algaeSelen-astrum capricornutum, Monoraphidium pusillum orChlorella emersonii. The maximum ECmax/ECmin ratio recorded was 19.5, for the primary amine.Anabaena flos-aquae was more sensitive by a factor 2–4 when grown under nitrogen fixation conditions than when supplied with combined nitrogen. Compared to other aquatic organisms, the algae show a particular sensitivity to amines. The microtitration test system was less sensitive than the flask test system. The low sensitivity of the microtitration test system is not an inherent property, but due to the use of an insensitive technique (visual inspection) for detection of algal biomass. The ECr50 and ECb50-values in the flask test system were both heavily time-dependent.     

Sources of the eutrophication problems associated with toxic algae: an overview.

Blooms of cyanobacteria (toxic blue-green algae) can produce health and environmental hazards in water, including water used for drinking or recreational purposes. How, why, and when these blooms are produced, as well as how to deal with them, are questions whose answers are vital to the safeguarding of public health in regions where the algae occur. The blooms are linked to eutrophication of water, and this paper discusses the eutrophication problems, their nature, and their relevance to the production of cyanobacteria. Nutrient limitations on algal productivity are considered, as is the involvement of the atmosphere, the storage of nutrients in soils, and the influence of anthropogenic activity.     

Seasonal changes of larval food and feeding of Chironomus crassicaudatus (Diptera: Chironomidae) in a subtropical lake

The food of Chironomus crassicaudatus midge larvae in Lake Monroe, central Florida, was investigated from May 1981 to April 1982. Gut contents of larvae collected monthly from 16 stations in the lake were analyzed. Quantitative samples of water collected monthly at the mud-water interface at each station were analyzed for the larval food composition in the water. The larvae fed primarily on Cyanobacteria (blue-green algae). Blue-green algae were predominant in the water as well as in the larval guts, forming 63-87% and 52-84% of the total organisms observed in the water and in the larval guts, respectively. Populations of these organisms in the water were lowest in the summer. A highly significant relationship existed between the monthly mean percent of blue-green algae in the larvae and in the water. In general, the larvae were nonselective feeders in that the organisms enumerated in the water were also found in the gut.     

水源水微囊藻毒素及其控制方法研究

饮用水源藻毒素污染已越来越引起人们的关注。微囊藻毒素（Microcystins，MCYST）是由蓝藻的部分藻属产生的环肽化合物，性质稳定，已被证明具有明显的肝毒性，是肝肿瘤促进剂之一。常规水处理工艺对MCYST的作用效果不理想，多项研究表明臭氧、光化学氧化、氯系氧化物、活性炭以及生物控制等方法能较好地去除毒素。     

Toxicity and quantitative structure-activity relationships of nitriles based on Pseudokirchneriella subcapitata

This study presents the toxicity data of various nitriles to Pseudokirchneriella subcapitata using a closed algal toxicity testing technique with no headspace. Two different response endpoints, i.e., dissolved oxygen (DO) production and algal growth rate, were used to evaluate the toxicity of nitriles. In general, the DO endpoint revealed higher inhibitory effects than that from algal growth rate. Furthermore, halogen-substituted nitriles were found to be extremely toxic to P. subcapitata. With increasing numbers of the halogen atoms, stronger toxicity was observed. The bromine substitutent also seems to be more toxic than chlorine substitutent. Quantitative structure-activity relationships (QSARs) were established based on the chemicals' Elumo values and hydrophobicity (logK(ow)). Such relationships may thus be useful in predicting the toxicity of other compounds of the same mode of toxic action. Furthermore, for various aquatic organisms, the relative sensitivity relationship is: Pimephales promelas > or = P. subcapitata> Tetrahymena Pyriformis>Daphnia magna>luminescent bacteria (Microtox). The alga, P. subcapitata, was found to be quite sensitive to nitriles compared to other organisms.     

Ecotoxicity of mixtures of antibiotics used in aquacultures

More or less well-defined mixtures of antibiotics used in aquacultures may be distributed in the aquatic environment. Therefore, a systematic mixture ecotoxicity study was performed with the aquaculture antibiotics oxytetracycline, oxolinic acid, erythromycin, florfenicol, and flumequine. Test organisms were freshwater algae (Pseudokirchneriella subcapitata), activated sludge microorganisms, and luminescent bacteria (Vibrio fischeri). Design and statistical analysis of test results were based on isobolographic analysis. Synergistic effects were observed when combinations of erythromycin and oxytetracycline were tested on activated sludge microorganisms, and in these cases model predictions indicate independent action on the different bacterial species in the sludge. As predicted from the modes of action, concentration addition was evident when flumequine and oxolinic acid were mixed and tested on sludge bacteria. In the algae test, the combined toxicity of antibiotics could not be predicted based on knowledge of the modes of action of the individual compounds. Independent of the test species, our results gave examples of combined effects that were higher than predicted based on the assumption of concentration addition. This result underlines the need to consider the effects of mixtures of antibiotics on environmental organisms. The isobolographic method appears to be a suitable tool for this purpose, particularly for well-defined mixtures with few substances.     

Alcohol, intestinal bacterial growth, intestinal permeability to endotoxin, and medical consequences: summary of a symposium.

This report is a summary of the symposium on Alcohol, Intestinal Bacterial Growth, Intestinal Permeability to Endotoxin, and Medical Consequences, organized by National Institute on Alcohol Abuse and Alcoholism, Office of Dietary Supplements, and National Institute of Diabetes and Digestive and Kidney Diseases of National Institutes of Health in Rockville, Maryland, October 11, 2006. Alcohol exposure can promote the growth of Gram-negative bacteria in the intestine, which may result in accumulation of endotoxin. In addition, alcohol metabolism by Gram-negative bacteria and intestinal epithelial cells can result in accumulation of acetaldehyde, which in turn can increase intestinal permeability to endotoxin by increasing tyrosine phosphorylation of tight junction and adherens junction proteins. Alcohol-induced generation of nitric oxide may also contribute to increased permeability to endotoxin by reacting with tubulin, which may cause damage to microtubule cytoskeleton and subsequent disruption of intestinal barrier function. Increased intestinal permeability can lead to increased transfer of endotoxin from the intestine to the liver and general circulation where endotoxin may trigger inflammatory changes in the liver and other organs. Alcohol may also increase intestinal permeability to peptidoglycan, which can initiate inflammatory response in liver and other organs. In addition, acute alcohol exposure may potentiate the effect of burn injury on intestinal bacterial growth and permeability. Decreasing the number of Gram-negative bacteria in the intestine can result in decreased production of endotoxin as well as acetaldehyde which is expected to decrease intestinal permeability to endotoxin. In addition, intestinal permeability may be preserved by administering epidermal growth factor, l-glutamine, oats supplementation, or zinc, thereby preventing the transfer of endotoxin to the general circulation. Thus reducing the number of intestinal Gram-negative bacteria and preserving intestinal permeability to endotoxin may attenuate alcoholic liver and other organ injuries.     

Opportunistic infections caused by Shewanella, new emergent bacteria

Shewanella putrefaciens and Shewanella algae are Gram negative, nonfermentative and oxidative bacilli whose the main phenotypic feature is the production of hydrogen sulfide gas. Widespread in the environment, both S. putrefaciens and S. algae species are rare human bacteria although they are reported with increasing frequency as a cause of opportunistic infection in humans, such as skin and soft tissue infections and bacteremia. Chronic infections of the lower limbs and liver disease have been identified as risk factors for bloodstream infection, with a faster course and a poorer prognosis in the last case. S. algae appears to be more virulent than S. putrefaciens. Most human S. putrefaciens strains are isolated from bacterial flora, which puts to question its clinical significance. Molecular biology must be used for an adequate identification because S. algae can easily be mistaken for S. putrefaciens with usual tests.     

Hospital infestation by the cluster fly, Pollenia rudis sensu stricto Fabricius 1794 (Diptera: Calliphoridae), and its possible role in transmission of bacterial pathogens in Germany

The potential of the cluster fly, Pollenia rudis sensu stricto, to transmit bacterial pathogens was investigated during a mass infestation that took place in a German hospital. Cluster flies were individually examined for mesophilic bacteria carried on the exoskeleton. Bacterial growth could only be detected by using the enrichment culture technique to increase sensitivity, but not by direct intoculation of fly samples to agar plates. All 50 cluster fly samples that were tested carried opportunistic aerobic mesophilic Bacillus spp., whereas 41 fly samples were positive for Erwinia spp., 16 samples for Erwinia amylovara, 24 samples for Stenotrophomonas maltophilia, and 4 samples for Flavobacterium odoratum. Staphylococcus lugdunensis and Pseudomonas aeruginosa were found in 5 samples. No bacteriologically sterile cluster fly samples were obtained. The whole bacterial pattern found on P. rudis s. s. is known for its potential to cause opportunistic and/or nosocomial infections in humans. The results obtained led to the assumption that mass infestations of cluster flies occurring in sensitive areas, especially in hospitals, may cause a low, but not neglectable health threat due to mechanical transmission of bacterial pathogens.