Pieter Slot

Competition for light between toxic and nontoxic strains of the harmful cyanobacterium Microcystis

ABSTRACT The cyanobacterium Microcystis can produce microcystins, a family of toxins that are of major concern in water management. In several lakes, the average microcystin content per cell gradually declines from high levels at the onset of Microcystis blooms to low levels at the height of the bloom. Such seasonal dynamics might result from a succession of toxic to nontoxic strains. To investigate this hypothesis, we ran competition experiments with two toxic and two nontoxic Microcystis strains using light-limited chemostats. The population dynamics of these closely related strains were monitored by means of characteristic changes in light absorbance spectra and by PCR amplification of the rRNA internal transcribed spacer region in combination with denaturing gradient gel electrophoresis, which allowed identification and semiquantification of the competing strains. In all experiments, the toxic strains lost competition for light from nontoxic strains. As a consequence, the total microcystin concentrations in the competition experiments gradually declined. We did not find evidence for allelopathic interactions, as nontoxic strains became dominant even when toxic strains were given a major initial advantage. These findings show that, in our experiments, nontoxic strains of Microcystis were better competitors for light than toxic strains. The generality of this finding deserves further investigation with other Microcystis strains. The competitive replacement of toxic by nontoxic strains offers a plausible explanation for the gradual decrease in average toxicity per cell during the development of dense Microcystis blooms.

Selective suppression of harmful cyanobacteria in an entire lake with hydrogen peroxide

Although harmful cyanobacteria form a major threat to water quality, few methods exist for the rapid suppression of cyanobacterial blooms. Since laboratory studies indicated that cyanobacteria are more sensitive to hydrogen peroxide (H(2)O(2)) than eukaryotic phytoplankton, we tested the application of H(2)O(2) in natural waters. First, we exposed water samples from a recreational lake dominated by the toxic cyanobacterium Planktothrix agardhii to dilute H(2)O(2). This reduced the photosynthetic vitality by more than 70% within a few hours. Next, we installed experimental enclosures in the lake, which revealed that H(2)O(2) selectively killed the cyanobacteria without major impacts on eukaryotic phytoplankton, zooplankton, or macrofauna. Based on these tests, we introduced 2 mg L(-1) (60 μM) of H(2)O(2) homogeneously into the entire water volume of the lake with a special dispersal device, called the water harrow. The cyanobacterial population as well as the microcystin concentration collapsed by 99% within a few days. Eukaryotic phytoplankton (including green algae, cryptophytes, chrysophytes and diatoms), zooplankton and macrofauna remained largely unaffected. Following the treatment, cyanobacterial abundances remained low for 7 weeks. Based on these results, we propose the use of dilute H(2)O(2) for the selective elimination of harmful cyanobacteria from recreational lakes and drinking water reservoirs, especially when immediate action is urgent and/or cyanobacterial control by reduction of eutrophication is currently not feasible. A key advantage of this method is that the added H(2)O(2) degrades to water and oxygen within a few days, and thus leaves no long-term chemical traces in the environment.

Degradation of anthracene by Mycobacterium sp. strain LB501T proceeds via a novel pathway, through o-phthalic acid.

ABSTRACT Mycobacterium sp. strain LB501T utilizes anthracene as a sole carbon and energy source. We analyzed cultures of the wild-type strain and of UV-generated mutants impaired in anthracene utilization for metabolites to determine the anthracene degradation pathway. Identification of metabolites by comparison with authentic standards and transient accumulation of o-phthalic acid by the wild-type strain during growth on anthracene suggest a pathway through o-phthalic acid and protocatechuic acid. As the only productive degradation pathway known so far for anthracene proceeds through 2,3-dihydroxynaphthalene and the naphthalene degradation pathway to form salicylate, this indicates the existence of a novel anthracene catabolic pathway in Mycobacterium sp. LB501T.

Clinical laboratory manifestations of exposure to background levels of dioxins in the perinatal period

Pluim HJ, Koppe JG, Olie K, van der Slikke JW, Slot PC, van Boxtel CJ. Clinical laboratory manifestations of exposure to background levels of dioxins in the perinatal period. Acta Pædiatr 1994;83:583–7. Stockholm. ISSN 0803–5253

Surface catalyzed formation of polychlorinated dibenzo-p-dioxins/dibenzofurans during municipal waste incineration

A series of reactions was carried out on different surfaces using carbon and CuCl2, and KCl or HCl as a Cl-source. The PCDD/PCDF congener distribution was seen to vary to a great extent but the isomer distribution remained fairly constant. It is concluded that thermodynamic properties are largely responsible for the PCDD/PCDF isomer distribution. With pentachlorobenzene Cl2 elimination, assisted by oxygen, appears to be the major pathway for PCDD/PCDF formation.

Chlorinated dioxin and dibenzofuran levels in food and wildlife samples in the North and South of Vietnam

Abstract More than 35 food and wildlife samples from North and South Vietnam were analyzed in order to study the long-term effects of “Agent Orange” spraying. The analytical results are presented. The results indicate that the levels in the South Vietnamese samples are higher than in the North Vietnamese samples. It is suggested that part of this difference may be due to the spraying of “Agent Orange”.

Rapid adaptation of harmful cyanobacteria to rising CO2

Significance Cyanobacterial blooms pose a major threat to the water quality of many eutrophic lakes and reservoirs. Cyanobacteria are thought to be very effective competitors when CO2 levels are depleted during dense blooms. Their response to elevated CO2 is less understood, however. We study competition among cyanobacteria, and find both laboratory and field evidence for natural selection of strains with different carbon uptake systems at different CO2 levels. Our results demonstrate that changes in inorganic carbon availability act as an important selective factor in cyanobacterial communities and suggest that future harmful cyanobacterial blooms will have a genotype composition that differs from contemporary blooms and will be tuned to the high-CO2 conditions. Rising atmospheric CO2 concentrations are likely to affect many ecosystems worldwide. However, to what extent elevated CO2 will induce evolutionary changes in photosynthetic organisms is still a major open question. Here, we show rapid microevolutionary adaptation of a harmful cyanobacterium to changes in inorganic carbon (Ci) availability. We studied the cyanobacterium Microcystis, a notorious genus that can develop toxic cyanobacterial blooms in many eutrophic lakes and reservoirs worldwide. Microcystis displays genetic variation in the Ci uptake systems BicA and SbtA, where BicA has a low affinity for bicarbonate but high flux rate, and SbtA has a high affinity but low flux rate. Our laboratory competition experiments show that bicA + sbtA genotypes were favored by natural selection at low CO2 levels, but were partially replaced by the bicA genotype at elevated CO2. Similarly, in a eutrophic lake, bicA + sbtA strains were dominant when Ci concentrations were depleted during a dense cyanobacterial bloom, but were replaced by strains with only the high-flux bicA gene when Ci concentrations increased later in the season. Hence, our results provide both laboratory and field evidence that increasing carbon concentrations induce rapid adaptive changes in the genotype composition of harmful cyanobacterial blooms.

Decomposition of octachlorodibenzofuran and formation of the hepta congeners during GLC analysis

Abstract For the identification and quantification of chlorinated dioxins and dibenzofurans a high resolution GLC coupled to a mass spectrometer is normally used. As a part of the clean-up procedure we use reversed phase HPLC. With the use of this method we isolated a fraction of pure OCDF. Injection of this fraction in the GLC resulted in peaks not only of OCDF but also of H 7 CDFs. At the longer retention time side of the latter peaks a higher background was found. This is probably caused by decomposition of OCDF at the beginning of the column and injection port. In this paper this problem is discussed and a method is suggested for overcoming the problem.

Diurnal variations in concentrations of PCDDs and PCDFs in human milk

Abstract To examine diurnal variations in concentrations of PCDDs and PCDFs in breast-milk, milk samples of eight well-nourished totally breast-feeding women were sampled during the morning and evening. Individual samples were analyzed on PCDDs and PCDFs. For every individual subject the concentrations in both milk samples were compared. The concentrations of PCDDs and PCDFs measured on fat basis were significantly higher in the evening than in the morning (p=0.033).