Toxicity of pentachlorophenol for micromycetes isolated from freshwater sediments

In order to evaluate the impact of xenobiotics on fungal communities of sediments, lentic ecosystems have been reconstituted in the laboratory and examined before as well as after contamination.Microcosms (2 litres) have been treated with three different concentrations of pentachlorophenol (PCP) (3, 100, and 1000 mg l^-1) at 22 degC. The fungal strains present in the sediments were first isolated and identified before contamination with PCP. Most of the strains belonged to Deuteromycetes (mainly Mucedinaceæ and Dematiaceæ) with a predominance of the genus Penicillium, and Ascomycetes were found in exceptional abundance. New isolations and identifications were made on days 1, 2, 4, 8, and 15 after contamination with PCP. The sensitivity of the various species were determined as a function of the level of PCP and the duration of contamination. Ascomycetes was particularly resistant to high concentrations of PCP. The toxicity of the xenobiotic towards strains belonging to various taxonomic groups is discussed, as well as the possibility that some of them may be useful for biodegradation and/or bioremediation processes, or as bioindicators of polluted sites.Groupe pour l'Étude du Devenir des Xénobiotiques dans l'Environnement (GEDEXE)Laboratoire de Botanique, Cryptogamie, Biologie Cellulaire et Génétique.     

Isolation of anaerobic oxalate-degrading bacteria from freshwater lake sediments

Enrichment cultures that anaerobically degraded oxalate were obtained from lake sediment inocula. From these, 5 pure cultures of anaerobic oxalate-degrading bacteria were isolated and partially characterized. The isolates were Gram-negative, non-sporeforming, non-motile, obligate anaerobes. Oxalate was required for growth and was stoichiometrically converted to formate; ¹⁴CO₂ was also recovered when ¹⁴C-oxalate was added. Maximal growth occurred when the oxalate concentration was 50 mM. Acetate stimulated growth in the presence of oxalate, however, ¹⁴C-experiments indicated that acetate was only utilized for cell carbon.The isolates were either spiral-shaped or rod-shaped organisms. The first morphotype grew much more slowly than the second and exhibited 13-fold lower cell yields. These isolates represent a new strain of oxalate-degrading bacteria. The second morphotype was similar to the anaerobic oxalate-degrading bacteria previously found in rumen. This report extends the known habitats in which anaerobic oxalate-degrading organisms have been found to include aquatic sediments.     

Biogeochemical transformations of arsenic in circumneutral freshwater sediments

Arsenic is a wide-spread contaminant of soils and sediments, andmany watersheds worldwide regularly experience severe arsenic loading. While the toxicityof arsenic to plants and animals is well recognized, the geochemical and biological transformationsthat alter its bioavailability in the environment are multifaceted and remain poorly understood.This communication provides a brief overview of our current understanding of the biogeochemistryof arsenic in circumneutral freshwater sediments, placing special emphasis on microbialtransformations. Arsenic can reside in a number of oxidation states and complex ions. The commoninorganic aqueous species at circumneutral pH are the negatively charged arsenates(H₂As^VO₄ ^- and Has^VO₄ ^2-) and zero-charged arsenite(H₃As^IIIO₃ ⁰). Arsenic undergoes diagenesis in response to both physicaland biogeochemical processes. It accumulates in oxic sediments by adsorption on and/orco-precipitation with hydrous iron and manganese oxides. Burial of such sediments in anoxic/suboxicenvironments favors their reduction, releasing Fe(II), Mn(II) and associatedadsorbed/coprecipitated As. Upward advection can translocate these cations and As into theoverlying oxic zone where they may reprecipitate. Alternatively, As may be repartitioned tothe sulfidic phase, forming precipitates such as arsenopyrite and orpiment. Soluble and adsorbedAs species undergo biotic transformations. As(V) can serve as the terminal electronacceptor in the biological oxidation of organic matter, and the limited number of microbes capableof this transformations are diverse in their phylogeny and physiology. Fe(III)-respiring bacteriacan mobilize both As(V) and As(III) bound to ferric oxides by the reductive dissolution ofiron-arsenate minerals. SO₄ ^2--reducing bacteria canpromote deposition of As(III) as sulfide minerals via their production of sulfide. A limited number of As(III)-oxidizing bacteriahave been identified, some of which couple this reaction to growth. Lastly, prokaryotic andeukaryotic microbes can alter arsenic toxicity either by coupling cellular export to its reductionor by converting inorganic As to organo-arsenical compounds. The degree to which each ofthese metabolic transformations influences As mobilization or sequestration in differentsedimentary matrices remains to be established.     

The role of sedimentation and resuspension for the transport of sediments and contaminants in the Skagerrak

An investigation was conducted in winter of 1997/1998 in the Skagerrak off southern Norway to collect data on the influence of sedimentation and resuspension on the transport of organic contaminants. Data from the water column and sediments, as well as on sedimentation and current regime near the sea floor, indicated that the deposition of contaminants is a continual process. Deposition is subject not only to seasonal biological processes such as growth and sedimentation of the spring phytoplankton bloom, but also to hydrographic events such as surges in near-bottom currents causing sediment resuspension. Contaminants at the sea floor may be transported considerable distances. It is suggested that in simplest terms, this transport can be envisaged as a conveyor belt skipping along the seabed. The dominant iterative processes regulating this near-bottom transport are sedimentation, resuspension and advection. In this way, particles and associated polycyclic aromatic hydrocarbons, as well as other hydrophobic contaminants, may be transported over hundreds of kilometers.     

The presence and activity of Desulfotomaculum spp in sulphate-limited freshwater sediments

Abstract Addition of pyrophosphate stimulated sulphate uptake and utilization of volatile fatty acids by anaerobic freshwater sediments. Population estimates of sulphate-reducing bacteria demonstrated that a larger number were capable of utilizing acetate then lactate. Estimates increased when pyrophosphate was added to the medium and decreased by the same degree when the sediment was heated. Addition of molybdate to the sulphate-limited sediments stimulated rather than inhibited methanogenesis. The results suggest that the sediment contains a metabolically active population of acetate-utilizing members of the genus Desulfotomaculum .     

Unexpected and novel putative viruses in the sediments of a deep-dark permanently anoxic freshwater habitat

Morphological diversity, abundance and community structure of viruses were examined in the deep and anoxic sediments of the volcanic Lake Pavin (France). The sediment core, encompassing 130 years of sedimentation, was subsampled every centimeter. High viral abundances were recorded and correlated to prokaryotic densities. Abundances of viruses and prokaryotes decreased with the depth, contrasting the pattern of virus-to-prokaryote ratio. According to fingerprint analyses, the community structure of viruses, bacteria and archaea gradually changed, and communities of the surface (0–10 cm) could be discriminated from those of the intermediate (11–27 cm) and deep (28–40 cm) sediment layers. Viral morphotypes similar to virions of ubiquitous dsDNA viruses of bacteria were observed. Exceptional morphotypes, previously never reported in freshwater systems, were also detected. Some of these resembled dsDNA viruses of hyperthermophilic and hyperhalophilic archaea. Moreover, unusual types of spherical and cubic virus-like particles (VLPs) were observed. Infected prokaryotic cells were detected in the whole sediment core, and their vertical distribution correlated with both viral and prokaryotic abundances. Pleomorphic ellipsoid VLPs were visible in filamentous cells tentatively identified as representatives of the archaeal genus Methanosaeta, a major group of methane producers on earth.     

Development of a protocol for recognizing sulfidic sediments (potential acid sulfate soils) in freshwater wetlands

Summary   The presence of sulfidic sediments (potential acid sulfate soils) is an emerging problem in the management of inland wetlands. Using data from 81 wetlands in the Murray-Darling Basin, a simple protocol was developed to assess whether a wetland will contain sulfidic sediments at levels that could cause ecological damage. Risk factors include whether or not the wetland receives municipal waste or irrigation return water, elevated salinity in the overlying water (>1750 µS/cm) or sediment (400 µS/cm in a 1:5 soil : water extract) and high levels of sulfate in the water column (>10 mg/L). Neutral or basic sediment pH indicates that, even if the sediment does contain sulfidic sediments, there is a reduced likelihood of acidification if the sediments are oxidized.     

Studies of heavy metal sorption by Trenton Channel (Detroit River) sediments

Sediment resuspension plays a dominant physical role in downstream transport of sediment-bound, or in-place pollutants. During resuspension, however, numerous sorption reactions may alter contaminant phase distributions. Previous field resuspension studies on heavily contaminated sediments (Theis et al., 1988, J. Great Lakes Res. 14, 216) showed parallel trends in metal partitioning with pH and time for each of 7 metals (Cd, Co, Cr, Cu, Ni, Pb, Zn), when pH was < 7.5 during resuspension. To improve our ability to interpret follow-up laboratory partitioning experiments using sediments from the field sites, we conducted an evaluation of sediment sample storage as a potential factor leading to field-laboratory partitioning differences. Although metal sorption observed in the laboratory differed substantially from that observed in the field, sample storage effects, reported as holding time and changes in solid phase metal fractionation, gave minimal support for the hypothesis that sample storage caused the differences. It appears, rather, than our in vitro batch equilibrium systems incompletely replicated those attributes of a sediment-water system that are relevant to adsorption and desorption of heavy metals during a resuspension event. Accordingly, we conclude that a general improvement in the understanding of contaminant partitioning would result if future studies would assign greater importance to evaluating the effects of relevant physical phenomena on partitioning (e.g. particle interaction and shear stress), in addition to such widely studied chemical determinants as pH, time, and metal species.     

Oxidation of short-chain fatty acids by sulfate-reducing bacteria in freshwater and in marine sediments

Colony counts of acetate-, propionate- and l-lactate-oxidizing sulfate-reducing bacteria in marine sediments were made. The vertical distribution of these organisms were equal for the three types considered. The highest numbers were found just beneath the border of aerobic and anaerobic layers.Anaerobic mineralization of acetate, propionate and l-lactate was studied in the presence and in the absence of sulfate. In freshwater and in marine sediments, acetate and propionate were oxidized completely with concomitant reduction of sulfate. l-Lactate was always fermented. Lactate-oxidizing, sulfate-reducing bacteria, belonging to the species Desulfovibrio desulfuricans, and lactate-fermenting bacteria were found in approximately equal amounts in the sediments. Acetate-oxidizing, sulfate-reducing bacteria could only be isolated from marine sediments, they belonged to the genus Desulfobacter and oxidized only acetate and ethanol by sulfate reduction. Propionate-oxidizing, sulfate-reducing bacteria belonged to the genus Desulfobulbus. They were isolated from freshwater as well as from marine sediments and showed a relatively large range of usable substrates: hydrogen, formate, propionate, l-lactate and ethanol were oxidized with concomitant sulfate reduction. l-Lactate and pyruvate could be fermented by most of the isolated strains.     

Environmental entrainment of tidally rhythmic behaviour in marine animals

Field and laboratory experiments show that endogenous circatidal rhythms in coastal animals are entrained by exposure to real or simulated tidal cycles of hydrostatic pressure, temperature, salinity, wave agitation, immersion and light. Short pulses (2–3 h) of simulated high tide induce slight phase advances or delays in the free-running circatidal rhythm of groups of experimental animals, depending upon the time of application. Phase-response curves derived in this way are less clear-cut than for typical circadian rhythms, but their pattern suggests that tidally rhythmic behaviour is controlled by truly circatidal (and not circadian) oscillators. The underlying circatidal oscillators appear, in general, to be fairly stable, suggesting that populations of coastal animals are relatively unsusceptible to irregularly timed environmental stimuli associated, say, with severe storms.     

The effects of chronic marijuana use on circadian entrainment

Animal literature suggests a connection between marijuana use and altered circadian rhythms. However, the effect has not yet been demonstrated in humans. The present study examined the effect of chronic marijuana use on human circadian function. Participants consisted of current users who reported smoking marijuana daily for at least a year and non-marijuana user controls. Participants took a neurocognitive assessment, wore actigraphs and maintained sleep diaries for three weeks. While no significant cognitive changes were found between groups, data revealed that chronic marijuana use may act as an additional zeitgeber and lead to increased entrainment in human users.     

Formal analysis of resonance entrainment by central pattern generator

The neuronal circuit controlling the rhythmic movements in animal locomotion is called the central pattern generator (CPG). The biological control mechanism appears to exploit mechanical resonance to achieve efficient locomotion. The objective of this paper is to reveal the fundamental mechanism underlying entrainment of CPGs to resonance through sensory feedback. To uncover the essential principle, we consider the simplest setting where a pendulum is driven by the reciprocal inhibition oscillator. Existence and properties of stable oscillations are examined by the harmonic balance method, which enables approximate but insightful analysis. In particular, analytical conditions are obtained under which harmonic balance predicts existence of an oscillation at a frequency near the resonance frequency. Our result reveals that the resonance entrainment can be maintained robustly against parameter perturbations through two distinct mechanisms: negative integral feedback and positive rate feedback.     

Resuspension studies in cylindrical microcosms: Effects of stirring velocity on the dynamics of redox sensitive elements in a coastal sediment

Effects of resuspension on the release of dissolved, redox sensitive elements (Fe, Mn) was studied in cylindrical microcosms. Effects from changing water stirring velocity in sediment pools were evaluated through measurements of pore water profiles of dissolved Mn, Fe and redox potential. Mn was a good natural marker to follow such effects. At current velocities below the threshold velocity for resuspension (37 cm s-1), Mn release rates to overlying water were 100 times higher compared to steady-state values. Pulse increases in Mn concentration were the result of convective currents inside flow chambers. These results were strongly supported by measurements of Eh profiles in the sediment pore water. Furthermore, impacts from increasing stirring velocity were found down to 1.9 cm depth below the resuspended layer of sediment.     

Pathways of ocular entrainment in Marpissa marina (Araneae,Salticidae)

Depending on the animal species, photoreceptors are located in the visual organs, in non-visual organs or in both. Because of unique characteristics of vision containing several different pairs of eyes, I chose the jumping spider (salticid) Marpissa marina (Araneae: Salticidae; Goyen, 1892) for this study. Eyes in spiders are categorized in two groups of principal and secondary. Specifically, my aim was to determine which eyes are dedicated to regulation of the central circadian rhythm and to illuminate the pathway(s) of ocular entrainment in jumping spiders. To achieve this, I used an opaque elastic paste to prevent entry of light to the photoreceptors. My procedure was to measure spider activity levels over eight days as well as spiders responses to a 6 h delay shift in light/dark cycle. This would be made first with uncovered eyes (and sham covers) and then with distinct pairs of eyes covered. The results revealed that, unlike the secondary eyes, light information gathered through AMEs did not lead directly or indirectly to the parts of the circadian system that contain circadian pacemakers.     

An entrainment model for semilunar rhythmic swimming behaviour in the marine isopod Eurydice pulchra Leach

Entrainment experiments have been carried out with geographically widely separated populations of the sand beach isopod Eurydice pulchra Leach subjected to periods of simulated tidal agitation imposed concurrently with a 24-h light: dark (L: D) cycle. Circatidal swimming rhythms of greatest amplitude were induced when agitation was applied with the subjective timing, within the L: D cycle, of local spring high tides. This occurred in a normal L: D regime and also when the L: D regime was phase shifted through 90°. Animals previously maintained in constant darkness (D: D) and subsequently exposed to simulated tidal disturbance at various times in constant darkness were unable to modulate the amplitude of circatidal swimming activity. Isopods previously maintained in a normal L: D cycle and subsequently subjected to artificial tidal agitation in constant darkness were, however, able to modulate circatidal activity. This indicates that E. pulchra is capable of detecting tidal agitation and daily light cues and using them in conjunction with its circadian “clock” to modulate its endogenous circatidal rhythmicity. The free-running semilunar rhythm of swimming activity entrained only when the timing of agitation within the day/night cycle mimicked the pattern of local spring high tides. Agitation with the timing of neap high tides entrained no free-running circa-semilunar activity pattern.     

Methanogenic bacteria in mangrove sediments

The occurrence of methanogenic bacteria in the Kodiakkarai (10° 18 N; 79° 52 E) mangrove sediments, whereAvicennia spp are predominant, was studied. Trimethylamine under N₂:CO₂ (80:20% v/v) was used as the substrate. Most Probable Number (MPN) of methanogenic bacteria was determined for a period of one year from July 1987 to June 1988 with monthly sampling. The methanogenic bacterial populations were found to be at the maximum of 1.1 × 10⁵ MPN gm^–1 of wet sediment during August 1987 and from February to June 1988. The bacterial numbers were found to decrease during October to December 1987 with a minimal value of 3.6 × 10² MPN gm^–1 during December 1987. Environmental factors were correlated with the methanogenic bacterial population.     

Selective effects of phytoplankton entrainment at the Surry Power Plant,James River,Virginia

Loss of cryptophyte cells entrained in the Surry Power Plant cooling water was significantly correlated with discharge water temperature in the range 27.2–37.5 °C. Entrained Skeletonema costatum and benthic diatom populations experienced losses of 25–80% in the summer, but correlations between % loss and discharge temperature were insignificant. Cropping by benthic filter feeders in the intake and discharge canals could account for the summer removal of diatoms. Shortening of entrained S. costatum chains was detected in both winter and summer, indicating a mechanical effect of turbulence.Benthic diatoms were vulnerable to entrainment only during daylight hours, when they migrated to the sediment surface at low tide. Skeletonema costatum was most vulnerable in the summer, when elevated salinities permitted it to range upstream to the intake area. Cryptophyte populations peaked in the summer when entrainment loss was greatest.The composition of the entrained phytoplankton community was altered by the species specific interactions of factors affecting vulnerability and entrainment loss. At Surry the discharged cooling water mixes rapidly with the main stem James River, and the selective effects of entrainment are not detectable in phytoplankton samples taken beyond the immediate discharge zone. More persistent modifications of the phytoplankton could be expected at sites where power plants discharge into creeks or embayments.Contribution No. 1106, Virginia Institute of Marine Science.Contribution No. 1106, Virginia Institute of Marine Science.     

Phosphorus in settling matter and bottom sediments in lakes loaded by agriculture

In shallow lakes, the cycling of P between water and bottom sediments is strongly influenced by wind-induced resuspension of particulate matter. The significance of this P flux as an algal nutrient source is unclear. We examined gross sedimentation in 3 open and shallow agriculturally loaded lakes. In addition, we estimated the potential P-release from settling and bottom matter by laboratory tests. The mean daily rate of gross sedimentation was 21–170 g m^–2 d^–1 of dry sediment, 0.04–0.18 g m^–2 d^–1 of P and 0.18–2.0 g m^–2 d^–1 of N; being the highest in the shallowest and most eutrophic lake. In Lake Karhijärvi, where the most intensive measurements were taken, wind explained the temporal variation in the gross sedimentation to some extent. The settling matter consisted of inorganic particles low in nutrients, especially during peak sedimentation periods. On average, 7.7 ± 3.1% (x ± 95% confidence interval) of the P in the settling matter in L. Karhijärvi was in an algal-available form according to 2–3 week bioassays. In the bottom matter of the three lakes, 3.0 ± 1.7% and 2.5 ± 3.6%, and 4.3 ± 3.7% of the P was utilized by the algae. In L. Karhijärvi, resuspension of the potentially available P exceeded 20 times the external loading during the open water season. According to sorption tests, P is released from the bottom matter only when the concentration of o-P is <2 g l^–1. Although such a low value cannot be determined with common analytical procedures, it seems probable that the P concentration allows P desorption during P-limited periods. However, the significance of resuspended matter as an algal nutrient source calls for further research.