Comparative Sensitivity of Freshwater Algae to Atrazine

Lockert, Christine; Hoagland, Kyle D.; Siegfried, Blair D.

doi:10.1007/s00128-005-0891-9

Cited by 40 publications

(27 citation statements)

References 14 publications

(24 reference statements)

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“…Algae were identified to genus, with a minimum of 300 cells counted per sample at 400× with light microscopy. Algae were divided into functional groups; diatoms (single-cell pennate, chain-forming pennate, single-cell centric, chain-forming centric), cyanobacteria (filamentous, coccoid), and green algae (filamentous, colonial, single cell) as atrazine tolerance can differ among major algal divisions [34]. Biovolume of each cell, colony, or filament was calculated by comparing algae to similar geometric shapes [28].…”

Section: Assemblage-level Structure and Functionmentioning

confidence: 99%

“…Although atrazine often reduces cellular chlorophyll content, low concentration may increase chlorophyll [46]. Additionally, the magnitude of chlorophyll response differs among species [24,34,54]. A 1-cm 2 area on each tile was scraped with a razor.…”

Section: Assemblage-level Structure and Functionmentioning

confidence: 99%

“…Extrapolating results from laboratory-based single species assays to natural, mixed species assemblages, however, has limitations. Environmental conditions may alter pollutant effect [23,29], and different species can have variable susceptibilities [34,48]. Complicating extrapolation to the real world is that pollutant levels in aquatic ecosystems are often lower than effective doses established in laboratory algal bioassays.…”

Section: Introductionmentioning

confidence: 99%

“…This variable response among species has led to the hypothesis that in natural systems, atrazine may cause compositional shifts in algal assemblages, leading to changes in assemblage function [33], or increased cyanobacteria blooms [41]. Green algae are often more susceptible to atrazine than diatoms and cyanobacteria [24,34,54], so assemblage species composition may play an important role in determining interactive effects of atrazine and nutrients.…”

Section: Introductionmentioning

confidence: 99%

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Macromolecular Response of Individual Algal Cells to Nutrient and Atrazine Mixtures within Biofilms

Murdock

Wetzel

2011

Microb Ecol

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Pollutant effects on biofilm physiology are difficult to assess due to differential susceptibility of species and difficulty separating individual species for analysis. Also, measuring whole assemblage responses such as metabolism can mask species-specific responses, as some species may decrease and others increase metabolic activity. Physiological responses can add information to compositional data, and may be a more sensitive indicator of effect. It is difficult, however, to separate individual species for biochemical analyses. Agricultural runoff often contains multiple pollutants that may alter algal assemblages in receiving waters. It is unclear how mixtures containing potential algal growth stimulators and inhibitors (e.g., nutrients and herbicides) alter algal assemblage structure and function. In research presented here, algal biofilms were exposed to nutrients, atrazine, and their mixtures, and assemblage-level structural and functional changes were measured. Synchrotron infrared microspectroscopy (IMS) was used to isolate the biochemical changes within individual cells from a dominant species of a green alga (Mougeotia sp.), a diatom (Navicula sp.), and a cyanobacterium (Hapalosiphon sp.). At the assemblage level, mixtures generally increased algal biovolume, decreased chlorophyll a, and had no effect on metabolism or ammonium uptake. Navicula had a strong negative response to atrazine initially, but later was more affected by nutrients. Hapalosiphon responded positively to both atrazine and nutrients, and Mougeotia did not exhibit any biochemical trends. Generally, biochemical changes in each species were similar to cells experiencing low stress conditions, with increased relative protein and decreased relative lipid. IMS provided direct evidence that individual species in a natural biofilm can have unique responses to atrazine, nutrients, and mixtures. Results suggest that the initial benthic community composition should have a strong influence on the overall impact of agricultural pollutants.

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Section: Assemblage-level Structure and Functionmentioning

confidence: 99%

Section: Assemblage-level Structure and Functionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Macromolecular Response of Individual Algal Cells to Nutrient and Atrazine Mixtures within Biofilms

Murdock

Wetzel

2011

Microb Ecol

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“…It has also been suggested that atrazine may be carcinogenic (21,22). Due to their broad specificity, atrazine and related triazine herbicides can also be toxic to nontarget photosynthetic species, from phototropic bacteria and freshwater algae to mangrove trees (4,31,49). Atrazine is also environmentally persistent: the half-life of atrazine in soil has been estimated at between 4 and 57 weeks (5), and atrazine has been detected in both surface and ground waters in several countries (15,51,53) at concentrations up to 4.6 M.…”

mentioning

confidence: 99%

Catalytic Improvement and Evolution of Atrazine Chlorohydrolase

Scott

Jackson

Coppin

et al. 2009

Appl Environ Microbiol

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The atrazine chlorohydrolase AtzA has evolved within the past 50 years to catalyze the hydrolytic dechlorination of the herbicide atrazine. It is of wide research interest for two reasons: first, catalytic improvement of the enzyme would facilitate its application in bioremediation, and second, because of its recent evolution, it presents a rare opportunity to examine the early stages in the acquisition of new catalytic activities. Using a structural model of the AtzA-atrazine complex, a region of the substrate-binding pocket was targeted for combinatorial randomization. Identification of improved variants through this process informed the construction of a variant AtzA enzyme with 20-fold improvement in its k cat /K m value compared with that of the wild-type enzyme. The reduction in K m observed in the AtzA variants has allowed the full kinetic profile for the AtzA-catalyzed dechlorination of atrazine to be determined for the first time, revealing the hitherto-unreported substrate cooperativity in AtzA. Since substrate cooperativity is common among deaminases, which are the closest structural homologs of AtzA, it is possible that this phenomenon is a remnant of the catalytic activity of the evolutionary progenitor of AtzA. A catalytic mechanism that suggests a plausible mechanistic route for the evolution of dechlorinase activity in AtzA from an ancestral deaminase is proposed.

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Effects of Pesticides on Freshwater Diatoms

Debenest

Silvestre

Coste

et al. 2009

Reviews of Environmental Contamination and Toxicology

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The study of pesticide effects on algae, and diatoms in particular, was focused on photosynthesis and biomass growth disturbances. Few studies have been performed to investigate the effects of these toxic agents on intracellular structures of diatom cells. Nuclear alterations and cell wall abnormalities were reported for diatoms exposed to toxic compounds. Nevertheless, the cellular mechanisms implicated in the development of such alterations and abnormalities remain unclear. Sensitivity to pesticides is known to be quite different among different diatom species. Eutrophic and small species are recognized for their tolerance to pesticides exposure. More pronounced cell defenses against oxidative stress may explain this absence of sensitivity in species of smaller physical size. Notwithstanding, on the whole, explaining the rationale behind tolerance variations among species has been quite difficult, thus far. In this context, the understanding of intracellular toxicity in diatoms and the relation between these intracellular effects and the disturbance of species composition in communities represent a key target for further research. The original community species structure determines the response of a diatom community to toxic agent exposure. Diatom communities that have species capable of switching from autotrophic to heterotrophic modes, when photosynthesis is inhibited (e.g., after pesticide exposure), can continue to grow, even in the presence of high pesticide pollution. How diatoms respond to toxic stress, and the degree to which they respond, also depends on cell and community health, on ecological interactions with other organisms, and on general environmental conditions. The general structural parameters of diatom communities (biomass, global cell density) are less sensitive to pesticide effects than are the specific structural parameters of the unicellular organisms themselves (cell density by species, species composition). For benthic species, biofilm development and grazing on this matrix as a source of food for invertebrates and fishes may also modify the response of diatom communities. Environmental parameters (light exposure, nutrient concentrations, and hydraulic conditions) affect, and often interfere with, the response of diatoms to pesticides. Therefore, the complexity of aquatic ecosystems and the complexity of pesticide to easily detect the effects of such pollutants on diatoms. Clearly more research will be required to address this problem.

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Comparative Sensitivity of Freshwater Algae to Atrazine

Cited by 40 publications

References 14 publications

Macromolecular Response of Individual Algal Cells to Nutrient and Atrazine Mixtures within Biofilms

Macromolecular Response of Individual Algal Cells to Nutrient and Atrazine Mixtures within Biofilms

Catalytic Improvement and Evolution of Atrazine Chlorohydrolase

Effects of Pesticides on Freshwater Diatoms

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