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

Abstract

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.

Toxicity of atrazine to Scenedesmus quadricauda under different nitrogen concentrations

“…Nitrogen and ATR have contrasting effects on S. quadricauda, with replete nitrogen stimulating growth and ATR inhibiting it (Dalton et al 2015). While there is evidence that low concentrations of ATR can stimulate algal growth (Murdock and Wetzel 2012), all concentrations used in the present study inhibited the growth of S. quadricauda, which is in accordance with the results obtained with several algal species (Guasch et al 2007;Jeannette et al 2007;Vallotton et al 2008;Richard et al 2012;Bai et al 2015;Chia et al 2015a). The reduction in growth, pigment content and biomass by ATR was caused by its interference with the capacity of the microalga to convert light energy into biologically available energy such as ATP and NADPH (Deblois et al 2013;Bai et al 2015).…”

A weight‐of‐evidence approach for deriving a level of concern for atrazine that is protective of aquatic plant communities

“…Giddings () subsequently expanded the cosm database to 116 data points with 55 data points associated with atrazine concentrations up to 50 μg/L. For this article, we added 5 new studies that have become available since 2012 (Knauer and Hommen ; Murdock and Wetzel ; Baxter et al ; Choung et al ; Halstead et al ).…”

Determining in situ periphyton community responses to nutrient and atrazine gradients via pigment analysis

“…Nutrients and atrazine were expected to have contrasting effects on periphyton with nutrients stimulating growth and atrazine inhibiting growth. However, atrazine can both stimulate (10 μg/L) (Murdock and Wetzel, 2012) and inhibit periphyton (100 μg/L) (Guasch et al, 2007). Indirect positive effects of atrazine (100 μg/L) may also occur through a reduction in phytoplankton and subsequent increase in light and nutrient availability (Rohr et al, 2008;Halstead et al, 2014).…”