Simazine biodegradation in soil: analysis of bacterial community structure by in situ hybridization

Abstract

Pesticide and nitrate contamination of soil and groundwater from agriculture is an environmental and public health concern worldwide. Simazine, 6-chloro-N2,N4-diethyl-1,3,5-triazine-2,4-diamine, is a triazine herbicide used in agriculture for selective weed control with several types of crops and it is frequently applied to soils receiving N-fertilizers. Degradation experiments were performed in the laboratory to assess whether the biodegradation of simazine in soil may be influenced by the presence of urea. Simazine degradation rates under different experimental conditions (presence/absence of urea, microbiologically active/sterilized soil) were assessed together with the formation, degradation and transformation of its main metabolites in soil. Simazine degradation was affected by the presence of urea, in terms both of a smaller half-life (t(1/2)) and of a higher amount of desethyl-simazine formed. The soil bacterial community was also studied. Microbial abundances were determined by epifluorescence direct counting. Moreover in situ hybridization with rRNA-targeted fluorescent oligonucleotide probes was used to analyze the bacterial community structure. Fluorescent in situ hybridization (FISH) was used to detect specific groups of bacteria such as the alpha,beta,gamma-subdivisions of Proteobacteria, Gram-positive bacteria with a high G + C DNA content, Planctomycetes, Betaproteobacterial ammonia-oxidizing bacteria and nitrifying bacteria. The presence of the herbicide and/or urea affected the bacterial community structure, showing that FISH is a valuable tool for determining the response of bacterial populations to different environmental conditions.

Planctomycetes and macroalgae, a striking association

“…A particular group of planctomycetes, the anaerobic ammonium oxidation (anammox) species, are strict anaerobes. Their diversified metabolism allows them to colonize a wide variety of ecosystems ranging from aquatic (marine, brackish, freshwater, sediments, and marine snow) to terrestrial habitats as well as several extreme environments such as desert soils (Abed et al, 2010; Andrew et al, 2012), hypersaline environments (Baumgartner et al, 2009; Schneider et al, 2013), hot springs (Tekere et al, 2011; Bohorquez et al, 2012), acidophilic habitats (Ivanova and Dedysh, 2012; Lucheta et al, 2013), glacial waters (Liu et al, 2006; Zeng et al, 2013) and Antarctic soils and waters (Newsham et al, 2010; Piquet et al, 2010), hydrocarbon polluted environments (Abed et al, 2011)and other polluted habitats (Reed et al, 2002; Chouari et al, 2003; Caracciolo et al, 2005; Akob et al, 2007; Halter et al, 2011). Furthermore, their association with a great number of diverse eukaryotic organisms has been reported.…”

Simazine application inhibits nitrification and changes the ammonia-oxidizing bacterial communities in a fertilized agricultural soil

“…It has been observed that simazine at high concentrations [200 lg g À1 d.w.s] reduced nitrification in soil (Gaur & Misra, 1977). Recently, FISH analyses showed that the addition of simazine to agricultural soils induced changes in the bacterial community structure, mainly affecting Alpha proteobacteria and Beta proteobacteria (Barra Caracciolo et al, 2005;Morgante et al, 2010).…”

Three Functional Biomarkers for Monitoring the Nanoscale Zero-Valent Iron (nZVI)-Induced Molecular Signature on Soil Organisms

“…The moisture content was adjusted to 22 % (w/w) in all microcosms, corresponding to 70 % of soil maximum water-holding capacity, which is recommended for laboratory incubations to determine microbial activity ( Barra-Caracciolo et al, 2005); the volume of water required to adjust the water content (approximately 9 mL) was calculated considering the final nZVI volume used to spike the treated microcosms. All microcosms were incubated for 21 days in a climatic chamber at 21 ± 0.5°C in the dark.…”