Microbial Community and Atrazine-Degrading Genetic Potential in Deep Zones of a Hypersaline Lake-Aquifer System

Abstract

The chemical composition of groundwater and related surface water ecosystems can be modified by intensive agricultural activities. This is the case of the Natural Reserve of Pétrola saline lake (Albacete, SE Spain), which constitutes the discharge area of an unconfined aquifer. The extended use of fertilizers and pesticides poses a threat to ecosystem sustainability. One of the most applied herbicides worldwide has been atrazine. Despite being prohibited in Spain since 2007 by European regulations, atrazine can still be detected due to its high persistence in the environment. Atrazine degradation pathways are mediated by biological processes performed by microorganisms with adapted metabolic mechanisms that make in situ bioremediation possible. To evaluate the presence of such microorganisms in the unconfined aquifer, groundwater was collected from a flowing 37.9 m deep piezometer. DNA was extracted, and the bacterial 16S rRNA gene was amplified and cloned. Later, 93 clones were sequenced, providing the first molecular assessment of bacterial community structure in the deep zones of the aquifer. Some of these bacteria have been previously described to be involved in atrazine degradation. In addition, 14 bacteria were isolated from the groundwater samples and identified by 16S rRNA gene sequencing. DNA from these bacteria was subjected to PCR assays with primers designed for the genes involved in the atrazine degradation pathway. Positive results in the amplification were found in at least three of these bacteria (Arthrobacter sp., Nocardioides sp. and Pseudomonas sp.). The atrazine-degrading genetic potential was shown to be dependent on the trzN and atzA,B,C gene combination. These results suggest for the first time the adaptation of the bacterial population present in deep aquifer zones to atrazine exposure, even after more than 15 years of its ban in Spain. In addition, this study provides the baseline data about the bacterial communities found in deep aquifer zones from the hypersaline lake-aquifer system.

Biodegradation of Atrazine Herbicide: A Mini-review

“…The main effect of hydroxyatrazine was kidney toxicity (owing to its low solubility in water, resulting in crystal formation and subsequent inflammatory response), and there was no evidence that hydroxyatrazine has neuroendocrine disrupting properties. Also, the acute oral toxicity of hydroxyatrazine in rats (LD50>5050 mgkg -1 body weight) was lower than that of atrazine or its chlorometabolites [17]. Fig.…”

Microbial ecology of a shallow alkaline hydrothermal vent: Strýtan Hydrothermal Field, Eyjafördur, northern Iceland

“…The third most abundant ASV in Big Strýtan vent fluids was sq31 (7.8%), which was classified as Acinetobacter sp. and has 100% similarity to a sequence from a subsurface aquifer ( Table 2 ; Espín et al, 2020 ). Two other ASVs belonging to the Pseudomonadales were classified at least the genus level and their best hits were also from hydrothermal vents: ASV sq63 (3.3%) is 100% similar to Psychrobacter sp.…”

Microbes as a potential bioremediation tool for atrazine-contaminated soil: A review

“…The degradation and utilization of atrazine by microflora are possible because of the complex catabolic pathway mediated by a diverse array of enzymes encode by a series of genes [16]. Different genes are involved in different steps throughout the degradation pathways that lead to the transformation of atrazine to its intermediate cyanuric acid [42]. To the best of our knowledge, the total number of eight genes involved in the atrazine metabolic pathway has been reported such as atzA, atzB, atzC, atzD, atzE, atzF, trzN, and trzD.…”

“…isolates which gives a piece of strong evidence for the genes are widespread. Some other bacteria such as Arthrobacter agilis and Nocardioides nanhaiensis are harbored atzA/trzN genes that code for atrazine chlorohydrolase that catalyze the dechlorination of atrazine into HA [42]. The same authors stated that atzD/trzD was involved in the conversion of cyanuric acid into biuret through ring cleavage by encoding an enzyme called cyanuric acid amidohydrolase.…”