The degradation of the herbicide bromoxynil and its impact on bacterial diversity in a top soil

Abstract

Aims: To study how repeated applications of an herbicide bromoxynil to a soil, mimicking the regime used in the field, affected the degradation of the compound and whether such affects were reflected by changes in the indigenous bacterial community present. Methods and Results: Bromoxynil degradation was monitored in soil microcosms using HPLC. Its impact on the bacterial community was determined using denaturing gradient gel electrophoresis (DGGE) and quantitative PCR of five bacterial taxa (Pseudomonads, Actinobacteria, α‐Proteobacteria, Acidobacteria and nitrifying bacteria). Three applications of 10 mg kg−1 of bromoxynil at 28‐day intervals resulted in rapid degradation, the time for removal of 50% of the compound decreasing from 6·4 days on the first application to 4·9 days by the third. Bacterial population profiles showed significant similarity throughout the experiment. With the addition of 50 mg kg−1 bromoxynil to soil, the degradation was preceded by a lag phase and the time for 50% of the compound to be degraded increased from 7 days to 28 days by the third application. The bacterial population showed significant differences 7 days after the final application of bromoxynil that correlated with an inhibition of degradation during the same period. Conclusions: These analyses highlighted that the addition of bromoxynil gave rise to significant shifts in the community diversity and its structure as measured by four abundant taxa, when compared with the control microcosm. These changes persisted even after bromoxynil had been degraded. Significance and Impact of the Study: Here we show that bromoxynil can exert an inhibitory effect on the bacterial population that results in decreased rates of degradation and increased persistence of the compound. In addition, we demonstrate that molecular approaches can identify statistically significant changes in microbial communities that occur in conjunction with changes in the rate of degradation of the compound in the soil.

Impacts of Organic and Conventional Crop Management on Diversity and Activity of Free-Living Nitrogen Fixing Bacteria and Total Bacteria Are Subsidiary to Temporal Effects

“…Initially a 360 bp fragment is amplified using using PolF and PolR primers [34] followed by nesting with PolFI and AQER-GC30 primers [33]. To amplify the total bacterial community, the V3 variable region of 16S rRNA was amplified using V3FC and V3R primers [35]. Full PCR conditions and primer sequences are described in Orr et al, [23].…”

“…DGGE was carried out using the D-Code system (Bio-Rad Laboratories) as described by Baxter & Cummings [35]. PCR products were electrophoresed through gels containing 35–55% denaturing gradient at 200 V for either 6 ( nifH ) or 4.5 (16S rRNA) hours.…”

Temporal Variations in Diazotrophic Communities and nifH Transcripts Level Across the Agricultural and Fallow Land at Jaipur, Rajasthan, India

“…Each 25 ll of PCR mixture contained 25 ng DNA, 1X Taq buffer, dNTP 200 lM each, primer 1 lM each, and Taq polymerase 1.5 U. PCR conditions as follows: 1 cycle at 94°C (5 min), 30 cycles at 94°C (1 min), 55°C (1 min), 72°C (2 min), 1 cycle at 72°C (7 min), and finally hold at 4°C in C1000TM Thermal Cycler (Bio-Rad). DGGE was done using D-Code system (Bio-Rad, Germany) at 60 V for 16 h at 60°C [15]. Bands were detected and relative intensities were calculated using Image lab software (BioRad).…”

Impact of Nitriles on Bacterial Communities

“…Unintended release of man-made nitriles can lead to environmental accumulation and impact natural communities. In addition, some nitriles are used as herbicides, e.g., dichlobenil (Holtze et al, 2007) or bromoxynil (Baxter and Cummings, 2008). The effect of these synthetic compounds on bacterial communities, the key players in most nutrient cycles (Tanner, 1985;Alongi, 1994;Rashid et al, 2016), is almost unknown.…”