Environmental Engineering Reference
In-Depth Information
Ferreira et al. (2009) used PCR-DGGE to study the effects of three insecticides (aldicarb,
chlorpyrifos, and deltamethrin) and two fungicides (tebuconazole and a mixture of meta-
laxyl and mancozeb) on the culturable bacterial communities of three soils with differ-
ent kinds of agroecological management. They analyzed 16S rDNA profiles of culturable
bacteria from soils cultivated with potato and treated with pesticides. The PCR-DGGE
patterns of culturable bacterial communities revealed that regardless of the type of the
pesticide used, the community structure of soil bacteria was disturbed and the similarity
values varied from 5% to 95% in comparison to the control. However, the biggest differ-
ences between microbial communities were observed in the first two harvests and, over
time, had a tendency to recover. The lowest percentages of similarity of soil bacterial com-
munities were found 32 days after the pesticide application when aldicarb, chlorpyrifos,
and tebuconazole had a higher impact on the microorganisms than deltamethrin and fun-
gicidal mixture in comparison to the control. Statistical analysis of the data showed that
the response of the bacteria depended on the type of soil and sampling time (Ferreira et al.
2009).
A response of soil microorganism to another fungicide, iprodione, was tested by Wang
et al. (2004). They estimated the impact of fungicide by counting the 16S rDNA bands in
the DGGE patterns. The differences between the DGGE profiles of 16S rDNA fragments
were observed on successive sampling days. The numbers of bands increased at the first
sampling times (3-7 days) and decreased after 16 days. No significant differences in the
microbial community structures between the control and the soil treated with iprodione
at a concentration of 5 μg/g soil was found. By contrast, the bacterial community did not
recover till that day in the soil with 50 μg fungicide per gram soil. An ability of the micro-
bial community to recover during 126 days after perturbations caused by carbendazim as
revealed by the comparison of the patterns of PCR-amplified 16S rDNA fragments using
DGGE obtained for fungicide and control samples was reported by Wang et al. (2009).
However, using the same method, they observed that the changes in microbial diversity as
a response to pencycuron application (100 mg/kg soil) were seen even on day 120, pointing
that the microbial community could not recover to its previous structure.
8.6.2 Phospholipid Fatty Acid Analysis
Phospholipid fatty acids (PLFAs) extracted from soils provide a means for direct in situ mea-
surements of the bacterial and fungal community structures and biomasses, and therefore,
they are used to assess the impact of pesticides on soil microbial diversity. Changes in the
microbial community structure in response to any environmental stressor are monitored
by comparison of relative abundance of signature fatty acids that are specific for groups
of microorganisms such as fungi, actinomycetes, Gram-negative (GN), and Gram-positive
bacteria (GN) (Zelles 1997; White et al. 1996). Recently, PLFA analysis proved to be a useful
tool for the assessment of changes in the community structure of the soil microorganisms
exposed to pesticides (Ratcliff et al. 2006; Wang et al. 2008).
Zhang et al. (2009) used this method to study the effect of foliar application of cyper-
methrin on biomass and the structure of the pepper phylosphere microbial community.
PLFA patterns obtained from pepper leaves showed that pesticide application signifi-
cantly increased the total and bacterial biomasses as compared with the control during the
21-day experiment. By contrast, the amount of fungal fatty acids significantly decreased
in the cypermethrin-treated samples. Analysis of the distribution of individual fatty acids
revealed that pesticide treatment also significantly decreased the ratio of GP to GN bac-
teria. Authors found that it was associated with the increase in the amount of four PLFAs
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