TY  - JOUR
AU  - Aguirre, Sandra Puente 
AU  - Lowe, Kristine L. 
PY  - 2010
TI  - Pesticide-Tolerant Bacteria Isolated from Agricultural Canals in the Lower Rio Grande Valley of South Texas
JF  - OnLine Journal of Biological Sciences
VL  - 10
IS  - 3
DO  - 10.3844/ojbsci.2010.126.135
UR  - https://thescipub.com/abstract/ojbsci.2010.126.135
AB  - Atrazine and oxamyl are commonly-used pesticides in the Lower Rio Grande Valley of
South Texas. Problem statement: Pesticides may become environmental contaminants due to
overuse, runoff and other mechanisms and may impact non-target organisms and ecosystems.
Pesticides may be degraded by indigenous microorganisms or by abiotic means. In this study, waterborne
bacteria from agricultural canals were examined to assess potential atrazine and oxamyl
degradation in the Lower Rio Grande Valley. Approach: Water samples were collected March 2007
and June 2009 and inoculated onto agar media containing either atrazine or oxamyl to estimate
densities of atrazine-tolerant and oxamyl-tolerant bacteria. Bacterial isolates were characterized
morphologically by visually observing colony shape and size and by gram-staining. Commercial test
strips and microplates were used to differentiate biochemical and nutritional capabilities of bacteria
and an inhibition disk assay was employed to determine pesticide sensitivity. Results: Average density
of atrazine-tolerant bacteria was 2,233 cfu mL-1 in March 2007 and 12, 845 cfu mL-1 in June 2009.
Average density of oxamyl-tolerant bacteria was 330 cfu mL-1 in 2007 and 1,158 cfu mL-1 in
2009.66.7% of bacteria were Gram-negative. Most isolates were resistant to atrazine or oxamyl
regardless of which pesticide medium they were originally grown. Only 2 of 30 tested isolates
displayed intermediate and sensitive inhibition phenotypes, respectively, to oxamyl. Biochemical
profiles were generally 70% or greater in similarity but still displayed diverse phenotypes. About half
of isolates exhibited a unique biochemical phenotypic profile. Microbial communities in the canals
could metabolize a variety of organic compounds and demonstrated high carbon substrate utilization
and activity. Conclusion: Overall, indigenous pesticide-tolerant microorganisms were present in lowto-
moderate densities, displayed diverse phenotypes and were able to use many organic substrates.
This may increase the likelihood that atrazine and oxamyl compounds will be degraded in the Lower
Rio Grande Valley.