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Title: Influence of fumigants on soil microbial diversity and survival of E. coli O157:H7

Author
item Ibekwe, Abasiofiok - Mark
item Schneider, Sharon
item Grieve, Catherine
item YANG, CHING-HONG - UNIVERSITY OF WISCONSIN

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2010
Publication Date: 7/1/2010
Citation: Ibekwe, A.M., Papiernik, S.K., Grieve, C.M., Yang, C. 2010. Influence of fumigants on soil microbial diversity and survival of E. coli O157:H7. Journal of Environmental Science and Health. 45(5):416-426.

Interpretive Summary: Methyl bromide (MeBr) is a versatile and highly effective fumigant used for pre-plant soil fumigation. It has been used extensively to control pests and plant pathogens such as nematodes, soil-borne diseases, and weeds in economically important crops such as strawberries and nursery stock throughout the world. MeBr was scheduled for phase-out in the United States and other developed countries by the year 2005 and in developing countries by 2015 because of its stratospheric ozone depletion potential. However, critical use exemptions have been granted for the continued use of MeBr for the production of strawberries, tomatoes, peppers, and other fruits and vegetables. This study was conducted to compare the impact of methyl bromide and methyl iodide on soil bacteria. Our data showed that the effects of MeBr and MeI on soil microbial communities in laboratory and growth chamber studies were most severe during the first week after application. After this period, stable microbial communities were obtained and from week 7 to week 12 new communities emerged that were quite different from the original community. Our data showed that application of fumigant did not have any significant impact on bacterial population on the root and the leaf surfaces.

Technical Abstract: The aim of this study was to assess the effects of soil fumigation with methyl bromide (MeBr; CH3Br) and methyl iodide (MeI, iodomethane; CH3I) on the microbial community structure and diversity in two soils and determine the effects of microbial diversity on the survival of Escherichia coli O157:H7 from contaminated irrigation water. Polymerase chain reaction (PCR) was used to amplify 16S rRNA from total bacterial community composition and the products were subjected to denaturing gradient gel electrophoresis (DGGE). The Shannon-Weaver index of diversity (H) was used to determine the effects of both fumigants on soil microbial diversity. The effect was more severe in sandy soil than in clay soil at the normal application rate of MeBr and MeI. Our results showed that MeBr and MeI have about the same effects on soil microbial diversity. The two fumigants had greater impact on microbial diversity in sandy soil than in clay soil and this resulted in higher survival of E. coli O157:H7 in sandy soil than in clay soil during the 50 days that the study was conducted. MeBr has been used as soil fumigant for >40 years with no serious detrimental effects on agricultural production and our research also suggests that the use of MeI may also produce no long-term detrimental effects on agricultural production since both fumigants had about the same effects on soil microbial communities. Therefore, soil systems with reduced microbial diversity may offer greater opportunities for the survival of pathogenic bacteria such as E. coli O157:H7.