In modern agriculture, agrichemicals are absolutely necessary to maintain stable crop yields and reduce the amount of labor and production cost. However, it has been revealed that agrichemicals used partially flow into rivers, lakes, groundwater, service water, etc., and therefore there is concern about the influence of agrichemicals on organisms in the general environment. Among various types of microorganisms living in soil, some microorganisms have the ability to decompose and detoxify organic chemicals such as agrichemicals. However, the density of such decomposing bacteria in the natural environment is low, and in addition, the decomposing bacteria are not uniformly distributed in the natural environment. Therefore, it is usually impossible to prevent the accumulation and dispersion of organic pollutants in the environment before they happen. Under the circumstances, decomposition of organic pollutants such as agrichemicals using decomposing soil bacteria selectively enriched and isolated, that is, so-called bioremediation, can be considered effective.
Triazine compounds have been heavily used as agrichemicals, defoaming agents, and dyes throughout the world for a long time, but are now regarded as problematic environmental pollutants. It has been already known that atrazine, which is a chlorotriazine agrichemical, can be decomposed by many kinds of microorganisms (see Patent Document 1). However, methylthiotriazine agrichemicals such as simetryn and methoxytriazine agrichemicals such as simeton are more difficult to decompose, and therefore reports about the microbial decomposition of methylthiotriazines and methoxytriazines are limited. For example, Cook and Hutter have reported that decomposing soil bacteria were enriched by using a synthetic medium containing ametryn or prometryn as a sulfur source, and then three kinds of the bacteria showing a higher growth rate were finally selected (see Non-Patent Document 1). According to this report, two of the three kinds of bacteria decomposed ametryn so that a demethylthiolated metabolite was generated, and the other one decomposed ametryn and prometryn so that demethylthiolated metabolites were generated. However, in this report, there is no description about the bacteriological studies of these strains. Further, Strong et al. have reported that Arthrobacter aurescens strain TC1 having the ability to decompose atrazine was isolated from a dumpsite polluted with a high level of atrazine and the Arthrobacter aurescens strain TC1 grew in a medium containing ametryn or prometryn as the sole source of nitrogen (see Non-Patent Document 2). Further, Shapir et al. have reported that ametryn was decomposed by an enzyme obtained by expressing an Arthrobacter aurescens strain TC1-derived atrazine-degrading enzyme gene spliced into E. coli (see Non-Patent Document 3) . Further, Topp et al. have reported that when dispersed in solutions each containing simetryn, ametryn, prometryn, or terbutryn and statically incubated under an anaerobic condition, whole cells or cell extracts of Nocardioides sp. strain C190 decomposed simetryn, ametryn, prometryn, and terbutryn so that demethylthiolated metabolites were generated (see Non-Patent Document 4). Further, Seffernick et al. have reported that ametryn was demethylthiolated by cell extracts of Clavibacter michiganensis strain ATZ1 (see Non-Patent Document 5).
As described above, there are some reports about the microbial decomposition of triazine compounds, but some of the isolated strains have not been sufficiently bacteriologically studied or need another carbon source to decompose a triazine compound and some of the reports have not shown the decomposition or decomposition rates of triazine compounds by living bacterial cells. For this reason, under the present circumstances, it is difficult to say that these strains can be practically used for bioremediation at this time.
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-27536
Non-Patent Document 1: Cook, A. M., Hutter, R. 1982. Appl. Environ. Microbiol. 43, 781-786
Non-Patent Document 2: Strong, L. C., Rosendahl, C., Johnson, G., Sadowsky, M. J., Wackett, L. P. 2002. Appl. Environ. Microbiol. 68, 5973-5980
Non-Patent Document 3: Shapir, N., Rosendahl, C., Johnson, G., Andreina, M., Sadowsky, M. J., Wackett, L. P., 2005. Appl. Environ. Microbiol. 71, 2214-2220
Non-Patent Document 4: Topp, E., Mulbry, W. M., Zhu, H., Nour, S. M., Cuppels, D. 2000. Appl. Environ. Microbiol. 66, 3134-3141
Non-Patent Document 5: Seffernick, J. L., Johnson, G., Sadowsky, M. J. Wackett, L. P. 2000. Appl. Environ. Microbiol. 66, 4247-4252