Dissipation of molinate in a rice field

Soderquist, Charles J.; Bowers, J. B.; Crosby, Donald G.

doi:10.1021/jf60212a022

Cited by 78 publications

(64 citation statements)

References 12 publications

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“…Molinate has been widely used in conventional rice crop protection and the field concentrations found in our study are in the range of values found in paddy waters worldwide (Portugal, Castro et al 2005;USA, Deuel et al 1978;Soderquist et al 1977;Australia, Quayle et al 2006;and Japan, Son et al 2006) and are consistent with half-life values of 3-10 days, reported for this herbicide (Deuel et al 1978;Johnson and Lavy 1995;Mabury et al 1996;Ross and Sava 1986). The drainage of paddy fields, taking place about 1 month after Ordram application, has been leading to the contamination of rivers and aquifers with molinate, frequently at concentrations above the values legally recommended (Albanis et al 1998;Castro et al 2005;Cerejeira et al 2003;Son et al 2006).…”

Section: Discussionsupporting

confidence: 66%

“…In the present study, the apparent inability of the autochthonous microbiota to degrade molinate may hint the physicochemical degradation of the herbicide in the studied paddy field water over time. For instance, volatilization has been reported as the major route of dissipation of this thiocarbamate (Quayle et al 2006;Ross and Sava 1986;Soderquist et al 1977).…”

Section: Discussionmentioning

confidence: 99%

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Bacterial diversity and bioaugmentation in floodwater of a paddy field in the presence of the herbicide molinate

2010

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This work aimed at studying variations on the diversity and composition of the bacterial community of a rice paddy field floodwater, subjected to conventional management, namely by using the herbicide molinate. The promotion of the herbicide biodegradation either by the autochthonous microbiota or by a bioaugmentation process was also assessed. This study comprehended four sampling campaigns at key dates of the farming procedures (seeding, immediately and 6 days after application of the herbicide molinate, and after synthetic fertilization) and the subsequent physic-chemical and microbiological characterization (pH, DOC and molinate contents, total cells, cultivable bacteria and DGGE profiling) of the samples. Multivariate analysis of the DGGE profiles showed temporal variations in the bacterial community structure and the Shannon's index values indicated that the bacterial diversity reached its minimum at the molinate application day. The highest bacterial diversity coincided with the periods with undetectable concentrations of the herbicide, although microcosm assays suggested that other factors than molinate may have been responsible for the decrease of the bacterial diversity. The ability of autochthonous microorganisms to degrade molinate and the influence of the herbicide on the bacterial community composition were assessed in microcosm assays using floodwater collected at the same dates. Given molinate was not degraded by autochthonous microorganisms, and considering it represents an environmental contaminant, bioaugmentation microcosms were assayed aiming the assessment of the feasibility of a bioremediation process to clean contaminated floodwater. A molinate-mineralizing culture, previously isolated, promoted molinate removal, induced alterations in the autochthonous bacterial community structure and diversity, and was undetected after 7 days of incubation, suggesting the feasibility of the process.

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Section: Discussionsupporting

confidence: 66%

Section: Discussionmentioning

confidence: 99%

Bacterial diversity and bioaugmentation in floodwater of a paddy field in the presence of the herbicide molinate

2010

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“…When this thiocarbamate herbicide is applied to the flooded paddies, it dissipates into the environment largely through volatilization. However, (photo)chemical and microbiological molinate transformation also occurs (28), resulting in accumulation of oxidized metabolites, such as oxomolinate and molinate sulfoxide (11,13), which have increased toxicity (5). The only biological system described so far as being able to mineralize molinate and use the herbicide as the sole source of carbon, energy, and nitrogen is a five-membered bacterial mixed culture (2,6).…”

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Gulosibacter molinativorax ON4 ^T Molinate Hydrolase, a Novel Cobalt-Dependent Amidohydrolase

et al. 2011

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A new pathway of molinate mineralization has recently been described. Among the five members of the mixed culture able to promote such a process, Gulosibacter molinativorax ON4 T has been observed to promote the initial breakdown of the herbicide into ethanethiol and azepane-1-carboxylate. In the current study, the gene encoding the enzyme responsible for molinate hydrolysis was identified and heterologously expressed, and the resultant active protein was purified and characterized. Nucleotide sequence analysis revealed that the gene encodes a 465-amino-acid protein of the metal-dependent hydrolase A subfamily of the amidohydrolase superfamily with a predicted molecular mass of 50.9 kDa. Molinate hydrolase shares the highest amino acid sequence identity (48 to 50%) with phenylurea hydrolases of Arthrobacter globiformis and Mycobacterium brisbanense. However, in contrast to previously described members of the metal-dependent hydrolase A subfamily, molinate hydrolase contains cobalt as the only active-site metal.Molinate is a herbicide which is extensively applied to rice fields worldwide. When this thiocarbamate herbicide is applied to the flooded paddies, it dissipates into the environment largely through volatilization. However, (photo)chemical and microbiological molinate transformation also occurs (28), resulting in accumulation of oxidized metabolites, such as oxomolinate and molinate sulfoxide (11, 13), which have increased toxicity (5). The only biological system described so far as being able to mineralize molinate and use the herbicide as the sole source of carbon, energy, and nitrogen is a five-membered bacterial mixed culture (2, 6). Among the five community members, Gulosibacter molinativorax ON4 T (gen. nov., sp. nov.), the only representative of this genus thus far (21), is responsible for the initial breakdown of molinate. In contrast to previously described molinate transformation reactions (13), G. molinativorax ON4T cleaves the thioester bond of molinate, releasing ethanethiol and azepane-1-carboxylate (ACA) (Fig. 1) (1). While this hydrolysis proceeds in the absence of oxygen, the further metabolism and mineralization of ACA by G. molinativorax ON4 T necessitate oxygen. Ethanethiol is not transformed by this organism but is spontaneously oxidized to diethyl disulfide. At molinate concentrations of Ͼ2 mM, the accumulating sulfur compounds are toxic for G. molinativorax ON4T and molinate mineralization is achieved only when other mixed-culture members able to degrade the sulfurcontaining metabolites are present (1, 2).In the present study, the molinate hydrolase (MolA) from G. molinativorax ON4T responsible for the key step of molinate breakdown was purified and characterized. The encoding gene was identified and expressed in Escherichia coli. This enzyme belongs to the metal-dependent hydrolase A subfamily of the amidohydrolase superfamily; however, in contrast to previously characterized members, it contains cobalt as a cofactor. To the best of our knowledge, this is the first description of an...

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“…Apparently this is the case for molinate. Initially it was described as co-metabolizable by three possible degradative routes: (1) the oxidation of the sulphur atom with production of molinate sulphoxide and molinate sulphone; (2) the oxidation of the azepane moiety with production of hydroxy-and oxomolinate; or (3) the oxidation of the S-ethyl moiety with production of molinate alcohol and molinate acid (Soderquist et al, 1977;Thomas & Holt, 1980;Golovleva et al, 1981;Imai & Kuwatsuka, 1986). Among those compounds, only trace amounts of 2-oxomolinate were detected in culture DC grown with molinate as the only source of carbon, nitrogen and energy , supporting the hypothesis that the herbicide is degraded by this mixed culture through a different catabolic route.…”

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New insights into a bacterial metabolic and detoxifying association responsible for the mineralization of the thiocarbamate herbicide molinate

et al. 2008

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A novel pathway of molinate mineralization promoted by a defined mixed culture composed of five bacteria (named ON1 to ON5) was proposed previously. Evidence was obtained of a metabolic association between Gulosibacter molinativorax ON4 T , capable of molinate breakdown, and the remaining bacteria. In the present study, the role of each isolate in that metabolic association was further explored and the possible synergistic effect of all the bacterial isolates for the stability of the mixed culture is discussed. The cleavage of the molinate thioester bond, whether occurring under aerobic or anaerobic conditions, releases ethanethiol (S-ethyl moiety) and an azepane moiety derivative, identified as azepane-1-carboxylic acid. This azepane moiety is degraded, in the presence of oxygen, by Pseudomonas strains ON1 and ON3 and G. molinativorax ON4 T . Ethanethiol, which inhibits G. molinativorax ON4 T , is consumed by Pseudomonas strain ON1 and Stenotrophomonas maltophilia ON2. Although a two-member mixed culture of G. molinativorax ON4 T and Pseudomonas strain ON1 was able to promote the aerobic mineralization of molinate, after 20 successive transfers of the five-member mixed culture in mineral medium with molinate, none of these isolates were lost. The results obtained indicate that the whole mixed culture may have a higher fitness than the two-member culture, even when the basic degradative and cross-protection functions are assured.

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Dissipation of molinate in a rice field

Cited by 78 publications

References 12 publications

Bacterial diversity and bioaugmentation in floodwater of a paddy field in the presence of the herbicide molinate

Bacterial diversity and bioaugmentation in floodwater of a paddy field in the presence of the herbicide molinate

Gulosibacter molinativorax ON4 ^T Molinate Hydrolase, a Novel Cobalt-Dependent Amidohydrolase

New insights into a bacterial metabolic and detoxifying association responsible for the mineralization of the thiocarbamate herbicide molinate

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Dissipation of molinate in a rice field

Cited by 78 publications

References 12 publications

Bacterial diversity and bioaugmentation in floodwater of a paddy field in the presence of the herbicide molinate

Bacterial diversity and bioaugmentation in floodwater of a paddy field in the presence of the herbicide molinate

Gulosibacter molinativorax ON4 T Molinate Hydrolase, a Novel Cobalt-Dependent Amidohydrolase

New insights into a bacterial metabolic and detoxifying association responsible for the mineralization of the thiocarbamate herbicide molinate

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Gulosibacter molinativorax ON4 ^T Molinate Hydrolase, a Novel Cobalt-Dependent Amidohydrolase