Fifteen bacteria capable of degrading carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) were isolated from soil samples with a history of pesticide application. All isolates were gram negative and were oxidase- and catalase-positive rods; they occurred singly or as short chains. All of the identified isolates belonged to one of two genera, Pseudomonas and Flavobacterium. They were separated into three groups based on their mode of utilization of carbofuran. Six isolates were placed in group I; these isolates utilized carbofuran as a sole source of nitrogen. Seven isolates were placed in group II; these isolates utilized the pesticide as a sole source of carbon. Isolates of both groups I and II hydrolyzed carbofuran to carbofuran phenol. Two isolates, designated group III, also utilized carbofuran as a sole source of carbon. They degraded the pesticide more rapidly, however, so up to 40% of [14C]carbofuran was lost as 14CO2 in 1 h. The results suggest that these isolates degrade carbofuran by utilizing an oxidative pathway.
Two mixed bacterial cultures isolated by soil enrichment were capable of utilizing methyl parathion (O,O-dimethyl O-p-nitrophenylphosphorothioate) and parathion (O,O-diethyl O-p-nitrophenylphosphorothioate) as a sole source of carbon. Four isolates from these mixed cultures lost their ability to utilize the pesticides independently in transfers subsequent to the initial isolation. One member of the mixed cultures, a Pseudomonas sp., however, hydrolyzed the pesticides to p-nitrophenol but required glucose or another carbon source for growth. The crude cell extracts prepared from this bacterium showed an optimum pH range from 7.5 to 9.5 for the enzymatic hydrolysis. Maximum enzymatic activity occurred between 35 and 40°C. The enzyme activity was not inhibited by heavy metals, EDTA, or NaN3. Another isolate from the mixed cultures, a Flavobacterium sp., used p-nitrophenol for growth and degraded it to nitrite. Nitrite was assimilated into the cells under conditions during which the nitrogen source was excluded from the minimal growth medium. The hybridization data showed that the DNAs from a Pseudomonas sp. and from the mixed culture had homology with the opd (organophosphate degradation) gene from a previously reported parathion-hydrolyzing bacterium, Flavobacterium sp. The use of the opd gene as a probe may accelerate progress toward understanding the complex interactions of soil microorganisms with parathions.MATERIALS AND METHODS Chemicals. Technical-grade parathion and methyl parathion were obtained from Chem Service (West Chester, Pa.) and from the U.S. Environmental Protection Agency. p-Nitrophenol was purchased from Sigma Chemical Co.
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Introduction: Environmental exposure to indoor dust is known to be associated with myriad health conditions, especially among children. Established routes of exposure include inhalation and non-dietary ingestion, which result in the direct exposure of gastrointestinal epithelia to indoor dust. Despite this, little prior research is available on the impacts of indoor dust on the health of human gastrointestinal tissue. Methods: Cultured human colonic (CCD841) cells were exposed for 24 h to standard trace metal dust (TMD) and organic contaminant dust (OD) samples at the following concentrations: 0, 10, 25, 50, 75, 100, 250, and 500 µg/mL. Cell viability was assessed using an MTT assay and protease analysis (glycyl-phenylalanyl-aminofluorocoumarin (GF-AFC)); cytotoxicity was assessed with a lactate dehydrogenase release assay, and apoptosis was assessed using a Caspase-Glo 3/7 activation assay. Results: TMD and OD decreased cellular metabolic and protease activity and increased apoptosis and biomarkers of cell membrane damage (LDH) in CCD841 human colonic epithelial cells. Patterns appeared to be, in general, dose-dependent, with the highest TMD and OD exposures associated with the largest increases in apoptosis and LDH, as well as with the largest decrements in metabolic and protease activities. Conclusions: TMD and OD exposure were associated with markers of reduced viability and increased cytotoxicity and apoptosis in human colonic cells. These findings add important information to the understanding of the physiologic effects of indoor dust exposure on human health. The doses used in our study represent a range of potential exposure levels, and the effects observed at the higher doses may not necessarily occur under typical exposure conditions. The effects of long-term, low-dose exposure to indoor dust are still not fully understood and warrant further investigation. Future research should explore these physiological mechanisms to further our understanding and inform public health interventions.
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