Effect of tungsten and molybdenum on growth of a syntrophic coculture of Syntrophobacter fumaroxidans and Methanospirillum hungatei.

The effect of tungsten (W) and molybdenum (Mo) on the growth of Syntrophobacter fumaroxidans and Methanospirillum hungatei was studied in syntrophic cultures and the pure cultures of both the organisms. Cells that were grown syntropically were separated by Percoll density centrifugation. Measurement of hydrogenase and formate dehydrogenase levels in cell extracts of syntrophically grown cells correlated with the methane formation rates in the co-cultures. The effect of W and Mo on the activity of formate dehydrogenase was considerable in both the organisms, whereas hydrogenase activity remained relatively constant. Depletion of tungsten and/or molybdenum, however, did not affect the growth of the pure culture of S. fumaroxidans on propionate plus fumarate significantly, although the specific activities of hydrogenase and especially formate dehydrogenase were influenced by the absence of Mo and W. This indicates that the organism has a low W or Mo requirement under these conditions. Growth of M. hungatei on either formate or H2/CO2 required tungsten, and molybdenum could replace tungsten to some extent. Our results suggest a more prominent role for H2 as electron carrier in the syntrophic conversion of propionate, when the essential trace metals W and Mo for the functioning of formate dehydrogenase are depleted.

A comparison of elementary schoolchildren's exposure to arsenic and lead.

One hundred fifty seven fifth-grade students (aged 10-12 years) from three elementary schools in three different towns in Taichung County, Taiwan were chosen as study subjects for the present arsenic and lead exposure study. The three towns--Longgang, Shalach, and Shuntain--are known to be highly, moderately, and lightly (control) polluted by As and Pb, respectively. Spot morning urine samples of students were collected and analyzed for arsenic and lead. The levels of As in the urine of Longgang schoolchildren showed the highest value among the three schools, while those of the control group (Shuntain) had the lowest values. In addition, the levels of Pb in the urine of the schoolchildren in Shuntain were significantly lower than those in Longgang and Shalach, while the levels of Pb in the urine of the schoolchildren in Longgang and Shalach showed no significant difference. Results of daily intake of metals from the different exposure pathways (i.e., ingestion from drinking water, household dust and food, and inhalation from airborne particles) showed that the Longgang area had the highest daily intake of As and Pb among the three areas, while the lowest daily intake of As and Pb occurred in the control area (Shuntain). A significant correlation between the doses of daily intake and urinary concentrations of As (p = 0.002) and Pb (p = 0.020) was observed. This correlation suggests that the increase of unit dose of the daily intake for As resulted in an increase of 0.953 microg g(-1) creatinine of As, whereas the increase of unit dose of the daily intake for Pb led to an increase of 0.053 microg g(-1) creatinine of Pb. These data indicate that the level of As in urine increased about 18 times higher than that of Pb for the same amount of increase in daily intake.