River Sediments Downstream of Villages in a Karstic Watershed Exhibited Increased Numbers and Higher Diversity of Nontuberculous Mycobacteria.

The impact of residential villages on the nontuberculous mycobacteria (NTM) in streams flowing through them has not been studied in detail. Water and sediments of streams are highly susceptible to anthropogenic inputs such as surface water flows. This study investigated the impact of seven residential villages in a karst watershed on the prevalence and species spectrum of NTM in water and sediments. Higher NTM species diversity (i.e., 19 out of 28 detected) was recorded downstream of the villages and wastewater treatment plants (WWTPs) compared to sampling sites upstream (i.e., 5). Significantly, higher Zn and lower silicon concentrations were detected in sediments inside the village and downstream of the WWTP's effluents. Higher phosphorus concentration in sediment was downstream of WWTPs compared to other sampling sites. The effluent from the WWTPs had a substantial impact on water quality parameters with significant increases in total phosphorus, anions (Cl-and N-NH3-), and cations (Na+ and K+). The results provide insights into NTM numbers and species diversity distribution in a karst watershed and the impact of urban areas. Although in this report the focus is on the NTM, it is likely that other water and sediment microbes will be influenced as well.

Nitrate and nitrite reductase activities of Mycobacterium avium.

Background: In spite of the fact that the standard test for nitrate reductase activity is negative for Mycobacterium avium, it can grow in a defined minimal medium with either nitrate (NO3) or nitrite (NO2) as sole nitrogen sources. Methods: NO3-and NO2-reductase activities were measured in soluble and membrane fractions of aerobically grown cells of M. avium and those grown aerobically and shifted to anaerobiosis. Results: NO3- and NO2-reductase activities were only detected in the membrane fractions and the two enzyme activities were significantly reduced if cells were grown aerobically in the presence of ammonia (NH4). The NO2-reductase activity of membrane fractions was 2-fold higher than that of NO3-reductase consistent with the fact that NO3-reductase activity of M. avium cannot be detected if measured by nitrite formation. Membrane fractions of M. avium cells grown 1 week aerobically and then 2 weeks under anaerobic conditions had NO3-and NO2-reductase activities. Conclusion: The results are consistent with the presence of assimilatory NO3-and NO2-reductase activities in cells of M. avium grown under aerobic conditions. Further, the data suggest that a shift to anaerobic conditions results in the appearance of ammonium-insensitive NO3-and NO2-reductase activities; quite possibly that function in a dissimilatory role (redox balancing).