A rapid collection of yet unknown ammonia oxidizers in pure culture from activated sludge.

Nitrification is an important reaction in the biological nitrogen removal process in wastewater treatment plants (WWTPs). As ammonia-oxidizing microbes are slow-growing and sensitive to environmental factors such as free ammonia, pure strains are hard to obtain, preventing our understanding of their physiological characteristics. To conquer this hurdle, we report a high-throughput isolation technique based on scattering signatures, which exploits the tendency of many ammonia-oxidizing bacteria (AOB) to form microcolonies in activated sludge. The AOB microcolonies were directly sorted from the activated sludge without long incubation and enrichment bias, and were sequentially inoculated into 96-well microtiter plates containing growth medium. Phylogenetic analysis of the pure strains isolated in this study revealed a deeply branching and unrecognized lineage and diversity within the genus Nitrosomonas, beyond our expectation.

The Effect of Nitric Oxide on Ammonia Decomposition in Co-cultures of Hepatocytes and Hepatic Stellate Cells.

Hepatic functions, such as albumin secretion and ammonia metabolism, are upregulated in response to hepatocyte growth factor (HGF) produced by hepatic stellate cells (HSC), as well as nitric oxide (NO) produced by endothelial cells under shear stress. However, the simultaneous effect of HSC and NO has not been previously investigated in a tri-co-culture model containing hepatocytes with HSC and endothelial cells under shear stress. We hypothesized that NO inhibits HGF production from HSC. To test this idea, we constructed a mono-culture model of hepatocytes and a co-culture model of hepatocytes and HSC and measured ammonia decomposition and HGF production in each model under NO load. Ammonia decomposition was significantly higher in the co-culture model under 0 ppm NO load, but no significant increase was observed under NO load. In the co-culture model, HGF was produced at 1.0 ng/mL under 0 ppm NO load and 0.3 ng/mL under NO load. Ammonia decomposition was increased by 1.0 ng/mL HGF, but not by 0.3 ng/mL HGF. These results indicated that NO inhibits HGF production from HSC; consequently, the effects of NO and co-culture with HSC cannot improve hepatic function simultaneously. Instead, the simultaneous effect of 1.0 ng/mL HGF and NO may further enhance hepatic function in vitro.