Environmental and metabolic parameters affecting the uric acid production of Arxula adeninivorans

The yeast Arxula adeninivorans has previously been shown to naturally secrete the redox molecule uric acid (UA). This property suggested that A. adeninivorans may be capable of functioning as the catalyst for a mediator-less yeast-based microbial fuel cell (MFC) if the level of UA it secretes could be increased. We investigated the effects of a number of parameters on the level of UA produced by A. adeninivorans. The concentration of UA accumulated in a dense cell suspension of A. adeninivorans after 20 h incubation was shown to be significantly lower in aerated suspensions compared with that in anaerobic conditions due to UA being rapidly oxidised by dissolved oxygen. The presence of carbon sources, glucose and glycerol, both caused a reduction in UA production compared with that in starvation conditions. The transgenic A. adeninivorans strain, G1221 (auox), showed higher UA production at 37 °C, but at 47 °C, the wild-type LS3 accumulated higher concentrations; however, elevated temperatures also resulted in very high cell mortality rates. An initial buffer pH of 8 caused a higher concentration of UA to accumulate, but high pH is detrimental to cell metabolism and the cells actively work to lower the pH of their environment. It appears that most parameters which increase the amount of UA produced by A. adeninivorans have concomitant disadvantages for cell metabolism, and as such, its potential as a self-mediating MFC catalyst seems doubtful.