Relative gene expression quantification in a fungal gas-phase biofilter

Monitoring of gas-phase biofilter performance generally relies on macroscale measurements that neglect the molecular level phenomena that can control the biodegradation process. The present study was undertaken to determine whether or not quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) could detect changes in relative gene expression resulting from feed variations typically encountered in the field. Specifically, homogentisate-1,2-dioxygenase, ElHDO, expression was quantified as a function of short-term chemical feed variations and shutdown period in a biofilter seeded with a pure culture of the fungus Exophiala lecanii-corni. ElHDO was previously shown to be involved in ethylbenzene degradation in E. lecanii-corni. Overall, relative gene target expression numbers (T(N)) were consistent with gas-phase biofilter performance during each short-term experiment although no direct mathematical correlation was found between T(N) and ethylbenzene removal rate. During the chemical feed experiments, no effect on T(N) was measured in the presence of o-xylene which does not affect ElHDO expression. In the presence of phenylacetate, an inducer of ElHDO, T(N) increased once a threshold substrate concentration was exceeded. When methyl propyl ketone, a repressor of ElHDO, was introduced, T(N) decreased rapidly and acted as a leading indicator of bioreactor failure. In the transient loading experiments, ElHDO expression slowly decreased over a 24-h time period when the ethylbenzene feed was discontinued, but rapidly recovered upon its re-introduction. These results indicate that qRT-PCR reflects microbial activity changes that occur in gas-phase biofilters in response to short-term changes in feed conditions and provides a useful complement to the macroscale measurements typically collected.