Aims:  To isolate and identify bacteria from a sand filter column capable of degrading the taste and odour compound, geosmin. In doing so, to investigate if these organisms degrade geosmin either individually or if an alternative mechanism is utilized. Methods and Results:  Geosmin‐degrading bacteria from a biologically active sand filter column were enriched by their growth in a minimal medium supplemented with geosmin as the sole carbon source. By day 51, 21·7 mg l−1 of geosmin had been degraded as determined by solid‐phase microextraction gas chromatography/mass spectrometry, and was accompanied by a 2·12 log10 increase in active bacterial numbers as measured using the BacLightTM bacterial viability kit and flow cytometric enumeration. During the onset of geosmin degradation, the predominance of three bacteria, most similar to previously cultured species of Sphingopyxis alaskensis, Novosphingobium stygiae and Pseudomonas veronii based on 16S rRNA gene sequences was detected by denaturing gradient gel electrophoresis. Subsequent isolation of these organisms revealed that degradation of geosmin, when present as either the sole carbon source (ranging from 40 ng l−1 to 20 mg l−1) or when spiked into sterile reservoir water (37 and 131 ng l−1), occurred only when all three isolates were present. None of the isolates was shown to be capable of degrading geosmin either individually or in any combination of two. Conclusions:  This study has reported, for the first time, the cooperative degradation of geosmin by a consortium comprising three gram‐negative bacteria isolated from a biologically active sand filter column. Significance and Impact of the Study:  These results are important for researchers currently employing molecular‐based approaches to further understand the biodegradation of geosmin by bacteria, as such studies may be complicated by the discovery of geosmin degradation occurring by a consortium. This study also advances the knowledge surrounding the types of bacteria capable of degrading the taste and odour compound, as investigations to date regarding this are limited.

Biological sand filters were assessed for their ability to remove geosmin, 2-methylisoborneol (MIB) and microcystin-LR. Microcystin-LR was the most readily degradable metabolite with a maximum lag period of only 5 days before it was undetected in the filter effluent. Geosmin and MIB were difficult to degrade, with a period in excess of 75 days before greater than 95% removal was achieved. A microcystin-degrading gene was detected in the biofilm from one of the filters, confirming that the biofilm possessed the ability to degrade microcystin. A Sphingomonas sp. was identified as a potential geosmin degrader based on denaturing gradient gel electrophoresis (DGGE) analysis. DGGE analysis revealed a more complex bacterial community during the degradation of MIB, suggesting that more than one bacterium may be responsible for its degradation.