Published online by Cambridge University Press: 27 March 2009
Sheathed filamentous bacteria, Leptothrix spp. and Gallionella spp., were observed in ochre samples from sites in England and Wales. Thiobacillus ferrooxidans was found in acidic samples (pH < 4·0) and in ochre from drainage water of near neutral pH suggesting that it can contribute to ochre formation over a wide range of drainage water pH, Heterotrophic bacteria capable of growing in artificial media of low pH and complexdegrading heterotrophic bacteria were also isolated. Some ochre deposits could be described as either pyritic or filamentous but the majority of samples fell between these extremes and had various combinations of T. ferrooxidans, sheathed filamentous bacteria and other heterotrophic bacteria.