PREFACE

Recognition of the biological nature of sulphate reduction in natural environments, and identification of the bacterial species involved dates to the latter part of the nineteenth century, and the seminal work of such giants of the early days of microbiology as Beijerinck and Winogradsky. The central role of environmental studies in highlighting the issues to be addressed and the problems to be solved, has remained to this day a constant theme in microbiological analyses of the sulphate reducers. The modern era of such analyses, however, can be said to date from the period around 1960 when the demonstrations by Postgate and Peck, respectively, of the presence of cytochromes and of phosphorylation linked to anaerobic respiration in sulphate-reducing bacteria (SRB), fundamentally altered our view of the biochemical nature of these organisms and, in particular, of their mechanisms of energy conservation. There then followed a period of intense activity centred on: elucidation of the metabolic pathways of substrate utilisation and the mechanisms of energy generation; cultural techniques and the identification of an everincreasing number of new species; and the appreciation of their significant role in maintaining, or disrupting, the biological balance of many natural and man-made ecosystems. These themes of biochemistry and cell physiology, phylogeny, and ecology remain central to the understanding of SRB themselves, and of their interactions with other components of the biosphere. In recent years, however, their study has undergone a further paradigm shift with the introduction of the many powerful experimental techniques and analytical approaches of molecular biology. As a direct consequence of these developments, sulphate-reducing prokaryotes (bacteria and archaea, as we have come to appreciate) are now the chosen organisms of study in many of the xvii