This short book attempts to give a reader who has a basic biochemical and microbiological background (one to two years at University level) an idea of the ecological, biochemical, physiological and biotechnological importance of methane, methanol and related compounds in the microbial world. Because the book covers several different scientific disciplines, readers may encounter unfamiliar terminology. The glossary at the end of the book defines the more obscure of these. The book has been written during a period of heavy teaching commit­ ments, and despite the helpful comments of many colleagues, it is likely that errors have crept in. As I have no co-author whom I can blame, I must accept sole responsibility for these! I wish to thank the many friends, students and colleagues who have read all or part of the manuscript: Charlie Bamforth, Rick Gibson, Jeff Green, Theo Hansen, Wim Harder, Geoff Haywood and, above all, Hans van Dijken.

1 The Biology and Ecology of Micro-organisms Metabolizing C1 Compounds.- Occurrence of reduced C1 compounds in nature.- The carbon cycle.- Ecology of methane formation and oxidation in nature.- Nitrogen metabolism.- Anaerobic methane oxidation.- Summary.- References.- 2 Physiology and Biochemistry of Methane-Producing (Methanogenic) Bacteria.- The role of methanogenic bacteria in nature.- Classification and characteristics of methanogenic bacteria.- Growth of methanogens.- Biochemistry of methane formation.- Energy coupling and ATP formation.- Synthesis of cell constituents in methanogenic bacteria.- Conclusions.- Summary.- References.- 3 Physiology and Biochemistry of Methylotrophic Bacteria.- Assimilatory pathways.- Energy requirement for the three assimilatory pathways.- Dissimilatory pathways for energy generation.- Oxidation of methane, methanol, formaldehyde and formate.- Oxidation of methylated amines.- Oxidation of methylated sulphur compounds.- Electron transport in methylotrophic bacteria.- Control of growth on C1 compounds.- Summary.- References.- 4 Physiology and Biochemistry of Methylotrophic Yeasts.- Dissimilatory pathway of methanol in yeasts.- Intracellular location of the enzymes of methanol oxidation.- Assimilatory pathway of methanol in yeasts.- Possible applications of methylotrophic yeasts.- Summary.- References.- 5 Biotechnological Applications of Methanogenic and Methylotrophic Micro-organisms.- The production of methane from organic waste.- Single-cell protein.- Biotransformations using methylotrophic organisms.- Summary.- References.- Overall Summary.- Further Reading.