John Raymond Postgate FRS (24 June 1922 – 22 October 2014) was an English microbiologist and writer, latterly Professor Emeritus of Microbiology at the University of Sussex. Postgate's research in microbiology investigated nitrogen fixation, microbial survival, and sulphate-reducing bacteria. He worked for the Agricultural Research Council's Unit of Nitrogen Fixation from 1963 until he retired, by then its director, in 1987. In 2011, he was described as a "father figure of British microbiology".

His admired popularizing book on microbes in human culture, Microbes and Man, first published in 1969, remains in print.

John Raymond Postgate was born on 24 June 1922, as the elder son of the writer Raymond Postgate and Daisy Postgate, née Lansbury, private secretary to her father George Lansbury, the politician who was Labour Party Leader of the Opposition 1932-35. He had one brother, Oliver Postgate, later a well-known animator and producer for British television. Several other members of the Postgate family were notable in a variety of fields. His cousin is the actress Angela Lansbury.

He attended kindergarten and primary private schools in Golders Green, North London, before moving at age 11 to Kingsbury County School; he was evacuated to Devon at the start of World War II. In 1941 he was awarded an exhibition scholarship to Balliol College, Oxford, where he achieved a first class degree in Chemistry. He had also taken a special biochemistry course. His final examination involved research on the adaptation of bacteria to unfavourable environments and, supported by a grant from the Medical Research Council plus a Studentship from Balliol (which the MRC deducted from his grant), he spent a year reading Microbial Chemistry before doing research for a doctorate on aspects of how bacteria adapt to resist sulphonamide drugs. Sulfomamide drugs had been shown by D D Woods, his supervisor, to block the enzyme assimilating the metabolite p-aminobenzoic acid (PABA for short), a precursor of folic acid, by blocking the enzyme's active site. A substantial excess of a sulfonamide needed to put a complete stop to PABA assimilation. Postgate's research was to study sulfonamide action on a species of bacteria that required PABA from the environment as a vitamin; it gave him valuable experience of competition in enzymology.

In 1948, Postgate obtained a Research Fellowship at the Chemical Research Laboratory (CRL) in Teddington, West London, to investigate the biochemistry of the sulphate-reducing bacteria. A small microbiology group, led by K R Butlin, was researching their role in iron corrosion and other civil and industrial nuisances. The group also investigated and advised on diverse problems in economic microbiology which had been brought to the laboratory. The bacteria were known to be strict anaerobes which live by converting mineral sulphates to hydrogen sulphide. They are difficult to culture and to separate from other soil bacteria in the laboratory, but Butlin's group had isolated a few pure strains. Postgate managed to culture large populations of the organism and his experience of competition informed his first paper, in which he showed that selenates are powerful competitive inhibitors of sulphate reduction. He went on to obtain biochemical evidence on how they consume sulphates and carbon sources, but his most influential finding was cytochrome C3., a discovery that has been described as "seminal". Cytochromes are iron-containing proteins found in the cells of all air-breathing creatures from bacteria and plants to humans; they were known to be part of the aerobic respiratory apparatus and were widely understood to be absent from anaerobes. The appearance of a cytochrome, one which had an unusually large amount of iron, in a strict anaerobe conflicted with current theory. However soon it became accepted and the concept emerged of "anaerobic respiration", based on reducing nitrate, carbonate or similar oxygen-containing minerals. Postgate's research formed the basis of worldwide research on these bacteria and their cytochromes, as well as the discovery of many new genera; sulphate reducers are now known to constitute a diverse biosphere of their own.

Postgate also enjoyed the Group's more practical problems. His laboratory strain reduced sulphates at hitherto unheard-of rates, and their speed revived a wartime possibility of using them to manufacture sulphur for industry by fermenting waste with sulphate. This would mimic the way in which most of the world's native sulphur was deposited over geological time. A post-war World sulphur shortage was damaging post-war British industry, so he and Butlin were sent to Cyrenaica to sample a sulphur spring and check specimens for even better performance. The trip caught the attention of the press, and the microbiological production of sulphur became Butlin's pet project, with Postgate advising.

Postgate enjoyed the practical side and also made advances in understanding the biochemistry of the bacteria. The group expanded and widened its remit to encompass the microbiological production of sulphur and the treatment of chemical effluents; it also took over the National Collection of Industrial Bacteria. He was absorbed into its staff in 1950 as Senior Scientific Officer and promoted Principal Scientific Officer in 1952. In 1959, for controversial reasons, Butlin's group was disbanded and its staff and collection redeployed.

Postgate was released to take a post at the Microbiological Research Establishment (MRE), part of the Porton Down research complex at Porton near Salisbury in Wiltshire, to undertake fundamental research on how bacteria survive mild stresses such as near starvation, using both continuous and synchronous culture of bacteria. His extensive paper on the survival of starvation by Klebsiella bacteria reopened a research topic largely dormant since the 1920s and introduced the concept of cryptic growth (a sort of necrophagy) in the persistence of bacterial populations in ancient isolated environments such as salt inclusions or fossils. He was promoted Senior Principal Scientific Officer in 1961. In 1962 he was given leave to take up a Visiting Professorship of Microbiology at the University of Illinois, in the United States, to finish off some earlier research on sulphate-reducing bacteria and undertake some teaching duties. He returned to MRE in early 1963.