Hayes, William (1913–94), bacteriologist and molecular geneticist, was born 18 January 1913 at Edmondstown Park, Rathfarnham, Co. Dublin, the son of William Hayes, businessman, then aged seventy-three, and Miriam Hayes (née Harris), the only child of his father's second marriage. His father had founded the chain of Dublin pharmacies Hayes, Conyngham and Robinson and served as president of the Pharmaceutical Society of Ireland (1891–5). His mother was the daughter of a Church of England clergyman, and his cousin was A. W. Barton (qv), Church of Ireland archbishop of Dublin. His father died when he was five years old and he was raised by his mother and grandmother.
After being educated at home by a governess for two years, Hayes entered Castle Park, Dalkey, in 1923, a preparatory boarding school for boys, which he disliked and where he acquired a lifelong stutter. In 1927 he attended St Columba's College, and there his interest in science, particularly radio and electronics, blossomed. He represented Ireland in an international oratorical contest in Washington, DC, attended by President Hoover, and though he did not win the competition he was invited for a screen test in Hollywood.
Hayes studied medicine at TCD (1931–7). Inspired by a third-year course in bacteriology, he took an extra year and completed an honours degree in natural sciences (1936), specialising in bacteriology, and obtained a first-class degree. Having developed a love of experimental science, on finishing his medical studies he pursued a research rather than a clinical career. He won the Haughton prize for medicine and was awarded the Adrian Stokes memorial travelling fellowship, but the outbreak of the Second World War preventing him from taking this up.
Hayes was employed at Trinity as a general assistant in bacteriology (1938–9) and then as senior assistant (1939–41). During this time he first learned about serology from Hans Sachs, an eminent scientist and refugee from Nazi Germany. He joined the Royal Army Medical Corps in late 1941, was trained at Liverpool in tropical medicine and pathology, then dispatched in 1942 to command the Army Enteric Reference Laboratory at Kasauli in India, though after ten months he moved to the Central Military Pathology Laboratory in Poona. During this time he distinguished himself as an able manager and an excellent teacher. He said he enjoyed the war years administering the laboratory and doing independent research on salmonella strains which formed the basis of his interest in bacterial genetics. He was demobilised in August 1946, and with his wife, who had joined him ten months previously, returned to Dublin.
While working as a lecturer in bacteriology at TCD (1947–50) Hayes was conferred by the college with a D.Sc. (1949), but, disappointed with the lack of opportunities for research there, he obtained a position as senior lecturer in bacteriology at the Royal Postgraduate Medical School at Hammersmith Hospital, London (1950–57). It was during this period that he became internationally famous for his work on sexuality in bacteria. His donor–recipient hypothesis, postulated for escherichia coli, led him to conclude that maleness was determined by a transmissible factor (subsequently termed plasmids). Many international collaborations resulted from this work.
Hayes was invited in 1957 to set up the Microbial Genetics Research Unit at Hammersmith Hospital, which he directed until 1968. In 1964 he published his first book – The genetics of bacteria and their viruses (1964 and 1968). The first textbook in the area of microbial genetics, it was hugely acclaimed, not least for its lucidity and emphasis on experimental design, Hayes's hallmarks. He designed courses in molecular genetics and, with Royston Clowes, edited Experiments in microbial genetics (1968), based on courses they ran, which promoted the innovative work of his research group at the unit internationally. In May 1968 the unit was renamed the Molecular Genetics Unit and relocated to Edinburgh University as Britain's first department of molecular biology, where Hayes became professor of medical genetics (1968–73). Over a short period the unit published 253 papers (1957–73). Frustrated by the lack of laboratory work in his life and the increasing burden of administration and committee work, in 1971 Hayes embarked on a tour of New Zealand and Australia, which brought new opportunities. In 1973 he resigned from the directorship of the unit, resulting in its closure, and was appointed professor of genetics at the Research School of Biological Sciences of the Australian National University (ANU) (1974–9). Hayes, who enjoyed classical music, poetry (the romantics), painting, walking, and swimming, found the improvement in the quality of life in Canberra together with the warm Australian climate very agreeable.
After a period as a Fairchild distinguished scholar at the California Institute of Technology (1979–80) Hayes was offered appointments at many prestigious universities, including Edinburgh and a variety of locations in the USA, but he accepted an emeritus professorial chair (1980–86) at the Department of Botany, ANU. He finally retired from science in 1985 when he became aware of memory deficiencies, the beginnings of a dementia that gradually diminished his faculties. He died 7 January 1994, shortly before his eighty-first birthday.
Hayes met his wife, Honora (Nora) Lee, daughter of Joseph and Margaret Lee of Oldham, while a house doctor at the Victoria Hospital, Blackpool. They were married on 2 July 1942 and had one son, Michael (b. 1950). Religiously sceptical, but not an atheist, Bill Hayes was informal, easy to get on with and very helpful – he wrote a detailed memoir in order to assist whomsoever would write his appreciation.
Hayes was elected to the RCPI (1943), the Royal Society of London (1964), the Royal Society of Edinburgh (1968), and the Australian Academy of Science (1976). He was awarded honorary degrees from the University of Leicester (D. Sc., 1968), the University of Dublin (D.Litt., 1970), the University of Kent (D. Sc., 1973), and the NUI (D. Sc. 1973). A bibliography of his works was prepared by the Royal Society Library.