Obituary for J.R. Quayle FRS (1927 - 2006)
By Prof. Chris Anthony, University of Southampton
In 1963 he moved to the University of Sheffield as a Senior Lecturer in Biochemistry, becoming the West Riding Professor of Microbiology two years later, and serving as Dean of the Faculty of Science from 1974 to 1976. In 1978 he was elected to The Royal Society and was awarded the CIBA Medal and Prize of The Biochemical Society. In 1983 he was appointed Vice-Chancellor of the University of Bath, a post he held until his retirement in 1992, also serving during this period as President of the Society for General Microbiology (1990-93). He was awarded Honorary Doctorates from the Universities of Göttingen (1989), Bath (1992) and Sheffield (1992).
At Oxford, Rod soon set off on his own track, establishing a magnificent line of research aimed at understanding the metabolism of methylotrophs - bacteria and yeast growing on reduced one-carbon compounds such as methane, methanol, methylamine and formate. For this he developed the experimental approaches used by the Calvin group for the isolation and identification of early labelled 14C intermediates during short-term incubations of bacteria and yeasts with C1 growth substrates. This involved lengthy paper chromatography, autoradiography, quantification and subsequent confirmation of identity of intermediates by co-chromatography with known compounds. The position of the label in the isolated labeled compounds was then determined by chemical degradation and analysis. These elegant and rigorous studies led to proposals of novel C1 assimilation pathways which were then firmly established by the discovery and characterization of novel specific enzymes characteristic of each of the pathways. The importance of these key enzymes was then demonstrated by studies of their induction during methylotrophic growth and by isolation and characterization of mutants lacking these enzymes.
He started this project on microbial growth on C1 compounds at Oxford with Pseudomonas oxalaticus which grows on formate or oxalate. It had been suggested that growth on reduced C1 compounds would involve oxidation to CO2 which would then be assimilated by the Calvin-Benson cycle. He confirmed that this is true for growth of Ps. oxalaticus on formate, and many years later showed that it is also true for some bacteria which assimilate methanol by the Calvin-Benson cycle; these include Paracoccus denitrificans and the first photosynthetic methylotroph, Rhodopseudomonas acidophila, isolated on a microbiologist’s holiday with Norbert Pfennig. Remarkably, Rod showed that during growth of Ps. oxalaticus on oxalate, this substrate is decarboxylated to formate, which is oxidised to CO2, but there is a completely unexpected additional pathway for oxalate assimilation (not involving the Calvin-Benson cycle). Oxalyl-coenzyme A is reduced to glyoxylate which is converted to tartronic semialdehyde by glyoxylate carboligase, an enzyme previously shown by Kornberg to be essential for assimilation of glycollate by the glycerate pathway. During energy generation oxalyl-coenzyme A is decarboxylated to formyl-coenzyme A, a process involving an intermediate in which a simple formyl group is bonded to both thiamine pyrophosphate and to coenzyme-A. His observation of this huge cofactor load upon the smallest possible substrate seemed to give Rod more pleasure than the discovery of the whole of the rest of the pathway.
At the same time as this work on oxalate assimilation at Oxford, Rod initiated work on methanol assimilation pathways with the isolation of what has become the best understood facultative methylotroph, now called Methylobacterium extorquens AM1. His studies of this organism led eventually to the elucidation of the serine pathway, a typical feature of this work being the discovery of the key enzyme malyl-coenzyme A lyase. He showed this pathway to be responsible for the assimilation of methane, methanol, methylamine and formate in many other methylotrophs. Similar studies using a methanotroph (growing on methane) turned up another new pathway, the ribulose monophosphate pathway in which formaldehyde combines with ribulose monophosphate to give a 3-hexulose phosphate; the first reactions are catalysed by a novel hexulose phosphate synthase and a specific isomerase, the subsequent rearrangement reactions being similar to those in the Calvin-Benson cycle. This pathway also operates in some of the obligate methylotrophs growing on methanol such as Methylophilus methylotrophus, used by ICI Billingham for production of single cell protein (“Pruteen”). Rod also demonstrated that these bacteria, by incorporating an extra enzyme into the pathway (6-phosphogluconate dehydrogenase), can oxidise formaldehyde to CO2 by a cyclic route instead of the usual linear pathway.
In the early 1970s Rod moved onto the recently-described methanol-utilising methylotrophic yeasts, playing a major part in the elucidation of yet another novel pathway, the dihydroxyacetone pathway in which formaldehyde is initially incorporated into dihydroxyacetone phosphate by way of a specific dihydroxyacetone synthase (a transketolase with xylulose phosphate as the second substrate); the xylulose phosphate is then regenerated by re-arrangement reactions as in the ribulose monophosphate pathway. After the initial proposal of the pathway it was rigorously confirmed by characterization of these specific inducible enzymes and of mutants lacking them, and by elegant studies of incorporation of 14C methanol.
The timely identification of important key questions is a common feature of this work, and a further example of this is seen in Rod’s work on methane oxidation, which demonstrated unequivocally that the initial reaction must be catalysed by a monoxygenase, incorporating 18O into methanol from 18O2, but not from water containing 18O. Such reactions require a reductant together with the oxygen and this necessarily means that less energy is likely to be available from oxidation of methane than from methanol oxidation. This will have influenced his advice to ICI when developing their ‘Pruteen’ process in the 1970s, leading to them using methanol rather than methane as feedstock.
This brief summary of Rod’s scientific career provides a useful summary of much of methylotrophic metabolism. What he started in the late 1950s is continuing, as illustrated by the series of International Symposia on Microbial Growth on C1-Compounds which he helped to initiate, the first unofficial one being held in Edinburgh Castle in 1973. Eight more were subsequently held between 1974 and 1995, before being taken up as Gordon Research Conferences [Molecular Basis of Microbial One-Carbon Metabolism], the fifth of which will be held in Oxford this year. In these Symposia his contributions were always eagerly anticipated; his lecturing style was usually formal, often guided by a full text, with the excitement coming from the ideas revealed and from the clarity of their exposition, while in the informal sessions his brilliantly humorous story telling was a major attraction.
Rod will be remembered as a very special scientist, and as a great example, teacher, adviser and friend. A great pleasure when informing him of some recent advance was his excitement, just as great as if he had made it himself; indeed, it sometimes felt that a new discovery could not be fully established until it had received this happy blessing. He was rarely possessive about his own discoveries; reading his own accounts of his work one does not immediately appreciate that the ‘groups’ referred to are his own students and post-docs. I do remember him being very possessive on one occasion however; while I was visiting the University of Bath, not long after he became Vice-Chancellor, a flock of goldfinches flew over us. “Here they come; my goldfinches”, reflecting his concern that proper management of the University grounds should offer them every encouragement to make their home there.
Rod Quayle died on 26 February 2006 aged 79. He was once referred to as the Godfather of Methylotrophy, and as our Godfather and friend he will be greatly missed. He is survived by his widow, Yvonne, by his children Susan and Rupert, and by five grandchildren (David, Hannah, James, Joseph and Rebecca).