Fig. 1
figure 1

Clete Kurtzman. Picture kindly provided by Álvaro Fonseca

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Monday November 27 2017, Mary Heffernan informed me that her father, Clete Kurtzman (Fig. 1), had died of a heart attack earlier in the morning. She said that Clete had often mentioned me as someone that he cared about; our phone conversation was brief and mired in tears. There ensued a flurry of emails as the international yeast researcher community expressed bewilderment and sadness. Many noted Clete’s scholarly stature, but more importantly, all remarked on his generous and gentlemanly manner. For many he had been a mentor and a lighthouse in the stormy sea of yeast systematics. The following are my personal thoughts as colleague and friend of over 40 years.

I know nothing of Clete’s early life in Mansfield, Ohio, his rise to the rank of Second Lieutenant in the United States Army, or his academic training at Ohio University, Purdue University, and West Virginia University. He joined the USDA in 1967. I believe that the Peoria institute was at the time called the Northern Regional Research Laboratory (NRRL), but as it housed an army of taxonomists, periodic name changes were in order. I so remarked to Clete at the time of the more recent name change (National Center for Agricultural Utilization Research), to which he uncharacteristically reacted with much displeasure. This was in quite some contrast to Clete’s superbly creative sense of humour, which I had grown to enjoy since the mid-1970s, when Clete spent a few days in Herman Phaff’s laboratory, where I was a doctoral student. The goal of Clete’s visit was to learn the radioisotope-labelled DNA reassociation technique used by Phaff’s students and to compare it with the spectrophotometric approach used in the Peoria laboratory. I immediately took notice of Clete’s baritone charm. Our subsequent interactions were through many conferences, international yeast systematics schools, and periodic phone conversations. In the mid-1980s, he served as external examiner to Deborah Sidenberg, my first doctoral student.

Mentor

Clete’s mission at the USDA was primarily as a researcher. He nonetheless never missed an opportunity to train the next generation. He was a good teacher, especially when it came to demonstrating laboratory techniques. In Oeiras, Portugal, in 1988, I clearly remember him taking us through the steps of purifying massive amounts of RNA and then performing old-fashioned reverse transcriptase sequencing reactions. He was a meticulous worker, and when his seminal paper (Kurtzman and Robnett 1998) appeared, all knew that the massive amounts of data deposited in support of the work were of impeccable quality. My participation in the international course on “Molecular Methods in Yeast Taxonomy” at the Gulbenkian Institute in Oeiras was entirely Clete’s doing. Even though he was already implementing sequencing technologies, he saw some value in the now obsolete approach I was using to apply rDNA restriction maps to the phylogenetic classification of yeasts. Nick van Uden, host and organizer of the course, had his doubts and felt the need to conduct a thorough phone interview before accepting me among his instructors. The Oeiras course opened the way to several other endeavours that combined exciting science with wonderful experiences in culture and friendship, notably interactions involving Jack Fell, Clete, and me, often accompanied by our wives Pam Reid, Mary Ann Dombrink, and Jane Bowles.

Clete had the habit of giving breaks to upcoming scientists. Among many examples, he later nominated me to serve on the Executive Committee of the International Mycological Society. I still wonder why, but am no less grateful for the honour. Clete vigorously promoted the participation of yeast researchers in International Mycology Congresses.

Reviewer

Clete was a generous contributor to the peer review process (including a great many reviews for Antonie van Leeuwenhoek), an increasingly rare commodity. I easily recognized his reviews of my papers, which always started with “This nicely written manuscript…”. Later on, as Associate Editor, my conceit was crushed somewhat when I found out that most of his reviews started with that same comment or something equally laudatory. In terms of reliability as a reviewer, Clete was simply stellar. As to difficulty rating, he was a ‘softie’, able to highlight the stronger points of a manuscript, however well concealed. Nonetheless, as our divergences of views on the species and genus concepts progressed, he did manage to be quite critical of some of my proposals. I vaguely remember his characterization of a newly proposed species of mine as being “neither good nor bad.” Although the review was anonymous, it did start with “This nicely written…”.

I was one of the reviewers for Clete’s masterpiece (Kurtzman and Robnett 1998). A paper reporting on barcode DNA sequences for all known ascomycetous yeast species was destined have an immeasurable impact on the future of yeast identification and I stated so at the beginning of the review. Indeed, the article has now been cited nearly two thousand times. I also remarked that for that reason, I was taking my role as reviewer seriously. I chided Clete’s use of the expression ‘sibling species’ when he meant ‘sister species’ and unsplit a few infinitives—an American thing, I reckon. More importantly, the paper postulated that strains differing by less than three substitutions were conspecific and those differing by six or more were distinct species. I insisted that this be presented as a prediction or a guideline, and not as a hard and fast species concept, which remains the interpretation made by many authors. To this day, I continue to feel privileged to have been part of the process.

Clete was generous in naming yeast species after colleagues, including some who at times were not always supportive of his accomplishments. I am endlessly proud of two papers co-authored by Clete and other cherished colleagues using my name as specific epithets (Giménez-Jurado et al. 2003; Phaff et al. 1999). In 2003, he bestowed upon me the distinct honour of creating the genus Lachancea for species that include model organisms (Kurtzman 2003). I was delighted to reciprocate with the creation of the genus Kurtzmaniella five years later (Lachance and Starmer 2008). One review of that paper was particularly harsh; it began with “This nicely written…”.

Loving rivalry

As Post-modern theorists love to point out, science involves a significant amount of less-than-rational, societal context. Clete and I, in addition to being colleagues, collaborators, dear friends, nay family, also entertained a hearty rivalry. We held stubborn but divergent views on such things as the species, the genus, the minimum sample size required for a species description, the significance of branch lengths in phylogenetic trees, changing the name of a taxon (my view: never; his, well…). At the Montpellier Yeast Symposium, Clete proudly handed me a reprint of his newest paper (Kurtzman 1984) rendering Hansenula a synonym of Pichia, based on the synonymy of species assigned to the two genera. I am still in shock, as are several researchers interested in the genetics of Hansenula/Pichia anomala a.k.a Wickerhamomyces anomalus. The change was scorned by a colleague in a plenary lecture many years later. The presenter used words that went beyond the scientific etiquette, which brought tears to my eyes—but a proud glimmer to Clete’s. Our disputes, as real as they were, never ceased to be couched in a nest of reverence.

I was greatly honoured when Clete invited me to co-author a few chapters in the 1998 edition of “The Yeasts, a Taxonomic Study”. This later led to a momentous liquid lunch in Darling Harbour, in Sydney, Australia (1999), when Clete conferred upon me the ultimate honour of authoring the Candida mega-chapter for the 2011 edition, a humanly impossible task, so elegantly led by Sally Meyer in the 1998 edition (Meyer et al. 1998). After years of labour, I sent Clete the thousand-page manuscript. I provided a full description of all Candida species that I was able to study in my laboratory (around 300), but for recently described species that I was not able to examine with my own eyes, entries were limited to a statement referring the reader to the original publication. I was never privy to the exchange that must have taken place among Clete and his co-editors, Jack Fell and Teun Boekhout, and prefer not to speculate. I eventually received a communication congratulating me on the superhuman effort and, no, this would not do. After several exchanges, I remained adamant and the missing descriptions were assigned to several co-authors, including Clete, Jack, and Teun. Now that the dust has settled, my magnum opus metricorum has become Clete’s eighth most cited publication (Lachance et al. 2011). For the metrically fixated, Clete’s h-index of 64 is assuredly unprecedented in the annals of yeast systematics.

Teamwork

Although Clete and I rarely joined efforts as co-authors, our 2013 article on Tortispora (Lachance and Kurtzman 2013) was a true collaboration between two partners with minds of their own, an exercise in diplomacy and synergistic consensus. First, the article certainly ranks in the hall of fame of unconscionably long titles. We reported the description of seven new species, the transfer of an existing species to a new genus, the merging of two other genera, and the assignment of three genera to a new family. The strains had been isolated by me and various colleagues, notably Phil Ganter, but Clete was responsible for resuscitating ascospore formation in the type species. The sequencing work was shared between Clete’s laboratory and mine, but I only succeeded in determining the more challenging sequences after obtaining his advice on the most suitable primers. The light micrographs came from both laboratories. The scanning electron micrographs were mine and the ascospore dissections were Clete’s. A DNA reassociation result had been obtained by Herman Phaff many years past. The species delineations entailed a complex to-and-fro. In exchange for my conceding to assign Botryozyma, Tortispora, and Trigonopsis to the family Trigonopsidaceae (which took little convincing but served as an admirable bargaining chip), Clete agreed to designate the asexual species as instances of the forma asexualis, a pet idea of mine aimed at encouraging the taxonomic community to exercise due diligence in documenting the sexual cycle of newly described yeasts, another skill destined to join the endangered list. Clete’s imprimatur was pivotal in spreading the meme. I also recall some animated exchanges regarding interpretation of some micrographs; the final figure legend is a model of conciliation. The paper is not destined to become a citation classic, but we were both proud of it.

Generous colleague, dear friend, and leading gentleman of the yeast researcher community, Clete Kurtzman will live in our minds, always. He was ready for many more years of an outstanding career, and his dream will be realized through all of the workers he has guided and inspired.