The bacterial taxonomist Norberto J. Palleroni passed away on March 5th 2018, at the age of 96. He was a colleague, dear friend and mentor, and we have lost a leading force in discovery and characterization of the bacterial world. Norberto Palleroni was an internationally recognized authority in bacterial taxonomy, particularly the genus Pseudomonas. His work on this genus culminated in the metabolic studies based on carbohydrate degradation tests and the first development of ribosomal RNA (rRNA) homology experiments as a tool of general use in bacterial taxonomic and phylogenetic studies. His early work on bacterial classification utilizing genomic DNA–DNA hybridization techniques commenced the exploration of the genome complexity of Pseudomonas and other bacterial taxa. The rRNA work stimulated research on other microbial groups, resulting in the development of new approaches in the study of bacterial phylogeny that eventually led to the ‘Tree of Life’.

Norberto Palleroni was born in Buenos Aires, Argentina. He earned his Ph.D. in Microbiology in 1947 at the University of Buenos Aires. The influence of Beijerinck and the ‘Delft School’ of microbiology can be traced through his family tree of scientists: Santos Soriano who studied with Beijerinck was Norberto Palleroni's microbiology teacher. Early in his career, Norberto received a Rotary International Fellowship to work on yeast genetics with Carl C. Lindegren at Southern Illinois University. He returned to Argentina, to the faculty of the University of Cuyo, in Mendoza, as Professor of Microbiology (1949–1968) and Director of the Institutes of Microbiology and of Industrial Fermentations. Shortly after this appointment, he received a John Simon Guggenheim Memorial Foundation Fellowship to study bacterial carbohydrate metabolism. This led to an almost 20‐year association with two ‘giants’ in microbial biology and biochemistry, Roger Stanier and Michael Doudoroff, in the Department of Bacteriology at the University of California, Berkeley. At that time, Palleroni also met C. B. Van Niel (former student to Albert Kluyver) which linked him again to the Delft School. He was impressed by the way in which Van Niel developed the course in general microbiology at the Hopkins Marine Station in California. Palleroni later emulated Van Niel's approach in his lectures and teaching.