Norberto J. Palleroni
1922-2018

image of Norberto Palleroni

Norberto J. Palleroni passed away on March 5th 2018, at the age of 96. He was internationally recognized as an authority in bacterial taxonomy, particularly the genus Pseudomonas. His work on this genus culminated in the first demonstration of the power of ribosomal RNA homology experiments as a tool of general use in bacterial taxonomic and phylogenetic studies. This work stimulated research along similar lines on other microbial groups, resulting in the development of new approaches in the study of bacterial phylogeny. In addition, his early work on bacterial classification utilizing genomic DNA-DNA hybridization techniques initiated the exploration of the genome complexity of Pseudomonas and other bacterial taxa.

Norberto Palleroni earned his Ph.D. in Microbiology in 1947 at the University of Buenos Aires. Early in his career, he received a Rotary International Fellowship and worked on yeast genetics with Carl C. Lindegren at Southern Illinois University. He then returned to Argentina, to the faculty of the University of Cuyo, in Mendoza, where he was 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 at the University of California, Berkeley. This led to an almost 20-year association with Roger Stanier and Michael Doudoroff in the Department of Bacteriology.

From 1954 to the early 1970s Dr. Palleroni was a Research Associate at the Department of Bacteriology of the University of California, Berkeley. His research with Stanier and Doudoroff focused on the biochemistry and taxonomy of members of the genus Pseudomonas. Work during this period resulted in the modern classification of this bacterial group, for which he is best known. The results of the morphological and physiological characterization of Pseudomonas species was published in an enormous article in the Journal of General Microbiology [R. Y. Stanier, N. J. Palleroni and M. Doudoroff. The Aerobic Pseudomonads: A Taxonomic Study. Journal of General Microbiology (1966) 43:159-271; doi:10.1099/00221287-43-2-159]. To better understand the great diversity of the genus Pseudomonas Norberto Palleroni began experiments to define the heterogeneity of the DNA of members of the genus. One of the major advances was the use of rRNA hybridization experiments, which demonstrated that the various species assigned to the genus Pseudomonas behaved as an entity of several genera. These have been reclassified into different classes of the Proteobacteria with the subsequent development of 16S rRNA phylogenetic analysis.

In the early 1970s he moved East (in his words "against the Buster Keaton recommendation of moving West") when he accepted an offer from the Research Division of Hoffman-La Roche in Nutley, New Jersey. As a Senior Research Fellow in the Department of Microbiology he was in charge of maintenance of the central microbial culture collection used in organic synthesis and in the production of antibiotics. During this period (1973 to 1985) he worked on the cultivation and characterization of a range of poorly known bacteria, including the Actinoplanes, an actinomycete with motile spores. To enable the isolation of Actinoplanes strains he invented a novel method which consisted in trapping the motile spores inside of capillary tubes.

After retiring from Hoffman-La Roche Dr. Palleroni was a Busch Visiting Scholar at the Waksman Institute of Microbiology at Rutgers University (1985 to 1986) followed by an appointment as an Adjunct Professor in the Department of Microbiology at New York University School of Medicine. In 1992 he returned to Rutgers University with appointments as a Research Professor at in the Biotechnology Center for Agriculture and the Environment and in the Department of Biochemistry and Microbiology, where he continued the study of the taxonomy of various bacterial groups with Lily Young, Gerben Zylstra and Max Häggblom. He was the academic advisor of a graduate student, Bongkeun Song, co-mentored with Max Häggblom.

Norberto Palleroni published over 150 papers on various microbiological subjects, including Pseudomonas taxonomy and phylogeny, and descriptions of several new species of the genera Burkholderia, Thauera, Azoarcus and Paenibacillus. He authored the central chapters on the pseudomonads in the many volumes and editions of Bergey's Manual of Systematic Bacteriology.

Several bacterial species and a genus have been named in Norberto Palleroni's honor. Although he would usually complain about non-descriptive taxonomic names, he did take some personal pride in these taxa. There is a Hydrogenophaga palleronii (an autotrophic hydrogen bacterium capable of fixing carbon dioxide using the energy of hydrogen oxidation and originally named Pseudomonas palleronii), an Actinoplanes palleronii (a rare actinomycete that has motile spores) and Pseudomonas palleroniana (a heterotrophic bacterium isolated from rice, belonging to the genus Pseudomonas, to which Palleroni has dedicated many years of his scientific life). Most recently to these three names, was added the description of a new genus, Palleronia, with the species Palleronia marisminoris, a moderate halophilic species isolated from the Mediterranean coast of Spain. These dedications recognized Dr. Palleroni's expertise on general microbiology, to which he has contributed with the introduction of molecular approaches to the taxonomy of bacteria, with the proposal of a new system of classification of Pseudomonas species, and with the design of original isolation and cultivation methods for members of various microbial groups.

Norberto Palleroni was Member of the National Academy of Sciences of Argentina and a Fellow of the American Academy of Microbiology. Among many honors are Honorary Doctorates from the University of Cuyo and University of Buenos Aires in Argentina, the Konex Foundation Prize in Biochemistry and Microbiology (1993), the Theobald Smith Society Selman A. Waksman Honorary Lectureship Award (1986), and the Bergey Medal (1995) in recognition of outstanding and life-long contributions to the field of systematics of Bacteria and Archaea.

Norberto, known for his Argentinian temperament, had a wonderful sense of humor. He loved music and photography. He played the flute and delighted in the challenge of teaching himself to play the violin, in his 80s. He was an accomplished photographer, of landscapes, flowers, and of course microbes. His photomicrographs of various bacterial species were indeed microbial portraits.

Norberto is survived by his sons, Sergio Palleroni and Alberto Palleroni, and their families. Norberto's wife Alicia Vallejo Palleroni, who worked as an immunologist at Hoffmann-La Roche before her retirement, passed away in 2015.

Norberto was an exceptional person with tremendous knowledge in science, art and music, that his friends, collaborators and students enjoyed to hear. We dearly miss him.

Bongkeun Song
Virginia Institute of Marine Sciences

Max Häggblom
Rutgers University


Photos:

image of Norberto Palleroni
Norberto Palleroni's "impersonation" of Beijerinck at the Laboratory of Microbiology at Delft University. The influence of Beijerinck and the "Delft School" of microbiology can be traced through the family tree of scientists: Santos Soriano who studied with Beijerinck was Norberto Palleroni's microbiology teacher.

image of Norberto Palleroni with Alexander Fleming
Norberto Palleroni (2nd from left) with Alexander Fleming (center) at the International Congresses of Microbiology in Rio de Janeiro in the 1950s.

image of Norberto Palleroni
Extracting DNA for hybridization studies.

Selected publications:

Stanier RY, Palleroni NJ and Doudoroff M (1966) The aerobic Pseudomonads: A taxonomic study. Microbiology 43:159-271. doi: 10.1099/00221287-43-2-159

Palleroni NJ, Kunisawa R, Contopoulou R and Doudoroff M (1973) Nucleic acid homologies in the genus Pseudomonas. Int J System Bacteriol. 23:333-339. doi: 10.1099/00207713-23-4-333

Palleroni NJ (1992) Introduction to the family Pseudomonadaceae. In: The Prokaryotes.

Palleroni NJ (1977) Prokaryotic diversity and the importance of culturing. Antonie van Leeuwenhoek 72: 3-19. doi.org/10.1023/A:100039410

Pallerioni NJ (2003) Prokaryote taxonomy of the 20th century and the impact of studies on the genus Pseudomonas: a personal view. Microbiology. 141:1-7. doi: 10.1099/mic.0.25952-0

Palleroni NJ (2010) The Pseudomonas Story. Environmental Microbiology. 12:1377-1383. doi:10.1111/j.1462-2920.2009.02041.x