Otto Kandler (23 October 1920 in Deggendorf – 29 August 2017 in Munich, Bavaria) was a German botanist and microbiologist. Until his retirement in 1986 he was professor of botany at the Ludwig-Maximilians-Universität München (LMU).
His most important research topics were photosynthesis, plant carbohydrate metabolism, analysis of the structure of bacterial cell walls (murein/peptidoglycan), the systematics of Lactobacillus, and the chemotaxonomy of plants and microorganisms. He presented the first experimental evidence for the existence of photophosphorylation in vivo. His discovery of the basic differences between the cell walls of bacteria and archaea (up to 1990 called "archaebacteria") convinced him that archaea represent an autonomous group of organisms distinct from bacteria. This was the basis for his cooperation with Carl Woese and made him the founder of research on the Archaea in Germany. In 1990, together with Woese, he proposed the three domains of life: Bacteria, Archaea, Eucarya. Finally, on the basis of his lifelong interest in the early evolution and diversification of life on this planet, Kandler presented his pre-cell theory, suggesting that the three domains of life did not emerge from an ancestral cell, e.g. the last universal common ancestor (LUCA), but from a population of pre-cells.
Life and education
Otto Kandler was born on 23 October 1920 in Deggendorf, Bavaria, as the 6th child of the family of a market gardener. Growing up and helping in his father's garden, early on, he became interested in plant life and nature in general. He attended school for 8 years. When he was about twelve years old he had read about Charles Darwin and mentioned it to a Catholic priest. The priest punished him with two strikes on his hands with a rod. However he remained interested in the origin and evolution of organisms for the rest of his life.
His parents could not afford to pay the fees for the gymnasium, and he was supposed to become a gardener or learn another trade. However his teachers convinced his parents that their talented son should continue school. So he attended the "Deutsche Aufbauschule" in Straubing, Bavaria, a school for the education of future teachers. His studies were, however, interrupted by the Second World War. In 1939 he and his fellow students had to join the Reichsarbeitsdienst, later he had to serve in the German army as a radio reporter in Russia. At the end of the war his group was transferred to Austria. He escaped by bicycle to the Western Front to avoid capture by the Russians. After spending a few months in an American prison camp he was allowed to return home. Between 1945 and 1946 he reconstructed his father's market garden and earned some money by growing and selling vegetable, especially cabbage, and flowers to finance his life and his future studies.
Kandler was very interested in science, but only in 1946 was he able to enroll at Ludwig-Maximilians-Universität München (LMU) in botany, zoology, geology, chemistry and physics. He also attended philosophy lectures. Since much of the Ludwig-Maximilians-Universität München had been bombed, the institute buildings were badly damaged and still in ruins. To be admitted, he and all the other students had to remove rubble and help reconstruct buildings. After three terms he found a research subject for his dissertation in botany. As the first in Germany he started to cultivate isolated plant tissues in vitro. He used these tissue cultures to study for instance metabolism and the influence of auxins under defined in vitro conditions, received his doctor's degree with honors in 1949 and became assistant professor of botany at the LMU. After his habilitation in 1953 he remained at the university until 1957. In 1953 he married Gertraud Schäfer, a graduate student of microbiology. They have three daughters and four grandchildren. For his early publications on photophosphorylation he received a generous research fellowship from the Rockefeller Foundation and, in 1956/1957 he was able to work on basic questions of photosynthesis for one year in the USA.
After his return, Kandler was dissatisfied with the poor laboratory conditions at the university at home, so he was glad to find a position as director of the Bacteriological Institute of the South German Dairy Research Center in Freising-Weihenstephan in 1957, where conditions were much better. In 1960 he was appointed full professor of Applied Botany of the Technical University of Munich, where research conditions still at that time were bad. So he kept his position in Weihenstephan in parallel until 1965. In 1968 he was appointed full professor and Head of the Department of Botany at the LMU, taught and conducted research until his retirement in 1986. His broad scientific interests are indicated by the titles of his more than 400 publications. His scientific legacy was handed over to the university archive of the LMU.
Kandler would have celebrated his 100th birthday on 23 October 2020. For this centenary Kandler's family gave his chronological collection of historical botany books, among them herbals of the 16th and 17th centuries, as a present to the library of the "Regensburgische Botanische Gesellschaft" (founded by David Heinrich Hoppe in 1790), which has been included in the library of the University of Regensburg. Through digitization these historical sources soon will be generally accessible.
Plant physiology
Otto Kandler was very interested in plant growth processes, photosynthesis, metabolism, especially of carbohydrates. As the first in Germany he started to grow isolated plant tissue cultures (e.g. of stems, roots, sprouts, embryos, callus growths) in vitro to study metabolism and the effect of auxins under defined in vitro conditions. As mentioned above, this formed the subject of his dissertation (summa cum laude) in 1949.
In his contribution „Historical perspectives on queries concerning photophosphorylation" Kandler describes the beginnings of photophosphorylation research and how he became interested: In 1948, he was inspired by a lecture on the phosphate metabolism of yeast by Feodor Lynen (1964 Nobel Prize in Physiology or Medicine). In these years, in the aftermath of World War II, the original Chemical Institute of the Ludwig-Maximilians-Universität München (LMU) was still in ruins and Feodor Lynen and his assistant Helmut Holzer were working temporarily as guests in the Botanical Institute just next door to the laboratory where Kandler was engaged in his thesis in botany. Kandler was impressed by the experimental methods in Lynen's laboratory and got acquainted with them; Holzer and Kandler became close friends. At that time, Holzer was able to present the first evidence for ATP formation in yeast oxidizing butanol to butyric acid. Kandler then decided to transfer their techniques for measuring phosphorylation rates in vivo to photosynthesis studies in Chlorella.
So, in 1950, he was the first to present experimental evidence for the light-dependent formation of ATP (photophosphorylation) in vivo in intact Chlorella cells. In 1954, Daniel I. Arnon discovered photophosphorylation in vitro using isolated chloroplasts and mentioned Kandler's pioneering work. Kandler's early publications on light-dependent formation of ATP led the Rockefeller Foundation to offer him a one-year research fellowship in the USA. So in 1956–1957 he worked for 6 months with Martin Gibbs at the Brookhaven National Laboratory and then for another 6 months with Melvin Calvin (1961 Nobel Prize in Chemistry) at the University of California, Berkeley on central questions of photosynthesis (e.g. the path of carbon in photosynthesis, today called the Calvin-Benson-Bassham Cycle).
The method of radioactive labelling, i.e. the use of radioactive isotopes for tracing the path of e.g. carbon in photosynthesis, was brought to Germany by Kandler.
Together with his coworkers, Kandler demonstrated the occurrence of ADP-glucose, the glucose donor of starch biosynthesis, for the first time in plants. He made an essential contribution to clarify the complicated biosynthesis of branched-chain monosaccharides (hamamelose, apiose). Finally he elucidated the biosynthesis of the sugars of the raffinose family, the most frequent oligosaccharides in plants. As a result of these findings, the function of galactinol, a galactoside of inositol, as a galactosyl donor, was elucidated, and hence the role of inositol as a co-factor of sugar transfer reactions in plants.
Microbiology
In addition to his interest in plant physiology and biochemistry Otto Kandler early on focused on bacteria, above all, on the presence or absence of their cell walls, since, in the early 1950s, such wall-less microorganisms were often regarded as representatives of "urbacteria". Together with his wife, he investigated the so-called PPLOs, (now mycoplasms), wall-less penicillin-resistant bacteria, and L-form bacteria (bacteria that lost their cell walls). They found that these organisms do not proliferate by binary fission but by a budding process. These publications are still cited at present.
During his time as director of the Bacteriological Institute of the South German Dairy Research Center in Freising-Weihenstephan, Kandler concentrated on dairy microbiology and investigated the physiology, biochemistry and systematics of lactobacilli, on which he wrote a chapter in Bergey's Manual, the ‘bible' of microbiologists. In addition he published numerous papers on the isolation, description and taxonomy of other bacteria.
Kandler was one of the first scientists who, together with his group, studied the chemistry and structure of the cell walls of bacteria. The primary structure of peptidoglycan (murein), the unique cell wall component of bacteria, was investigated. Kandler recognized that the amino acid sequence of peptidoglycan is a valuable chemotaxonomic marker. The different peptidoglycan types and their taxonomic implications were described in detail by Schleifer and Kandler. As a result, they suggested comparative cell wall chemistry as a marker for the deep branches in the phylogenetic tree of bacteria. Kandler’s cell wall studies also included methanogenic "bacteria" (methanogens) and halophilic "bacteria" (halophiles).
In October 1976 Kandler discovered that two strains of the methanogen Methanosarcina barkeri did not contain peptidoglycan. Consequently, he came to the conclusion that methanogens are basically different from bacteria. In his group, also "halobacteria" were found to lack peptidoglycan, confirming the idea, that also these organisms are not bacteria and belong to a group of organisms soon called "archaebacteria" (in 1990 classified as archaea). In some "archaebacteria" Kandler and König identified pseudomurein, now also called pseudopeptidoglycan, a novel cell wall component, and elucidated its structure and biosynthesis.
The methanogen Methanopyrus kandleri was named in honor of Kandler by Karl O. Stetter as a present for Kandler's 70th birthday.
Together with Hans Günter Schlegel, Kandler was substantially involved in the foundation of the German collection of microorganisms and cell cultures (DSMZ) in Braunschweig.
Kandler was the founder and editor of Systematic and Applied Microbiology, co-editor of the Archives of Microbiology and of Zeitschrift für Pflanzenphysiologie.
Archaea and the three domains of life
Otto Kandler's main subject in microbiology was his research on archaea (before 1990 called "archaebacteria"). His discovery (October 1976) that peptidoglycan (murein), a typical cell wall component of bacteria, is missing in two strains of methanogenic "bacteria" (methanogens) became one of the first three pieces of evidence that methanogens belong to a group of organisms distinct from bacteria.