Mary Jane Osborn (September 24, 1927 – January 17, 2019)[1] was an American biochemist and microbiologist known for her research on the biosynthesis of lipopolysaccharide (bacterial endotoxin), a key component of the outer membrane of Gram-negative bacteria, and discovering the mechanism of action of the anti-cancer drug methotrexate.

[5] She then earned a Ph.D. in biochemistry from the University of Washington in 1958, where her thesis research investigated the function of folic acid-dependent enzymes and vitamins.

[2] After receiving her Ph.D., she began a postdoctoral microbiology fellowship at the New York University College of Medicine, and was appointed assistant professor there in 1962.

[2] She served as professor of microbiology in the Department of Molecular, Microbial and Structural Biology[5] and remained at the University of Connecticut until her retirement in 2014.

[2] It was during her postdoctoral fellowship that she switched research focus to microbiology, examining the biosynthesis of lipopolysaccharides[8] which contributed to the development of new antibiotics.

[6] She used a combination of biochemical experiments, bacterial genetics, and electron microscopy to investigate how bacteria transport lipopolysaccharides from the cellular interior where they are produced to the outer membrane where they reside.