Mary Belle Allen (November 11, 1922, Morristown, New Jersey –1973, Fairbanks, Alaska) was an American botanist, chemist, mycologist, algologist, and plant pathologist, and a pioneer of biochemical microbiology.

[12][13][14] Allen is listed as an assistant at the Lawrence Radiation Laboratory at the University of California in Berkeley for 1941-42[2][15] and as a chemist for the Manhattan District for 1942-44.

[12] Allen received a DuPont fellowship for 1945-1946[2] and completed her Ph.D. in physical chemistry at Columbia University in 1946,[2][12] with a thesis on Phosphorus in Starch.

[2][18][19][20][12] She also spent a year at the Marine Biological Laboratory at the University of Chicago as a visiting fellow with James Franck and Hans Gaffron, possibly around 1951.

[23] At Hopkins Marine Station Allen worked with C. B. van Niel on the physiology and biochemistry of thermophiles, bacteria that can survive at high temperatures.

[22][23] In 1952, she reported that she had isolated an "unidentified unicellular alga" from the acid waters of "Lemonade Spring", The Geysers, Sonoma County, California.

Later work suggested that it was similar to forms of Cyanidium caldarium independently discovered by Hiroyuki Hirose (1950), Felix Eugen Fritsch (1945),[24] and Kenichiro Negoro (1935).

[4][26][27] In the mid 1950s, Allen worked at the University of California, Berkeley with Daniel I. Arnon and F. Robert Whatley in breakthrough research on the role of chloroplasts in photosynthesis processes.

where, in fact, three different people – Arnon, myself and Mary Belle Allen – had suddenly decided, from different points of view, that chloroplasts must be able to make ATP.

And Marybelle and Bob, the four of us, lined up when Arnon, in a pristine white coat and so forth, marched in with a tray full of spinach that had been kept in the cold room to be nice and crisp.

[36] In January 1957 she was listed by the Phycological Society of America as studying plankton as an assistant research biochemist and lecturer in physiology in the Department of Soils and Plant Nutrition, University of California, Berkeley.

[4] In 1960 she edited the published proceedings of the First Annual Symposium on Comparative Biology of the Kaiser Permanente Research Institute in Richmond.