ABOVE: Jon Chase/Harvard University

Howard Curtis Berg, a biophysicist who sought to understand the mechanics of bacterial movement, particularly that of E. coli, died on December 30, 2021, at the age of 87.

Berg was born in Iowa City on March 16, 1934, according to an obituary from Harvard University. His father was a biochemist at the University of Iowa and Berg followed a similar path, receiving his undergraduate chemistry degree from Caltech in 1956. According to his CV, he then completed a Fulbright Fellowship at Carlsberg University in Copenhagen before going to Harvard Medical School to do preclinical studies. He remained in that position until 1959, when he changed gears and pursued further education at the university, getting his master’s in physics in 1960 and his PhD in chemical physics four years later. He stayed at Harvard to teach and study cell membrane structure until 1970, when he took a faculty position at the University of Colorado Boulder (CU Boulder).

See “Digital Chemotaxis

During this time, Berg began to study E. coli’s use of environmental chemical cues to guide its movement, known as chemotaxis. For this, he invented a microscope capable of tracking the bacteria’s unpredictable movements, according to the Harvard obituary. He discovered that E. coli was more motile when put in conditions with attractive chemical gradients. However, when the environment was subpar because of substrate viscosity or other factors, the microbes moved along as normal, dispelling popular wisdom at the time that bacteria would actively avoid adverse conditions. In 1973, he discovered that flagella move some bacteria by means of a corkscrew-like rotation. Berg then returned to studying bacterial membrane structures as part of his goal of determining the energetics of flagellar motion.

Berg left CU Boulder in 1978 for a yearlong sabbatical at the Pasteur Institute in Paris and the State Serum Institute in Copenhagen.

Heading back stateside, he took on a professorship at Caltech in 1979, teaching at his alma mater for seven years. During this stage of his career, he used optical tweezers to further probe the dynamics of bacterial movement mechanisms and how they were affected by different stimuli.

See “The Optical Trap

In 1983, Berg published the book Random Walks in Biology, a basal introduction to biological physics.

The following year, he was made a fellow of the National Academy of Sciences and was honored with the Max Delbrück Prize in Biological Physics by the American Physical Society “for the elucidation of complex biological phenomena, in particular chemotaxis and bacterial locomotion, through simple but penetrating physical theories and brilliant experiments.” In 1985, he was elected into the American Academy of Arts & Sciences.

Berg returned to Harvard in 1986. According to his obituary, Berg thought of retirement as “going to pasture,” and thus remained active in research up until his death. He published more than 120 papers during that time, eagerly adopting emerging technologies to better see or understand aspects of motility.

In February 2022, Berg had a study posthumously published in PNAS that examines how microbes are able to interact with their environments while on a glass surface. The cover for this month’s issue of Nature Reviews Microbiology was dedicated to Berg and includes a review article he cowrote last autumn.

He is survived by his wife Mary, three children, and five grandchildren.