John Roger Roth (born 14 March 1939)[2] is an American geneticist, bacterial physiologist, and evolutionist.

He became well known for his early studies on the structure and regulation of the his operon of Salmonella,[3] and went on to investigate regulation in systems as diverse as suppression by tRNA,[4] NAD biosynthesis,[5] and the Vitamin B12-dependent metabolism of small molecules such as ethanolamine and propanediol.

[6] In collaboration with David Botstein and Nancy Kleckner, he developed the use of transposons as genetic tools.

[7] As a by-product of his study of transposons, he developed an interest in chromosomal duplications, which are frequent in bacteria.

In 2011, ASM Press published a festschrift in his honor ("The Lure of Bacterial Genetics: A Tribute to John Roth").