[1] It is a syntrophic process by which H2 is transferred from one organism to another, particularly in the rumen and other anaerobic environments.
[1] IHT was discovered between Methanobacterium bryantii strain M.o.H and an "S" organism in 1967 by Marvin Bryant, Eileen Wolin, Meyer Wolin, and Ralph Wolfe at the University of Illinois.
[2] It was shown in 1973 that this process occurs between Ruminococcus albus and Wolinella succinogenes.
[3] A more recent publication describes how the gene expression profiles of these organisms changes when they undergo interspecies hydrogen transfer; of note, a switch to an electron-confurcating hydrogenase occurs in R. albus 7.
[4] This process affects the carbon cycle: methanogens can participate in interspecies hydrogen transfer combining H2 and CO2 to produce CH4.