Within the focus of bioengineering, various cell modification methods are utilized to alter inherent properties of cells such as growth density, growth rate, growth yield, temperature resistance, freezing tolerance, chemical sensitivity, and vulnerability to pathogens. For example, in 1988 one group of researchers from the Illinois Institute of Technology successfully expressed a Vitreoscilla hemoglobin gene in E. Coli to create a strain that was more tolerant to low-oxygen conditions such as those found in high density industrial bioreactors.