The bacteria Vibrio fischeri forms a symbiosis with Euprymna scolopes wherein the bacterial bioluminescence is used by the host to evade predators. In the host, V. fischeri growth on sulfur is controlled by CysB transcription. I hypothesize that mutations in the tcyJ promoter of ΔcysB mutants restore growth on sulfur independently of CysB transcription. This investigation will lead to a better understanding of alternative gene regulation in the fields of microbiology and genetics.