Can the bacteria "Thiobacillus thiooxidans" be nutritionally stressed to degrade more sulfur than its actual diet? What is the procedure to make them competitive? How long does it take?
A useful study for you to consider would be "Applied and Environmental Microbiology, June 2007, p. 3752-3754, Vol. 73, No. 11" - these researchers studied what % of sulfur was being used for various metabolic functions and discuss what steps are taken in culture to increase sulfur oxidation. A link to the paper is provided: http://aem.asm.org/cgi/reprint/73/11/3752 (but you may have to have a subscription to view it).