|MadSci Network: Microbiology|
Bacteria do not cause rust in metals, rather they cause metals to corrode and this corrosion does resemble rust. Certain types of bacteria cause metals to corrode as a result of their metabolic activity. Just as we ingest food for energy and growth some bacteria will use metals for energy and growth. By using metals for energy the bacteria will oxidize the metal and cause it to corrode.
Other bacteria corrode metals indirectly by producing waste products during growth that can react with the metal. For example a bacteria named Desulfovibrio produces hydrogen sulphide as a waste product. The sulphur in this compound can react with iron to produce a new compound known as iron sulphide. The iron metal therefore is changing into iron sulphide and is corroding.
This is a very interesting part of microbial ecology, although these processes can cause problems for industries the processes are also very important for recycling of minerals and these bacteria can be used in aiding mining processes.
More information on this topic can be found in, Bioextraction and Biodeterioration of Metals,/U>, edited by Gaylarde and Videla. Maybe your library could borrow it from the nearest university library.
Hope this helps.
Try the links in the MadSci Library for more information on Microbiology.