RpoS regulates chitobiose and chitin utilization. Growth of A74 (rpoS mutant) in BSK-II without GlcNAc and supplemented with 7% unboiled (A) or boiled serum (B). Late-log phase cells were diluted to 1.0 × 105 cells ml-1 and cultures were supplemented with the following substrates: 1.5 mM GlcNAc (closed circle), No addition (open circle), 75 μM chitobiose (closed triangle) or 25 μM chitohexose (open triangle). Cells were enumerated daily by darkfield microscopy. This is a representative experiment that was repeated three times.