β-N-acetylhexosaminidase ( bb0002 ) and β-glucosidase ( bb0620 ) double mutant utilizes chitin. Growth of RR60 (double mutant) in the presence of chitobiose or chitohexose. Late-log phase cells were diluted to 1.0 × 105 cells ml-1 in BSK-II containing 7% boiled serum, lacking GlcNAc and 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 twice.