Chitin utilization in medium supplemented with boiled rabbit serum. Wild-type cells (B31-A) were cultured in BSK-II without GlcNAc and supplemented with 7% boiled rabbit serum. Late-log phase cells were diluted to 1.0 × 105 cells ml-1 and the following substrates were added: 1.5 mM GlcNAc (closed circle), No addition (open circle), 75 μM chitobiose (closed triangle), 50 μM chitotriose (open triangle), 25 μM chitohexose (closed square) or 0.4% chitin (open square). Cells were enumerated daily by darkfield microscopy. This is a representative experiment that was repeated five times.