Copper and cobalt alter the cell wall composition of Cunninghamella blakesleeana

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Abstract
Cunninghamella blakesleeana was highly sensitive to Cu and Co on a medium containing NaNo3 as the sole nitrogen source. The nitrate reductive pathway was altered by Cu and Co, and .**GRAPHIC**. accumulated in the medium. Under conditions of Cu toxicity, the mycelium and the cell walls acquired a blue color, and most of the Cu was located in the cell walls, which differed in several aspects from cell walls derived from Co-containing or control cultures. At half-maximal growth inhibition by Cu (2.5 .mu.g/mL or 39.3 .mu.M) or Co (3.5 .mu.g/mL or 59.4 .mu.M), the mycelia contained 1.5 .mu.g Cu or 1.0 .mu.g Co/mg dry tissue, respectively, but the isolated cell walls contained 33.5 .mu.g Cu or 1.8 .mu.g Co/mg dry cell wall. The phosphorous content of mycelia from Co-containing cultures was the same as that from control cultures, whereas that of mycelia from Cu-containing cultures contained 36% less. However, the phosphorous content of the cell walls from mycelia cultured in the presence of Cu or Co was two- and three-fold higher, respectively, than that of cell walls from mycelia cultured in the presence of Cu or Co was two- and three-fold higher, respectively, than that of cell walls from control cultures. The cell walls of Cu-containing cultures contained significantly less hexosamine than the control cell walls, and chitin and chitosan were present in equal quantities. The cell walls of Co-containing cultures had the same amount of hexosamine as the control cell walls, but 88% of the hexosamine was present as chitosan and bound very little Co. The control cell walls contained approximately 60% chitosan. The cell walls of Cu-containing cultures also contained less alkali-soluble neutral sugar, but more protein, than did the walls from the control or Co-containing cultures. Only the protein of the cell walls of Cu-containing cultures contained hydroxyproline, which is usually absent in the cell walls of fungi and may have been involved in the binding of Cu and in the acquisition of the blue color. The protein of the cell walls from Co-containing cultures was abnormally high in citrulline. Chitinase not only had a greater affinity for the cell walls of Cu-containing cultures, but these were more easily hydrolyzed by the enzyme than the cell walls from Co-containing and control cultures. Melanin was not responsible for the differential rates of hydrolysis by chitinase. The cell walls from control cultures bound more DNA than did the walls from Cu- and Co-containing cultures.