Copper and cobalt alter the cell wall composition of Cunninghamella blakesleeana

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 NO-2 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 micrograms/mL or 39.3 microM) or Co (3.5 micrograms/mL or 59.4 microM), the mycelia contained 1.5 micrograms Cu or 1.0 microgram Co/mg dry tissue, respectively, but the isolated cell walls contained 33.5 micrograms Cu or 1.8 micrograms 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 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.(ABSTRACT TRUNCATED AT 250 WORDS)