By Agbata_erica Nwachukwu C
Ten heavy metal-tolerant fungi were isolated from the University of Nigeria
sewage treatment plant. The two isolates Cul and Pbl identified as Aspergillus niger
and Fusariwn sp. exhibited very high tolerance for CU~+(MIoCf 1500mg/L) and pb2+
(10,00Omg/L) respectively, were employed in this study. Sub-lethal effects of CU"
and pb2' levels on both isolates were assessed by microbial growth, total amylase
production, starch hydrolysis, reducing sugar content, and changes in medium pH.
Biomass was determined gravimetrically. Effects L
microbial growth and activity were determined with t
of cu2' and pb2+ speciation on
CuSO4, CU(NU,)~a, nd CuC12 a1
f i r . ,T .. . 0 - I - 16Omg/L or Pb(N03)2, PbC12, (CH3C00)2Pba t 20uumgr~re specnvely, ror tne LUand
Pb-tolerant fungi, respectively. Heavy metal biossrption by sterile and nonsterile
mycelia of the isolates were determined by atomic absorption
spectrophotometer (AAS) foIIowing desorption in 0.1N HN03. Microbial growth,
amylase production and starch hydrolysis in both isolates were significantly (P <
0.05) influenced by the level of heavy metal ions in the medium. In A. niger,
maximum amylase production and starch hydrolysis in the presence of cu2+ was
obtained at 16Omg/L; while biomass level at 320 and 400mglL of cu2'were
significantly (P < 0.05) higher than the value for control. Amylase production by
Fusariunz sp., was higher than values for the control at 4000, 3000,2000, and
1000rngK of pb2+. he speciation of cu2+ and pb2+ also significantly (P < 0.05)
influenced the level of resistance in both moulds. The general trend showed that cu2+
toxicity on A. niger increased in the order CuS04< Cu(N03)2 < CuC12; while PbC12
was more toxic than Pb(N03)2 and (CH3C00)2Pb in that order. Sterile and non -
sterile mycelia of both isolates biosorbed the ions of the two metals in a zero order
kinetic. Metal biosorption was also influenced by the nature of the buffer and pH of
the medium.