2.1 Sample preparation
Carbon sources; glucose (GA), Beta vulgaris (BA), and Beta
vulgaris with cyanide (BCN) were used for the cultivation ofFusarium oxysporum in gold mine wastewater as shown in
[26]. Briefly, Fusarium
oxysporum was grown in a 1 litre continuously stirred tank reactor
(CSTR) containing metal-laden synthetic gold mine wastewater at 25±2°C.
The wastewater contains (per litre): 47 mg CuSO45H2O, 42 mg
Fe2(SO4)3 H2O, 278 mg
(NH4)2SO4, 27mg
KH2PO4, 3mg ZnSO47H2O, 0.9 mg PbBr2, and 40 mg
Na2HAsO4 7H2O. The
reactor was inoculated with 10% (v/v) F. oxysporum and 0.3 g
glucose as refined carbon source. Subsequently, experiments on 0.3 g
pulverised B. vulgaris followed by 0.3 g pulverised B.
vulgaris with 100 ppm CN-/L in form of KCN. Biomass
was harvested once the carbon source was used up and/or when the
microbial growth reached stationary phase. The harvested biomass was
centrifuge at 4°C for 10 min at a speed of 10,000rpm in an Avanti® J-E
centrifuge (Beckman Coulter, Inc. USA). Recovered biomass were washed
thrice in sterile distilled water, dried in a Duran® vacuum desiccator
(DURAN Group GmbH, Germany), and stored at -20 °C for further analyses.
Sample dried biomass was dissolved in sterile distilled water in a 1:1,
weight: volume ratio and incubated at 298.15 K for 16 h to ferment any
residual carbohydrates. The Durham tube method was used to test for any
residual carbohydrates in the suspension
[24]. The procedures were repeated
until an appropriate quantity of dry biomass was obtained. The elemental
analysis of the samples was determined by a Thermo Flash EA 1112 series
analyser in a Helium carrier gas (Thermo Fisher Scientific Inc. Waltham,
USA) subsequent to estimation of molar mass of dried biomass containing
a unit carbon as 23.03, 33.14 and 27.06 g/C-mol for GA, BA and BCN
samples, respectively. The detailed elemental analysis of the samples
are presented in [26].