Molecular Soil Biology (online), 2013, Vol. 4 No.1, 1-6
ISSN 1925-2005
http://msb.sophiapublisher.com
2
investigated like
Talaromyces helicus
(
Romero et al.
2006),
Rhizopus arrhizus
(
Subudhi and Kar, 2008),
Polyporus squamosus
(
Wuyep et al., 2007),
Trichoderma reesei
(
Kim et al., 2003)
,
Cunninghamella
echinulata
(
El-Sayed and El-Morsy, 2004),
Aspergillus niger
(
Awofolu et al., 2006),
Penicillium
chrysogenum
(
Niu and Volesky, 1999). However there
is no sufficient data available on the metal removal
capacity of
Trichoderma harzianum
.
So in the present
study an attempt was made to study the Cr (VI)
removal ability of
T. harzianum
in vitro
.
The effect of
different physical parameters like pH and temperature
on metal removal was also investigated.
1
Material and Methods
1.1
Organism and culture conditions
A strain of
Trichoderma harzianum
was obtained from
center for advance studies in botany (CAS),
University of Madras, and was routinely maintained
on readymade potato dextrose agar (PDA) of HI-
MEDIA make.
1.2
Reagents
Metal stock solution was prepared by dissolving
potassium dichromate (K
2
Cr
2
O
7
)
salt of SRL AR
grade in distilled water (DW).
1.3
Sensitivity/Tolerance of
T. harzianum
strain to
Cr (VI)
In vitro
sensitivity/tolerance of
T. harzianum
strain to
different concentrations of Cr (VI) was determined by
poisoned food technique (Dhingra and Sinclair, 1985).
Appropriate quantity of the Cr (VI) stock solution was
added to molten Czapek Dox agar (CDA) medium to
get the required concentration (5, 10, 20, 30 and 50
mg/L) and poured in to sterilized petri plates (9 cm)
after gentle shaking. Metal un-amended medium
served as the control. The plates were inoculated by
placing 5 mm discs of 4 days old culture of
T.
harzianum
strain and incubated at room temperature
(25
± 2)
?
.
Inhibition of radial growth was measured
based on colony diameter, by using the formula stated
by Sundar et al (1995).
Percent Inhibition (PI) = [(X-Y/X) x 100]
Where,
X = Radial growth (mm) of control plates
Y = Radial growth (mm) of treated plates
1.4
Biomass preparation
For preparation of the fungal biomass,
T. harzianum
strain was inoculated in CDA plates and incubated
at room temperature. After 5 days, a small portion
(0.5
mm) of the fungus mycelium was cut and
transferred into 200 mL Czapek Dox broth (CDB)
broth in a 500 mL Erlenmeyer flask and incubated at
27
?
.
After the incubation period, the pellets thus
formed were harvested from the medium, washed
thrice with sterilized distilled water and stored at 4
?
until further studies.
1.5
Biosorption of Cr (VI)
The biosorption experiment was conducted in
Erlenmeyer flask (500 mL) containing 200 mL of
Czapek Dox broth (CDB) and known concentration of
Cr (VI) solution in triplicates.
T. harzianum
pellets
were inoculated in to the flask and incubated at
different day’s intervals (4, 5, 6 and 7 days).
Measurement of Cr (VI) residue in the growth
medium was conducted with Perkin- Elmer A-Analyst,
AA800 (Perkin-Elmer Corporation, Shelton, USA)
atomic absorption spectrophotometer.
The adsorption isotherm was calculated by Freundlich
and Langmuir isotherm pattern using the following
formulas:
Freundlich isotherm
log (x/m) =1/n log C+ log K
Where, x/m is the amount of metals adsorbed (mg of
Cr kg
-1
),
C is the equilibrium concentration in soil
solution and n and K is the constants of adsorption
isotherms. Values of log K represent the amount of
metals adsorbed at unit concentration and 1/n
represents the concentration gradient.
Langmuir adsorption isotherms
C/x = 1/ (K n) + C/n
Where C= equilibrium concentration of Cr, x is the
amount of metals adsorbed, K is the constant related
to binding energy and n is the metals adsorption
maxima. From a linear plot of C/x verses C,
adsorption maxima was calculated, as the inverse of
the slope and constant related to bonding energy was
determined as slope (or) intercept.