3.2. Investigation of degradation of chrysene by selected fungi
The rate of degradation was above 20% for 30 days of incubation
with Polyporus sp. S133. Polyporus sp. S133 degraded 24% of
chrysene at 1mMin 30 days. Itwas observed that by 30 days in the
stationary cultures, Polyporus sp. S133 formed filamentous mats at
the surface of the growth medium, while in the set incubated with
agitation, uniform pelletswere formed. FromFig. 1, it could be seen
that 65% degradation was achieved in 120rpm agitated cultures in
30 days, as compared to 24% degradation in stationary cultures.
The increased efficiency of degradation could be due to the physiological
state of the fungus as pellets and increased mass transfer
between the cells and the medium. Biodegradation by white rot
fungi has been attributed to the extracellular activity of oxidative
enzymes such as laccase. Laccase production was greatest in agitated
cultures and hence maximum degradation was achieved in
agitated cultures. The oxygen concentration is directly dependent
on the air flow rate. Stirring increases the contact between the
reagents (substrate, oxygen, and biomass), thus enhancing mass
transfer and, as a consequence, the biodegradation rate [30]. In
stationary culture, the formation of a mat at the surface restricts
the transfer of oxygen to the cells beneath the surface and in the
medium resulting in oxygen limitation, which inhibits the oxidative
enzymes and prevents degradation.