## 3 Use of Microbial Agents in Remediation System
### Use of Other Microorganisms (Yeast and Fungi)  
The ability of a thermo-tolerant strain of yeast _Kluyveronyces marxianus_ has been investigated by [PERSON] et al. [20] to decolourise a commonly used textile dye, Remazol-BlackB. The effect of important culture conditions, e.g., of pH and temperature, were studied. No appreciable effect on decolourisation was seen in a pH range of 3.0-5.5. Maximum colour removal up to 98%, was achieved when yeast grew at 37 \({}^{\circ}\)C. No colour removal was observed in the experiment of _K. marxianus_ grown under anaerobic cultivation conditions. Further studies for decolourisation were conducted under conditions of extreme temperature and lower pH (to inhibit the yeast growth and to study the role of yeast in decolourisation). When using ten times concentrated yeast inoculum, the results proved that the decolourisation of medium appeared by adsorption of colour onto the yeast cells; no metabolic reaction happened in the breaking down of dye molecules [20].  
Few fungi also have been studied for their ability to break down five different textile-dyes when mixed together in an artificial lab-made dye-effluent. The experiments were performed using _Coriolopsis gallica_ and _Planerochaete chrysosporium_ in nitrogen-rich medium at C:N ratio set at 11.6:1, and in nitrogen-limited medium at C:N ratio set at 116:1 [14]. _P. chrysosporium_ showed 53.6% decolourisation of the effluent in N-rich medium and a bit lower at 48% in a medium of limited N. However, in another fungal culture of _C. gallica_, the decolourisation capability was higher, up to 86.9% in N-limited and 80.7% in N-rich medium. The supplementation of nitrogen helped in the stimulation of enzyme activities, and, as a result, dye decolourisation was improved for _P. chrysosporium_. However, the increasing nitrogen level stimulated enzyme production in _C. gallica_ without any improvement in the rate of decolourisation. These results highlighted the possible use of fungal cultures for the treatment of dye effluent.  
During ongoing experiments for a search of effective microorganisms capable of degrading synthetic dyes in effluents, a filamentous fungi growing under facultative anaerobic condition was isolated from a vessel containing dyes-effluent stored for a longer period [21]. This fungi showed the ability to grow on dyes as the sole source of carbon when cultivated under two different conditions, aerobic and anaerobic. This fungal isolate grew in the form of a thick mycelial mat in dye-containing medium, but no decolourisation of the medium was observed, indicating that the fungus did not produce required enzymes to break the azo-bond present in dye molecules, though it metabolised other parts in dye structure to support its thick mycelial growth.  
The evidence for the use of dyes by fungus for its growth came from the physical examination of fermented medium in comparison with the control mycelium-free dye-supplemented growth medium. This was confirmed analytically using capillary electrophoresis and UV-vis spectrophotometry. The analysis showed that though the dye solution was not decolourised, but results showed changes in the UV-vis spectra. The results were indicative of degradative-changes, which occurred in the parts of dye molecules other than on their chromophoric centres. The authors concluded from the study of the degraded dyes by capillary-electrophoresis that the thick mycelial growth of fungus induced the structural changes in dyes [21].