Studies on Biodegradation of Substituted Phenols by Arthrobacter Chlorophenolicus A6

Abstract

The presence of substituted phenols in water, soil and wastewater is of severe public health concern due to their detrimental effect on human and many other living organisms. Their removal from contaminated water and wastewater is necessary for protection of environment and human well being. Substituted phenols especially chloro, bromo and nitro phenols are one of the most widely used chemical compounds in many industries throughout the world. Although several techniques such as photo-decomposition, physical adsorption, solvent extraction, chemical oxidation and electrochemical methods have been tested for the removal of phenol and phenolic compounds from wastewaters, high cost, low efficiency and generation of toxic by-products are some of the limiting factors of these methods. The ecofriendly biodegradation process has gained maximum attention due to its many advantages over the traditional physico-chemical methods. The main objective of the present investigation was to develop a complete treatment system for substituted phenols bearing wastewater in aerobic process using an actinomycetes strain of Arthrobacter chlorophenolicus A6. The substituted phenols investigated in this study were 4-chlorophenol (4-CP), 4- bromophenol (4-BP) and 4-nitrophenol (4-NP) both as single substrate and mixed substrate system. As a first step, optimization of culture media components were carried out employing statistical design of experiments including 2-level factorial design, central composite design and response surface methodology (RSM). The media optimization results revealed 100% of 4-chlorophenol biodegradation efficiency with a maximum specific growth rate of 0.093 h-1 at an optimum composition of (g l-1) K2HPO4 initial concentration as high as 375 mgl-1 within a time period of 40 h, which is so far the best 4-CP degradation concentration in literature in batch shake flask. 2.62, KH2PO4 0.4, NH4NO3 0.58, MgSO4 0.171, CaCl2 0.038 and FeCl3 0.002 in the medium. Similarly the RSM optimized result of physical parameter revealed that at the optimized settings of 7.5 pH, 207 rpm, 29.6 DC and 39.5 h inoculum age, 100% biodegradation of 4-CP even at a high initial concentration of 300 mg l-1 could be achieved within a short span of 18.5 h of culture. The enhancement in the 4-CP biodegradation efficiency was found to be 23% higher than that obtained at the unoptimized settings of the culture conditions. In addition, at the optimized culture conditions the actinomycetes could degrade 4-CP at an Biomass growth data were also obtained, which sugested that even though 4-NP was degraded prior to 4-CP and 4-BP, it had a stronger negative impact on the cells than the other two. The maximum yield value obtained in the present study (0.2152 gg-1 at 125, 125, and 50 mgl-1 of 4-CP, 4-BP and 4-NP respectively) also less when compared with several literatures reported values which ranges from 0.44-0.88 gg-1 on biodegradation of phenolic compounds using different microbial culture. inhibition constant (Ki) of 5FU. I also persuaded in silico molecular dynamics stimulation to confer interactions of uracil and its selective inhibitor 5FU with UPRT enzyme. The computational results revealed key residues of UPRT involved in ligand binding interactions. In this part of my thesis, I have developed a biodegradable chitosan based nanocarrier (NC) for protein encapsulati.