Biodegradation kinetics of chlorinated ethylenes by Methylosinus trichosporium (OB3b)

The focus of this work is on biodegradation of chlorinated ethylenes (CEs) by Methylosinus trichosporium strain OB3b. The compound trans-1,2-dichloroethylene was degraded at higher concentrations (6.52 mM) and faster rates than the other dichloroethylenes (DCEs). The degradation of cis-1,2-dichloroethylene and 1,1-DCE occurred only at concentrations under 309 and 206 μM, respectively. Using the Michaelis-Menten model, the maximum velocities (V_max) for 1,1-DCE, cis-1,2-DCE, trans-1,2- DCE, and TCE degradation were estimated to be 16, 28, 21,250 and 14 nmol/hr/mg protein, respectively. The respective Michaelis constants (K_m) were 83, 97.2, 973, and 105.7 μM. In a mixture of TCE and DCE, the extent of TCE degradation depended on the DCE isomer present and its concentration. Below 309 μM, trans-1,2-DCE did not inhibit TCE degradation. At 309 μM DCE, TCE degradation was completely inhibited with 1,1-DCE but to a lesser extent with cis-1,2-DCE. At 206 μM DCE, only 1,1-DCE inhibited TCE degradation. The addition of 6 μM of 1,1-DCE or tetrachloroethylene (PCE) resulted in a decrease of the V_max for trans-1,2-DCE degradation to 2.13, and 7.03 μmol/hr/mg protein, respectively. However, the V_max was unaffected when 6.3 μM TCE was present. The introduction of 1,1-DCE decreased the K_m for trans-1,2-DCE to 214 μM while PCE decreased it to 732 μM. In contrast, the K_m for trans-1,2-DCR was increased to 1399 μM by the addition of TCE. The inhibition of trans-1,2-DCE degradation by other CEs may be a combination of competitive and mixed noncompetitive interactions. Competitive inhibition was evident in the interaction between trans-1,2-DCE and TCE where The V_max for trans-1,2-DCE degradation was unchanged by the presence of TCE but the K_m was increased. Mixed-noncompetitive inhibition was evident in the inhibition of trans-1,2-DCE by PCE and 1,1-DCE, where the V_max and K_m were decreased.