Analysis of redox responses during TNT transformation by Clostridium acetobutylicum ATCC 824 and mutants exhibiting altered metabolism

The transformation of trinitrotoluene (TNT) by several mutant strains of Clostridium acetobutylicum has been examined to analyze the maximal rate of initial transformation, determine the effects of metabolic mutations of the host on transformation rate, and to assess the cell metabolic changes brought about during TNT transformation. Little difference in the maximal rate of TNT degradation in early acid phase cultures was found between the parental ATCC 824 strain and strains altered in the acid forming pathways (phosphotransacetylase, or butyrate kinase) or in a high-solvent-producing strain (mutant B). This result is in agreement with the previous findings of a similar degradation rate in a degenerate strain (M5) that had lost the ability to produce solvent. A series of antisense constructs were made that reduced the expression of hydA, encoding the Fe-hydrogenase, or hydE and hydF, genes encoding hydrogenase maturating proteins. While the antisense hydA strain had only ∼30 % of the activity of wild type, the antisense hydE strain exhibited a TNT degradation rate around 70 % that of the parent. Overexpression of hydA modestly increased the TNT degradation rate in acid phase cells, suggesting the amount of reductant flowing into hydrogenase rather than the hydrogenase level itself was a limiting factor in many situations. The redox potential, hydrogen evolution, and organic acid metabolites produced during rapid TNT transformation in early log phase cultures were measured. The redox potential of the acid-producing culture decreased from -370 to -200 mV immediately after addition of TNT and the hydrogen evolution rate decreased, lowering the hydrogen to carbon dioxide ratio from 1.4 to around 1.1 for 15 min. During the time of TNT transformation, the treated acidogenic cells produced less acetate and more butyrate. The results show that during TNT transformation, the cells shift metabolism away from hydrogen formation to reduction of TNT and the resulting effects on cell redox cofactors generate a higher proportion of butyrate.

Characterization of the effects of Bcl-2 and Bcl-xl deletion mutant expression in cell lines used for antibody production

Strategies to maximize monoclonal antibody (MAb) yields by in vitro production methods entail that hybridoma cells be maintained at high density. Approaches to increase culture density and antibody yields from hybridomas by inhibiting apoptosis through over-expression of exogenous Bcl-2 family genes have produced variable results. In order to determine if expression of mutant forms of Bcl-2 and Bcl-xl could increase viable culture densities and batch MAb yields when compared to parental cell lines, recombinant delta loop deletion mutant of these apoptotic inhibitory genes were expressed in a myeloma and two hybridoma cell lines. Expression of either Bcl-2-delta or Bcl-xl-delta in P3x63Ag8.653 myeloma cells did not significantly increase viable cell densities in cultures over time. However, the rapid post-peak decline in viable cell density was significantly reduced in Bcl-xl-delta-expressing hybridoma cell lines 552 and 7.16.4 and in Bcl-2-expressing hybridoma 7.16.4. Significant increases in MAb yield were only observed in cultures of Bcl-xl-delta-expressing hybridoma 7.16.4. Annexin staining in hybridoma 7.16.4 confirmed that apoptosis was the primary means of cell death in this cell line, and expression of Bcl-2-delta and Bcl-xl-delta inhibited programmed cell death. These results suggest that cell viability in cultures can be improved by transfection and selection of hybridomas that express delta loop deletion mutant forms of Bcl-2 family genes; however, improvements in MAb yields are dependent upon the genetic background of each manipulated cell line.