Impact of carbon dioxide gas and carbonate ions on the growth of Escherichia coli K-12 B23 and on the induced β-galactosidase activity: exploring models for global regulation

Global regulation of cell metabolism and lac operon expression in response to CO2 in Escherichia coli K-12 B23 was investigated. Two experimental systems were applied to test the effects of CO2. One of the systems involved adding CO2 as bicarbonate (ion-phase system) to three separate test cultures; the concentrations of sodium bicarbonate tested were 0.0 M, 39.4 mM, and 61.5 mM Na2CHO3. Carbon dioxide was added as a gas in the second system, known as the gas-phase system. The types of gases used in this system were air, CO2 mixture (5% CO2, 10.4% H2, and 84.5% N2) and pure N2 at 850 cc/min, 110 cc/min and 120 cc/min respectively. Our results indicate the bicarbonate had limited effects on cell growth and enzyme activity in β-galactosidase (β-gal). But we found that anaerobic conditions in our gas system hindered cell growth greatly but significantly increased the levels of βgalactosidase in the gas-phase experiment. The results were tied into three models of global regulation: catabolite regulation, stringent response and redox regulation. From this experiment we concluded that anaerobic conditions could have affected intracellular levels of adenosine 3’,5’-cyclic monophosphate (cAMP), cyclic AMP receptor protein (CRP), and/or guanosine 3’,5’-bispyrophosphate (ppGpp); which in turn regulated downstream activities such as growth rate and expression of the lac operon.