Effect of chelating agents and respiratory inhibitors on regulation of the cadA gene in Escherichia coli

Abstract

The cadA gene that encodes lysine decarboxylase in Escherichia coli is induced by low pH and - during anaerobic growth - by the substrate, lysine. We used operon fusions of cadA to lacZ to investigate the effects of aeration on cadA regulation. When an insertion mutation in osmZ (= hns) was introduced, a cadA-lacZ fusion was derepressed in the presence of air to approximately the same level as seen during anaerobic growth. However, the pH-dependent regulation of cadA was not affected by osmZ. Introduction of mutations in rpoS, fur, or fnr had no significant effect on cadA expression. However, defects in arcB or arcA largely abolished expression of cadA during anaerobic growth. Nonetheless, strains defective in both arcB and osmZ showed the same high cadA-lac expression in air as seen in the single osmZ derivatives. Blocking the respiratory chain with mutations or chemical inhibitors also caused derepression of a cadA-lacZ fusion in air, while agents affecting the proton gradient had no effect. Derepression of cadA in air was also mediated by several chelating agents, in particular by methoxyindole carboxylic acid. Addition of Fe2+ overcame this effect. Chelating agents also abolished the expression during aerobic growth of several genes known to be under arcAB control and which are normally repressed during anaerobic growth but induced in the presence of air. This implies that the effect of chelating agents on cadA expression is mediated via the arcAB regulatory system.

CadC-Mediated Activation of the <i>cadBA</i> Promoter in <i>Escherichia coli</i>

“…These results clearly indicate that H-NS binding upstream of the CadC-binding sites causes a transcriptional silencing of the cadBA -operon at neutral external pH. Reams et al [1997] reported that a cadA-lacZ fusion in an hns mutant was de-repressed under aerobic conditions to approximately the same level as observed during anaerobic growth. Therefore, the same strains as described above were used to determine reporter activity in cells grown under aerobic and anaerobic conditions.…”

Bacterial strategies to inhabit acidic environments.

“…The major metabolic pathway that produces carbon dioxide is the TCA cycle, and TCA activity declines when oxygen is limited through linkage with the respiratory chain. Reams et al (1997) showed that blocking the respiratory chain derepressed a cadA-lacZ fusion gene under aerobic condi-tions. The induction of lysine decarboxylase increased the growth yield in a mutant deficient in heme synthesis, but not in the wild type in well-buffered acid medium (Futatsugi et al, 1997).…”

Study on antitumor activity of metal-based diketone complexes

“…Organometallic complexes have tremendous potential use as anticancer agents, due to their wide and diverse structural types, varied ligand bonding modes (Dorcier et al, 2008;Allardyce et al, 2005). Among these, acetylacetone metals exhibit inhibitory effect on superoxide anion radical (O 2 Á ), which show broad-spectrum antibiosis, virus resistance, and antitumor activity (Ream, 1997;King, 1994;Wang et al, 1997). To the best of our knowledge, there is no report on antitumor activity evaluation of acetylacetone metal containing Mo and Co. Mo and Co are the essential trace elements for human beings, with biological activity including relevant molybdoenzymes (Ream, 1997), and the composition of Vb-12.…”

“…Among these, acetylacetone metals exhibit inhibitory effect on superoxide anion radical (O 2 Á ), which show broad-spectrum antibiosis, virus resistance, and antitumor activity (Ream, 1997;King, 1994;Wang et al, 1997). To the best of our knowledge, there is no report on antitumor activity evaluation of acetylacetone metal containing Mo and Co. Mo and Co are the essential trace elements for human beings, with biological activity including relevant molybdoenzymes (Ream, 1997), and the composition of Vb-12. García-Tojal et al (2001) reported the antitumor activity of transition metal complexes including Cu 2?…”