Group X Aldehyde Dehydrogenases of Pseudomonas aeruginosa PAO1 Degrade Hydrazones

Abstract

Hydrazones are natural and synthetic compounds containing a C‫؍‬N-N moiety. Here we found that the opportunistic pathogen Pseudomonas aeruginosa PAO1 produced NAD ؉ -or NADP ؉ -dependent hydrazone dehydrogenase (HDH), which converts hydrazones to the corresponding hydrazides and acids rather than to the simple hydrolytic product aldehydes. Gene cloning indicated that the HDH is part of the group X aldehyde dehydrogenase (ALDH) family, which is distributed among bacteria, although the physiological roles of the ALDH family remain unknown. The PAO1 strain upregulated HDH in the presence of the hydrazone adipic acid bis(ethylidene hydrazide) (AEH). Gene disruption of the HDH-encoding hdhA (PA4022) decreased growth rates in culture medium containing AEH as the sole carbon source, and this effect was more obvious in the double gene disruption of hdhA and its orthologous exaC (PA1984), indicating that these genes are responsible for hydrazone utilization. Recombinant proteins of group X ALDHs from Escherichia coli, Paracoccus denitrificans, and Ochrobactrum anthropi also acted as HDHs in that they produced HDH activity in the cells and degraded hydrazones. These findings indicated the physiological roles of group X ALDHs in bacteria and showed that they comprise a distinct ALDH subfamily.

Ethanolamine Catabolism in Pseudomonas aeruginosa PAO1 Is Regulated by the Enhancer-Binding Protein EatR (PA4021) and the Alternative Sigma Factor RpoN

“…5B and C). As mentioned earlier, PA4022 was reported to be involved in the breakdown of hydrazones (29), and it was interesting to find that a hydrazone did positively regulate expression of the PA4022 gene. Hydrazones are compounds having a basic structure of R 1 R 2 CANNR 3 R 4 (39).…”

“…The synthesis of valeric acid ethylidene hydrazide, referred simply to as hydrazone, was done as described previously, with minor modifications (28,29). Briefly, in a round-bottom flask, valeric acid hydrazide (250 mg, 2.2 mmol) was dissolved in tetrahydrofuran and cooled in an ice bath.…”

“…This genetic redundancy would explain why PA4022 was nonessential for growth on ethanolamine, i.e., ExaC was expressed or present under the conditions used. Interestingly, in addition to accepting acetaldehyde as a substrate, PA4022 was shown to catalyze oxidative hydrolysis of the carbon-nitrogen double bond of hydrazones to generate hydrazides and acetate as products (29). Consumption of the acetate product was believed to be responsible for the growth of P. aeruginosa PAO1 on hydrazones (29).…”

“…2B). In addition to PA4022, the PA1984 (exaC) gene also encodes an acetaldehyde dehydrogenase that was originally identified as a possible component of the ethanol oxidation system in P. aeruginosa (29,36). PA4022 and ExaC are nearly identical proteins (98% identity), and both have been biochemically characterized as acetaldehyde dehydrogenases (29).…”

“…1). PA4022 encodes a NAD ϩ -dependent acetaldehyde dehydrogenase that has no significant homology to the EutE acetaldehyde dehydrogenases found in Enterobacteriaceae (29). PA4023 encodes a homolog of the ethanolamine transporter Eat, a member of the amino acid-polyamine-organocation family (35).…”