Genes Important for Catalase Activity in Enterococcus faecalis

Michael Baureder,Lars Hederstedt,Riccardo Manganelli

doi:10.1371/journal.pone.0036725

Abstract

Little in general is known about how heme proteins are assembled from their constituents in cells. The Gram-positive bacterium Enterococcus faecalis cannot synthesize heme and does not depend on it for growth. However, when supplied with heme in the growth medium the cells can synthesize two heme proteins; catalase (KatA) and cytochrome bd (CydAB). To identify novel factors important for catalase biogenesis libraries of E. faecalis gene insertion mutants were generated using two different types of transposons. The libraries of mutants were screened for clones deficient in catalase activity using a colony zymogram staining procedure. Analysis of obtained clones identified, in addition to katA (encoding the catalase enzyme protein), nine genes distributed over five different chromosomal loci. No factors with a dedicated essential role in catalase biogenesis or heme trafficking were revealed, but the results indicate the RNA degradosome (srmB, rnjA), an ABC-type oligopeptide transporter (oppBC), a two-component signal transducer (etaR), and NADH peroxidase (npr) as being important for expression of catalase activity in E. faecalis. It is demonstrated that catalase biogenesis in E. faecalis is independent of the CydABCD proteins and that a conserved proline residue in the N-terminal region of KatA is important for catalase assembly.

Highlights

Catalase is a well-known enzyme found in all three domains of life
The bacterium can produce a NADH peroxidase (Npr) that degrades hydrogen peroxide to water and which seems sufficient for protection against high concentrations of hydrogen peroxide when heme is not available [4]
We made use of a zymogram staining reagent, modified from that described by Hanker and Rabin [6], which leads to the formation of a purple color around colonies due to catalase activity

Summary

Introduction

Catalase is a well-known enzyme found in all three domains of life. It plays a role in oxidative stress defense by degrading hydrogen peroxide to molecular oxygen and water [1].Enterococcus faecalis is one of the few species of lactic acid bacteria that exhibit catalase activity, but only when grown in the presence of heme [2]. Catalase is a well-known enzyme found in all three domains of life. It plays a role in oxidative stress defense by degrading hydrogen peroxide to molecular oxygen and water [1]. E. faecalis catalase (KatA) belongs to the group of heme-containing mono-functional catalases (EC 1.11.1.6). It is a homo-tetrameric protein containing one heme group (protoheme IX) per subunit and its crystal structure has been determined [3]. Catalase protects E. faecalis against hydrogen peroxide stress but is not the only enzyme with this function. E. faecalis cells cannot synthesize heme and have to take it up from the environment in order to form active catalase

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Conclusion