KatG Is the Primary Detoxifier of Hydrogen Peroxide Produced by Aerobic Metabolism in Bradyrhizobium japonicum

Abstract

Bacteria are exposed to reactive oxygen species from the environment and from those generated by aerobic metabolism. Catalases are heme proteins that detoxify H 2 O 2 , and many bacteria contain more than one catalase enzyme. Also, the nonheme peroxidase alkyl hydroperoxide reductase (Ahp) is the major scavenger of endogenous H 2 O 2 in Escherichia coli. Here, we show that aerobically grown Bradyrhizobium japonicum cells express a single catalase activity. Four genes encoding putative catalases in the B. japonicum genome were identified, including a katG homolog encoding a catalase-peroxidase. Deletion of the katG gene resulted in loss of catalase activity in cell extracts and of exogenous H 2 O 2 consumption by whole cells. The katG strain had a severe aerobic growth phenotype but showed improved growth in the absence of O 2 . By contrast, a B. japonicum ahpCD mutant grew well aerobically and consumed H 2 O 2 at wild-type rates. A heme-deficient hemA mutant expressed about one-third of the KatG activity as the wild type but grew well aerobically and scavenged low concentrations of exogenous H 2 O 2 . However, cells of the hemA strain were deficient in consumption of high concentrations of H 2 O 2 and were very sensitive to killing by short exposure to H 2 O 2 . In addition, KatG activity did not decrease as a result of mutation of the gene encoding the transcriptional activator OxyR. We conclude that aerobic metabolism produces toxic levels of H 2 O 2 in B. japonicum, which is detoxified primarily by KatG. Furthermore, the katG level sufficient for detoxification does not require OxyR.

The Catalase-Peroxidase KatG Is Required for Virulence of Xanthomonas campestris pv. campestris in a Host Plant by Providing Protection against Low Levels of H 2 O 2

“…Nevertheless, the katA katG double mutant had no aerobic growth defects when grown in either liquid or solid enriched medium (SB). This is unlike a Bradyrhizobium japonicum katG mutant that has defects in aerobic growth, suggesting that the gene has a primary role in the detoxification of H 2 O 2 generated from aerobic life (22). We have shown in X. campestris pv.…”

Positive Control of Ferric Siderophore Receptor Gene Expression by the Irr Protein inBradyrhizobium japonicum

“…To do this, each open reading frame plus 500 bp of flanking DNA was isolated by PCR using genomic DNA as a template and ligated into pBluescript SKϩ. For each construct, a deletion removing the open reading frame was constructed by inverse PCR as described previously (19), and the deleted fragment was replaced with an ⍀ DNA cassette carrying genes for spectinomycin and streptomycin resistance (20). The construct was introduced into pLO1 (14), mobilized into strain LO, and selected for double recombinants as described previously (19).…”

Posttranslational control of transcription factor FixK 2 , a key regulator for the Bradyrhizobium japonicum –soybean symbiosis

“…(ii) When the transcriptome of micro-oxically grown strain 8854 was compared with that of the WT grown under the same condition, we noticed several differentially expressed genes that were also differentially expressed in the H 2 O 2 -stressed WT compared with untreated WT. Among them were 2 genes with 8.7-and 5.9-fold increased expression, ahpC and ahpD, coding for alkyl hydroperoxide reductase, an H 2 O 2 detoxification enzyme (22).…”