Combined effect of loss of the caa3 oxidase and Crp regulation drives Shewanella to thrive in redox-stratified environments

Abstract

Shewanella species are a group of facultative Gram-negative microorganisms with remarkable respiration abilities that allow the use of a diverse array of terminal electron acceptors (EA). Like most bacteria, S. oneidensis possesses multiple terminal oxidases, including two heme-copper oxidases (caa 3 -and cbb 3 -type) and a bd-type quinol oxidase. As aerobic respiration is energetically favored, mechanisms underlying the fact that these microorganisms thrive in redox-stratified environments remain vastly unexplored. In this work, we discovered that the cbb 3 -type oxidase is the predominant system for respiration of oxygen (O 2 ), especially when O 2 is abundant. Under microaerobic conditions, the bd-type quinol oxidase has a significant role in addition to the cbb 3 -type oxidase. In contrast, multiple lines of evidence suggest that under test conditions the caa 3 -type oxidase, an analog to the mitochondrial enzyme, has no physiological significance, likely because of its extremely low expression. In addition, expression of both cbb 3 -and bd-type oxidases is under direct control of Crp (cAMP receptor protein) but not the well-established redox regulator Fnr (fumarate nitrate regulator) of canonical systems typified in Escherichia coli. These data, collectively, suggest that adaptation of S. oneidensis to redox-stratified environments is likely due to functional loss of the caa 3 -type oxidase and switch of the regulatory system for respiration.

The Terminal Oxidase cbb 3 Functions in Redox Control of Magnetite Biomineralization in Magnetospirillum gryphiswaldense

“…Consistent with our previously reported findings that deletion of Mgfnr affected neither oxygen consumption nor microaerobic magnetite biomineralization in the absence of nitrate (Li et al, submitted), we found that the expression level of the three cbb 3 , aa 3 , and bd terminal oxidase operons was increased by O 2 but not regulated by the global oxygen sensor MgFnr, similar to what was shown previously for Shewanella oneidensis (33). This suggested that some as-yet-unknown O 2 regulators probably mediate the expression of aerobic terminal oxidase genes in response to different oxygen concentrations.…”

A Matter of Timing: Contrasting Effects of Hydrogen Sulfide on Oxidative Stress Response in Shewanella oneidensis

“…We have previously shown that S. oneidensis prefers insoluble to soluble electron acceptors for respiration, such as Fe (III) oxide versus oxygen, thus preventing endogenous generation of ROS from autoxidation of components of the respiratory chain (35,59). In addition, unlike other organisms containing cytochrome caa 3 -type and cbb 3 -type oxidases, where the low-affinity (caa 3 -type) oxidase plays a dominant role under high-oxygen conditions and the cbb 3 oxidase is induced only at low O 2 concentrations, S. oneidensis utilizes the cbb 3 -type oxidase under both high-and low-oxygen conditions and does not express the caa 3 oxidase (39,40). As respiration of oxygen by the cbb 3 oxidase is relatively slow, less ROS would be generated.…”

Protection from Oxidative Stress Relies Mainly on Derepression of OxyR-Dependent KatB and Dps in Shewanella oneidensis

“…To detect an interaction, vectors containing "bait" (DNA) and "target" (DNA-binding regulator) are cotransformed into BacterioMatch II Validation Reporter competent cells, of which those having positive DNA-protein interactions are able to grow on 3-amino-1,2,4-triazole (3-AT). To calibrate this system, we took advantage of S. oneidensis Crp, which was shown previously to bind to motif sequences upstream of the cyd operon (cytochrome bd oxidase) (55,56). The crp SO gene was cloned into the target vector pTRG, and the cyd promoter containing the Crp SObinding motif was generated by PCR and inserted into the reporter vector pBXcmT.…”

“…Although multiple scavenging proteins are encoded in the genome, KatB is apparently the most pivotal one for detoxifying exogenous H 2 O 2 . The dispensability of KatG-2 is likely due to its low expression levels, a scenario similar to the functional loss of cytochrome caa 3 oxidase (56). Given that expression of the katG-1 gene is responsive to H 2 O 2 , why the deletion of the gene fails to elicit any detectable impact remains to be determined.…”