Title: Differential Regulation of the Two Ferrochelatase Paralogues in Shewanella loihica PV-4 in Response to Environmental Stresses

Abstract

ABSTRACT Determining the function and regulation of paralogues is important in understanding microbial functional genomics and environmental adaptation. Heme homeostasis is crucial for the survival of environmental microorganisms. MostShewanellaspecies encode two paralogues of ferrochelatase, the terminal enzyme in the heme biosynthesis pathway. The function and transcriptional regulation of two ferrochelatase genes,hemH1andhemH2, were investigated inShewanellaloihicaPV-4. The disruption ofhemH1but nothemH2resulted in a significant accumulation of extracellular protoporphyrin IX (PPIX), the precursor to heme, and decreased intracellular heme levels.hemH1was constitutively expressed, and the expression ofhemH2increased whenhemH1was disrupted. The transcription ofhemH1was regulated by the housekeeping sigma factor RpoD and potentially regulated by OxyR, whilehemH2appeared to be regulated by the oxidative stress-associated sigma factor RpoE2. When an oxidative stress condition was mimicked by adding H₂O₂to the medium or exposing the culture to light, PPIX accumulation was suppressed in the ΔhemH1mutant. Consistently, transcriptome analysis indicated enhanced iron uptake and suppressed heme synthesis in the ΔhemH1mutant. These data indicate that the two paralogues are functional in the heme synthesis pathway but regulated by environmental conditions, providing insights into the understanding of bacterial response to environmental stresses and a great potential to commercially produce porphyrin compounds. IMPORTANCEShewanellais capable of utilizing a variety of electron acceptors for anaerobic respirationmore » because of the existence of multiplec-type cytochromes in which heme is an essential component. The cytochrome-mediated electron transfer across cellular membranes could potentially be used for biotechnological purposes, such as electricity generation in microbial fuel cells and dye decolorization. However, the mechanism underlying the regulation of biosynthesis of heme and cytochromes is poorly understood. Our study has demonstrated that two ferrochelatase genes involved in heme biosynthesis are differentially regulated in response to environmental stresses, including light and reactive oxygen species. This is an excellent example showing how bacteria have evolved to maintain cellular heme homeostasis. More interestingly, the high yields of extracellular protoporphyrin IX by theShewanella loihicaPV-4 mutants could be utilized for commercial production of this valuable chemical via bacterial fermentation.« less

Authors:

Qiu, Dongru ^[1]; Xie, Ming ^[2]; Dai, Jingcheng ^[3]; An, Weixing ^[3]; Wei, Hehong ^[3]; Tian, Chunyuan ^[4]; Kempher, Megan L. ^[2]; Zhou, Aifen ^[2]; He, Zhili ^[2]; Gu, Baohua ^[5]; Zhou, Jizhong ^[6]

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+ Show Author Affiliations

1. Chinese Academy of Sciences (CAS), Wuhan (China). Inst. of Hydrobiology; Univ. of Chinese Academy of Sciences, Beijing (China); Univ. of Oklahoma, Norman, OK (United States). Inst. for Environmental Genomics, Dept. of Microbiology and Plant Biology
2. Univ. of Oklahoma, Norman, OK (United States). Inst. for Environmental Genomics, Dept. of Microbiology and Plant Biology
3. Chinese Academy of Sciences (CAS), Wuhan (China). Inst. of Hydrobiology; Univ. of Chinese Academy of Sciences, Beijing (China)
4. Hubei Engineering Univ., Xiaogan (China). School of Life Sciences and Technology
5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Earth Science Division
6. Univ. of Oklahoma, Norman, OK (United States). Inst. for Environmental Genomics, Dept. of Microbiology and Plant Biology; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Science Division; Tsinghua Univ., Beijing (China). State Key Joint Lab. of Environment Simulation and Pollution Control, School of Environment

Publication Date:

Fri Jun 10 00:00:00 EDT 2016

Research Org.:

Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC); Chinese Academy of Sciences (CAS)

OSTI Identifier:

1378739

Alternate Identifier(s):

OSTI ID: 1394586

Grant/Contract Number:  

AC02-05CH11231; FG02-07ER64383; Y15103-1-401; AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Applied and Environmental Microbiology

Additional Journal Information:

Journal Volume: 82; Journal Issue: 17; Journal ID: ISSN 0099-2240

Publisher:

American Society for Microbiology

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; 60 APPLIED LIFE SCIENCES