Open Access Highly Accessed Research article

Knock-out of SO1377 gene, which encodes the member of a conserved hypothetical bacterial protein family COG2268, results in alteration of iron metabolism, increased spontaneous mutation and hydrogen peroxide sensitivity in Shewanella oneidensis MR-1

Weimin Gao1, Yongqing Liu1, Carol S Giometti2, Sandra L Tollaksen2, Tripti Khare2, Liyou Wu1, Dawn M Klingeman1, Matthew W Fields3 and Jizhong Zhou14*

Author Affiliations

1 Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

2 Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA

3 Department of Microbiology, Miami University, Oxford, OH 45056, USA

4 Institute for Environmental Genomics and Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019, USA

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BMC Genomics 2006, 7:76  doi:10.1186/1471-2164-7-76

Published: 6 April 2006

Abstract

Background

Shewanella oneidensis MR-1 is a facultative, gram-negative bacterium capable of coupling the oxidation of organic carbon to a wide range of electron acceptors such as oxygen, nitrate and metals, and has potential for bioremediation of heavy metal contaminated sites. The complete 5-Mb genome of S. oneidensis MR-1 was sequenced and standard sequence-comparison methods revealed approximately 42% of the MR-1 genome encodes proteins of unknown function. Defining the functions of hypothetical proteins is a great challenge and may need a systems approach. In this study, by using integrated approaches including whole genomic microarray and proteomics, we examined knockout effects of the gene encoding SO1377 (gi24372955), a member of the conserved, hypothetical, bacterial protein family COG2268 (

    C
lusters of
    O
rthologous
    G
roup) in bacterium Shewanella oneidensis MR-1, under various physiological conditions.

Results

Compared with the wild-type strain, growth assays showed that the deletion mutant had a decreased growth rate when cultured aerobically, but not affected under anaerobic conditions. Whole-genome expression (RNA and protein) profiles revealed numerous gene and protein expression changes relative to the wild-type control, including some involved in iron metabolism, oxidative damage protection and respiratory electron transfer, e. g. complex IV of the respiration chain. Although total intracellular iron levels remained unchanged, whole-cell electron paramagnetic resonance (EPR) demonstrated that the level of free iron in mutant cells was 3 times less than that of the wild-type strain. Siderophore excretion in the mutant also decreased in iron-depleted medium. The mutant was more sensitive to hydrogen peroxide and gave rise to 100 times more colonies resistant to gentamicin or kanamycin.

Conclusion

Our results showed that the knock-out of SO1377 gene had pleiotropic effects and suggested that SO1377 may play a role in iron homeostasis and oxidative damage protection in S. oneidensis MR-1.