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BioMed Research International
Volume 2015, Article ID 847945, 14 pages
Review Article

Bioenergetics and the Role of Soluble Cytochromes c for Alkaline Adaptation in Gram-Negative Alkaliphilic Pseudomonas

T. Matsuno1,2 and I. Yumoto1,2

1Laboratory of Environmental Microbiology, Graduate School of Agriculture, Hokkaido University, Kita-ku, Sapporo 060-8589, Japan
2Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi Toyohira-ku, Sapporo 062-8517, Japan

Received 25 April 2014; Revised 27 November 2014; Accepted 29 November 2014

Academic Editor: Stanley Brul

Copyright © 2015 T. Matsuno and I. Yumoto. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Very few studies have been conducted on alkaline adaptation of Gram-negative alkaliphiles. The reversed difference of H+ concentration across the membrane will make energy production considerably difficult for Gram-negative as well as Gram-positive bacteria. Cells of the alkaliphilic Gram-negative bacterium Pseudomonas alcaliphila AL15-21T grown at pH 10 under low-aeration intensity have a soluble cytochrome c content that is 3.6-fold higher than that of the cells grown at pH 7 under high-aeration intensity. Cytochrome c-552 content was higher (64% in all soluble cytochromes c) than those of cytochrome c-554 and cytochrome c-551. In the cytochrome c-552-dificient mutant grown at pH 10 under low-aeration intensity showed a marked decrease in [h−1] (40%) and maximum cell turbidity (25%) relative to those of the wild type. Considering the high electron-retaining abilities of the three soluble cytochromes c, the deteriorations in the growth of the cytochrome c-552-deficient mutant could be caused by the soluble cytochromes c acting as electron storages in the periplasmic space of the bacterium. These electron-retaining cytochromes c may play a role as electron and H+ condenser, which facilitate terminal oxidation at high pH under air-limited conditions, which is difficult to respire owing to less oxygen and less H+.