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

Abstract EN

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 μ max [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+.