A Hydrophobic Small Protein, BpOF4_01690, Is Critical for Alkaliphily of Alkaliphilic Bacillus pseudofirmus OF4.

Tetsuaki Takahashi,Masahiro Ito,Terry A Krulwich

doi:10.3389/fmicb.2018.01994

Abstract

A monocistronic small protein, BpOF4_01690, was annotated in alkaliphilic Bacillus pseudofirmus OF4. It comprises 59 amino acids and is hydrophobic. Importantly, homologs of this protein were identified only in alkaliphiles. In this study, a mutant with a BpOF4_01690 gene deletion (designated Δ01690) exhibited weaker growth than that of the wild type in both malate-based defined and glucose-based defined media under low-sodium conditions at pH 10.5. Additionally, the enzymatic activity of the respiratory chain of Δ01690 was much lower than that of the wild type. These phenotypes were similar to those of a ctaD deletion mutant and an atpB-F deletion mutant. Therefore, we hypothesize that BpOF4_01690 plays a critical role in oxidative phosphorylation under highly alkaline conditions.

Highlights

Alkaliphilic microorganisms usually grow vigorously in highly alkaline environments and require Na+ for their growth (Horikoshi, 1991; Krulwich et al, 2011; Preiss et al, 2015)
It is extremely difficult to produce and utilize a proton-motive force (PMF) at highly alkaline pH, ATP synthesis by oxidative phosphorylation (OXPHOS) using F1Fo-ATP synthase is driven by PMF in alkaliphilic Bacillus species (Guffanti and Krulwich, 1994)
Descriptions of a unique “alkaliphily” motif in the c-ring of ATP synthase from alkaliphilic B. pseudofirmus OF4 had been noted in earlier studies of alkaliphilic bacteria (Liu et al, 2009; Fujisawa et al, 2010)

Summary

INTRODUCTION

Alkaliphilic microorganisms usually grow vigorously in highly alkaline environments and require Na+ for their growth (Horikoshi, 1991; Krulwich et al, 2011; Preiss et al, 2015). It has been suggested that accumulation of protons on the outer surface of the cytoplasmic membrane (Yoshimune et al, 2010) facilitates energy coupling that is more efficient than usual, thereby increasing the feasibility of ATP synthesis in a highly alkaline pH environment (Krulwich, 1995). The alkaliphilic Bacillus clarkia K24-1U was proposed to efflux protons by the respiratory chain, accumulating them on the outer surface of the cytoplasmic membrane (Cherepanov et al, 2003; Mulkidjanian, 2006). Another possibility is the activity of an unidentified proton carrier that depends on the dielectric properties of the membrane potential (Liu et al, 2007). The mutational loss of membrane cardiolipin did not significantly affect alkaliphile ATP synthesis in alkaliphilic B. pseudofirmus OF4 (Liu et al, 2014)

A Small Protein Involved in Alkaliphilic Adaptation

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSION