Measuring magnetosomal pH of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using pH-sensitive fluorescent proteins

• Published in: Bioscience, biotechnology, and biochemistry Vol. 82; no. 7; pp. 1243 - 1251
• Main Authors: Eguchi, Yukako, Fukumori, Yoshihiro, Taoka, Azuma
• Format: Journal Article
• Language: English
• Published: England Taylor & Francis 03.07.2018; Oxford University Press
• Subjects: Bacterial organelle; intracellular compartments; magnetosome; magnetotactic bacteria; single live cell pH measurement; Bacterial organelle; intracellular compartments; magnetotactic bacteria; single live cell pH measurement; magnetosome
• ISSN: 0916-8451; 1347-6947
• DOI: 10.1080/09168451.2018.1451739

Magnetotactic bacteria synthesize uniform-sized and regularly shaped magnetic nanoparticles in their organelles termed magnetosomes. Homeostasis of the magnetosome lumen must be maintained for its role accomplishment. Here, we developed a method to estimate the pH of a single living cell of the magnetotactic bacterium Magnetospirillum magneticum AMB-1 using a pH-sensitive fluorescent protein E 2 GFP. Using the pH measurement, we estimated that the cytoplasmic pH was approximately 7.6 and periplasmic pH was approximately 7.2. Moreover, we estimated pH in the magnetosome lumen and cytoplasmic surface using fusion proteins of E 2 GFP and magnetosome-associated proteins. The pH in the magnetosome lumen increased during the exponential growth phase when magnetotactic bacteria actively synthesize magnetite crystals, whereas pH at the magnetosome surface was not affected by the growth stage. This live-cell pH measurement method will help for understanding magnetosome pH homeostasis to reveal molecular mechanisms of magnetite biomineralization in the bacterial organelle. We succeeded in measuring pH in the magnetosomes within living magnetotactic bacterium Magnetospirillum magneticum AMB-1 cells using the pH-sensitive fluorescent protein.