Effects of dissolved oxygen concentration and iron addition on immediate-early gene expression of Magnetospirillum gryphiswaldense MSR-1

Abstract

We report effects of dissolved oxygen (DO) concentration and iron addition on gene expression of Magnetospirillum gryphiswaldense MSR-1 cells during fermentations, focusing on 0.25-24 h after iron addition. The DO was strictly controlled at 0.5% or 5% O 2 , and compared with aerobic condition. Uptake of iron (and formation of magnetosomes) was only observed in the 0.5% O 2 condition where there was little difference in cell growth and carbon consumption compared to the 5% O 2 condition. Quantitative reverse transcription PCR analysis showed a rapid (within 0.25 h) genetic response of MSR-1 cells after iron addition for all the genes studied, except for MgFnr (oxygen sensor gene) and fur (ferric uptake regulator family gene), and which in some cases was oxygen-dependent. In particular, expression of sodB1 (superoxide dismutase gene) and feoB1 (ferrous transport protein B1 gene) were markedly reduced in cultures at 0.5% O 2 compared to those at higher oxygen tensions. Moreover, expression of katG (catalaseperoxidase gene) and feoB2 (ferrous transport protein B2 gene) was reduced markedly by iron addition, regardless of oxygen conditions. The data provides a greater understanding of molecular response of MSR-1 cells to environmental conditions associated with oxygen and iron metabolisms, especially relevant to immediate-early stage of fermentation.

An automated oxystat fermentation regime for microoxic cultivation of Magnetospirillum gryphiswaldense

“…During an investigation of oxygen and iron impact on gene expression, an automated oxystat regime in a 1 L bioreactor based on dynamic gas blending of nitrogen and air was applied, whereas agitation and maximal gas flow remained constant at 120 rpm and 1 SLPM, respectively [ 42 ]. In this study, set dO 2 values of 0.5% and 5% were kept stable over the fermentation, however this regime led to a steady decrease of oxygen concentration during growth at set dO 2 values above 15% [ 42 ].…”