A key time point for cell growth and magnetosome synthesis of Magnetospirillum gryphiswaldense based on real-time analysis of physiological factors

Abstract

Pure culture of magnetotactic bacteria with high magnetosome yield has been achieved for only a few strains. The major obstacles involve the nutritional requirements and culture conditions of the cells. To increase cell density and magnetosome production, it is necessary to elucidate the physiological characteristics of a particular strain during cell growth and develop an appropriate artificial control strategy. Large-scale culture of Magnetospirillum gryphiswaldense strain MSR-1 was successfully performed for 48 h in a 42-L autofermentor, and several key physiological parameters were measured in real time. Maximal values of cell density (OD565) (19.4) and cell yield (dry weight) (4.76 g/L) were attained at 40 h. The key time point for cell growth and magnetosome formation was found to be 18–20 h. At this point, cells entered the log phase of growth, the maximal values of Cmag (1.78), iron content (0.47%), and magnetosome number (26 ± 3 per cell) were observed, superoxide dismutase (SOD) activity began to decrease more rapidly, ATP content dropped to an extremely low level (0.17 fmol), and reducing power (NADH/NAD+ ratio) began to increase very rapidly. Excessive levels of dissolved oxygen (≥20 ppb) and lactic acid in the medium caused notable cytotoxic effects after 20 h. Artificial control measures for fermentation must be based on realistic cell physiological conditions. At the key time point (18–20 h), cell density is high and magnetosomes have matured. The process of magnetosome synthesis involves a high consumption of ATP and reducing power, and the cells require replenishment of nutrients prior to the 18–20 h time point. Culture conditions that effectively minimize dissolved oxygen accumulation, lactic acid content, and reducing power at this point will enhance magnetosome yield without obvious inhibition of cell growth.

Transcriptome analysis reveals physiological characteristics required for magnetosome formation in Magnetospirillum gryphiswaldense MSR‐1

“…Previous studies have shown that magnetosome development requires low oxygen concentration (Sch€ uler et al, 1998;Yang et al, 2013). In submerged culture of MSR-1, relative dissolved oxygen concentration (dO 2 ) < 1% was required for magnetosome formation (Zhang et al, 2011).…”

A Method for Producing Highly Pure Magnetosomes in Large Quantity for Medical Applications Using Magnetospirillum gryphiswaldense MSR-1 Magnetotactic Bacteria Amplified in Minimal Growth Media

“…Fermentation was carried out at 29.5 • C under agitation at 200 rpm during 2 days at pH maintained at 6.9 by adding an acidic fed-batch medium containing FeCl 3 .6H 2 O as the iron source. Growth of MSR-1 bacteria was stimulated by bubbling oxygen in the growth medium at a percentage of dO 2 kept below 1 % to enable magnetosome synthesis (Sun et al, 2008;Zhang et al, 2011;Yang et al, 2013;Fernández-Castané et al, 2018). Temperature, agitation speed, pH, feeding pump flow and oxygen concentration were monitored and adjusted using a DASGIP controller and a DASware software from Applikon Eppendorf.…”

Nanoparticle Tracking Analysis: A powerful tool for characterizing magnetosome preparations

“…Despite numerous efforts to improve the yields of magnetosomes [4,12,13], their large-scale biomanufacture remains significant barrier to future widespread industrial application. Fundamental to this are: (i) appropriate means for analysing MTB growth and physiology [14,15]; (ii) investigating the biomineralization of magnetic iron-containing minerals, which is still not fully understood [16 -18]; (iii) the ability to both produce batches of nanoparticles that are consistent in structure, chain length and functionality -this is key to unlocking the potential of magnetosomes as therapeutic agents; and (iv) to be able to rapidly analyse these characteristics.…”