An\nIntegrated Approach to Elucidate the Interplay\nbetween Iron Uptake Dynamics and Magnetosome Formation at the Single-Cell\nLevel in <i>Magnetospirillum gryphiswaldense</i>

Iron is a crucial\nelement integral to various fundamental biological\nmolecular mechanisms, including magnetosome biogenesis in magnetotactic\nbacteria (MTB). Magnetosomes are formed through the internalization\nand biomineralization of iron into magnetite crystals. However, the\ninterconnected mechanisms by which MTB uptake and regulate intracellular\niron for magnetosome biomineralization remain poorly understood, particularly\nat the single-cell level. To gain insights we employed a holistic\nmultiscale approach, <i>i</i>.<i>e</i>., from\nelemental iron species to bacterial populations, to elucidate the\ninterplay between iron uptake dynamics and magnetosome formation in <i>Magnetospirillum gryphiswaldense</i> MSR-1 under near-native\nconditions. We combined a correlative microscopy approach integrating\nlight and X-ray tomography with analytical techniques, such as flow\ncytometry and inductively coupled plasma spectroscopy, to evaluate\nthe effects of iron and oxygen availability on cellular growth, magnetosome\nbiogenesis, and intracellular iron pool in MSR-1. Our results revealed\nthat increased iron availability under microaerobic conditions significantly\npromoted the formation of longer magnetosome chains and increased\nintracellular iron uptake, with a saturation point at 300 μM\niron citrate. Beyond this threshold, additional iron did not further\nextend the magnetosome chain length or increase total intracellular\niron levels. Moreover, our work reveals (i) a direct correlation between\nthe labile Fe<sup>2+</sup> pool size and magnetosome content, with\nhigher intracellular iron concentrations correlating with increased\nmagnetosome production, and (ii) the existence of an intracellular\niron pool, distinct from magnetite, persisting during all stages of\nbiomineralization. This study offers insights into iron dynamics in\nmagnetosome biomineralization at a single-cell level, potentially\nenhancing the industrial biomanufacturing of magnetosomes.