FeoB 2 functions in magnetosome formation and oxidative stress 2 protection in Magnetospirillum gryphiswaldense strain

24 Magnetotactic bacteria (MTB) synthesize unique organelles, the magnetosomes, 25 which are intracellular nanometer-sized, membrane-enveloped magnetite. The 26 biomineralization of magnetosomes involves the uptake large amounts of iron. 27 However, the iron metabolism of MTB is not well understood. The genome of the 28 magnetotactic bacterium Magnetospirillum gryphiswaldense strain MSR-1 contains 29 two ferrous iron transport genes, feoB1 and feoB2. The FeoB1 protein was reported to 30 be responsible mainly for the transport of ferrous iron and to play an accessory role in 31 magnetosome formation. To determine the role of feoB2 gene, we constructed feoB2 32 deletion mutant (ΔfeoB2), and feoB1 / feoB2 double deletion mutant (NfeoB). The 33 single feoB2 mutation did not affect magnetite crystal biomineralization. NfeoB had a 34 significantly lower average magnetosome number per cell (~65%) than ΔfeoB1, 35 indicating that FeoB2 plays a role in magnetosome formation when the feoB1 gene is 36 deleted. Our findings showed that FeoB1 has a greater ferrous iron transport ability 37 than FeoB2 and revealed the differential roles of FeoB1 and FeoB2 in MSR-1 iron 38 metabolism. Interestingly, the feoB mutants, compared with wild-type, showed 39 increased sensitivity to oxidative stress and lower activities of the enzymes superoxide 40 dismutase and catalase, indicating that the FeoB proteins help protect bacterial cells 41 from oxidative stress. 42 43