In this preliminary study, we try to understand whether MTB can uptake and accumulate iron from the animal body. This investigation was essential to understand the behavior of bacteria toward iron in in vivo environment. MTB have a remarkable potential to accumulate a large amount of iron in different environments and may play a key role in the regulation of the iron cycle in sedimentary environments, in which this ability is based on magnetosomes [25]. Bacteria require large amounts of iron to synthesis their magnetosomes; they may accumulate up to 100 times more iron than non-magnetotactic heterotrophic bacteria [26, 27].
In this study, to obtain the iron overloaded animal model, iron dextran was administrated twice a week for four consecutive weeks, and the iron level was measured as it was described earlier in mice [23] and rats [33]. As it is known, initially, iron dextran is taken up by the reticuloendothelial system, but then equilibrates with the parenchymal system [28]. In an earlier study by Moon et al., the author suggested a chronic iron overloaded model by administration of iron dextran for 2–8 weeks and showed that mice were not dead and adjusted well up to the cumulative iron dose of 300 mg and long term survival was confirmed [29].
To investigate whether bacteria can uptake the iron in in vivo, MSR-1 was injected to iron overloaded mice, and normal mice and alteration of the iron level in plasma and liver were measured and compared with iron overloaded mice and normal mice which received only PBS. In a study by Benoit et al., Magnetospirillum magneticum (AMB-1) were injected intrathecal (i.t.) and intravascular (i.v.) to mice in order to visualize implanted tumors with magnetic resonance imaging by bacteria [30]. The authors showed that bacteria were cleared completely from other organs after six days of post-injection and remained only in tumors [30]. Setayesh et al. injected MSR-1, either i.v., peritoneal (i.p.) and subcutaneous (s.c.), and the clearance of MSR-1 in healthy mice was investigated [20]; the authors showed that mice clear MSR-1 from their body with different routes of injection after 96 hours. In the same study, the serum iron level was measured to understand by which routs of injection; bacteria effect on iron level [20].
In this experiment, after i.v. injection of MSR-1 to mice, serum iron, and total liver iron levels were decreased. The reduction of iron levels were highly significant during the first three days (p < 0.05). Notably, the percentages of serum and total liver iron reduction were similar in IO + MSR-1 and in Cont.+MSR-1, which may explain the amount of iron taken by the same number of bacteria (109 in 200 µl PBS) are a consistent amount. Moreover, the CFUs of MSR-1 after 96 hours were zero in the liver, spleen, and lymph nodes that may explain the sharp reduction of iron levels during the first three days after the entrance of bacteria into the animal body. Therefore, it may conclude that as long as there are alive MSR-1 in mice (during the first three days), iron levels in plasma and liver were reduced. The urinary iron excretion was higher between 24 to 96 hours after MSR-1 injection, and in parallel, the number of bacteria in mice was at the highest level in 24 hours post-injection, and it gradually reduced until 96 hours post-injection which we could not detect bacteria in liver, spleen and lymph nodes (see Fig. 3).
In this study, we reported the ability of iron uptake by MSR-1 in in vivo. MSR-1 has the potential to help to design a better biological tool that can multiply the effectiveness of the treatment of iron overloaded disorders. Therefore, our preliminary study opens the question of whether the bacteria can be a better replacement for chemical iron chelation drugs. However, our knowledge concerning the physiological characteristics and mechanism of iron uptake by MSR-1 in in vivo remains fragmentary. There are more studies warranted to understand the mechanism of bacterial clearance and cytotoxicity and genotoxicity effects of bacteria as well as an immune response in in vivo model. We also recommend future studies on optimizing the biological magnetic systems.