Microbiological Formation Of Magnetosomes In Acidithiobacillus Ferrooxidans

The magnetosome formed by BCM method could be an ideal kind of bio-nano-magnetic material,because of its specific properties such as superior crystalline,well biocompatible,uniform nano-sized,non-agglomerated and specific magnetic characteristics.Intracellular magnetite(Fe₃O₄)or greigite(Fe₃S₄)formed in magnetotactic bacteria are the typical kind of the biomineralization.The researchers in this group discovered the fact that the Acidithiobacillus ferrooxidans could synthesize intracellular electron-dense magnetic particles and this study researched the formation of magnetosomes in Acidithiobacillus ferrooxidans.In order to isolate the strain which has the capacity to produce more magnetic particles,the solid-plate magnetophoresis method was firstly created as well as the extracting and purifying methods of magnetosomes.In addition,the whole genome of of the type strain Acidithiobacillus ferrooxidans ATCC 23270 was analysized by bioinformatics and some homolog genes of functional ones in magnetotactic bacteria were available.This study analysized the Fe stress response of Acidithiobacillus ferrooxidans ATCC 23270 by using real-time PCR analysis.Moreover,the function of magnetosomes in Acidithiobacillus ferrooxidans was discussed.We isolated a stain YN-3 by using the solid-plate magnetophoresis method from the acid mine drainage in Dongchuan,Yun Nan province,China,which was identified as Acidithiobacillus ferrooxidans.After isolation using the method,the rate of the cells which contain intra-cellular magnetic particles was increased from 30%to more than 90%,in addition,after isolation each cell possessed 2-5 magnetic particles which disperse in cells.The strain YN-3 cultured in FeSO₄ appeared in thin section to contain several electron-dense particles,correspondingly,the iron starvation control of strain YN-3 lack these bacterial inclusion bodies.The isolated cells are able to orient and migrate to the magnet in artificial magnetic field but could not orient swimming only under the geomagnetic field.Magnetosomes produced by Acidithiobacillus ferrooxidans were range from 60nm to 90 nm according to the results of TEM.Energy dispersive X-ray analysis indicated that extracted magnetic particles consisted of oxygen and iron.We analyzed the whole genome of the type strain Acidithiobacillus ferrooxidans ATCC 23270,and found that proteins incoded by 8 ORFs 1622,0276,1124,2572,1403,1439,1143,2403 were homologous with MpsA,Iron Reductase(Thy), MagA,MamB,Bfr,MamE,MamK,MamH in magnetotactic bacteria,respectively. This study analyzed the conserved domain and amino acid sequences as well as protein homologs of ORF1622,0276,1124,2572,1403.According to our bioinformatics results we supposed that ORF1622,1124,2572,1403 were related to the formation of magnetosomes in Acidithiobacillus ferrooxidans and the formation mechanism of magnetosomes in Acidithiobacillus ferrooxidans might be different from that in magnetotactic bacteria.To obtain further knowledge of the magnetosomes formation mechanisms of Acidithiobacillus ferrooxidans in response to different kinds of Fe ions,temporal gene expression profiles were examined in cells subjected to 20mM FeCl₃ and FeSO₄·7H₂O stress by using Real-time PCR.The results indicated that the expressions of mpsA,magA and mamB were related to Fe²⁺,and according to the fact that the strain YN-3 only cultured in FeSO₄ could be able to synthesize intracellular magnetosomes,we supposed that the mpsA,magA and mamB were related with the magnetosome formation in Acidithiobacillus ferrooxidans.Moreover,according to the difference of magnetosomes arrangement as well as the habitat condition between Acidithiobacillus ferrooxidans and magnetotactic bacteria,we supposed that the magnetosomes in Acidithiobacillus ferrooxidans and magnetotactic bacteria have different functions. Magnetosomes in Acidithiobacillus ferrooxidans might play an important role in controlling the intracellular Fe level to reducing toxicity of Fe²⁺.Although the exact function of magnetosomes in Acidithiobacillus ferrooxidans is currently unknown, knowledge of its formation and maintenance in Acidithiobacillus ferrooxidans is essential for describing the role of Acidithiobacillus ferrooxidans in the biochemical recycling of iron and important for generating a comprehensive description of the mechanism that how Acidithiobacillus ferrooxidans involved in bioleaching regulates its cellular iron homeostasis.