Diversity And Culture Of Magnetotactic Bacteria From Heihuquan Spring

Magnetotactic bacteria (MTB) are globally abundant in water columns or sediments with horizontal chemical stratification. MTB and their magnetosomes are great interests in microbiology, biomagnetism and advanced magnetic materials. But only about 10 strains of MTB have been cultured until now because they need complex growth conditions.In the present study, the diversity of magnetotactic bacteria was studied in a freshwater spring, Heihuquan spring, in Jinan, China. Diverse morphology types of MTB were observed with the transmission electron microscopy (TEM) including cocci, ovoids, spirilla, vibrios and rods. The coccoid shape was the most frequently observed. The chains of.magnetosomes in MTB cells arranged in one, two, four or multiple lines respectively. Disorganized magnetosome chains in MTB cells were also observed. We found that the morphology types of MTB changed when the season changed. It indicates that MTB are extremely sensitive to the microenvironment they lived. The diversity of MTB in fresh spring waters was further confirmed by restriction fragment length polymorphism analysis (RFLP) and sequence analysis of 16S rRNA genes. At least 13 different taxonomic groups of MTB were identified. One of these sequences was 99% similarity to uncultured magnetotactic cocci from Germany. It suggests that MTB have not only diversity but also similarity in the world.Several other methods including denaturing gradient gel electrophoresis (DGGE) combined with 16S rRNA genes sequence analysis of all sediment bacteria and "race track" purified MTB were being adopted to analyze the variation of MTB communities under different laboratorial incubation conditions. We found that when under the conditions of 16℃, pH 8.0, moderately nutrient concentration, the diversity of MTB communities was most abundant. These results can be expected to provide helpful information to cultivation experiments.We also had the cultivation experiments, a multitude of different growth media were used in an attempt to isolate MTB. In numerous repeated experiments, we failed to detected growth of MTB. Neither the addition of complex supplements nor incubation with different oxygen levels or agar gradients stimulated the growth of these MTB.