| Magnetotactic bacteria (MTB) have been discovered for almost40years. They are a group of morphologically and phylogentically heterogenous prokaryotes which synthesize intracellular membrane-enclosed and nano-sized magnetite and/or greigite crystals called magnetosome. Magnetosome can help fast orientation in the aquatic environment and looking for the suitable ecological environment. MTB, therefore, are ideal model organisms to study biological response mechanism of the magnetic field and microbial biomineralization. Magnetotactic bacteria are ubiquitous in water columns and sediments of freshwater or marine habitats, and are believed to play an important role in biogeochemical circulation of iron and sulfur elements. In addition, the population distribution and the synthesis of magnetosome are influenced by environmental factors, so to study magnetotactic bacteria have important scientific significance in paleomagnetism, ancient environment and early life.In this paper, we aim to study biological diversity and magnetic properties of magnetotactic bacteria recently collected from Xiaoshi Island in Weihai, Shandong Province and Lake Weiyang in Xi’an city, Shaanxi Province. We want to further understand the contact between the diversity of magnetotactic bacteria and geographical distribution.Natural collections of magnetotactic bacteria from the intertidal sediment samples near Xiaoshidao at Weihai were dominated by coccid morphotypes that produced e-prismatic magnetosome. Combining the energy dispersive x-ray spectrometer and the High-resolution transmission electron microscopy with selected area electron diffraction results indicated that almost all cells contain two chains of magnetosome composed of magnetite crystals. In addition, the bacteria in the cells including phosphorus and sulfur granules, suggest that this may relate to the metabolism. For a detailed phylogenetic analysis, according to the restriction fragment length polymorphism(RFLP) and16S rRNA gene analysis from the intertidal region samples analysis of90clones, these magnetotactic bacteria mainly composed of Alphaproteobacteria, belonging to eight different populations. The WHI-2strain was the dominant species. The fluorescence in situ hybridization(FISH) furthermore revealed the presence of a homogenous population. Together, these results suggest that the characteristics with highly diversities of magnetotactic bacteria are in relevance with the environment.In this study, the diversity and magnetic properties of magnetotactic bacteria collected from Lake Weiyang in Xi’an city, Shaanxi Province, were analyzed and characterized. Transmission electron microscopy analyses have revealed that rod-shaped bacteria containing bullet-shaped magnetsomes were the dominant group of magnetotactic bacteria in Lake Weiyang. Other kinds of magnetotactic bacteria, such as cocci and spirilla, were also observed. Interestingly, the energy dispersive x-ray spectrometer of transmission electron microscopy showed some rod-shaped bacteria were able to simultaneously biomineralize magnetite and greigite magnetosomes in a single cell, which is unusual in magnetotactic bacteria. Magnetic property measurements including hysteresis loop, first-order reversal curve and low temperature magnetisms, indicate that these magnetotactic bacteria mineralize single domain magnetite with relatively lower Verwey transition temperature. Furthermore, according to the16S rRNA gene analysis, these magnetotactic bacteria mainly composed of the Deltaproteobacteria (75%), and the Alphaproteobacteria (25%), belonging to the eight populations(OTU1～OTU8). Fluorescence in situ hybridization further confirmed that the sequences obtained from the rod-shaped bacteria are truly from the Deltaproteobacteria. Our results indicate that the community of the Deltaproteobacteria MTB in freshwater environment is more diverse than previously thought, which provides new insights into the overall diversity of magnetotactic bacteria in nature.In this article, we intend to do two piece of work using AMB-1as material, including AMB-1(WT) and nitrate reductase mutant(AMB08). As comprehensive utilization of transmission electron microscopy and rock magnetism method discusses the electron acceptor for the influence of the synthesis of magnetosome of AMB-1, with the three different nitrogen source and two different oxygen concentrations(aerobic static:AS, anaerobic static:ANS)conditions.Cell growth curves showed that, the AMB-1undergone a comparable trend of cell growth under eight different growth conditions, the number of cells increases slowly during a lag phase from0-16h, it then increased rapidly during an exponential phase from16-36h, and remained nearly constant or decreased slightly during a stationary phase from36-72h. But under anaerobic conditions cell growth speed slowed down obviously, the number of cells also significantly reduced at the same time. The results of Room temperature magnetic hysteresis loop and the FORC diagram also showed that the increasing of oxygen in different extent influenced the magnetosome of mineralization. Rock magnetism results found that the crystal type, size and the chain of wild type strains were superior to mutant strains under AS condition. The laboratory results indicate that oxygen could promote the growth of cells, and with anaerobic static conditions it may be more conducive to biomineralization of AMB-1.Under ANS condition, the AMB-1could only growth in the medium of nitrate, but the mutant didn’t growth, the result showed that the nitrate through denitrification could be used as a single electron acceptor for cell growth and synthesis of magnetosome. AMB-1could grow with ammonium as sole nitrogen source under aerobic condition, but ammonium could not support AMB-l’s growth under anaerobic condition, which means the bacteria need an energy supplement pathway depending on nitrate. Under AS condition, when there is oxygen and nitrate, cells can also use oxygen and nitrate as electron acceptor for cell growth and mineralization of magnetosome. But as nitrate supply decreases, size and the coercive force of magnetosome become decreased. To show that oxygen as electron acceptor energy supply is conducive to cell growth, but the nitrate as electron acceptor is more advantageous to the synthesis of magnetosome.Therefore, the results showed that denitrification is directly involved in biomineralization of the magnetosome. This article only is analyzed from the physical and chemical properties and the magnetic method, further reveal the relationship between the denitrification in AMB-1and the synthesis of magnetosome and the growth of the bacteria. But the specific influence mechanism remains to be studied. |
PDF Full Text Request