趋磁细菌磁小体合成的相关操纵子和基因

The operons and genes related to magnetosome biogenesis in magnetotactic bacteria

趋磁细菌的磁小体合成现象自20世纪发现以来,一直是微生物研究的热点之一.各类研究指出多个操纵子及其内部的基因与磁小体合成密切相关.近些年来,随着磁小体合成的全过程被细化成3~5个主要步骤,负责各个步骤顺利进行的基因也逐步被人们发现和认识.通过各种生物实验和生物信息分析,研究者不断揭示出这些基因及所在操纵子的具体功能和意义. mamAB操纵子及其内部的多个基因在磁小体合成中具有关键作用. 4个小型操纵子包括mamGFDC, mamXY, mms6, feoAB1在磁小体的生物矿化中发挥辅助作用.此外,研究者还发现了其他一些与磁小体合成相关的新基因和基因组区域,比如δ-变形菌的mad基因簇和趋磁硝化螺旋菌的man基因.操纵子和基因的研究为人们探索磁小体合成的主要机制提供了重要信息,而多位研究者基于这些研究成果提出了各种各样的磁小体合成假定机制模型.操纵子和基因的研究为今后开发各种纳米生物科技研究工具,并把趋磁细菌应用于环境修复等领域打下了坚实的基础.本文以负责磁小体合成的各类操纵子和基因为线索,较详细地介绍了近年来磁小体合成研究的主要发现和进展.

Magnetosomes are natural magnetic nanoparticles with special properties that are synthesized by magnetotactic bacteria.Bacterial magnetosomes have become increasingly attractive for researchers in biology, medicine, geology and other fields of scientific researches. It is significant to explore a promising nanomaterial for multiple applications in science and industry.Magnetosomes contains magnetic particles that are enclosed by intracellular membrane. These particles can be either ferrimagnetic crystal of magnetite(Fe3 O4) or the iron sulfide greigite(Fe3 S4). Three crystal morphologies including roughly cuboidal, roughly rectangular, bullet-shaped have been found in magnetotactic bacteria. Magnetosomes are organized as well-ordered chains which orient magnetotactic bacteria in geomagnetic fields. The question ‘what and how is genetic material responsible for magnetosome genesis and following diversity’ was raised when biologists tried to understand the formation mechanism of magnetosome in the last century. Now almost two decades have passed since 2000,magnetosome biogenesis still remains one of the hotspots in scientific researches. Both bioinformatic analyses and gene deletion experiments are extensively carried out in the study of magnetosome biogenesis. Consequently, multiple operons and genes are found to be involved in the process of magnetosome formation. This article introduces important findings in the field of operons and genes as controllers of magnetosome biogenesis. The mam AB operon is found to be more critical than other operons to magnetosome biogenesis and it is necessary for rudimentary biomineralization in bacteria. Less than10 genes within the mam AB operon are essential for the magnetosome formation. Moreover, other four small operons(mam GFDC, mam XY, mms6 and feo AB1) play non-critical roles for magnetosome biogenesis. Non-essential genes can be found in both the mam AB operon and non-critical operons. In addition, several genes and genomic regions outside of magnetosome-related operons such as the mms16 gene in Magnetospirillum magneticum AMB1 or the mad gene clusters in Deltaproteobacteria are also related to magnetosome synthesis. These discoveries provide insights into the molecular mechanisms of magnetosome biogenesis. Some researchers have separated the whole process of magnetosome formation into three or five key steps, they proposed several hypothesized mechanisms of magnetosome formation in magnetotactic bacteria by summarizing functional genes and proteins in each of key steps. The Arakaki’s model in 2018 is a relatively comprehensive model of magnetosome formation and can offer detail information about molecular and cellular mechanisms. With rapid development of research on magnetotactic bacteria emerging in China in recent years, Chinese scientists have made various types of research achievements such as discoveries of novel magnetotactic bacteria,calculations of diversity of magnetotactic bacteria in specific water areas and evolutionary mechanism of microbial magnetoreception. It is expected that more valuable achievements would be obtained from bacterial research than ever before.Natural magnetic nanoparticles have potentials to bring many advancements in science and they can help overcome technical challenges in various scientific fields. To release the power within magnetosomes, biologists are required to reveal the genetic foundation of magnetosome biogenesis and help material scientists invent new technology using biological knowledge. Magnetosome researches are attracting more and more scientists from all areas of science.Interdisciplinary research has become an increasingly common method of study in magnetosome. How well the material scientists can cooperate with other scientists will be crucial for important discoveries in magnetosomes in the future.