Department of Bioengineering, University of California, Los Angeles, Los Angeles, California, USA.
Department of Biomedical Engineering, National University of Singapore, Singapore.
Appl Environ Microbiol. 2018 Aug 17;84(17). doi: 10.1128/AEM.01308-18. Print 2018 Sep 1.
Magnetic nanoparticles (MNPs) are useful for many biomedical applications, but it is challenging to synthetically produce them in large numbers with uniform properties and surface functionalization. Magnetotactic bacteria (MTB) produce magnetosomes with homogenous sizes, shapes, and magnetic properties. Consequently, there is interest in using MTB as biological factories for MNP production. Nonetheless, MTB can only be grown to low yields, and wild-type strains produce low numbers of MNPs/bacterium. There are also limited technologies to facilitate the selection of MTB with different magnetic contents, such as MTB with compromised and enhanced biomineralization ability. Here, we describe a magnetic microfluidic platform combined with transient cold/alkaline treatment to temporarily reduce the rapid flagellar motion of MTB without compromising their long-term proliferation and biomineralization ability for separating MTB on the basis of their magnetic contents. This strategy enables live MTB to be enriched, which, to the best of our knowledge, has not been achieved with another previously described magnetic microfluidic device that makes use of ferrofluid and heat. Our device also facilitates the high-throughput (25,000 cells/min) separation of wild-type (MSR-1) from nonmagnetic Δ MSR-1 mutants with a sensitivity of up to 80% and isolation purity of up to 95%, as confirmed with a gold-standard fluorescent-activated cell sorter (FACS) technique. This offers a 25-fold higher throughput than other previously described magnetic microfluidic platforms (1,000 cells/min). The device can also be used to isolate (AMB-1) mutants with different ranges of magnetosome numbers with efficiencies close to theoretical estimates. We believe this technology will facilitate the magnetic characterization of genetically engineered MTB for a variety of applications, including using MTB for large-scale, controlled MNP production. Our magnetic microfluidic technology can greatly facilitate biological applications with magnetotactic bacteria, from selection and screening to analysis. This technology will be of interest to microbiologists, chemists, and bioengineers who are interested in the biomineralization and selection of magnetotactic bacteria (MTB) for applications such as directed evolution and magnetogenetics.
磁性纳米粒子（MNPs）在许多生物医学应用中非常有用，但在大量合成具有均匀性质和表面功能化的磁性纳米粒子方面具有挑战性。趋磁细菌（MTB）产生具有均匀大小、形状和磁性的磁小体。因此，人们有兴趣将 MTB 用作 MNP 生产的生物工厂。尽管如此，MTB 只能以低产量生长，并且野生型菌株产生的 MNPs/细菌数量很少。也有限制性技术来促进具有不同磁含量的 MTB 的选择，例如磁矿化能力受损和增强的 MTB。在这里，我们描述了一种磁微流控平台，结合瞬时冷/碱性处理，暂时降低 MTB 的快速鞭毛运动，而不会损害它们的长期增殖和生物矿化能力，从而基于其磁含量分离 MTB。这种策略可以实现活 MTB 的富集，据我们所知，这是以前使用铁磁流体和热量的另一种磁性微流控设备所无法实现的。我们的设备还促进了高吞吐量（25,000 个细胞/分钟）的分离，从非磁性 ΔMSR-1 突变体中分离野生型（MSR-1），灵敏度高达 80%，分离纯度高达 95%，这与金标准荧光激活细胞分选器（FACS）技术确认。这比以前描述的其他磁性微流控平台（1,000 个细胞/分钟）高 25 倍。该设备还可用于分离具有不同磁小体数量范围的（AMB-1）突变体，效率接近理论估计。我们相信，这项技术将促进各种应用中基因工程 MTB 的磁性表征，包括使用 MTB 进行大规模、可控的 MNP 生产。我们的磁性微流控技术可以极大地促进磁细菌的生物应用，从选择和筛选到分析。这项技术将引起对生物矿化和磁细菌（MTB）选择感兴趣的微生物学家、化学家和生物工程师的兴趣，例如定向进化和磁遗传学。
