Flow cytometry as a rapid analytical tool to determine physiological responses to changing O2 and iron concentration by Magnetospirillum gryphiswaldense strain MSR-1

Magnetotactic bacteria (MTB) are a diverse group of bacteria that synthesise magnetosomes, magnetic membrane-bound nanoparticles that have a variety of diagnostic, clinical and biotechnological applications. We present the development of rapid methods using flow cytometry to characterize several aspects of the physiology of the commonly-used MTB Magnetospirillum gryphiswaldense MSR-1. Flow cytometry is an optical technique that rapidly measures characteristics of individual bacteria within a culture, thereby allowing determination of population heterogeneity and also permitting direct analysis of bacteria. Scatter measurements were used to measure and compare bacterial size, shape and morphology. Membrane permeability and polarization were measured using the dyes propidium iodide and bis-(1,3-dibutylbarbituric acid) trimethine oxonol to determine the viability and ‘health’ of bacteria. Dyes were also used to determine changes in concentration of intracellular free iron and polyhydroxylakanoate (PHA), a bacterial energy storage polymer. These tools were then used to characterize the responses of MTB to different O2 concentrations and iron-sufficient or iron-limited growth. Rapid analysis of MTB physiology will allow development of bioprocesses for the production of magnetosomes, and will increase understanding of this fascinating and useful group of bacteria

Imaging Technologies for Biomedical Micro‐ and Nanoswimmers

The last decade has seen the rapid development of untethered mobile micro‐ and nanorobots able to navigate liquids by means of external power sources or by harvesting chemicals from their surrounding media. These tiny devices hold great promise for applications in the biomedical field including targeted drug delivery, localized diagnostics, microsurgery, and cell stimulation. However, to translate small‐scale robots from the laboratory to the clinic, many challenges remain. A major obstacle is the lack of imaging technologies that will allow for precise tracking of the devices in vivo. Here, the current progress, challenges, and future possibilities in the monitoring and tracking of biomedical micro‐ and nanomachines using established as well as less conventional imaging technologies are reviewed