Biology subjects

Hartmann, F. S. F.

Publications and source records attributed to Hartmann, F. S. F..

4 recordsLinked to original sources

bioRxiv2022

Precise and versatile microplate reader-based analyses of biosensor signals from arrayed microbial colonies

Genetically encoded fluorescent biosensors have emerged as a powerful tool to support phenotypic screenings of microbes. Optical analyses of fluorescent sensor signals from colonies grown on solid media can be challenging as imaging devices need to be equipped with appropriate filters matching the properties of fluorescent biosensors. Towards versatile fluorescence analyses of different types of biosensor signals derived from arrayed colonies, we investigate here the use of monochromator equipped microplate readers as an alternative to imaging approaches. Indeed, for analyses of the LacI-controlled expression of the reporter mCherry in Corynebacterium glutamicum, or promoter activity using GFP as reporter in Saccharomyces cerevisiae, an improved sensitivity and dynamic range was observed for a microplate reader-based analyses compared to their analyses via imaging. The microplate reader allowed us to capture signals of ratiometric fluorescent reporter proteins (FRPs) with a high sensitivity and thereby to further improve the analysis of internal pH via the pH-sensitive FRP mCherryEA in Escherichia coli colonies. Applicability of this novel technique was further demonstrated by assessing redox states in C. glutamicum colonies using the FRP Mrx1-roGFP2. By the use of a microplate reader, oxidative redox shifts were measured in a mutant strain lacking the non-enzymatic antioxidant mycothiol (MSH), indicating its major role for maintaining a reduced redox state also in colonies on agar plates. Taken together, analyses of biosensor signals from microbial colonies using a microplate reader allows comprehensive phenotypic screenings and thus facilitates further development of new strains for metabolic engineering and systems biology.

synthetic biology↗

bioRxiv2022

Combined sensor-based monitoring of mycothiol redox potential and DNA-damage response in Corynebacterium glutamicum

Excessive amounts of reactive oxygen species (ROS) can cause irreversible damages to essential cellular components such as DNA. Genetically encoded biosensors targeting oxidative stress and DNA-stress have emerged to a powerful analytical tool to assess physiological states in a non-invasive manner. In this study, we aimed to combine the redox biosensor protein Mrx1-roGFP2 with a transcriptional biosensor for DNA-damage based on the PrecA promoter fused to a reporter gene (e2-crimson) in Corynebacterium glutamicum. Therefore, the redox biosensor strains C. glutamicum WT_Mrx1-roGFP2 and the mycothiol (MSH)-deficient mutant strain C. glutamicum {Delta}mshC_Mrx1-roGFP2 were equipped with the DNA-stress reporter plasmid pJC1_PrecA_e2-crimson. Exposure of the double-sensor equipped C. glutamicum WT strain to hypochlorite resulted in an oxidative redox shift, accompanied by an induction of the DNA-stress reporter system. In absence of the major non-enzymatic antioxidant MSH, the induction of the DNA-stress response was even more pronounced. This confirms the linkage of oxidative stress and DNA-damage response, and therefore making antioxidants a crucial player to protect DNA. Furthermore, exposure of the double biosensor strains to a DNA-damage inducing agent resulted in an oxidative redox shift. These results suggest a direct link of DNA-damage and oxidative stress response in C. glutamicum. Finally, we observed that inhibition of cell wall biosynthesis by penicillin caused both an oxidative redox shift and a DNA-damage response in C. glutamicum. The excellent compatibility of Mrx1-roGFP2 with E2-Crimson shown here provides a powerful combinatorial biosensor concept for in-depth studies of redox-related physiology in future studies.

microbiology↗

bioRxiv2021

Impedance flow cytometry for viability analysis of Corynebacterium glutamicum

Corynebacterium glutamicum efficiently produces glutamate when growth is inhibited. Analyses of viability in this non-growing state requires time consuming plating and determination of colony forming units. We here establish impedance flow cytometry measurements to assess the viability of non-growing, glutamate producing C. glutamicum cultures within minutes.

microbiology↗

bioRxiv2021

Visualizing the pH in Escherichia coli colonies via the sensor protein mCherryEA allows high-throughput screening of mutant libraries

Cytoplasmic pH is tightly regulated by diverse active mechanisms and interconnected regulatory processes in bacteria. Many processes and regulators underlying pH-homeostasis have been identified via phenotypic screening of strain libraries towards non-growth at low or high pH values. Direct screens with respect to changes of the internal pH in mutant strain collections are limited by laborious methods including fluorescent dyes or radioactive probes. Genetically encoded biosensors equip single organisms or strain libraries with an internal sensor molecule already during the generation of the strain. In this study, we used the pH-sensitive mCherry variant mCherryEA as ratiometric pH biosensor. We visualized the internal pH of E. coli colonies on agar plates by the use of a Gel-Doc imaging system. Combining this imaging technology with robot-assisted colony picking and spotting allowed us to screen and select mutants with altered internal pH values from a small transposon mutagenesis derived E. coli library. Identification of the TN- insertion sites in strains with altered internal pH levels revealed that the transposon was inserted into trkH (encoding a transmembrane protein of the potassium uptake system) or the rssB gene (encoding the anti-adaptor protein RssB which mediates the proteolytic degradation of the general stress response regulator RpoS), two genes known to be associated with pH-homeostasis and pH stress adaptation. This successful screening approach demonstrates that the pH- sensor based analysis of arrayed colonies on agar plates is a sensitive approach for the fast identification of genes involved in pH-homeostasis or pH stress adaptation in E. coli. ImportancePhenotypic screening of strain libraries on agar plates has become a versatile tool to understand gene functions and to optimize biotechnological platform organisms. Screening is supported by genetically encoded biosensors that allow to easily measure intracellular processes. For this purpose, transcription-factor-based biosensors have emerged as the sensor-type of choice. Here, the target stimulus initiates the activation of a response gene (e.g. a fluorescent protein) followed by transcription, translation and maturation. Due to this mechanistic principle, biosensor readouts are delayed and cannot report the actual intracellular state of the cell in real-time. To capture fast intracellular processes adequately, fluorescent reporter proteins are extensively applied. But these sensor-types are not utilized for phenotypic screenings so far. To take advantage of their properties, we here established an imaging method, which allows to apply a fast ratiometric sensor protein for assessing the internal pH of colonies in a high-thoughput manner.

microbiology↗