The Stickland Reaction Precursor trans-4-Hydroxy-l-Proline Differentially Impacts the Metabolism of Clostridioides difficile and Commensal Clostridia.

An intact gut microbiota confers colonization resistance against Clostridioides difficile through a variety of mechanisms, likely including competition for nutrients. Recently, proline was identified as an important environmental amino acid that C. difficile uses to support growth and cause significant disease. A posttranslationally modified form, trans-4-hydroxyproline, is highly abundant in collagen, which is degraded by host proteases in response to C. difficile toxin activity. The ability to dehydrate trans-4-hydroxyproline via the HypD glycyl radical enzyme is widespread among gut microbiota, including C. difficile and members of the commensal Clostridia, suggesting that this amino acid is an important nutrient in the host environment. Therefore, we constructed a C. difficile ΔhypD mutant and found that it was modestly impaired in fitness in a mouse model of infection, and was associated with an altered microbiota when compared to mice challenged with the wild-type strain. Changes in the microbiota between the two groups were largely driven by members of the Lachnospiraceae family and the Clostridium genus. We found that C. difficile and type strains of three commensal Clostridia had significant alterations to their metabolic gene expression in the presence of trans-4-hydroxyproline in vitro. The proline reductase (prd) genes were elevated in C. difficile, consistent with the hypothesis that trans-4-hydroxyproline is used by C. difficile to supply proline for energy metabolism. Similar transcripts were also elevated in some commensal Clostridia tested, although each strain responded differently. This suggests that the uptake and utilization of other nutrients by the commensal Clostridia may be affected by trans-4-hydroxyproline metabolism, highlighting how a common nutrient may be a signal to each organism to adapt to a unique niche. Further elucidation of the differences between them in the presence of hydroxyproline and other key nutrients will be important in determining their role in nutrient competition against C. difficile. IMPORTANCE Proline is an essential environmental amino acid that C. difficile uses to support growth and cause significant disease. A posttranslationally modified form, hydroxyproline, is highly abundant in collagen, which is degraded by host proteases in response to C. difficile toxin activity. The ability to dehydrate hydroxyproline via the HypD glycyl radical enzyme is widespread among gut microbiota, including C. difficile and members of the commensal Clostridia, suggesting that this amino acid is an important nutrient in the host environment. We found that C. difficile and three commensal Clostridia strains had significant, but different, alterations to their metabolic gene expression in the presence of hydroxyproline in vitro. This suggests that the uptake and utilization of other nutrients by the commensal Clostridia may be affected by hydroxyproline metabolism, highlighting how a common nutrient may be a signal to each organism to adapt to a unique niche. Further elucidation of the differences between them in the presence of hydroxyproline and other key nutrients will be important to determining their role in nutrient competition against C. difficile.

Performance of a high-temperature superconducting probe for in vivo microscopy at 2.0 T.

The use of a high-temperature superconducting probe for in vivo magnetic resonance microscopy at 2 T is described. To evaluate the performance of the probe, a series of SNR comparisons are carried out. The SNR increased by a factor of 3.7 compared with an equivalent copper coil. Quantitative measures of the SNR gain are in good agreement with theoretical predictions. A number of issues that are unique to the application of HTS coils are examined, including the difficulty in obtaining homogenous excitation without degrading the SNR of the probe. The use of the HTS probe in transmit-receive mode is simple to implement but results in nonuniform excitation. The effect of using the probe in this mode of operation on the T1 and T2 contrast is investigated. Methods for improving homogeneity are explored, such as employing a transmit volume coil. It is found that the cost of using an external transmit coil is an increased probe noise temperature and a reduced SNR by approximately 30%. Other important aspects of the probe are considered, including the effect of temperature on probe stability. Three-dimensional in vivo imaging sets are acquired to assess the stability of the probe for long scans. High-resolution images of the rat brain demonstrate the utility of the probe for microscopy applications.

Superconducting receiver coils for sodium magnetic resonance imaging.

We present the results from sodium magnetic resonance imaging (MRI) experiments using high-temperature superconducting (HTS) receiver coils. Sodium imaging has been shown to have great potential for the assessment of cell integrity but suffers from a substantially lower signal-to-noise ratio (SNR) than that of a hydrogen imaging. The use of an HTS receiver coil was found to significantly increase the SNR relative to an equivalent copper receiver coil at room temperature. The SNR gains afforded by HTS coils can also be used to decrease the imaging time.