PubMed · 6183326
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J R Stephenson, D J Wright. 1982. Clostridial bacteraemia.. https://doi.org/10.1016/0195-6701(82)90052-4
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Using treated municipal wastewater for crop irrigation is a key strategy to combat drought-induced water scarcity. However, current wastewater reclamation standards systematically underestimate risks from spore-forming pathogens. As highlighted in a recent minireview by A. Mrozinski, C. Le Maréchal, and E. Topp in Applied and Environmental Microbiology (92:e00173-26, 2026, https://doi.org/10.1128/aem.00173-26), Clostridioides difficile and Clostridium perfringens survive conventional disinfection, persist indefinitely in agricultural soils, and harbor critical antibiotic resistance genes. To safeguard the food supply and protect public health, regulatory frameworks must shift from relying solely on standard vegetative bacterial indicators and include monitoring resilient, spore-forming pathogens.
The extent and strength of the hydrogen bond networks in rubredoxins from the hyperthermophile Pyrococcus furiosus (PfRd), and its mesophilic analogue Clostridium pasteurianum (CpRd), are examined and compared using NMR spectroscopy. NMR parameters examined in this study include through-hydrogen bond (h3)J(NC)(') scalar couplings and (1)H, (13)C, and (15)N chemical shifts, as well as covalent (1)J(NH) and (1)J(NC)(') scalar couplings. These parameters have allowed the characterization in solution of 12 hydrogen bonds in each protein. Despite a 83% sequence homology and a low RMSD for the backbone heavy atoms (0.648 A) in the crystalline state, subtle, but definite, changes have been identified in the detailed hydrogen-bonding patterns. CpRd shows an increased number of hydrogen bonds in the triple-stranded beta-sheet and an additional hydrogen bond in the multiple-turn segment including residues 14-32. On the other hand, PfRd exhibits an overall strengthening of N-H...O=C hydrogen bonds in the loops involved at the metal binding site as well as evidence for an additional NH...S(Cys) hydrogen bond involving the alanine residue 44. These data, as well as temperature dependence of the NMR parameters, suggest that the particular NMR hydrogen bond pattern found in the hyperthermophile rubredoxin leads to an increased stabilization at the metal binding pocket. It seems to result from a subtle redistribution of hydrogen-bonding interactions between the triple-stranded beta-sheet and the actual metal binding site.
15N NMR hyperfine-shift data were collected for wild-type and site-specific mutant (V44I, V44A, and V44G) Clostridium pasteurianum rubredoxins in the oxidized state. Whereas most of the (15)N NMR signals did not exhibit large systematic changes upon mutation of residue 44, the signal from the backbone nitrogen of residue 44 itself (arrows) shifted by approximately 400 ppm. These shifts were used to determine the lengths of the hydrogen bond between the backbone amide of residue 44 and the side-chain sulfur of cysteine-44, which is covalently ligated to the iron of the metal center. The results, which demonstrated that this hydrogen bond is shorter in mutants with higher reduction potential, point to the importance of hydrogen bonds in modulating the reduction potential of iron-sulfur proteins.