Sterilization Resistance of Bacterial Spores Explained with Water Chemistry

Comparing Spore Resistance of Bacillus Strains Isolated from Hydrothermal Vents and Spacecraft Assembly Facilities to Environmental Stressors and Decontamination Treatments

Submarine hydrothermal vents are inhabited by a variety of microorganisms capable of tolerating environmental extremes, making them ideal candidates to further expand our knowledge of the limitations for terrestrial life, including their ability to survive the exposure of spaceflight-relevant conditions. The spore resistance of two Bacillus spp. strains, APA and SBP3, isolated from two shallow vents off Panarea Island (Aeolian Islands, Italy), to artificial and environmental stressors (i.e., UVC radiation, X-rays, heat, space vacuum, hydrogen peroxide [H₂O₂], and low-pressure plasma), was compared with that of two close phylogenetic relatives (Bacillus horneckiae and Bacillus oceanisediminis). Additional comparisons were made with Bacillus sp. isolated from spacecraft assembly facilities (B. horneckiae, Bacillus pumilus SAFR-032, and Bacillus nealsonii) and the biodosimetry strain and space microbiology model organism Bacillus subtilis. Overall, a high degree of spore resistance to stressors was observed for the strains isolated from spacecraft assembly facilities, with an exceptional level of resistance seen by B. pumilus SAFR-032. The environmental isolate SBP3 showed a more robust spore resistance to UVC, X-rays, H₂O₂, dry heat, and space vacuum than the closely related B. horneckiae. Both strains (SBP3 and APA) were more thermotolerant than their relatives, B. horneckiae and B. oceanisediminis, respectively. SBP3 may have a novel use as a bacterial model organism for future interrogations into the potential of forward contamination in extraterrestrial environments (e.g., icy moons of Jupiter or Saturn), spacecraft sterilization and, broadly, microbial responses to spaceflight-relevant environmental stressors.

Hydroxyapatite nanoparticle based fluorometric turn-on determination of dipicolinic acid, a biomarker of bacterial spores

Hydroxyapatite nanoparticles (HAP-NPs) were rendered fluorescence by doping with Eu(III) ion. The resulting fluorescent NPs are shown to be viable probes for sensitive and selective determination of dipicolinic acid (DPA), a major constituent of bacterial spores as used in bioterrorism. It is found that the addition of DPA to solutions of such HAP-NPs result in an enhancement of fluorescence due to the coordination of DPA with the Eu(III) dopant. The assay allows DPA to be detected in the 0.1 to 40 μM concentration range and with a 77 nM detection limit. The assay was applied to the detection of spores of Bacillus subtilis. The attractive properties of the probe make it a promising candidate for used in rapid detection of pathogenic bacterial spores. Graphical abstract Fluorescent hydroxyapatite nanoparticles (HAP-NPs) are shown to be a viable probe for detection of dipicolinic acid, a major constituent of bacterial spores. The red asterisks represent the fluorescence intensity of the HAP-NPs.

Picosecond orientational dynamics of water in living cells

Cells are extremely crowded, and a central question in biology is how this affects the intracellular water. Here, we use ultrafast vibrational spectroscopy and dielectric-relaxation spectroscopy to observe the random orientational motion of water molecules inside living cells of three prototypical organisms: Escherichia coli, Saccharomyces cerevisiae (yeast), and spores of Bacillus subtilis. In all three organisms, most of the intracellular water exhibits the same random orientational motion as neat water (characteristic time constants ~9 and ~2 ps for the first-order and second-order orientational correlation functions), whereas a smaller fraction exhibits slower orientational dynamics. The fraction of slow intracellular water varies between organisms, ranging from ~20% in E. coli to ~45% in B. subtilis spores. Comparison with the water dynamics observed in solutions mimicking the chemical composition of (parts of) the cytosol shows that the slow water is bound mostly to proteins, and to a lesser extent to other biomolecules and ions.

The cytoplasm’s crowdedness leads one to expect that cell water is different from bulk water. By measuring the rotational motion of water molecules in living cells, Tros et al. find that apart from a small fraction of water solvating biomolecules, cell water has the same dynamics as bulk water.

Water in cellulose: evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR

The organization of water molecules adsorbed onto cellulose and the supramolecular hydrated structure of microfibril aggregates represents, still today, one of the open and complex questions in the physical chemistry of natural polymers.

Functionalized Nano-MoS2 with Peroxidase Catalytic and Near-Infrared Photothermal Activities for Safe and Synergetic Wound Antibacterial Applications

We have developed a biocompatible antibacterial system based on polyethylene glycol functionalized molybdenum disulfide nanoflowers (PEG-MoS₂ NFs). The PEG-MoS₂ NFs have high near-infrared (NIR) absorption and peroxidase-like activity, which can efficiently catalyze decomposition of low concentration of H₂O₂ to generate hydroxyl radicals (·OH). The conversion of H₂O₂ into ·OH can avoid the toxicity of high concentration of H₂O₂ and the ·OH has higher antibacterial activity, making resistant bacteria more vulnerable and wounds more easily cured. The PEG-MoS₂ NFs combine the catalysis with NIR photothermal effect, providing a rapid and effective killing outcome in vitro for Gram-negative ampicillin resistant Escherichia coli (Amp^r E. coli) and Gram-positive endospore-forming Bacillus subtilis (B. subtilis) as compared to catalytic treatment or photothermal therapy (PTT) alone. Wound healing results indicate that the synergy antibacterial system could be conveniently used for wound disinfection in vivo. Interestingly, glutathione (GSH) oxidation can be accelerated due to the 808 nm irradiation induced hyperthermia at the presence of PEG-MoS₂ NFs proved by X-ray near-edge absorption spectra and X-ray spectroscopy. The accelerated GSH oxidation can result in bacterial death more easily. A mechanism based on ·OH-enhanced PTT is proposed to explain the antibacterial process.

Bacillus pumilus SAFR-032 Genome Revisited: Sequence Update and Re-Annotation

Bacillus pumilus strain SAFR-032 is a non-pathogenic spore-forming bacterium exhibiting an anomalously high persistence in bactericidal environments. In its dormant state, it is capable of withstanding doses of ultraviolet (UV) radiation or hydrogen peroxide, which are lethal for the vast majority of microorganisms. This unusual resistance profile has made SAFR-032 a reference strain for studies of bacterial spore resistance. The complete genome sequence of B. pumilus SAFR-032 was published in 2007 early in the genomics era. Since then, the SAFR-032 strain has frequently been used as a source of genetic/genomic information that was regarded as representative of the entire B. pumilus species group. Recently, our ongoing studies of conservation of gene distribution patterns in the complete genomes of various B. pumilus strains revealed indications of misassembly in the B. pumilus SAFR-032 genome. Synteny-driven local genome resequencing confirmed that the original SAFR-032 sequence contained assembly errors associated with long sequence repeats. The genome sequence was corrected according to the new findings. In addition, a significantly improved annotation is now available. Gene orders were compared and portions of the genome arrangement were found to be similar in a wide spectrum of Bacillus strains.