Biofilm disruption and bactericidal activity of aqueous ozone coupled with ultrasonic dental scaling.

Background: The COVID-19 pandemic has heightened the awareness of a common hazard encountered in the dental clinic: aerosol transmission of pathogens. Treatment of sources of infection before or during dental procedures is one means of decreasing pathogen load and aerosol transmission. Methods: An ultrasonic scaler supplied with aqueous ozone was used to examine the effect of its viability on planktonic cultures and biofilms formed by 2 model bacteria: Rothia mucilaginosa and Escherichia coli. Results: Both organisms showed susceptibility to aqueous ozone alone (97% and 99.5% lethality, respectively). When combined with manual scaling using an ultrasonic scaler, a greater than 99% reduction in colony-forming units (CFUs)/mL could be reached with an aqueous ozone concentration of approximately 2 mg/L (R. mucilaginosa) or 0.75 mg/L (E. coli) after 5 through 6 seconds of scaling. Conclusions: Aqueous ozone coupled with ultrasonic scaling exhibited a higher efficiency of microbial kill than either method used alone. Both gram-positive and gram-negative species were affected by this treatment. Studies on other oral microbiota constituents, including fungi and viruses, will provide information on the efficacy of this method on a greater biological scale. Studies to verify concomitant reduction of microbial load in dispersed aerosols in clinical settings should be completed to support practical applications of this treatment.

Ice nucleation in a Gram-positive bacterium isolated from precipitation depends on a polyketide synthase and non-ribosomal peptide synthetase.

Earth's radiation budget and frequency and intensity of precipitation are influenced by aerosols with ice nucleation activity (INA), i.e., particles that catalyze the formation of ice. Some bacteria, fungi, and pollen are among the most efficient ice nucleators but the molecular basis of INA is poorly understood in most of them. Lysinibacillus parviboronicapiens (Lp) was previously identified as the first Gram-positive bacterium with INA. INA of Lp is associated with a secreted, nanometer-sized, non-proteinaceous macromolecule or particle. Here a combination of comparative genomics, transcriptomics, and a mutant screen showed that INA in Lp depends on a type I iterative polyketide synthase and a non-ribosomal peptide synthetase (PKS-NRPS). Differential filtration in combination with gradient ultracentrifugation revealed that the product of the PKS-NRPS is associated with secreted particles of a density typical of extracellular vesicles and electron microscopy showed that these particles consist in "pearl chain"-like structures not resembling any other known bacterial structures. These findings expand our knowledge of biological INA, may be a model for INA in other organisms for which the molecular basis of INA is unknown, and present another step towards unraveling the role of microbes in atmospheric processes.

A central role for the transcriptional regulator VtlR in small RNA-mediated gene regulation in Agrobacterium tumefaciens.

LysR-type transcriptional regulators (LTTRs) are the most common type of transcriptional regulators in prokaryotes and function by altering gene expression in response to environmental stimuli. In the class Alphaproteobacteria, a conserved LTTR named VtlR is critical to the establishment of host-microbe interactions. In the mammalian pathogen Brucella abortus, VtlR is required for full virulence in a mouse model of infection, and VtlR activates the expression of abcR2, which encodes a small regulatory RNA (sRNA). In the plant symbiont Sinorhizobium meliloti, the ortholog of VtlR, named LsrB, is involved in the symbiosis of the bacterium with alfalfa. Agrobacterium tumefaciens is a close relative of both B. abortus and S. meliloti, and this bacterium is the causative agent of crown gall disease in plants. In the present study, we demonstrate that VtlR is involved in the ability of A. tumefaciens to grow appropriately in artificial medium, and an A. tumefaciens vtlR deletion strain is defective in motility, biofilm formation, and tumorigenesis of potato discs. RNA-sequencing analyses revealed that more than 250 genes are dysregulated in the ∆vtlR strain, and importantly, VtlR directly controls the expression of three sRNAs in A. tumefaciens. Taken together, these data support a model in which VtlR indirectly regulates hundreds of genes via manipulation of sRNA pathways in A. tumefaciens, and moreover, while the VtlR/LsrB protein is present and structurally conserved in many members of the Alphaproteobacteria, the VtlR/LsrB regulatory circuitry has diverged in order to accommodate the unique environmental niche of each organism.

Chryseobacterium angstadtii sp. nov., isolated from a newt tank.

As part of an undergraduate microbiology course, a yellow-orange-pigmented, Gram-staining negative, rod-shaped, non-motile bacterial strain was isolated from a glass tank housing several red-spotted newts (Notophthalmus viridescens). The sequence of the 16S rRNA gene of this strain, designated KM(T), was 97.4-98.0 % similar to those of the type strains of Chryseobacterium luteum, C. shigense and C. vrystaatense, while the similarity levels for protein-coding genes were less than 94.7 % for rpoB, less than 92.1 % for groEL and less than 87.1 % for gyrB. These values are lower than for many other established distinct species. Polyphasic characterization and comparison to these relatives revealed that strain KM(T) was similar to other Chryseobacterium strains in that it contained MK-6 as its major respiratory quinone and phosphatidylethanolamine as the most abundant polar lipid, produced flexirubin-type pigments, oxidase and catalase and primarily contained the fatty acids iso-C15 : 0, iso-C17 : 1ω9c, iso-C17 : 0 3-OH and summed feature 3 (comprising C16 : 1ω6c and/or C16 : 1ω7c). Based on the results of this study, strain KM(T) represents a novel species, for which the name Chryseobacterium angstadtii sp. nov. is proposed. The type strain is KM(T) ( = ATCC BAA-2160(T) = NRRL B-59516(T) = KCTC 23297(T)).

Chryseobacterium piperi sp. nov., isolated from a freshwater creek.

As part of an undergraduate microbiology course, a yellow-orange pigmented, Gram-staining negative, rod-shaped, non-motile bacterial strain, designated CTM(T), was isolated from a creek in North-central Pennsylvania during the winter of 2006. The 16S rRNA gene sequence of the strain showed ~97 % similarity to that of Chryseobacterium soldanellicola PSD1-4(T) and Chryseobacterium soli JS6-6(T), while the protein-coding gyrB gene sequence of strain CTM(T) showed <87 % similarity to those of its two closest relatives. Using a polyphasic approach, strain CTM(T) was characterized and compared to these and other closely related species of the genus Chryseobacterium. Strain CTM(T) was similar to other strains of the genus Chryseobacterium in that it contained MK-6 as its major respiratory quinone, produced flexirubin-type pigments, oxidase and catalase, hydrolysed DNA, gelatin and aesculin and contained the fatty acids iso-C15:0, iso-C17:1ω9c, iso-C17:0 3-OH and summed feature 3 (C16:1ω6c, C16:1ω7c and/or iso-C15:0 2-OH). Based on the results of this study, strain CTM(T) represents a novel species of the genus Chryseobacterium, for which the name Chryseobacterium piperi sp. nov. is proposed. The type strain is CTM(T) ( = ATCC BAA-1782(T)  = CCUG 57707(T)  = JCM 15960(T)  = DSM 22249(T)  = KCTC 23267(T)).