The mutagenicity of sodium bisulfite on base-substitution strains of Salmonella typhimurium

Analysis of Transcriptomic Response to SO2 by Oenococcus oeni Growing in Continuous Culture

To successfully complete malolactic fermentation (MLF), Oenococcus oeni must overcome wine stress conditions of low pH, high ethanol, and the presence of SO2. Failure to complete MLF may result in detrimental effects to the quality and stability of the resulting wines. Research efforts to date have focused on elucidating the mechanisms and genetic features that confer the ability to withstand low pH and high ethanol concentrations on O. oeni; however, the responses to SO2 stress are less well defined. This study focused on characterizing the transcriptional response of O. oeni to SO2 challenge during cultivation in a continuous system at wine-like pH (3.5). This experimental design allowed the precise discrimination of transcriptional changes linked to SO2 stress from responses associated with growth stage and cultivation parameters. Differential gene expression analysis revealed major transcriptional changes following SO2 exposure and suggested that this compound primarily interacts with intracellular proteins, DNA, and the cell envelope of O. oeni. The molecular chaperone hsp20, which has a demonstrated function in the heat, ethanol, and acid stress response, was highly upregulated, confirming its additional role in the response of this species to SO2 stress. This work also reports the first nanopore-based complete genome assemblies for O. oeni. IMPORTANCE Malolactic fermentation is an indispensable step in the elaboration of most wines and is generally performed by Oenococcus oeni, a Gram-positive heterofermentative lactic acid bacterium species. While O. oeni is tolerant to many of the wine stresses, including low pH and high ethanol concentrations, it has high sensitivity to SO2, an antiseptic and antioxidant compound regularly used in winemaking. Understanding the physiological changes induced in O. oeni by SO2 stress is essential for the development of more robust starter cultures and methods for their use. This study describes the main transcriptional changes induced by SO2 stress in the wine bacterium O. oeni and provides foundational understanding on how this compound interacts with the cellular components and the induced protective mechanisms of this species.

Final Report on the Safety Assessment of Sodium Sulfite, Potassium Sulfite, Ammonium Sulfite, Sodium Bisulfite, Ammonium Bisulfite, Sodium Metabisulfite and Potassium Metabisulfite

Sodium Sulfite, Ammonium Sulfite, Sodium Bisulfite, Potassium Bisulfite, Ammonium Bisulfite, Sodium Metabisulfite, and Potassium Metabisulfite are inorganic salts that function as reducing agents in cosmetic formulations. All except Sodium Metabisulfite also function as hair-waving/straightening agents. In addition, Sodium Sulfite, Potassium Sulfite, Sodium Bisulfite, and Sodium Metabisulfite function as antioxidants. Although Ammonium Sulfite is not in current use, the others are widely used in hair care products. Sulfites that enter mammals via ingestion, inhalation, or injection are metabolized by sulfite oxidase to sulfate. In oral-dose animal toxicity studies, hyperplastic changes in the gastric mucosa were the most common findings at high doses. Ammonium Sulfite aerosol had an acute LC50 of >400 mg/m3 in guinea pigs. A single exposure to low concentrations of a Sodium Sulfite fine aerosol produced dose-related changes in the lung capacity parameters of guinea pigs. A 3-day exposure of rats to a Sodium Sulfite fine aerosol produced mild pulmonary edema and irritation of the tracheal epithelium. Severe epithelial changes were observed in dogs exposed for 290 days to 1 mg/m3 of a Sodium Metabisulfite fine aerosol. These fine aerosols contained fine respirable particle sizes that are not found in cosmetic aerosols or pump sprays. None of the cosmetic product types, however, in which these ingredients are used are aerosolized. Sodium Bisulfite (tested at 38%) and Sodium Metabisulfite (undiluted) were not irritants to rabbits following occlusive exposures. Sodium Metabisulfite (tested at 50%) was irritating to guinea pigs following repeated exposure. In rats, Sodium Sulfite heptahydrate at large doses (up to 3.3 g/kg) produced fetal toxicity but not teratogenicity. Sodium Bisulfite, Sodium Metabisulfite, and Potassium Metabisulfite were not teratogenic for mice, rats, hamsters, or rabbits at doses up to 160 mg/kg. Generally, Sodium Sulfite, Sodium Metabisulfite, and Potassium Metabisulfite were negative in mutagenicity studies. Sodium Bisulfite produced both positive and negative results. Clinical oral and ocular-exposure studies reported no adverse effects. Sodium Sulfite was not irritating or sensitizing in clinical tests. These ingredients, however, may produce positive reactions in dermatologic patients under patch test. In evaluating the positive genotoxicity data found with Sodium Bisulfite, the equilibrium chemistry of sulfurous acid, sulfur dioxide, bisulfite, sulfite, and metabisulfite was considered. This information, however, suggests that some bisulfite may have been present in genotoxicity tests involving the other ingredients and vice versa. On that basis, the genotoxicity data did not give a clear, consistent picture. In cosmetics, however, the bisulfite form is used at very low concentrations (0.03% to 0.7%) in most products except wave sets. In wave sets, the pH ranges from 8 to 9 where the sulfite form would predominate. Skin penetration would be low due to the highly charged nature of these particles and any sulfite that did penetrate would be converted to sulfate by the enzyme sulfate oxidase. As used in cosmetics, therefore, these ingredients would not present a genotoxicity risk. The Cosmetic Ingredient Review Expert Panel concluded that Sodium Sulfite, Potassium Sulfite, Ammonium Sulfite, Sodium Bisulfite, Ammonium Bisulfite, Sodium Metabisulfite, and Potassium Metabisulfite are safe as used in cosmetic formulations.

Base damage within single-strand DNA underlies in vivo hypermutability induced by a ubiquitous environmental agent

Chromosomal DNA must be in single-strand form for important transactions such as replication, transcription, and recombination to occur. The single-strand DNA (ssDNA) is more prone to damage than double-strand DNA (dsDNA), due to greater exposure of chemically reactive moieties in the nitrogenous bases. Thus, there can be agents that damage regions of ssDNA in vivo while being inert toward dsDNA. To assess the potential hazard posed by such agents, we devised an ssDNA-specific mutagenesis reporter system in budding yeast. The reporter strains bear the cdc13-1 temperature-sensitive mutation, such that shifting to 37°C results in telomere uncapping and ensuing 5' to 3' enzymatic resection. This exposes the reporter region, containing three closely-spaced reporter genes, as a long 3' ssDNA overhang. We validated the ability of the system to detect mutagenic damage within ssDNA by expressing a modified human single-strand specific cytosine deaminase, APOBEC3G. APOBEC3G induced a high density of substitutions at cytosines in the ssDNA overhang strand, resulting in frequent, simultaneous inactivation of two reporter genes. We then examined the mutagenicity of sulfites, a class of reactive sulfur oxides to which humans are exposed frequently via respiration and food intake. Sulfites, at a concentration similar to that found in some foods, induced a high density of mutations, almost always as substitutions at cytosines in the ssDNA overhang strand, resulting in simultaneous inactivation of at least two reporter genes. Furthermore, sulfites formed a long-lived adducted 2'-deoxyuracil intermediate in DNA that was resistant to excision by uracil-DNA N-glycosylase. This intermediate was bypassed by error-prone translesion DNA synthesis, frequently involving Pol ζ, during repair synthesis. Our results suggest that sulfite-induced lesions in DNA can be particularly deleterious, since cells might not possess the means to repair or bypass such lesions accurately.

Conditions affecting the mutagenicity of sodium bisulfite in Salmonella typhimurium

Sodium bisulfite is a weak mutagen at pH 5 and 6 in S. typhimurium strains carrying the hisG46 and hisD6610 mutations, but is not mutagenic in strains with the hisC3076 or hisD3052 mutations. The bisulfite-induced base-pair substitution mutations were slightly enhanced by the presence of the plasmid, pKM101, but inhibited by the presence of the uvrB and rfa mutations. The hisO1242 mutation which causes constitutive expression of the histidine operon, produced a slight enhancement of frameshift (hisD6610), but not base-pair substitution (hisG46) mutations. Bisulfite-induced mutations appear to be the result of two different mechanisms which may be a function of the repair capacity of the strains. The data suggest that the deamination of cytosine may not be responsible for frameshift mutations, but may be responsible for base-pair substitution mutagenesis. Because the rate of bisulfite autooxidation appears to play a role in the mutagenic process, we are suggesting that the deamination of cytosine may be the result of oxidative damage rather than through the direct formation of a cytosine-bisulfite adduct. This is further supported by the much lower concentrations of bisulfite needed to cause mutagenicity than the 1 M concentrations cited to produce cytosine-bisulfite adducts.