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Natural clays have been used in ancient and modern medicine, but the mechanism(s) that make certain clays lethal against bacterial pathogens has not been identified. We have compared the depositional environments, mineralogies, and chemistries of clays that exhibit antibacterial effects on a broad spectrum of human pathogens including antibiotic resistant strains. Natural antibacterial clays contain nanoscale (<200 nm), illite-smectite and reduced iron phases. The role of clay minerals in the bactericidal process is to buffer the aqueous pH and oxidation state to conditions that promote Fe2+ solubility. Chemical analyses of E. coli killed by aqueous leachates of an antibacterial clay show that intracellular concentrations of Fe and P are elevated relative to controls. Phosphorus uptake by the cells supports a regulatory role of polyphosphate or phospholipids in controlling Fe2+. Fenton reaction products can degrade critical cell components, but we deduce that extracellular processes do not cause cell death. Rather, Fe2+ overwhelms outer membrane regulatory proteins and is oxidized when it enters the cell, precipitating Fe3+ and producing lethal hydroxyl radicals.

Honey from stingless bees (Tetragonula laeviceps) was collected from Chantaburi and Trat provinces in Thailand where bees are kept for commercial honey production. The honey was studied for its physiochemical, antimicrobial and antioxidant properties. For physiochemical analysis, compared to Apis mellifera honey, the honey samples collected from stingless bees were significantly greater in total moisture amount (26.98 ± 0.23 g/100g), ash content (0.26 ± 0.04 g/100g), pH (3.62 ± 0.01), total acidity (81.37 ± 0.55 meq/kg), electrical conductivity (0.62 ± 0.00 mS/cm), and HMF (1.08 ± 0.13 ppm), but no diastase activity could be detected. The sum of fructose and glucose was lower than 65% g/100g standards of A. mellifera honey, but sucrose was much higher. An agar well diffusion method was used to determine antimicrobial activities of the honey against fourteen species of bacteria (Klebsiella pneumoniae, Listeria monocytogenes, Micrococcus luteus, Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus epidermidis, Streptococcus pyogenes, methicillin-resistantStaphylococcus aureus (MRSA), Serratia marcescens, Salmonella typhimurium, Bacillus cereus, Escherichia coli, Staphylococcus aureus, and Propionibacterium acnes) and two species of yeasts (Candida albicans and Saccharomyces cerevisiae). The honey was found to inhibit the growth of thirteen species of bacteria except P. acnes and the two species of yeasts. The broth micro dilution method was used to assess the minimum inhibitory concentration (MIC) of stingless bee honey. The scavenging activity of honey samples was determined by 2, 2-diphenylpicrylhydrazyl (DPPH). It was found that the IC 50 in the honey samples from Chantaburi and Trat province were 0.07 ± 0.01 and 0.04 ± 0.00 mg/ml, respectively. Propiedades químicas y biológicas de la miel de abeja sin aguijón de Tailandia (Tetragonula leaviceps)Resumen Se recolectó miel de abejas sin aguijón (Tetragonula laeviceps) de las provincias de Tailandia Chantaburi y Trat, donde se crían las abejas para la producción comercial de miel. La miel se ha estudiado por sus propiedades físico-químicas, antimicrobianas y antioxidantes. Para el análisis físico-químico, en comparación con la miel de Apis mellifera, las muestras de miel de las abejas sin aguijón recogidas fueron significativamente mayores en la cantidad de humedad total (26,98 ± 0,23 g/100 g), contenido de cenizas (0,26 ± 0,04 g/100 g), pH (3,62 ± 0,01) , acidez total (81,37 ± 0,55 meq / kg), la conductividad eléctrica (0,62 ± 0,00 mS / cm), y el HMF (1,08 ± 0,13 ppm), pero no se detectó actividad de la diastasa. La suma de fructosa y glucosa fue menor que el estándar 65%g/100g de miel de A. mellifera, pero la de sacarosa fue mucho mayor. Se utilizó un método de difusión en agar para determinar las actividades antimicrobianas de la miel contra catorce especies de bacteria (

Thermodynamic calculations provide valuable insights into the reactions that drive the profound fluid transformations during serpentinization, where surface fluids are transformed into some of the most reduced and alkaline fluids on Earth. However, environmental observations usually deviate from thermodynamic predictions, especially those occurring at low temperatures where equilibrium is slowly reached. In this work, we analyzed 138 low‐temperature (<40°C) fluids from the Samail ophiolite in Oman to test thermodynamic predictions with environmental observations. Four fluid types were identified through this work. (i) Type 1 circumneutral (pH 7–9) fluids result from fluid interactions with serpentinized rocks common in the shallow subsurface. (ii) Fluids with pH ranging from 9 to 11 and low Si concentrations are products of intermediate stages of serpentinization. (iii) Type 2 hyperalkaline (pH > 11) fluids approach equilibrium with diopside, and with serpentine and brucite actively forming during advanced stages of serpentinization. Lastly, (iv) most fluids sampled in this work deviate from predicted equilibrium compositions and depict various degrees of mixing between Type 1 and 2 fluids. Mixed fluids fall within the same pH range but have considerably higher dissolved Si than intermediate‐type fluids. Hyperalkaline fluids exhibit variable degrees of mixing despite maintaining pH > 11, implying strong buffering capacity of serpentinization‐generated fluids. Overall, this work demonstrates that predicted and measured compositions of serpentinization‐derived fluids can be reconciled using a combination of equilibrium and fluid‐transport simulations. This work substantiates these calculations as useful tools in exploring serpentinization reactions in continents and perhaps in other low‐temperature environments on Earth and beyond.

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