Iron availability enhances the cellular energetics of aerobic Escherichia coli cultures while upregulating anaerobic respiratory chains.

Aerobic Escherichia coli growth at restricted iron concentrations (≤ 1.75 ± 0.04 µM) is characterized by lower biomass yield, higher acetate accumulation and higher activation of the siderophore iron-acquisition systems. Although iron homeostasis in E. coli has been studied intensively, previous studies focused only on understanding the regulation of the iron import systems and the iron-requiring enzymes. Here, the effect of iron availability on the energy metabolism of E. coli has been investigated. It was established that aerobic cultures growing under limiting iron conditions showed lower ATP yield per glucose, lower growth rate and lower TCA cycle activity and respiration, at the same time as increased glucose consumption, acetate and pyruvate accumulation, practically mimicking microaerobic growth. However, at excess iron, independent of oxygen availability, the cultures showed high cellular energetics (5.8 ATP/mol of glucose) by using pathways requiring iron-rich complex proteins found in the TCA cycle and respiratory chain. In conditions of iron excess, some iron-requiring terminal reductases of the respiratory chain, that were thought to function only under anaerobiosis, were used by the E. coli, when in aerobic conditions, to maintain high respiratory activity. This allowed it to produce more biomass and more reactive oxygen species that were controlled by the higher activity of the antioxidant defenses (SOD, peroxidase and catalase) and the iron-sulfur cluster repair systems.

The Probiotical Potential of Lactobacilli from Therapeutic Preventive Beverage Kurunga.

INTRODUCTION: Kurunga is a dairy drink made of a mix of lactic acid and alcoholic fermentation, characterized by high biological value based on protein composition, amino acid spectrum, fatty acid composition of lipids, vitamin and mineral substances, and physiological activity of microbiota containing lactobacilli, lactococci, bifidobacteria, and yeast. Among the probiotic correctors of normal microbiota isolated from national products, lactobacilli was of particular interest, with regards to a therapeutic - preventive effect. The aim of the study was to examine the probiotic properties of lactobacilli from kurunga. METHODS: We isolated lactic acid bacteria strains from kurunga. The isolated cultures were identified using common microbiological methods and phylogenetic analysis. The antibiotic activities of these strains were determined by measuring the growth inhibition zone of test cultures. The probiotic properties were measured as levels of resistance to bile and hydrochloric acids, in addition to the presence of superoxide dismutase (SOD) activity using the xanthine oxidase-cytochrome method. Proteolitic activity was determined at the various levels of pH (3.0, 4.2, 5.3, and 7.0). RESULTS: According to the morphological, cultural, physiological, biochemical properties and the genotypic analysis of the oligonucleotides sequence of specific genes, the most effective strain was identified as Lactobacillus diolivorans KL-2 (GenBank database KC438372). The isolated strain suppressed the growth of Gram-positive bacteria, such as Bacillus, Staphylococcus, and Listeria sp., as well as Gram-negative bacteria, such as E.coli, Proteus, Salmonella sp. They also possessed fungicidal action (based on Penicillum, Aspergillus sp, and Candida sp.). The strain was resistant to the action of the bile acids at concentrations of 0.8% to 1.0% and hydrochloric acid. The strain KL-2 possessed a relatively high SOD activity (25.74 U/mg of protein), a low proteolytic activity at a pH 3.0 (4.74·10-3 PU/ml), and high proteolytic activity at pH 4.2 (294.74·10-3 PU/ml), pH 5.3 (330.52·10-3 PU/ml) and pH 7.0 (713.68·10-3 PU/ml). CONCLUSION: The unique properties of this strain, such as stability in the gastrointestinal tract, the wide spectrum of bactericidal and fungicidal action to the pathogenic species, the relatively high superoxide dismutase and proteolytic activities, and the absence of toxicity, make it a prime candidate for probiotic culturing.