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Microbial contamination in aircraft fuel-containing systems poses significant threats to flight safety and operational integrity as a result of microbiologically influenced corrosion (MIC). Regular monitoring for microbial contamination in these fuel systems is essential for mitigating MIC risks. However, the frequency of monitoring remains a challenge due to the complex environmental conditions encountered in fuel systems. To investigate the impact of environmental variables such as water content, oxygen levels, and temperature on the MIC of aluminum alloy in aircraft fuel systems, orthogonal experiments with various combinations of these variables were conducted in the presence of sulfate-reducing bacteria. Among these variables, water content in the fuel oil demonstrated the most substantial influence on the corrosion rate of aluminum alloys, surpassing the effects of oxygen and temperature. Notably, the corrosion rate of aluminum alloys was the highest in an environment characterized by a 1:1 water/oil ratio, 0% oxygen, and a temperature of 35 °C. Within this challenging environment, conducive to accelerated corrosion, changes in the corrosion behavior of aluminum alloys over time were analyzed to identify the time point at which MIC intensified. Observations revealed a marked increase in the depth and width of corrosion pits, as well as in the corrosion weight-loss rate, starting from the 7th day. These findings offer valuable insights for determining the optimal frequency of microbial contamination detection in aircraft fuel systems. [ABSTRACT FROM AUTHOR]

Bioleaching of Cu from the copper concentrate of Armanis gold-bearing polymetallic ore (Armenia) was investigated. The main objective was revealing high active bacteria and their association, as well as optimizing the bioleaching process with their application to ensure the most efficient recovery of copper from the tested concentrate. To obtain optimal bacterial associations, bottom-up and top-down approaches were used. Bioleaching of copper concentrate was carried out using pure cultures of iron- and sulfur-oxidizing bacteria and their mixed culture, as well as indigenous bacterial consortium. Comparative studies of copper bioleaching by mixed cultures of Acidithiobacillus caldus, Leptospirillum ferriphilum CC, Sulfobacillus thermosulfidooxidans 6, and indigenous consortium Arm of iron-oxidizing bacteria were performed. At the beginning of bioleaching, the amounts of extracted copper by mixed culture and Arm consortium were equal; afterward, between 20–27 days, the Arm indigenous consortium showed significantly higher activity in terms of copper extraction. In parallel, mineralogical and liberation analyses of feed material and bioleaching residues were performed. [ABSTRACT FROM AUTHOR]

A new strain of Leptospirillum sp. Ksh-L was isolated from a dump-bioleaching system of the Kashen copper-molybdenum mine (South Caucasus). Ksh-L is an obligate chemolithoautotroph, capable of oxidizing ferrous iron (Fe2+). Cells are Gram-negative and vibrio- or spirillum-shaped of a 0.5–3 µm size. The optimal conditions for the growth are 35 °C and pH 1.6–1.8. Cu2+ and Zn2+ have different effects on the oxidizing ability of the Leptospirillum sp. Ksh-L culture depending on the phase of growth and concentration of Fe2+. Under the conditions of gradually increasing the concentration of copper in the medium, during 4–5 successive subculturing experiments, it was possible to obtain an adapted culture of Leptospirillum sp. Ksh-L, capable of growing in the medium in the presence of up to 400 mM Cu2+. A bioleaching experiment indicates that Ksh-L can efficiently oxidize chalcopyrite. However, the bioleaching of copper from chalcopyrite by Leptospirillum ferrodiazotropum Ksh-L increased about 1.8 times in association with At. thiooxidans ATCC 19377. Phylogenetic analysis based on 16S rRNA gene sequences (GenBank ID ON226845) shows that strain Ksh-L forms a single cluster into Group III. The strain possesses 99.59%, 99.52%, and 96.60% sequence similarity with the strains YTW-96-06, YTW-66-06, and Leptospirillum ferrodiazotrophum 5C in Group III, respectively. [ABSTRACT FROM AUTHOR]