Unlocking Survival Mechanisms for Metal and Oxidative Stress in the Extremely Acidophilic, Halotolerant Acidihalobacter Genus

Abstract

Microorganisms used for the biohydrometallurgical extraction of metals from minerals must be able to survive high levels of metal and oxidative stress found in bioleaching environments. The Acidihalobacter genus consists of four species of halotolerant, iron–sulfur-oxidizing acidophiles that are unique in their ability to tolerate chloride and acid stress while simultaneously bioleaching minerals. This paper uses bioinformatic tools to predict the genes and mechanisms used by Acidihalobacter members in their defense against a wide range of metals and oxidative stress. Analysis revealed the presence of multiple conserved mechanisms of metal tolerance. Ac. yilgarnensis F5T, the only member of this genus that oxidizes the mineral chalcopyrite, contained a 39.9 Kb gene cluster consisting of 40 genes encoding mobile elements and an array of proteins with direct functions in copper resistance. The analysis also revealed multiple strategies that the Acidihalobacter members can use to tolerate high levels of oxidative stress. Three of the Acidihalobacter genomes were found to contain genes encoding catalases, which are not common to acidophilic microorganisms. Of particular interest was a rubrerythrin genomic cluster containing genes that have a polyphyletic origin of stress-related functions.

Genome-wide transcriptional response to silver stress in extremely halophilic archaeon Haloferax alexandrinus DSM 27206 T

“…As thioredoxin fold proteins (thioredoxins, preoxiredoxins, oxidoreductases, etc.) are considered prominent cellular protectors against oxidative stress [ 73 , 74 ], these results seem rather intriguing and demand further investigations.…”

Adaptive Response of Thermophiles to Redox Stress and Their Role in the Process of dye Degradation From Textile Industry Wastewater

“…It results from the imbalance between pro-oxidative and antioxidative species that are generated from endogenous or exogenous sources ( Sen and Imlay, 2021 ) . Prooxidants that include reactive oxygen species (ROS) are produced mainly produced during aerobic respiration ( Khaleque et al, 2020 ; Farías et al, 2021 ) . The ROS causes oxidative damage to cellular components by attacking nucleic acids, cell membranes, and proteins, which causes mutation, protein denaturation, enzyme inactivation, or lipid peroxidation and disrupts intracellular homeostasis ( Stewart et al, 2012 ; Zhang et al, 2012 ; Ren et al, 2020 ) .…”

“…Besides normal metabolic sources, environmental factors such as high oxygen pressure, lack of water, temperature, high metal ion concentrations, radiation, salinity, and other chemicals contribute to the generation of ROS ( Figure 3 ) ( Khaleque et al, 2020 ) . Many pollutants including dyes are redox-active, which, after uptake by microorganisms, cause univalent reduction of molecular oxygen, leading to the generation of superoxide radicals, H 2 O 2, and hydroxyl radical (•OH) ( Zhang et al, 2012 ).…”

“…The control of iron homeostasis and responses to OS are interrelated ( Cornelis et al, 2011 ) because iron is an essential nutrient (a cofactor for many enzymes) for the growth of microorganisms. Iron can generate ROSs through the Fenton reaction ( Cárdenas et al, 2012 ; Sen and Imlay, 2021 ) where H 2 O 2 reacts with Fe 2+ (Equ 1) to form the highly reactive hydroxyl radical (.OH) which is a strong oxidizing agent among the ROS leading to damage of DNA, proteins, lipids, and carbohydrates ( Khaleque et al, 2020 ). Thus, microbes regulate iron uptake and storage in such a way that restricts the accumulation of ROS in the metabolic process to reduce or prevent damage to the cell from oxidative stress.…”

Prediction and Inferred Evolution of Acid Tolerance Genes in the Biotechnologically Important Acidihalobacter Genus

“…Currently four organisms belonging to the Acidihalobacter genus have been isolated and cultivated in laboratory conditions: Acidihalobacter prosperus DSM 5130 T from the geothermally heated seafloor at Porto di Levante, Vulcano, Italy; Acidihalobacter aeolianus DSM 14174 T , and Acidihalobacter ferrooxydans DSM 14175 T from the hydrothermal pools at the Aeolian Islands, Vulcano Italy and Acidihalobacter yilgarnensis DSM 105917 T from an acidic saline lake drain in Western Australia ( Huber and Stetter, 1989 ; Simmons and Norris, 2002 ; Zammit et al, 2009 ). Several studies have been conducted on the Acidihalobacter genus, understanding its response to chloride ions, osmotic stress, metal stress and oxidative stress ( Dopson et al, 2016 ; Khaleque et al, 2018 , 2019 , 2020 ) but there has been limited focus on their mechanisms of survival at extremely low pH. The Acidihalobacter are interesting not only because they are deeply intriguing polyextremophiles but also because they are among the few organisms that can be used for copper recovery (bioleaching) from chalcopyrite ( Khaleque et al, 2017a ).…”