Structure and functional properties of the cold-adapted catalase from Acinetobacter sp. Ver3 native to the Atacama plateau in northern Argentina

The Structural Biology of Catalase Evolution

Catalases are essential enzymes for removal of hydrogen peroxide, enabling aerobic and anaerobic metabolism in an oxygenated atmosphere. Monofunctional heme catalases, catalase-peroxidases, and manganese catalases, evolved independently more than two billion years ago, constituting a classic example of convergent evolution. Herein, the diversity of catalase sequences is analyzed through sequence similarity networks, providing the context for sequence distribution of major catalase families, and showing that many divergent catalase families remain to be experimentally studied.

Diverse Repertoire and Relationship of Exopolysaccharide Genes in Cold-Adapted Acinetobacter sp. CUI-P1 Revealed by Comparative Genome Analysis

This study focused on the exploration of microbial communities inhabiting extreme cold environments, such as the Passu and Pisan glaciers of Pakistan, and their potential utilization in industrial applications. Among the 25 initially screened strains, five were found to be suitable candidates for exopolysaccharide (EPS) production, with strain CUI-P1 displaying the highest yield of 7230.5 mg/L compared to the other four strains. The purified EPS from CUI-P1 was tested for its ability to protect probiotic bacteria and E. coli expressing green fluorescence protein (HriGFP) against extreme cold temperatures, and it exhibited excellent cryoprotectant and emulsification activity, highlighting its potential use in the biotechnological industry. Furthermore, the genome of Acinetobacter sp., CUI-P1 comprised 199 contigs, with a genome size of 10,493,143bp and a G + C content of 42%, and showed 98.197% nucleotide identity to the type genome of Acinetobacter baumannii ATCC 17978. These findings offer promising avenues for the application of EPS as a cryoprotectant, an essential tool in modern biotechnology.

The distinctive roles played by the superoxide dismutases of the extremophile Acinetobacter sp. Ver3

Acinetobacter sp. Ver3 is a polyextremophilic strain characterized by a high tolerance to radiation and pro-oxidants. The Ver3 genome comprises the sodB and sodC genes encoding an iron (^AV3SodB) and a copper/zinc superoxide dismutase (^AV3SodC), respectively; however, the specific role(s) of these genes has remained elusive. We show that the expression of sodB remained unaltered in different oxidative stress conditions whereas sodC was up-regulated in the presence of blue light. Besides, we studied the changes in the in vitro activity of each SOD enzyme in response to diverse agents and solved the crystal structure of ^AV3SodB at 1.34 Å, one of the highest resolutions achieved for a SOD. Cell fractionation studies interestingly revealed that ^AV3SodB is located in the cytosol whereas ^AV3SodC is also found in the periplasm. Consistently, a bioinformatic analysis of the genomes of 53 Acinetobacter species pointed out the presence of at least one SOD type in each compartment, suggesting that these enzymes are separately required to cope with oxidative stress. Surprisingly, ^AV3SodC was found in an active state also in outer membrane vesicles, probably exerting a protective role. Overall, our multidisciplinary approach highlights the relevance of SOD enzymes when Acinetobacterspp. are confronted with oxidizing agents.