Diversidade de genes de resistência em bactérias de ambientes extremos.

Abstract

Bacteria from extreme environments are poorly understood and the evolutionary histories linked to resistance and virulence gene patterns are still hidden. Although they are usually associated with a single extreme condition, they are often described as multi-resistances, which we assume is due to their rich genetic arsenal. Studying the diversity of these genes can help us to understand how bacterial life adapts in the scenario of environmental changes resulting from human action. This work studied the diversity of resistance mechanisms in bacteria and their shared genes between representatives of the Terrabacteria and Proteobacteria taxa. 16 genomes from 12 genera was selected, including thermophilic, psychrophilic, halotolerant, radiotolerant, acidophilic and resistant to heavy metals bacteria, in addition to 44 resistance genes. A phylogenetic tree was constructed with the 16S rRNA sequences (MEGA software). The sequences of the genes of interest were aligned against the NCBI/BLAST database, and their relationships to Mobile Genetic Elements (MGEs) obtained (IslandViewer 4). Among the gene products, we highlight the Quorum Sensing molecules for biofilm formation, present among phylogenetically distant taxa, where homologous signalers and receptors can be used to understand multi-resistances in extreme environments. On the other hand, we also found genes that act together in the creation of resistance, such as the mutS/mutL DNA repair genes, or the resistance genes to several phaE/phaC stressors, but which in some taxa showed the absence of one of alleles, or significant variations in the percentage of alignment of the alignments, indicating a possible difference in functionality. Other genes were more restricted to certain taxa, such as the ddrD of the radiotolerant Deinococcus radiodurans, which acts within a specific scenario of radiation and nutritional scarcity, in which case the improvement of a single gene/product led to a multi-resistance mechanism. Another example of restrictiveness is the phaE gene of the multidrug-resistant Rubrobacter xylanophilus, which cooperates in robustness and resistance to stress in this species. We also observed three cases of correlation between MGEs and resistance genes: the first in the occurrence of the radiotolerance gene recA in Genomic Islands in Thermus sp; another in the relationship of MGEs and Genomic Islands with the ars and cad genes, for arsenic and cadmium resistance, respectively, in Geobacillus stearothermophilus; and finally, the relationship of the Acidiphilium sp gene kdpB with plasmids in several of the taxa studied. This evidence indicates that, at least for a small part of these mechanisms, there is a potential for sharing resistance genes through Horizontal Gene Transfer (HGT). This potential for mobility could be an excellent biotechnological tool in the genomic editing of bacteria used in the bioremediation of contaminated environments. We believe that further studies of patterns and variations, phylogenetic analyzes and correlation of these genes with MGEs and genomic islands, may be ways to understand more about the diversity of resistance genes in extremophile bacteria.