Biology subjects

Quesada, A.

Publications and source records attributed to Quesada, A..

2 recordsLinked to original sources

bioRxiv2020

Response of endolithic Chroococcidiopsis strains from the polyextreme Atacama Desert to light radiation

The Atacama Desert is known to be the place on Earth with one of the highest solar radiation limiting the presence of life to endolithic microhabitats and soil microbial ecosystems. Endolithic microbial communities are supported by photosynthetic primary producers, mainly cyanobacteria, which can be injured by UVR. Nevertheless, cyanobacteria exposed to high solar radiation and its harmful effects have developed a series of defense mechanisms: avoidance, antioxidant systems or production of photoprotective compounds such as scytonemin among others. Scytonemin is a liposoluble pigment whose absorption maxima are located in UVA and UVC range and highly absorbing in the UVB range. In order to elucidate the protection capacity of endolithic cyanobacteria against harmful radiation, two cyanobacterial strains from Chroococcidiopsis genus were isolated from different endolithic microhabitats in the Atacama Desert: UAM813 strain, originally from the cryptoendolithic microhabitat of halite (NaCl), and UAM816 strain from chasmoendolithic microhabitat of calcite (CaCO3). Both were exposed to PAR and UVR+PAR conditions studying their short-term response, as oxidative stress and long-term response, as scytonemin production, metabolic activity and ultrastructural damage. The observed response of both strains reveals a high sensitivity to direct light exposure, even to PAR. The differences in their acclimation suggest specific adaptation strategies related to their original microhabitat, revealing their protective potential and the strain specific environmental pressure selection to inhabit different microhabitats and exposed to different light conditions. ImportanceCyanobacteria are photosynthetic prokaryotes that inhabit most types of illuminated environments, even the endolithic microhabitats in cold and hot deserts. The environmental pressure caused by the extreme solar irradiation in the Atacama Desert involve that only those cyanobacterial strains able to cope with it can be found in these endolithic communities, usually dominated by members belonging to the extremotolerant Chroococcidiopsis genus. Here, a comprehensive analysis of multiple lines of defense against harmful sun radiation was conducted to diagnose the response of two Chroococcidiopsis strains isolated from different endolithic microhabitats and lithic substrates, and identify its relation with the original microenvironmental conditions of each strain. Our results contribute to a better understanding of the acclimation strategies developed by these cyanobacterial strains and its potential protective role for the whole endolithic microbial community.

microbiology↗

bioRxiv2020

Mobilization of a Kluyvera-like arnBCADTEF operon, besides mcr genes, confers colistin resistance to Escherichia coli isolated from healthy animals

The use of colistin as a last resort antimicrobial is compromised by the emergence of resistant enterobacteria with acquired determinants like mcr genes, mutations that activate the PmrAB two-component system and also by some other(s) still unknown mechanism(s). This work analyzed 74 E. coli isolates from healthy swine, turkey or bovine animals, characterizing their colistin resistance determinants. The mcr-1 gene, detected in 69 isolates, was the main determinant found among which 45% were carried by highly mobile plasmids, followed by four strains lacking previously known resistance determinants or two with mcr-4 (one in addition to mcr-1), whose phenotypes were not transferred by conjugation. Although a fraction of isolates carrying mcr-1 or mcr-4 genes also presented missense polymorphisms in pmrA or pmrB, constitutive activation of PmrAB was not detected, in contrast to control strains carrying mutations that confer colistin resistance. The expression of mcr genes negatively controls arnBCADTEF expression, a down-regulation that was also observed in the four isolates lacking known resistance determinants, three of them sharing the same macrorestriction and plasmid profiles. Genomic sequencing of one of these strains, isolated from a bovine in 2015, revealed a IncFII plasmid of 60 Kb encoding an arnBCADTEF operon closely related to Kluyvera ascorbata homologs. This element, named pArnT1, was cured by ethidum bromide and lost in parallel to colistin resistance. This work reveals that, besides mcr genes and chromosomal mutations, mobilization of arnBCADTEF operon represents a colistin resistance mechanism whose spread and relevance for public health should be carefully surveyed. Abstract ImportanceColistin is an old antibiotic that has returned to first-line fighting against (Gram negative) microorganisms after pandemic rising of antimicrobial resistance. However, low susceptibility to colistin is also becoming spread, mainly by plasmid mobilization of one of the enzymes (encoded by mcr genes) that modify covalently the external layer (the lipid A component of the lipopolysaccharide) of bacterial envelope, interfering antibiotic effectiveness. The second enzymatic system that performs envelope modification and confers colistin resistance when overexpressed is encoded by arnBCADTEF operon, a set of seven genes with location restricted (up to now) to the chromosome of Gram negative bacteria. This work describes plasmid mobilization of this operon between enterobacteria, from Kluyvera to Escherichia coli, where a Kluyvera-like arnBCADTEF operon carried by pArnT1 might represent, besides mcr genes, a potential risk for antimicrobial therapy and might require careful surveillance.

microbiology↗