Something Old, Something New, Something Borrowed; How the Thermoacidophilic Archaeon Sulfolobus solfataricus Responds to Oxidative Stress

Abstract

To avoid molecular damage of biomolecules due to oxidation, all cells have evolved constitutive and responsive systems to mitigate and repair chemical modifications. Archaea have adapted to some of the most extreme environments known to support life, including highly oxidizing conditions. However, in comparison to bacteria and eukaryotes, relatively little is known about the biology and biochemistry of archaea in response to changing conditions and repair of oxidative damage. In this study transcriptome, proteome, and chemical reactivity analyses of hydrogen peroxide (H2O2) induced oxidative stress in Sulfolobus solfataricus (P2) were conducted. Microarray analysis of mRNA expression showed that 102 transcripts were regulated by at least 1.5 fold, 30 minutes after exposure to 30 µM H2O2. Parallel proteomic analyses using two-dimensional differential gel electrophoresis (2D-DIGE), monitored more than 800 proteins 30 and 105 minutes after exposure and found that 18 had significant changes in abundance. A recently characterized ferritin-like antioxidant protein, DPSL, was the most highly regulated species of mRNA and protein, in addition to being post-translationally modified. As expected, a number of antioxidant related mRNAs and proteins were differentially regulated. Three of these, DPSL, superoxide dismutase, and peroxiredoxin were shown to interact and likely form a novel supramolecular complex for mitigating oxidative damage. A scheme for the ability of this complex to perform multi-step reactions is presented. Despite the central role played by DPSL, cells maintained a lower level of protection after disruption of the dpsl gene, indicating a level of redundancy in the oxidative stress pathways of S. solfataricus. This work provides the first “omics” scale assessment of the oxidative stress response for an archeal organism and together with a network analysis using data from previous studies on bacteria and eukaryotes reveals evolutionarily conserved pathways where complex and overlapping defense mechanisms protect against oxygen toxicity.

Hydrogen Peroxide Cycling in High-Temperature Acidic Geothermal Springs and Potential Implications for Oxidative Stress Response

“…Relative expression data show similar transcript levels of SOD (Equation 7) and internal PRX (Equation 8) in both organisms at all sites, which may indicate co-expression of these two genes to coordinate the removal of ROS inside the cell, as previously observed in the archaeon Sulfolobus solfataricus where they form an enzymatic complex (Maaty et al, 2009). Normalized expression of these two genes is higher in M. yellowstonensis than in Hydrogenobaculum in BE_d, ECH_b, and ECH_c Fe(III)-oxide mats, which may reflect a higher level of internal oxidative stress in the bacterial population, and thus a higher cellular response to mitigate ROS.…”

“…Normalized expression of these two genes is higher in M. yellowstonensis than in Hydrogenobaculum in BE_d, ECH_b, and ECH_c Fe(III)-oxide mats, which may reflect a higher level of internal oxidative stress in the bacterial population, and thus a higher cellular response to mitigate ROS. Higher FDX gene transcripts detected in Hydrogenobaculum at all sites also support this hypothesis, as ferredoxin is involved in maintaining intracellular redox potentials (Maaty et al, 2009). In Hydrogenobaculum spp., both rubrerythrin (11) and ferredoxin (Equation 12) enzymes (Weinberg et al, 2004) may participate equally in Fe cycling, as indicated by comparable expression levels at all sites.…”

“…Several of the ROS stress response genes tested have been shown to be upregulated under high H 2 O 2 levels (∼30 µM) in controlled conditions using a Sulfolobus sp. (Maaty et al, 2009), however, the H 2 O 2 values observed in acidic Fe-oxide environments were 10-fold lower, thus difficult to compare. Regarding the widespread genetic machinery across the three domains of life to cope with oxidative stress (Pedone et al, 2004;Maaty et al, 2009), our gene expression results might suggest a more constitutive response to ROS in Fe-mat populations, and more generally during aerobic metabolism.…”

“…Given the large changes in ROS that may be expected in natural environments as a function of photon flux, it is highly likely that microorganisms vary the production of enzymes known to react with these highly labile redox-active species across a diel cycle. Reactions involving ROS and Fe can represent an environmental stress for both aerobic and anaerobic organisms, leading to oxidative damage of DNA, RNA, proteins, lipids, and cofactors (Henle and Linn, 1997;Cabiscol et al, 2000;Green and Paget, 2004;Maaty et al, 2009). …”

“…Organisms of all domains of life (Archaea, Bacteria, and Eukarya) possess defense mechanisms against intra-and extracellular ROS. These detoxification enzymes participate directly in H 2 O 2 and Fe cycling (Table 1), and are thought to work in concert to avoid oxidative stress (Pedone et al, 2004;Maaty et al, 2009). Metagenomes of Fe(III)-oxide microbial communities collected in high-temperature acidic geothermal springs of Yellowstone National Park (YNP, Wyoming, USA) have identified chemolithoautotrophic organisms contributing to the early development and production of these microbial mats (Inskeep et al, 2010Kozubal et al, 2012;Beam et al, 2016).…”