Enzymatic Antioxidant Systems in Early Anaerobes

Enzymatic Antioxidant Systems in Early Anaerobes: Theoretical Considerations

Authors:

Ireneusz et al

Abstract:

It is widely accepted that cyanobacteria-dependent oxygen that was released into Earth's atmosphere ca. 2.5 billion years ago sparked the evolution of the aerobic metabolism and the antioxidant system. In modern aerobes, enzymes such as superoxide dismutases (SODs), peroxiredoxins (PXs), and catalases (CATs) constitute the core of the enzymatic antioxidant system (EAS) directed against reactive oxygen species (ROS). In many anaerobic prokaryotes, the superoxide reductases (SORs) have been identified as the main force in counteracting ROS toxicity. We found that 93% of the analyzed strict anaerobes possess at least one antioxidant enzyme, and 50% have a functional EAS, that is, consisting of at least two antioxidant enzymes: one for superoxide anion radical detoxification and another for hydrogen peroxide decomposition. The results presented here suggest that the last universal common ancestor (LUCA) was not a strict anaerobe. O2 could have been available for the first microorganisms before oxygenic photosynthesis evolved, however, from the intrinsic activity of EAS, not solely from abiotic sources.

Cyanobacteria: The Great Hub of Anaerobe and Obligate Aerobe Genomes

Deciphering Primordial Cyanobacterial Genome Functions from Protein Network Analysis

Authors:

Harel et al

Abstract:

The Great Oxidation Event (GOE) ∼2.4 billion years ago resulted from the accumulation of oxygen by the ancestors of cyanobacteria. Cyanobacteria continue to play a significant role in primary production and in regulating the global marine and limnic nitrogen cycles. Relatively little is known, however, about the evolutionary history and gene content of primordial cyanobacteria. To address these issues, we used protein similarity networks, containing proteomes from 48 cyanobacteria as the test group, and reference proteomes from 84 microbes representing four distinct metabolic groups from most reducing to most oxidizing: methanogens, obligate anaerobes (nonmethanogenic), facultative aerobes, and obligate aerobes. These four metabolic groups represent extant bioinformatic proxies for ancient redox chemistries, extending from an anoxic origin through the GOE and ultimately to obligate aerobes. Analysis of the network metric degree showed a strong relationship between cyanobacteria and obligate anaerobes, from which cyanobacteria presumably arose, for core functions that include translation, photosynthesis, energy conservation, and environmental interactions. These data were used to reconstruct primordial functions in cyanobacteria that included nine gene families involved in photosynthesis, hydrogenases, and proteins involved in defense from environmental stress. The presence of 60% of these genes in both reaction center I (RC-I) and RC-II-type bacteria may be explained by selective loss of either RC in the evolutionary history of some photosynthetic lineages. Finally, the network reveals that cyanobacteria occupy a unique position among prokaryotes as a hub between anaerobes and obligate aerobes.

Anaerobic Metazoans!!!

Living exclusively oxygen-free was thought to be a lifestyle open only to viruses and single-celled microorganisms. A group of Italian and Danish researchers has now found three species of multicellular animal, or metazoan, that apparently spend their entire lives in oxygen-starved waters in a basin at the bottom of the Mediterranean Sea.

The discovery "opens a whole new realm to metazoans that we thought was off limits", says Lisa Levin, a biological oceanographer at Scripps Institution of Oceanography in La Jolla, California.

Roberto Danovaro from the Polytechnic University of Marche in Ancona, Italy, and his colleagues pulled up the animals during three research cruises off the south coast of Greece. The species, which have not yet been named, belong to a phylum of tiny bottom-dwellers called Loricifera. Measuring less than 1 millimetre long, they live at a depth of more than 3,000 metres in the anoxic sediments of the Atalante basin, a place so little explored that Danovaro likens his team's sampling to "going to the Moon to collect rocks".

Researchers have previously found multicellular animals living in anoxic environments, but Danovaro says that it was never clear whether those animals were permanent residents. The new loriciferans, which he and his team reported this week (R. Danovaro et al. BMC Biol. doi:10.1186/1741-7007-8-30; 2010), seem to "reproduce and live all their life in anoxic conditions", he says.

The researchers identified an adaptation that helps these loriciferans to survive in their environment. Instead of mitochondria, which rely on oxygen, the creatures have organelles that resemble hydrogenosomes, which some single-celled organisms use to produce energy-storing molecules anaerobically.

Just.

Plain.

*WOW*