Response of Anaerobic Protozoa to Oxygen Tension in Anaerobic System

Benthic Heterotrophic Protist Communities of the Southern Baltic Analyzed with the Help of Curated Metabarcoding Studies

Heterotrophic protists are key components of marine ecosystems. They act as controllers of bacterial and microphytobenthos production and contribute significantly to the carbon flux to higher trophic levels. Still, metabarcoding studies on benthic protist communities are much less frequent than for planktonic organisms. Especially in the Baltic Sea, representing the largest brackish water environment on earth, so far, no extensive metabarcoding studies have been conducted to assess the diversity of benthic protists in this unique and diverse habitat. This study aims to give first insights into the diversity of benthic protist communities in two different regions of the Baltic Sea, Fehmarnbelt, and Oderbank. Using amplicon sequencing of the 18S rDNA V9 region of over 100 individual sediment samples, we were able to show significant differences in the community composition between the two regions and to give insights into the vertical distribution of protists within the sediment (0-20 cm). The results indicate that the differences in community composition in the different regions might be explained by several abiotic factors such as salinity and water depth, but are also influenced by methodological aspects such as differences between DNA and RNA results.

The macronuclear genome of anaerobic ciliate Entodinium caudatum reveals its biological features adapted to the distinct rumen environment

Entodinium caudatum is an anaerobic binucleated ciliate representing the most dominant protozoal species in the rumen. However, its biological features are largely unknown due to the inability to establish an axenic culture. In this study, we primally sequenced its macronucleus (MAC) genome to aid the understanding of its metabolism, physiology, ecology. We isolated the MAC of E. caudatum strain MZG-1 and sequenced the MAC genome using Illumina MiSeq, MinION, and PacBio RSII systems. De novo assembly of the MiSeq sequence reads followed with subsequent scaffolding with MinION and PacBio reads resulted in a draft MAC genome about 117 Mbp. A large number of carbohydrate-active enzymes were likely acquired through horizontal gene transfer. About 8.74% of the E. caudatum predicted proteome was predicted as proteases. The MAC genome of E. caudatum will help better understand its important roles in rumen carbohydrate metabolism, and interaction with other members of the rumen microbiome.

Microorganisms: A Potential Source of Bioactive Molecules for Antioxidant Applications

Oxidative stress originates from an elevated intracellular level of free oxygen radicals that cause lipid peroxidation, protein denaturation, DNA hydroxylation, and apoptosis, ultimately impairing cell viability. Antioxidants scavenge free radicals and reduce oxidative stress, which further helps to prevent cellular damage. Medicinal plants, fruits, and spices are the primary sources of antioxidants from time immemorial. In contrast to plants, microorganisms can be used as a source of antioxidants with the advantage of fast growth under controlled conditions. Further, microbe-based antioxidants are nontoxic, noncarcinogenic, and biodegradable as compared to synthetic antioxidants. The present review aims to summarize the current state of the research on the antioxidant activity of microorganisms including actinomycetes, bacteria, fungi, protozoa, microalgae, and yeast, which produce a variety of antioxidant compounds, i.e., carotenoids, polyphenols, vitamins, and sterol, etc. Special emphasis is given to the mechanisms and signaling pathways followed by antioxidants to scavenge Reactive Oxygen Species (ROS), especially for those antioxidant compounds that have been scarcely investigated so far.