Balance of nature: viruses are a vital component (Introduction)

by David Turell , Monday, July 24, 2023, 15:44 (278 days ago) @ David Turell

Giant viruses plentiful in forest soil:

https://www.biorxiv.org/content/10.1101/2023.06.30.546935v1.full?et_rid=825383635&e...

"Abstract
Large DNA viruses of the phylum Nucleocytoviricota infect diverse eukaryotic hosts from protists to humans, with profound consequences for aquatic and terrestrial ecosystems. While nucleocytoviruses are known to be highly diverse in metagenomes, knowledge of their capsid structures is restricted to a few characterized representatives. Here, we visualize giant virus-like particles (VLPs, diameter >0.2 µm) directly from the environment using transmission electron microscopy. We found that Harvard Forest soils contain a higher diversity of giant VLP morphotypes than all hitherto isolated giant viruses combined. These included VLPs with icosahedral capsid symmetry, ovoid shapes similar to pandoraviruses, and bacilliform shapes that may represent novel viruses. We discovered giant icosahedral capsids with structural modifications that had not been described before including tubular appendages, modified vertices, tails, and capsids consisting of multiple layers or internal channels. Many giant VLPs were covered with fibers of varying lengths, thicknesses, densities, and terminal structures. These findings imply that giant viruses employ a much wider array of capsid structures and mechanisms to interact with their host cells than is currently known. We also found diverse tailed bacteriophages and filamentous VLPs, as well as ultra-small cells. Our study offers a first glimpse of the vast diversity of unexplored viral structures in soil and reinforces the potential of transmission electron microscopy for fundamental discoveries in environmental microbiology."

From discussion:

[In a 2018 study] "Metagenome analysis of soil from the same location resulted in genome assemblies for 16 novel giant viruses. These included relatives of pithoviruses, tupanviruses, and klosneuviruses, for which we found potentially matching VLP types: large ovoid, tailed icosahedral, and plain or fibered icosahedral particles, respectively. Although we currently cannot link metagenome-assembled genomes to any of the morphotypes described here, we show that the morphological diversity of giant VLPs clearly exceeds the metagenomic diversity of giant viruses in Harvard Forest soil.

***

"We discovered an unexpected diversity of soil VLPs in the 0.2 µm to 1.2 µm size fraction, which is typically excluded from virome studies. The cornucopia of viral morphotypes found in Harvard Forest alone questions our current understanding of the virosphere and its structural heterogeneity. This fascinating window into the complex world of soil viruses leaves little doubt that the high genetic diversity of giant viruses is matched by diverse and previously unimaginable particle structures, whose origins and functions remain to be studied."

Comment: this huge descriptive study cannot be reduced to a size here. What it shows us is that there is a working macro-viral world at work in our soils and I assume improving their quality for vegetative fertility and productivity. This shows the vast population of viruses is working for the good. It answers theodicy criticisms of the existence of viruses.