19 October 2023

New insights into the relationship between viruses and soil bacteria


According to UC Davis researchers, soil viruses appear to act “like lawnmowers, culling older cells and giving space for new growth”

by Matteo Cavallito


Viruses in the soil may be less destructive to bacteria than previously thought. This is highlighted by research from the University of California Davis and Lawrence Livermore National Laboratory. The study, published in recent weeks in the journal Nature Ecology and Evolution, offers a new contribution to the still limited knowledge about the impact of these microorganisms.

Viruses have the potential to drive substantial microbial mortality and nutrient turnover,” the study states. However, “Pinpointing viral contributions to terrestrial ecosystem processes remains a challenge, as temporal dynamics are difficult to unravel in the spatially and physicochemically heterogeneous soil environment.”

Never before studied dynamics

The hypothesis that emerged from the research is that viruses, far from wiping out bacteria act “like lawnmowers, culling older cells and giving space for new growth,” says a statement from the US university. The first annual rain affecting California ecosystems after the dry period “provides an ecosystem reset, triggering microbial activity during a tractable window for capturing short-term dynamics,” the study explains.

Scientists sampled soil from four California grasslands, transferring the samples to the laboratory. There they simulated precipitation by watering them. This allowed them to generate “144 viromes, 84 metagenomes and 84 16S ribosomal RNA gene amplicon datasets to characterize viral, prokaryotic and relic DNA dynamics over 10 days.” These dynamics, explained Joanne B. Emerson, professor of plant pathology at UC Davis and co-author of the study, had never been observed before.

Viruses are less dangerous than expected for bacteria

“Wet-up triggered a significant increase in viral richness, followed by extensive compositional turnover,” the research continues. The population change was remarkable, to the point that only 15 percent of the different types of viruses observed at the beginning were also present at the end of the period under study. This cannot be said for bacteria.

“Temporal succession in prokaryotic communities (Archaea e Bacteria, ed.) was much less pronounced, perhaps suggesting differences in the scales of activity captured by viromes (representing recently produced, ephemeral viral particles) and total DNA,” the study notes.

The viruses, in short, preyed on the dominant bacteria, but somehow ensured that some balance was maintained. “Results suggest the potential for ‘Cull-the-Winner’ dynamics, whereby viruses infect and cull but do not decimate dominant host populations,” the researchers continue.

New knowledge for the soil

The study thus offers a new contribution in research into the most hidden aspects of the ecosystem. For example, the authors found that the behavior of viruses was similar in the soils of all four grasslands examined. Which also had different compositions and came from different places. The hypothesis, in short, is that descriptive patterns of the investigated dynamics can be unveiled that are valid for different soil types.

Viruses, the researchers briefly note, influence the composition of bacterial communities which, in turn, influence carbon and nutrient cycles in the soil. “Bacteria can affect plant health, ecosystem dynamics, all sorts of things,” Emerson explains. The research results, the statement further notes, “suggests that viruses behave differently than once thought and this knowledge could lead to a better understanding of soil dynamics when it comes to bacteria.”