Surrogate Virus Decay and Effects in Biosphere 2 Soils

Abstract

In 2022, over 50% of disposed biosolids were used for land application. Although treated, biosolids may contain a measurable number of pathogens, particularly viruses, that can contaminate natural systems. Given the threat of emergent and (re)emerging viruses and the increased use of biosolids-amended soil, it is essential to understand the fate and effects of viruses within the soils of different ecosystems. In this study, a co-spike of three surrogate viruses (PhiX-174, MS2, and Phi 6) was seeded into 10 soil types collected from five distinct biomes located within Biosphere 2: rainforest, savanna, thorn scrub, desert, and ocean. Microcosms of the spiked soils were prepared (~200g per microcosm), and non-spiked microcosms were also prepared. At specified timepoints over 21 days, double agar overlay assays were performed to determine the levels of viable plaque forming units (PFUs) per gram (dry weight) of soil. Both 16S rRNA sequencing and FTICR-MS techniques were also utilized to assess impacts on soil bacterial communities and functional activity following the introduction of the viruses. Overall, the persistence of the enveloped virus, Phi 6, was significantly lower than the non-enveloped viruses, MS2 and PhiX-174. The three viruses had varying decay rate patterns in response to soil characteristics including texture, cation concentrations, and pH. Amplicon sequencing revealed that the soil bacterial communities across ecosystems did not exhibit an overall change in taxa following the virus co-spike, although composition shifts in beach sand, savanna (upper), and rainforest (low elevation) soils were observed. Metabolomic data indicated that soil organic matter metabolome composition was driven by the ecosystem and, to a lesser extent, the addition of viruses. The results of this study demonstrate that non-resident viruses can persist in soils derived from varying ecosystems for several weeks and that their presence can affect resident soil bacterial communities. However, more research is needed to determine the long-term impacts of virus inputs into soil systems to ensure environmental and public health.