Viral Transfer and Inactivation through Zooplankton Trophic Interactions

Uptake without inactivation of human adenovirus type 2 by Tetrahymena pyriformis ciliates

Human adenoviruses are ubiquitous contaminants of surface water. Indigenous protists may interact with adenoviruses and contribute to their removal from the water column, though the associated kinetics and mechanisms differ between protist species. In this work, we investigated the interaction of human adenovirus type 2 (HAdV2) with the ciliate Tetrahymena pyriformis. In co-incubation experiments in a freshwater matrix, T. pyriformis was found to efficiently remove HAdV2 from the aqueous phase, with ≥4 log₁₀ removal over 72 hours. Neither sorption onto the ciliate nor secreted compounds contributed to the observed loss of infectious HAdV2. Instead, internalization was shown to be the dominant removal mechanism, resulting in the presence of viral particles inside food vacuoles of T. pyriformis, as visualized by transmission electron microscopy. The fate of HAdV2 once ingested was scrutinized and no evidence of virus digestion was found over the course of 48 hours. This work shows that T. pyriformis can exert a dual role in microbial water quality: while they remove infectious adenovirus from the water column, they can also accumulate infectious viruses.

Pathogens and Passengers: Roles for Crustacean Zooplankton Viruses in the Global Ocean

Viruses infect all living organisms, but the viruses of most marine animals are largely unknown. Crustacean zooplankton are a functional lynchpin in marine food webs, but very few have been interrogated for their associated viruses despite the profound potential effects of viral infection. Nonetheless, it is clear that the diversity of viruses in crustacean zooplankton is enormous, including members of all realms of RNA viruses, as well as single- and double-stranded DNA viruses, in many cases representing deep branches of viral evolution. As there is clear evidence that many of these viruses infect and replicate in zooplankton species, we posit that viral infection is likely responsible for a significant portion of unexplained non-consumptive mortality in this group. In turn, this infection affects food webs and alters biogeochemical cycling. In addition to the direct impacts of infection, zooplankton can vector economically devastating viruses of finfish and other crustaceans. The dissemination of these viruses is facilitated by the movement of zooplankton vertically between epi- and mesopelagic communities through seasonal and diel vertical migration (DVM) and across long distances in ship ballast water. The large potential impact of viruses on crustacean zooplankton emphasises the need to clearly establish the relationships between specific viruses and the zooplankton they infect and investigate disease and mortality for these host-virus pairs. Such data will enable investigations into a link between viral infection and seasonal dynamics of host populations. We are only beginning to uncover the diversity and function of viruses associated with crustacean zooplankton.

Waterborne Human Pathogenic Viruses in Complex Microbial Communities: Environmental Implication on Virus Infectivity, Persistence, and Disinfection

Waterborne human pathogenic viruses challenge global health and economy. Viruses were long believed to transmit among hosts as individual, free particles. However, recent evidence indicates that viruses also transmit in populations, so-called en bloc transmission, by either interacting with coexisting bacteria, free-living amoebas, and other higher organisms through endosymbiosis and surface binding, or by being clustered inside membrane-bound vesicles or simply self-aggregating with themselves. En bloc transmission of viruses and virus-microbiome interactions could enable viruses to enhance their infectivity, increase environmental persistence, and resist inactivation from disinfection. Overlooking this type of transmission and virus-microbiome interactions may underestimate the environmental and public health risks of the viruses. We herein provide a critical perspective on waterborne human pathogenic viruses in complex microbial communities to elucidate the environmental implication of virus-microbiome interactions on virus infectivity, persistence, and disinfection. This perspective also provides insights on advancing disinfection and sanitation guidelines and regulations to protect the public health.

Removal of Waterborne Viruses by Tetrahymena pyriformis Is Virus-Specific and Coincides with Changes in Protist Swimming Speed

Biological treatment of waterborne viruses, specifically grazing of viruses by protists, can enhance microbial water quality while avoiding the production of toxic byproducts and high energy costs. However, tangible applications are limited by the lack of understanding of the underlying mechanisms. Here, we examined the feeding behavior of Tetrahymena pyriformis ciliates on 13 viruses, including bacteriophages, enteric viruses, and respiratory viruses. Significant differences in virus removal by T. pyriformis were observed, ranging from no removal (Qbeta, coxsackievirus B5) to ≥2.7 log10 (JC polyomavirus) after 48 h of co-incubation of the protist with the virus. Removal rates were conserved even when protists were co-incubated with multiple viruses simultaneously. Video analysis revealed that the extent of virus removal was correlated with an increase in the protists' swimming speed, a behavioral trait consistent with the protists' response to the availability of food. Protistan feeding may be driven by a virus' hydrophobicity but was independent of virus size or the presence of a lipid envelope.

An integrated cell culture reverse transcriptase quantitative PCR (ICC-RTqPCR) method to simultaneously quantify the infectious concentrations of eight environmentally relevant enterovirus serotypes

Enterovirus (EV) infectivity is typically measured as a bulk parameter, yet EV serotypes vary in their susceptibility to natural and engineered stressors. Here we developed an integrated cell culture reverse transcriptase quantitative PCR (ICC-RTqPCR) method to simultaneously and specifically quantify the infectious concentrations of eight EV serotypes commonly encountered in sewage (coxsackieviruses A9, B1, B2, B3, B4 and B5, and echoviruses 25 and 30). The method uses two cell lines for virus replication and serotype-specific qPCR primers for quantification. Primers were designed to target multiple environmental strains of a given serotype and displayed high specificity. The ICC-RTqPCR method exhibited a linear calibration range between 50 and 1000 (echoviruses) or 5000 (coxsackieviruses) infectious units per mL. Over this range, measurements were not influenced by the presence of non-target serotypes, and calibration slopes were reproducible for different virus batches and cell ages. The ICC-RTqPCR method was able to accurately quantify the infectious concentration of a virus after inactivation by heat, and the concentration of a virus within a wastewater matrix. This method will be valuable to assess the differing fates of EV serotypes in natural or engineered systems, and to portray the associated changes in EV population composition.