Size-dependent Catalysis of Chlorovirus Population Growth by a Messy Feeding Predator

Many chloroviruses replicate in endosymbiotic zoochlorellae that are protected from infection by their symbiotic host. To reach the high virus concentrations that often occur in natural systems, a mechanism is needed to release zoochlorellae from their hosts. We demonstrate that the ciliate predator Didinium nasutum foraging on zoochlorellae-bearing Paramecium bursaria can release live zoochlorellae from the ruptured prey cell that can then be infected by chloroviruses. The catalysis process is very effective, yielding roughly 95% of the theoretical infectious virus yield as determined by sonication of P. bursaria. Chlorovirus activation is more effective with smaller Didinia, as larger Didinia typically consume entire P. bursaria cells without rupturing them, precluding the release of zoochlorellae. We also show that the timing of Chlorovirus growth is tightly linked to the predator-prey cycle between Didinium and Paramecium, with the most rapid increase in chloroviruses temporally linked to the peak foraging rate of Didinium, supporting the idea that predator-prey cycles can drive cycles of Chlorovirus abundance

The consumption of viruses returns energy to food chains

Viruses impact host cells and have indirect effects on ecosystem processes. Plankton such as ciliates can reduce the abundance of virions in water, but whether virus consumption translates into demographic consequences for the grazers is unknown. Here, we show that small protists not only can consume viruses they also can grow and divide given only viruses to eat. Moreover, the ciliate Halteria sp. foraging on chloroviruses displays dynamics and interaction parameters that are similar to other microbial trophic interactions. These results suggest that the effect of viruses on ecosystems extends beyond (and in contrast to) the viral shunt by redirecting energy up food chains. Many known viruses cause diseases, and consequently, virology has long focused on viruses as pathogens. Viruses also affect ecosystem processes, however, by lysing microbes and causing the release of nutrients (i.e., the viral shunt) and through the indirect consequences of host mortality (1, 2). Both of these research domains place viruses as the top “predator” in their food chains, but like most predators, viruses also can serve as food. Many foragers that swallow water, soil particles, or leaves routinely ingest virus particles. Given the small mass of virus particles relative to other foods, the consumption of viruses is thought to be calorically unimportant (3, 4) and not of sufficient magnitude to influence ecosystem processes. Nonetheless, viruses contain amino acids, nucleic acids, and lipids (5), and if consumed in sufficient quantities could influence the population dynamics of the species that consume them. Some ciliates and flagellates may ingest many viruses (3, 4, 6, 7), but the demographic impact of virus consumption (virovory) is unclear. Here, we investigate the potential for virovory to fuel population growth and alter the pathways of energy flow in food webs. We measured the population growth of Halteria sp. and Paramecium bursaria in foraging trials with and without supplemental chloroviruses. We also tracked the reduction in chloroviruses and fit a classic trophic link model to the data to determine whether the Halteria–chlorovirus interaction can be viewed as a trophic interaction. Finally, we used fluorescent microscopy to confirm the ingestion of chloroviruses by ciliates

Social impacts of occupational heat stress and adaptation strategies of workers: A narrative synthesis of the literature

Dimensions of risks and impacts of occupational heat stress due to climate change on workers\u27 health and safety, productivity, and social well-being are significantly deleterious. Aside from empirical evidence, no systematic review exists for policy development and decision making in managing occupation heat stress impacts and adaptation strategies of workers. This study sought to synthesise evidence on the social impacts of occupational heat stress and adaptation strategies of workers. From a review of existing literature, eight categories were obtained from 25 studies and grouped into three syntheses: (1) awareness of occupational heat stress, (2) social impacts of occupational heat stress and (3) workers\u27 adaptation to occupational heat stress due to changing climate. Awareness of occupational heat stress among workers varied and their social impacts were related to workers\u27 health and safety, productivity and social well-being. Sustainable adaptation to occupation heat stress due to climate change hinges on financial resource availability. Adequate investment and research are required to develop and implement policies to combat the threat of rising temperature and climate change to enhance workers\u27 adaptive capacity, boost resilience and foster sustainable development

Barriers to occupational heat stress risk adaptation of mining workers in Ghana

Increasing temperature and climate warming impacts are aggravating the vulnerability of workers to occupational heat stress. Adaptation and social protection strategies have become crucial to enhance workers’ health, safety, productive capacity and social lives. However, the effective implementation of work-related heat stress adaptation mechanisms appears to be receiving little attention. This study assessed the barriers to occupational heat stress adaptation and social protection strategies of mining workers in Ghana. Based on a mixed methods approach, focus group discussions and questionnaires were used to elicit data from 320 mining workers. Workers’ adaptation strategies (water intake, wearing loose and light-coloured clothing, participating in training programmes, taking regular breaks, use of mechanical equipment, use of cooling systems and housing designs) varied significantly across the type of mining activity (p \u3c .001). Workers’ social protection measures were adequate. The disparities in workers’ social protection measures significantly differed across the type of mining activity (p \u3c .001). Barriers of workers to the implementation of relevant adaptation strategies (inadequate knowledge of coping and adaptive behaviour, lack of regular training on adaptation measures, lack of specific heat-related policy regulations, lack of management commitment and the lack of access to innovative technology and equipment) also differed across the type of mining activity (p \u3c .001). Adaptation policy options and recommendations centred on overcoming the barriers that constrain the adaptive capacity of workers and employers have the potential to reduce workers’ vulnerability to occupational heat stress

Optimal experimental design for mathematical models of haematopoiesis.

The haematopoietic system has a highly regulated and complex structure in which cells are organized to successfully create and maintain new blood cells. It is known that feedback regulation is crucial to tightly control this system, but the specific mechanisms by which control is exerted are not completely understood. In this work, we aim to uncover the underlying mechanisms in haematopoiesis by conducting perturbation experiments, where animal subjects are exposed to an external agent in order to observe the system response and evolution. We have developed a novel Bayesian hierarchical framework for optimal design of perturbation experiments and proper analysis of the data collected. We use a deterministic model that accounts for feedback and feedforward regulation on cell division rates and self-renewal probabilities. A significant obstacle is that the experimental data are not longitudinal, rather each data point corresponds to a different animal. We overcome this difficulty by modelling the unobserved cellular levels as latent variables. We then use principles of Bayesian experimental design to optimally distribute time points at which the haematopoietic cells are quantified. We evaluate our approach using synthetic and real experimental data and show that an optimal design can lead to better estimates of model parameters

The nexus between social impacts and adaptation strategies of workers to occupational heat stress: A conceptual framework

Adverse effects of occupational heat stress in the context of the changing climate on working populations are subtle but considerably harmful. However, social dimensions and impacts of climate change–related occupational heat concerns on workers’ safety and health, productivity and well-being are often overlooked or relegated as minor issues in social impact analyses of occupational heat exposure due to climate change. This paper offers a conceptual framework based on an appraisal and synthesis of the literature on social impacts of climate change–related occupational heat exposure on workers’ safety and health, productivity and social welfare and the quest to localise and achieve sustainable development goals. A sustained global, national, institutional and individual collaborative involvement and financial support for research, improved adaptation and social protection strategies, predominantly in the developing world, where a large number of people work outdoors, can reduce heat exposure and boost the resilience and adaptive capacity of workers to facilitate efforts to achieve sustainable development goals

Catalysis of Chlorovirus Production by the Foraging of \u3ci\u3eBursaria truncatella\u3c/i\u3e on \u3ci\u3eParamecia bursaria\u3c/i\u3e Containing Endosymbiotic Algae

Chloroviruses are large viruses that replicate in chlorella-like green algae and normally exist as mutualistic endosymbionts (referred to as zoochlorellae) in protists such as Paramecium bursaria. Chlorovirus populations rise and fall in indigenous waters through time; however, the factors involved in these virus fluctuations are still under investigation. Chloroviruses attach to the surface of P. bursaria but cannot infect their zoochlorellae hosts because the viruses cannot reach the zoochlorellae as long as they are in the symbiotic phase. Predators of P. bursaria, such as copepods and didinia, can bring chloroviruses into contact with zoochlorellae by disrupting the paramecia, which results in an increase in virus titers in microcosm experiments. Here, we report that another predator of P. bursaria, Bursaria truncatella, can also increase chlorovirus titers. After two days of foraging on P. bursaria, B. truncatella increased infectious chlorovirus abundance about 20 times above the controls. Shorter term foraging (3 h) resulted in a small increase of chlorovirus titers over the controls and more foraging generated more chloroviruses. Considering that B. truncatella does not release viable zoochlorellae either during foraging or through fecal pellets, where zoochlorellae could be infected by chlorovirus, we suggest a third pathway of predator virus catalysis. By engulfing the entire protist and digesting it slowly, virus replication can occur within the predator and some of the virus is passed out through a waste vacuole. These results provide additional support for the hypothesis that predators of P. bursaria are important drivers of chlorovirus population sizes and dynamics

Predators catalyze an increase in chloroviruses by foraging on the symbiotic hosts of zoochlorellae

Virus population growth depends on contacts between viruses and their hosts. It is often unclear how sufficient contacts are made between viruses and their specific hosts to generate spikes in viral abundance. Here, we show that copepods, acting as predators, can bring aquatic viruses and their algal hosts into contact. Specifically, predation of the protist Paramecium bursaria by copepods resulted in a \u3e100-fold increase in the number of chloroviruses in 1 d. Copepod predation can be seen as an ecological “catalyst” by increasing contacts between chloroviruses and their hosts, zoochlorellae (endosymbiotic algae that live within paramecia), thereby facilitating viral population growth. When feeding, copepods passed P. bursaria through their digestive tract only partially digested, releasing endosymbiotic algae that still supported viral reproduction and resulting in a virus population spike. A simple predator–prey model parameterized for copepods consuming protists generates cycle periods for viruses consistent with those observed in natural ponds. Food webs are replete with similar symbiotic organisms, and we suspect the predator catalyst mechanism is capable of generating blooms for other endosymbiont-targeting viruses. Movie file (.mp4) attached below

Predators catalyze an increase in chloroviruses by foraging on the symbiotic hosts of zoochlorellae

Virus population growth depends on contacts between viruses and their hosts. It is often unclear how sufficient contacts are made between viruses and their specific hosts to generate spikes in viral abundance. Here, we show that copepods, acting as predators, can bring aquatic viruses and their algal hosts into contact. Specifically, predation of the protist Paramecium bursaria by copepods resulted in a \u3e100-fold increase in the number of chloroviruses in 1 d. Copepod predation can be seen as an ecological “catalyst” by increasing contacts between chloroviruses and their hosts, zoochlorellae (endosymbiotic algae that live within paramecia), thereby facilitating viral population growth. When feeding, copepods passed P. bursaria through their digestive tract only partially digested, releasing endosymbiotic algae that still supported viral reproduction and resulting in a virus population spike. A simple predator–prey model parameterized for copepods consuming protists generates cycle periods for viruses consistent with those observed in natural ponds. Food webs are replete with similar symbiotic organisms, and we suspect the predator catalyst mechanism is capable of generating blooms for other endosymbiont-targeting viruses. Movie file (.mp4) attached below

Chloroviruses lure hosts through long-distance chemical signaling

Chloroviruses exist in aquatic systems around the planet where they infect certain eukaryotic green algae that are mutualistic endosymbionts in a variety of protists and metazoans. Natural chlorovirus populations are seasonally dynamic but the precise temporal changes in these populations and the mechanisms that underlie them have, heretofore, been unclear. We recently reported the novel concept that predator/prey-mediated virus activation regulates chlorovirus population dynamics, and in the current manuscript demonstrate virus packaged chemotactic modulation of prey behavior. Viruses have not previously been reported to act as chemotactic/chemo-attractive agents. Rather, viruses as extracellular entities are generally viewed as non-metabolically active spore-like agents that await further infection events upon collisions with appropriate host cells. That a virus might actively contribute to its fate via chemotaxis and change the behavior of an organism independent of infection is unprecedented