RESEARCH PROJECT TOPIC ON EFFECTS OF XENOBIOTICS ON SOIL MICROBIAL DIVERSITY AND FUNCTION
Container aquatic habitats support a specialized community of macroinvertebrates (e.g. mosquitoes) that feed on microbial communities associated with decaying organic matter. These aquatic habitats are often embedded within and around agricultural lands and are frequently exposed to pesticides. We used a microcosm approach to examine the single and combined effects of two herbicides (atrazine, glyphosate), and three insecticides (malathion, carbaryl, permethrin) on microbial communities of container aquatic habitats. MiSeq sequencing of the V4 region of both bacterial and archaeal 16S rRNA gene was used to characterize the microbial communities of indoor microcosms that were either exposed to each pesticide alone, a mix of herbicides, a mix of insecticides, or a mix of all five insecticides. Individual insecticides but not herbicides reduced the microbial diversity and richness and two insecticides, carbaryl and permethrin, also altered the microbial community structure. A mixture of herbicides had no effect on microbial diversity or structure but a mixture of insecticides or all five pesticides reduced microbial diversity and altered the community structure. These findings suggest that exposure of aquatic ecosystems to individual pesticides or their mixtures can disrupt aquatic microbial communities and there is need to decipher how these changes affect resident macroinvertebrate communities.
Container aquatic habitats, both natural (phytotelmata) and man-made (e.g. storm water catch basins, discarded tires and tins) harbor a specialized community of macroinvertebrates that is dominated by mosquitoes. These aquatic ecosystems are detritus-based and derive most of their carbon inputs from allochthonous organic matter primarily leaf litter. The microbial communities associated with these aquatic ecosystems fulfil critical roles in decomposition of organic matter, nutrient cycling, and provides a critical food resource for mosquito larvae and other container-dwelling macroinvertebrate consumer,. Therefore, the microbial communities inhabiting these aquatic systems present a complex network of interwoven relationships between organisms of different trophic levels and their disruption can lead to many direct and indirect effects, some of which may cascade into the terrestrial environment and affect human health.
Pesticides which are comprised of insecticides, herbicides, and fungicides are a group of potentially toxic substances that are capable of disrupting the microbial structure and function in aquatic habitats. Every year, the world uses approximately 2.6 billion pounds of pesticides and the U.S. accounts for 22% of the world’s pesticide consumption Nearly 80% of these chemicals are used for agricultural purposes while a fraction of the remainder is devoted to the control of structural and public health pests. Many container aquatic habitats are embedded within agricultural landscapes and may unintentionally be exposed to agricultural pesticides through spray drift, leaching and/or surface runoff. In addition, pesticides may be applied directly into these habitats to control vector mosquitoes. While most pesticides are designed to target a specific pest or particular pest group, they often extend their effects to non-target species. In fact, the frequent detection of pesticides in both surface and ground water has been associated with loss of biodiversity and detrimental effects on human and wildlife health. However, despite the fundamental role of microorganisms in aquatic food webs, our understanding of how they respond to exposure to pesticides is limited.
Pesticides can cause direct toxic or beneficial effects on microbial communities similar to those reported for higher organisms. Some microbes particularly bacteria may utilize pesticides as a source of nutrients facilitating their growth and survival, while sensitive species may be impaired or decimated by pesticides. These ecological alterations may trigger a cascade of indirect effects. For example, elimination or reduction of certain microbial populations by pesticides may release pesticide-tolerant microbes from competition for shared resources and thereby promote their growth and survival5,12. Similarly, some protozoan species prey on bacteria and their suppression by pesticides may facilitate survival of bacterial prey13. These processes may lead to dramatic shifts in microbial communitie that may interfere11 or have little effect on microbial functions