Dust in the Wind: How Global Desertification Is Affecting Pathogenic Marine Vibrios

Deposition of African dust in surface waters of the Gulf of Mexico has been shown to elicit microbial
growth responses. While much of the work on the ecological effects of dust deposition have centered on its potential stimulation of phytoplankton activity, here we show that growth of pathogenic Vibrio spp. may also be directly stimulated by dust deposition and its associated nutrients and trace metals. As the global abundance of airborne dust is projected to increase as a result of climate change, the long-term effects of dust deposition to the marine environment will likely have significant impacts on marine pathogens and human health. In particular, Vibrio infection rates have increased by 85% in the US over the last 14 years. Given that the occurrence of Vibrio spp. in the environment corresponds with human exposure risk and that in tropical and subtropical waters, warm temperatures already support endemic populations of Vibrio spp., there is a compelling case that dust trajectories could improve predictive tools for increased risk of exposure and disease, especially under climate change scenarios for the near to mid-future (i.e., 21st century). In this study, we focused on desert areas in western Africa likely to grow over the coming century due to climate change. Dust storms in these areas are also projected to increase and with them, transport of dust across the Atlantic Ocean Basin. Dust deposited in the Gulf of Mexico and Caribbean contains significant levels of trace elements (e.g., iron) and other nutrients (e.g., nitrogen and phosphorous) that may stimulate microbial growth in marine waters where these elements are usually limited. Vibrio bacteria, including important human pathogens such as V. cholerae, V. parahaemolyticus and V. alginolyticus, are well adapted to respond to influx of such nutrients and trace metals. Using a newly developed iron limited minimal medium, the sole addition of dust from source areas (i.e., desert dust from Morocco) significantly stimulated growth of toxigenic V. cholerae, V. vulnificus and V. alginolyticus within 48 hours of exposure. Dust-amended microcosms showed equivalent growth responses as the addition of 5 µM iron, suggesting that dust amendments may have relieved iron limitation in these systems. These results suggest that in addition to rising sea surface temperatures, increased global production and oceanic deposition of desert dust may have a significant effect on population dynamics of key marine pathogens and may ultimately increase exposure rates and infection risk in humans.