Interactions between <i>Bacillus anthracis</i> and Plants May Promote Anthrax Transmission

<div><p>Environmental reservoirs are essential in the maintenance and transmission of anthrax but are poorly characterized. The anthrax agent, <i>Bacillus anthracis</i> was long considered an obligate pathogen that is dormant and passively transmitted in the environment. However, a growing number of laboratory studies indicate that, like some of its close relatives, <i>B. anthracis</i> has some activity outside of its vertebrate hosts. Here we show in the field that <i>B. anthracis</i> has significant interactions with a grass that could promote anthrax spore transmission to grazing hosts. Using a local, virulent strain of <i>B. anthracis</i>, we performed a field experiment in an enclosure within a grassland savanna. We found that <i>B. anthracis</i> increased the rate of establishment of a native grass (<i>Enneapogon desvauxii</i>) by 50% and that grass seeds exposed to blood reached heights that were 45% taller than controls. Further we detected significant effects of <i>E. desvauxii, B. anthracis</i>, and their interaction on soil bacterial taxa richness and community composition. We did not find any evidence for multiplication or increased longevity of <i>B. anthracis</i> in bulk soil associated with grass compared to controls. Instead interactions between <i>B. anthracis</i> and plants may result in increased host grazing and subsequently increased transmission to hosts.</p>