Interactions between Bacillus anthracis and plants may promote anthrax transmission.

Holly H Ganz,Heniritha Sibanda,Tamas Torok,Martina Kusters,Ying Shi,Wendy C Turner,Wayne M Getz,Eoin L Brodie,Joseph M Vinetz

doi:10.1371/journal.pntd.0002903

Abstract

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

Highlights

The causative agent of anthrax in humans, livestock and wildlife, Bacillus anthracis was long considered an obligate pathogen that is dormant in the environment [1,2]
The causative agent of anthrax, Bacillus anthracis is transmitted by spores that persist for long periods of time in the environment
We describe the results of a field experiment designed to test whether the interaction of B. anthracis with plants might affect its persistence and potential transmission to grazing hosts

Summary

Introduction

The causative agent of anthrax in humans, livestock and wildlife, Bacillus anthracis was long considered an obligate pathogen that is dormant in the environment [1,2]. This view was supported by early laboratory studies conducted by Minett and Dhanda [3] and Minnet [4] that suggest that B. anthracis is unable to compete with other soil bacteria. An insect pathogen commonly used as a pesticide in agriculture [14], B. thuringiensis occurs in soil and can be found living symbiotically in caterpillar guts [9]

Methods

Results

Discussion

Conclusion