Figure 1.
The grass, Enneapogon desvauxii growing near the bones of a plains zebra that died from anthrax one year previously in Etosha National Park, Namibia.
Figure 2.
Experimental design: a. The fenced field enclosure situated in the grassland savanna in central Etosha.
b. One of twenty-five 1 m2 plots established within the field enclosure. Each plot contained two replicates for each of eight treatments.
Figure 3.
Carcass materials, such as spores and blood may promote plant growth.
a. Percentage of sample units where at least one grass plant established: control (grass alone), spore, spore + blood, blood; confidence intervals are provided; N = 50 per treatment. b. Distributions of maximum stem height (cm) in the four treatments with grass present: control (grass alone), spore, spore + blood, blood; N = 9 per treatment.
Figure 4.
Total B. anthracis counts in soil (CFU ×104 per g dry soil ± standard error) for eight different treatments at four different time points: a. early first rainy season (three months), b. end of first rainy season (five months), c. end of second rainy season (17 months), d. end of third rainy season (29 months).
Counts are corrected for soil moisture. N = 3 per treatment.
Figure 5.
Total B. anthracis counts in soil (log (CFU +1) per g dry soil) for the four B. anthracis treatments from January 2009 until April 2011.
CFU counts are indicated with open circles that are connected by a line through the mean of each of the time points. The four treatments are color coded as described in the figure legend. N = 3 per time point.
Figure 6.
Composition of bacterial communities in bulk soil in four treatments: grass, spore + grass, spore, control (soil alone): a. Mean number of OTUs per phylum, b. Community composition (%). N = 3 per treatment.
Figure 7.
An ingestion-transmission cycle of B. anthracis.
Many anthrax infections occur in herbivorous animals, such as zebra, that consume infectious spores while grazing or browsing [17], [29], [30]. Spores germinate within the host to produce vegetative cells that cause a fulminant infection. After host death, terminal hemorrhaging and scavenging releases blood, body fluids, and vegetative B. anthracis cells that inoculate soil in the surrounding area [17], [69], [70]. While it has long been held that these vegetative cells cannot survive competition with soil-dwelling bacteria and must sporulate rapidly [3], [4], [55], recent studies indicate the potential for B. anthracis to form biofilms [6], [71] and to persist in the rhizosphere [5]. In addition to the nutrients found in carcass materials, B. anthracis inoculation appears to promote plant growth, which may attract grazing hosts and increase the rate of anthrax transmission. Illustration by Kelsey Wood.