**Core Concept**
Bacillus anthracis is a Gram-positive, rod-shaped bacterium that causes the zoonotic disease anthrax. This pathogen is typically found in soil and can infect a wide range of mammals, including humans. The bacterium forms spores that are highly resistant to environmental stressors.

**Why the Correct Answer is Right**
Bacillus anthracis is a virulent pathogen that produces several key virulence factors, including the anthrax toxin and capsule. The anthrax toxin is composed of three components: edema factor (EF), lethal factor (LF), and protective antigen (PA). The capsule, made of poly-D-glutamic acid, helps the bacterium evade the host immune system. These virulence factors enable B. anthracis to cause severe disease in humans, including cutaneous, inhalational, and gastrointestinal anthrax.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it contradicts the established fact that B. anthracis is a Gram-positive bacterium.
**Option B:** This option is incorrect because it is not a recognized characteristic of B. anthracis. While the bacterium does produce several virulence factors, this is not one of them.
**Option C:** This option is incorrect because it is not a known feature of B. anthracis. While some bacteria do produce toxins that affect the nervous system, this is not a characteristic of B. anthracis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that anthrax spores can survive for decades in the environment, making this bacterium a potential bioterrorism agent. Early recognition and treatment of anthrax are critical to preventing severe disease and mortality.

**Correct Answer: A. Bacillus anthracis is a Gram-negative bacterium.**