Sphaerotilus and Leptothrix are examples of A. purple sulfur bacteria. B. Enterobacteriaceae. C. sheathed bacteria. D. green nonsulfur bacteria.

sheathed bacteria

Explanation:

Sphaerotilus and Leptothrix are examples of sheathed bacteria that have a filamentous appearance because of which they look like fungus and hence, are also known as sewage fungus. They are usually found onto the surface of contaminated waters. These are sheathed bacteria as the filament-like appearing sheath bears the single cells of gram-negative bacteria. These organisms thrive on organic matter and hence, sewage-contaminated water is a common habitat for them.