Step 1: Understand the metabolic classification
The prefix "chemo" means it obtains energy from chemical compounds (not light).
"litho" indicates the electron donor is inorganic.
"heterotroph" indicates it depends on organic carbon for its carbon source.
Step 2: Apply this to Beggiatoa
Beggiatoa uses inorganic chemicals as an electron donor $\Rightarrow$ litho
It depends on organic carbon $\Rightarrow$ heterotroph
Its energy is derived from chemical reactions $\Rightarrow$ chemo
Conclusion: Therefore, Beggiatoa is correctly classified as a Chemolithoheterotroph.