Answer:
Chemotrophs
Step-by-step explanation:
As these bacterium live deep in the sea, they have no access to sunlight and thus cannot be phototrophs. Therefore, they must chemotrophs. Chemotrophs use inorganic material, such as minerals, as energy sources.
The question does not specify the carbons source of the bacterium. So, in addition to being chemotrophs, they could be autotrophs (carbon from CO₂) or heterotrophs (carbon from other organic material).