Can diatoms eat bacteria in the absence of light?

Autotrophic heterokonts do not consume other organisms and produce energy by harvesting light, whereas heterotrophic heterokonts obtain their energy by consuming other organisms regardless of the presence of light.

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The above is actually a good answer although a little difficult to understand. (although heterotrophic heterokonts are NOT carnivores).

In essence the diatoms that yu are thinking about (the ones that live on light) do not eat bacteria when placed in the dark.