Is Biological Computation a theme covered by the Theoretical Computer Science? I want to say computation realized by biological systems themselves. I'm not talking about bio-inspired algorithms, or applications in computation using living systems. This question is more about an empirical theory of computation in the natural world than applications of biological systems in the industry of the computation.

Reference:
MITCHELL, Melanie. Biological Computation.
Yes there is some overlap, for instance the conference Unconventional Computation and Natural Computation (UCNC) covers theoretical computer science topics related to biological computation.

From the call for papers, UCNC topics of interest include (but are not restricted to): 


  
  Molecular computing 
  Quantum computing 
  Optical computing 
  Chaos computing 
  Physarum computing 
  Collision-based computing 
  Self-assembling and self-organizing systems 
  Super-Turing computation 
  Cellular automata 
  Neural computation 
  Evolutionary computation 
  Swarm intelligence 
  Ant algorithms 
  Artificial immune systems 
  Artificial life 
  Membrane computing 
  Amorphous computing 
  Computational systems biology 
  Computational neuroscience 
  Synthetic biology 
  Cellular (in-vivo) computing