Can bacteria metabolize fatty acids for fuel?
I found this review about bacterial lipid metabolism. There it says:


  Exogenous long chain fatty acids are utilized by E. coli in two ways. Firstly, they can
  be incorporated into the membrane phospholipids by the acyltransferase system (PlsB
  and PlsC; Section 4). Secondly, they can be used as the sole carbon source for growth,
  and are in fact an important source of energy for E. coli in their normal habitat, the
  intestine [16]. The CoA thioester of the fatty acid is the substrate for both of these
  pathways. Fatty acids greater than 10 carbons in length require the fadL gene product
  to be taken up from the growth medium in sufficient quantities to support growth. 


So yes, bacteria can grow on fatty acids alone and they can utilize long fatty acids as an energy source. However the uptake of the long fatty acids requires the protein produced by the fadL gene.