Fig. 4

Extracellular polymeric substances and wire-like structures in C. acetobutylicum biofilm. Samples were stained with safranin O and imaged in a fluorescence microscope. a the early stage of biofilm development; b high-density cell colonies; c wire-like structures; d cellular morphology at the mid stage of biofilm development; e wires imbedded in cells aggregates; f EPS pellicles observed in the biofilm