Information exchange between cellular compartments allows us to engineer systems based around cooperative principles. In this chapter we consider a unique bacterial communication system, the conjugative plasmid transfer of Enterococcus faecalis. Using these bacteria, we describe how to engineer a logically controlled information gate and build a logical inverter based upon it. Cellular computing is an alternative computing paradigm based on living cells. Microscale organisms, especially bacteria, are well suited for computing for several reasons. A small culture provides an almost limitless supply of bacterial “hardware.” Bacteria can be stored and easily modified by gene recombination. In addition, and important for our purposes, bacteria can produce various signal molecules that are useful for computation. DNA-binding proteins recognize specific regulatory regions of DNA, bind them, and regulate their genetic expression. These proteins are available for use as computing signals inside the cell. Weiss et al. have shown, for example, how to construct logic circuits based on gene expression regulated by DNA-binding proteins. Some signal molecules are associated with intercellular communications between individuals. Intercellular communication is one of the fundamental characteristics of multicellular organisms, but it is also found in single-celled microorganisms, including bacteria. Communication mediated by homoserine lactones can widely be seen in various Gram-negative bacteria. The mechanism of this behavior was well characterized in Vibrio fischeri, due to their bioluminescent activity mediated by homoserine lactones. It has been shown that bacterial information transfer can be engineered as an extension of Escherichia coli into which the lux genes of Vibrio fischeri are transformed. The communication abilities of bacteria therefore allow us to build microbial information processors for cellular computing. Communication mechanisms in Gram-positive bacteria are not yet well understood. One of the exceptions to this is the conjugative plasmid transfer system in Enterococcus faecalis. E. faecalis conjugate in response to a pheromone is released by other cells. Pheromones are seven- or eight-residue amino peptides produced in E. faecalis. In the case of cPD1, the pheromone is produced by truncation of a 22-residue precursor that is the signal peptide of a lipoprotein.