Yet, our two interacting clones remind of theoretical models like “”hawks-doves”" or “”prisoners dilemma”" (or even interaction of a monoculture with weeds or pathogens). The third possibility – regular patterns of colony ontogeny – allows even genuine convergent development entering the game. Our observations suggest that development of bacterial bodies in Serratia sp. includes both events taking place within a body, and transmission of signals between distinct bodies. Signals act at a distance, i.e. they do not require physical contact (as reported,

e.g., in [16, 35, MCC950 ic50 36]). Experiments with conditioned agar show that signals do not require simultaneous presence of living entities; hence, actively emitted light, sound, electrical or even chemical pulses of whatever nature can be excluded as carriers of the signal. We are left with a compound or a cocktail of compounds, emitted by living entities into their environment, persisting there for some time, and being actively interpreted by recipients that happen to be present in their range. While our observations do

not provide any hints yet as to the chemical identity of these signals, they at least point towards some of their properties. Experiments with signaling across the septum suggest that the signal from the macula spreads via the gas phase. For a different bacterial system, indole could be the carrier of a volatile signal ([37]; however, this conclusion was later questioned [38]). Ammonia appeared to be the signal carrier in yeast colonies [39]. As a first step HDAC activity assay towards characterizing our signal, we demonstrated that it is readily cleared away by non-volatile acid or alkali traps. We propose a simple model capable of simulating some aspects of our experimentally characterized examples of bacterial body morphogenesis (the F and R colonies).

This model involves two PD184352 (CI-1040) factors carrying information for both morphogenesis and mutual find protocol influencing of neighbors, generated in bodies at certain developmental stages, and diffusible to the environment. One of the signals travels (slowly) through the substrate, the other is transmitted via the gas phase. These bearers of the signals (or even a sign) are perceived by all cells, allowing their orientation and behavior in the developing colony; timing may be the second critical factor at play. While several theoretical models of microbial colony morphogenesis have been published, they mostly focus on such aspects as kinetics of colony expansion controlled by nutrient diffusion through the colony and surrounding medium [40–43], intra-colony spatial organization of cells [44, 45] or fine patterning of the colony margin based on interplay of nutrient and signal diffusion and, in some cases, also swarming behavior of the bacteria [46–48].