FIG. 5.

Alternative models for signal processing in B. subtilis spore germination based on both previous and current work. (A) The receptors can operate either alone or when complexed with other receptors to give a particular rate of spore germination. While only complexes of two receptors are shown, all three receptors could be in a complex in this model. The short arrows beneath GerB and GerK indicate that these receptors alone give little if any germination. (B) The signals from individual receptors, which may be very different in intensity, are fed into a hypothetical signal integrator that integrates and/or sums all signals to generate an output that is a particular rate of spore germination. The specific role of K⁺ is not shown in either A or B, since K⁺ may interact with all three receptors. Abbreviations used for receptors are in boxes and are as follows: A, GerA; B, GerB; B*, GerB*; K, GerK. Abbreviations used for germinants or cogerminants are as follows: A, l-alanine; AA, l-alanine, l-asparagine, l-serine, or l-threonine; f, fructose; g, glucose; V, l-valine. The symbol “/” indicates “or.” Cogerminants are shown in parentheses above the affected receptor; germinants are also shown above the affected receptor.