by S. Mar­vin Fried­man — Bac­te­ria en­gage in a va­ri­ety of be­hav­iors that re­quire co­or­di­nated gene ex­pres­sion, such as bi­o­lu­mi­nes­cence, biofilm for­ma­tion, pro­duc­tion of vir­u­lence fac­tors, and an­tibi­otic re­sis­tance. In these sit­u­a­tions, gene ex­pres­sion re­quires a crit­i­cal num­ber of cells. In its ab­sence, the ex­er­cise would be in vain, some­thing like...