Are Microbes Optimal Strategists?

In an earlier peper [ I ] on the experimental evd~~iit ioll of cyhernetic models for 1)acterial growth on multiple substrates, we presented certain hasic postulates 1)ased on all existing experimental literatnre known to us that all models for bacterial growth in a multisuhstrate environment must satisfy. At the suggestion of one of the reviewers of that paper, we are presenting an analysis of the experimental literature that led 11s to the elucidation of the postulates mentioned above. It is our belief that this analysis will provide a greater understanding of the optimal nature of cellular regulatory processes controlling the bacterial growth on mriltiple substrates. Bacterial growth is a highly regulated process involving thousands of biochemical reactions. Some of these regulatory actions become strikingly tipparent during the growth of bacteria on media containing more than one functionally equivalent ( i e , serving the same physiological function, such a s carbon source, energy source, nitrogen source, etc.) su1)strates. The regulation of mnltiple substrate utilizsition was detected as early as the turn of this century, when Dienert [ Z ] found that glucose had an inhibitory effect on the galactose fermentation hy yeast. Similar interactions between carbohydrates were reported by some other early investigators [31, [ 4 ] . A systematic and extensive study of bacterial growth on inultiple substrates was conducted by Monod [S], who discovered the phenomenon of “diauxie” and established its close relationship to enzymatic adaptation. Since that time, numerous researchers have observed the sequential utilizations of multiple substrates by a variety of inicroorganisms. A close scrutiny of many of these reports shows several basic characteristics apparent in all the observations of bacterial growth on multiple substrates and we listed below.