HOLOTRANSFORMATIONS OF BACTERIAL COLONIES AND GENOME CYBERNETICS

We present a study of colony transformations during growth of Bacillus subtilis under adverse environmental conditions. It is a continuation of our pilot study of ''Adaptive self-organization during growth of b acterial colonies'' (Physica A 187 (1992) 378). First we identify and describe the transformations pathway, i.e. the excitation of the branc hing modes from Bacillus subtilis 168 (grown under diffusion limited c onditions) and the phase transformations between the tip-splitting pha se (phase F) and the chiral phase (phase C) which belong to the same m ode. This pathway shows the evolution of complexity as the bacteria ar e exposed to adverse growth conditions. We present the morphology diag ram of phases F and C as a function of agar concentration and pepton l evel. As expected, the growth of phase F is ramified (fractal-like or DLA-like) at low pepton level (about 1 g/l) and turns compact at high pepton level (about 10 g/l). The growth of phase C is also ramified at low pepton level and turns denser and finally compact as the pepton l evel increases. Generally speaking, the colonies develop more complex patterns and higher micro-level organization for more adverse environm ents. We use the growth velocity as a response function to describe th e growth. At low agar concentration (and low pepton level) phase C gro ws faster than phase F, and for a high agar concentration (about 2%) p hase F grows faster. We observe colony transformations between the two phases (phase transformations). They are found to be consistent with the ''fastest growing morphology'' selection principle adopted from az oic systems. The transformations are always from the slower phase to t he faster one. Hence, we observe F -> C transformations at low agar co ncentrations and C -> F transformations at high agar concentrations. W e have observed both localized and extended transformations. Usually, the transformations are localized for more adverse growth conditions, and extended for growth conditions close to the boundaries between mor phologies. We have observed also transformations between different bra nching modes, as well as transformations via virtual states. Motivated by the contemporary knowledge about phages and plasmids, we postulate a theoretical framework to comply with our experimental findings. We explain our observations using these assumptions as well as our propos al of co-mutations and auto-catalytic mutations as presented in the ab ove mentioned pilot paper. This theoretical framework is a part of the new evolving picture of genome cybernetics. We also discuss the conce pt of adaptive genome changes which are based on pre-existing knowledg e as well as the concept of genetic learning, i.e. changes (in respons e to a new problem) which develop the potential for adaptive genome ch anges. These concepts follow naturally if the picture of genome cybern etics is accepted. We conclude with a discussion of the implications a nd with further predictions (to be tested experimentally) derived from our assumptions.