Bacterial body plans

Abstract

The bacterium Serratia marcescens produces a plethora of multicellular shapes of different colorations on solid substrates, allowing immediate visual detection of varieties. Such a plasticity allows studies on multicellular community scale spanning two extremes, from well-elaborated individual colonies to undifferentiated cell mass.For a single strain and medium, we obtained a range of different multicellular bodies, depending on the layout of initial plating. Four principal factors affecting the morphogenetic pathways of such bodies can be distinguished: (1) amount, density and distribution pattern of founder cells; (2) the configuration of surrounding free medium; (3) the presence and character of other bacterial bodies sharing the same niche; and (4) self-perception, resulting in delimitation towards other bodies. The last feature results in an ability of well-formed multicellular individuals to maintain their identity upon a close mutual contact, as well as in spontaneous separation of cell masses in experimental chimeras. We propose an "embryo-like" colony model where multicellular bacterial bodies develop along genuine ontogenetic pathways inherent to the given species (clone), while external shaping forces (like nutrient gradients, pH, etc.,) exert not formative, but only regulative roles in the process.

Variations and heredity in bacterial colonies

“…1; for details see ref. 1). The pattern is stable in the course of many passages, and develops regardless whether the colony originates from a single cell, bunch of biomass or droplet of dense suspension.…”

“…1C; see also refs. 1, 13) and also tendency to form deviations. Abovementioned typical development of F colony occurs only when colony density does not exceed 20–30 bodies on 9 cm Petri dish.…”

“…From this viewpoint, bacterial colonies may be taken for (i) an extremely reduced biofilm, or (ii) a multicellular body with controlled morphogenesis that cannot come to realization when hampered by the presence of partners in the consortium. Our previous work encourages us to prefer the second interpretation 1,13,14 . What is important, ontogenesis of multicellular body is uncoupled from natural selection: an ability to build colony is rarely a matter of survival—hence rich patterns and the play of variations.…”

“…refs. 1, 6-15), even if processes in the background are far from being understood in detail. Changes in colony shape were studied, caused by mutations either in mother colony, or upon long-term cultivation 16-18 …”

“…ABSTRACTSpontaneous variation in appearance was studied in bacterial colonies of Serratia marcescens F morphotype 1 : (i) A defined array of non-heritable phenotype variations does appear repeatedly; (ii) The presence of colonies of different bacterial species will narrow the variability toward the typical F appearance, as if such an added environmental factor curtailed the capacity of colony morphospace; (iii) Similarly the morphospace becomes reduced by random mutations leading to new, heritable morphotypes—at the same time opening a new array of variations typical for the mutant but not accessible directly from the original F morphospace. Results are discussed in context with biphasic model of early morphogenesis applicable to all multicellular bodies.…”