Developmental plasticity of bacterial colonies and consortia in germ-free and gnotobiotic settings

Abstract

BackgroundBacteria grown on semi-solid media can build two types of multicellular structures, depending on the circumstances. Bodies (colonies) arise when a single clone is grown axenically (germ-free), whereas multispecies chimeric consortia contain monoclonal microcolonies of participants. Growth of an axenic colony, mutual interactions of colonies, and negotiation of the morphospace in consortial ecosystems are results of intricate regulatory and metabolic networks. Multicellular structures developed by Serratia sp. are characteristically shaped and colored, forming patterns that reflect their growth conditions (in particular medium composition and the presence of other bacteria).ResultsBuilding on our previous work, we developed a model system for studying ontogeny of multicellular bacterial structures formed by five Serratia sp. morphotypes of two species grown in either "germ-free" or "gnotobiotic" settings (i.e. in the presence of bacteria of other conspecific morphotype, other Serratia species, or E. coli). Monoclonal bodies show regular and reproducible macroscopic appearance of the colony, as well as microscopic pattern of its growing margin. Standard development can be modified in a characteristic and reproducible manner in close vicinity of other bacterial structures (or in the presence of their products). Encounters of colonies with neighbors of a different morphotype or species reveal relationships of dominance, cooperation, or submission; multiple interactions can be summarized in "rock – paper – scissors" network of interrelationships. Chimerical (mixed) plantings consisting of two morphotypes usually produced a “consortium” whose structure is consistent with the model derived from interaction patterns observed in colonies.ConclusionsOur results suggest that development of a bacterial colony can be considered analogous to embryogenesis in animals, plants, or fungi: to proceed, early stages require thorough insulation from the rest of the biosphere. Only later, the newly developing body gets connected to the ecological interactions in the biosphere. Mixed “anlagen” cannot accomplish the first, germ-free phase of development; hence, they will result in the consortium of small colonies. To map early development and subsequent interactions with the rest of the biospheric web, simplified gnotobiotic systems described here may turn to be of general use, complementing similar studies on developing multicellular eukaryots under germ-free or gnotobiotic conditions.

Variations and heredity in bacterial colonies

“…1d; ref. 14). This reaction is not caused by newly obtained variants, thus we consider them as homospecific to F .…”

“…Obviously, in such ecosystems they are unable to display structures typical for a colony, like symmetry, coloring and/or structural patterning, defined growth pattern, or maintaining its individuality when faced with neighbors 14 . Their survival and reproduction under such conditions is thus independent on their capacity of colony-building, and natural selection may be indifferent toward such traits.…”

Noise-free accurate count of microbial colonies by time-lapse shadow image analysis

“…Serratia sp. forms different morphologies whether it is grown in the absence or the presence of other Serratia species or E. coli (Patkova et al, 2012). Therefore the colony morphology has received much attention not only from the viewpoint of species specific detection but also from fundamental cell physiology.…”

The fitness change and the diversity maintenance in the growing mixed colony of two Serratia rubidaea clones

“…Mixed (or chimeric) colony was grown at nutrient agar enriched with glucose (Pátková et al 2012). Chimeric colony was planted by dropping dense suspension (10 8 cells/ ml) with equal contribution of both clones involved (diameter of such inoculation droplet is about 2 mm).…”