Colony shape as a genetic trait in the pattern-forming Bacillus mycoides

SIN and DX strains isolated from the environment were classified as B. mycoides by biochemical and molecular biology tests. Growth on agar of different hardness and nutrient concentration did not abolish colony patterns, nor was conversion between SIN and DX morphotypes ever noticed. A number of morphotype mutants, all originating from one SIN strain, were obtained. Some lost turn direction becoming fluffy, others became round and compact. All mutants lost wild type tight aggregation in liquid culture. Growth on agar was followed by microscopy, exploring the process of colony formation and details of cell divisions. A region of the dcw (division cell wall) cluster, including ftsQ, ftsA, ftsZ and murC, was sequenced in DX and SIN strains as a basis for studying cell division. This confirmed the relatedness of DX and SIN strains to the B. cereus group.DX and SIN asymmetric morphotypes stem from a close but not identical genomic context. Asymmetry is established early during growth on agar. Wild type bacilli construct mostly uninterrupted filaments with cells dividing at the free ends: they "walk" longer distances compared to mutants, where enhanced frequency of cell separation produces new growing edges resulting in round compact colonies.Bacteria growing on agar plates display a variety of colony forms called "patterns" or "morphotypes" [1,2]. Colony pattern, an important taxonomic element for early microbiologists, is the first step of differentiation occurring in a population of individuals otherwise identical. Advantages stemming from multicellularity and patterned growth in bacteria are several: increased proliferation due to easier diffusion of positive growth signals and from coordination of biochemical activities; access to nutrients that could not be reached by single individuals and collective defense against adverse conditions [3].Formation of bacterial colonies was analyzed by mathematical models as an example of complexity in open systems. Variables such