Correlation between the spatial distribution and colony size was common for monogenetic bacteria in laboratory conditions

Abstract

Background Geographically separated population growth of microbes is a common phenomenon in microbial ecology. Colonies are representative of the morphological characteristics of this structured population growth. Pattern formation by single colonies has been intensively studied, whereas the spatial distribution of colonies is poorly investigated. Results The present study describes a first trial to address the questions of whether and how the spatial distribution of colonies determines the final colony size using the model microorganism Escherichia coli, colonies of which can be grown under well-controlled laboratory conditions. A computational tool for image processing was developed to evaluate colony density, colony size and size variation, and the Voronoi diagram was applied for spatial analysis of colonies with identical space resources. A positive correlation between the final colony size and the Voronoi area was commonly identified, independent of genomic and nutritional differences, which disturbed the colony size and size variation. Conclusions This novel finding of a universal correlation between the spatial distribution and colony size not only indicated the fair distribution of spatial resources for monogenetic colonies growing with identical space resources but also indicated that the initial localization of the microbial colonies decided by chance determined the fate of the subsequent population growth. This study provides a valuable example for quantitative analysis of the complex microbial ecosystems by means of experimental ecology.

Contribution of the genomic and nutritional differentiation to the spatial distribution of bacterial colonies

“…The value of Cor k was close to 1, which revealed that the area charged by the colony was highly positively correlated with the growth capacity of the colony. The results clearly demonstrated the generality of the Voronoi correlation ( Cor k ) in colony growth, which strongly supported our previous finding ( Xue et al, 2021 ) and indicated the commonly fair division of the space area for colony growth.…”

“…To evaluate the effect of the spatial distribution on the growth of colonies, the spatial analysis was performed using the Voronoi diagram, a practical method to divide the multiple distributed points into regions, as reported previously ( Chacón et al, 2018 ; Xue et al, 2021 ). The parameter of the Voronoi area ( Vor i ) was calculated, indicating the space region on the plate assigned to the corresponding colony ( Figure 4A ).…”

“…The plates were photographed with a high-sensitivity monochrome CCD camera of a gel imager (AE-6932GXES print graph, ATTO Co., Ltd.). Brightness, contrast, saturation, hue, sharpness, OSD time, and exposure time were set as previously described ( Xue et al, 2021 ). Temporal changes in colony growth were captured at intervals of 12 h ( Supplementary Figure 1B ).…”

“…The Voronoi region, Vor i (i = 1∼n; n, number of colonies), which is the theoretical region assigned to each colony, was calculated according to the following formula, as previously described (Xue et al, 2021). Here, V(c l ) and d represent the Voronoi area of the colony c l and the function of the distance, respectively.…”

“…The landmark study first applied spatial analysis of Voronoi diagram to observe the size variation of the colonies grown on identical plates ( Chacón et al, 2018 ). The correlation of the colony size to the spatial area assigned to the colony (i.e., Voronoi area) was observed ( Xue et al, 2021 ). Whether such a correlation in the spatial distribution of colonies was affected by the environmental conditions was required to be addressed.…”