Biofilms are environmentally relevant lifestyles of microorganisms. Biofilms are usually isolated from surfaces or interfaces, where cells grow together, differentiate, produce a matrix and communicate through the matrix. This matrix also protects them from environmental insults, such as antimicrobials and several other stress conditions. Biofilms possess high complexity that is changing in time and space. To achieve such a differentiation cells enter various phenotypic pathways. Several studies present example how phenotypic heterogeneity (subpopulation of cells harbouring same genotype but expressing different sets of genes therefore showing diverged phenotype) plays a role during the development of biofilms. However, most of these studies concentrate on the genes coding for enzymes involved in the production of the biofilm matrix. Therefore studies that concentrate on the genes and regulation of genes that are involved in development of biofilm structures are desired. In this proposal, I will concentrate on the interplay between different cell types present in the biofilm and the role of heterogeneity in the development of biofilm structures and maturation. This proposal aims to unravel how the structure development is modulated in B. subtilis biofilms, what is the role of the cell growth strategies, the cell-cell communication, local cell level environment and gene expression in biofilm formation.The main objectives include (1) the development of an experimental system for bacterial biofilms, where heterogeneity in metabolic status of the cells can be followed; (2) the generation of a novel theoretical model for B. subtilis biofilms; (3) the isolation of growth yield favouring phenotypes; (4) detection of heterologously expressed transcripts at the single cell level. These objectives contain state of the art molecular biology techniques (fluorescent reporters), recently developed methods(single cell transcriptome) and novel approaches.