The optimal performance of industrial processes often depends on the control over biofilm growth and distribution. Hence, we welcome contributions describing the newest methods for both biofilm monitoring and control at the biofilms 9 conference. Applications can range from drinking water and membrane processes to processes in traditional industries with water reuse (pulp and paper, food, etc.). Especially, advanced examples or cutting-edge research projects combining, for example, on-line monitoring and disinfection/cleaning strategies based on monitoring data are highly appreciated.

Heterogeneity is the most reliable companion of biofilm development in all types of environments. Structural heterogeneity can be described by parameters like texture, roughness, and porosity among others. Variations in these parameters are often indicative of the performance of biofilm systems in terms of turnover, substrate consumption, and mass transfer at the biofilm-water interface. Hence, structural heterogeneity will often correlate with heterogeneity on a molecular level. Challenges appear if we want to predict the amount of substrate, which can be converted or the amount of product, which can be generated by a biofilm of a certain surface area over time. We would like to approach the term heterogeneity in biofilm systems with advanced imaging techniques both on the micrometre scale but also on the mesoscale with molecular techniques like single cell sequencing. Moreover, we would like to have contributions which can show that heterogeneity can be quantified and linked to biofilm performance measures.

For decades, biofilm research has been trying to provide a comprehensive description of the biofilm matrix. Due to the complexity of the biofilm matrix, an easy characterisation seems somehow impossible. Recently, optical coherence tomography has been pushed and very much contributes to an advanced structural characterisation of the mesoscopic biofilm structure. However, the biofilm matrix is a highly complex matter with various physical (e.g. distribution of biomass, material properties), chemical (e.g. composition, constituents) and (micro)biological (e.g. microorganisms and interactions) properties.
We are thus looking for contributions improving the structural (physical, chemical, micro biological) understanding of the biofilm matrix. Very much appreciated are inputs correlating results of different methodologies.

We define productive biofilms as microbial communities utilised in biotechnological processes as biocatalysts for the production of value-added chemicals. For successful implementation, it is essential to merge engineering and natural sciences to equally address biological aspects like biofilm growth, structure and physiology, as well as technical challenges like reactor configuration, mass transfer issues and scale up. Productive biofilms growing on active substrate like membranes (delivering gaseous substrates) or electrodes (acting as electron donor or acceptor) are perfect model systems to study the benefits, challenges and limitations of continuous productive biofilm systems. Hence, we welcome contributions that present new processes and/or biocatalysts thriving on active substrata, describe new solutions for reactor design or highlight the impact of the biofilm matrix and heterogeneity on productivity.

Biofilms form and disperse following complex regulatory regimes, which are the consequence of both endogenous and exogenous signals. These signals are sensed and translated into the regulation of the expression of a number of target genes. It seems that the type of the natural environment has formed the complex response of the microorganisms. Consequently, one signal can inhibit biofilm formation in one organism while it promotes biofilm formation for others. Although elements like flagellar motility, carbon metabolism, quorum sensing molecules or c-di-GMP have over the last years been established as major players for biofilm regulation, we are also aware that we are still far away from completely understanding the full regulatory networks or the impact of cellular heterogeneity on the regulation of biofilm formation. Also, the development of molecules that interfere with the regulatory machinery and can hence be used for the dispersal or enhanced formation of biofilms is still in its infancy. Hence, we welcome contributions that would address the above mentioned emerging fields in the regulation of the biofilm lifecycle.

The synthetic engineering of biofilms can lead to processes with increased productivities, biofilm matrices with better properties or the tailor-made interaction of microorganisms. Meanwhile, we have molecular tools to engineer the synthetic interaction of organisms by designing the share of labour or by precipitating organisms with each other. Moreover, bioprinting gives us the possibility to print organisms in defined mixtures and densities and with specifically adapted inks. Nevertheless, the question on the long-term applicability of synthetic biofilms or organisms in synthetic matrices has not been conclusively answered yet. At biofilms 9, we hope to discuss results and maybe answer fundamental questions with respect to the synthetic development of biofilms like how can we achieve long-term interactions in biofilms, what defines an advanced synthetic biofilm matrix, or what are the benefits that we can gain by the synthetic development of tailored biofilm communities and structures.