Design of Co-culturing system of diazotrophic cyanobacteria and filamentous fungi for potential application in self-healing concrete

Microbe-mediated self-healing concrete has been extensively investigated for more than three decades, but it still suffers from one important limitation, i.e., none of the current self-healing approaches are fully autonomous since they still require external supply of nutrients for the healing agents to continuously produce repair materials. The goal of this study is to create a synthetic lichen system with a phototroph-heterotroph symbiosis, similar to natural lichens, so that the system can produce biomaterials in a self-sustained manner. With the aim to construct the simplest synthetic community, the following two species are used, i.e., diazotrophic cyanobacteria that are mainly responsible for fixing CO2 and N2 from the air and filamentous fungi that are mainly responsible for attracting Ca2 + and promoting large amounts of CaCO3 precipitates. It has been tested that three such coculture systems can grow very well solely on air and light in an inorganic liquid medium without any additional carbon or nitrogen source, i.e., Trichoderma reesei paired with Anabaena inaequalis, T. reesei paird with Nostoc punctiforme, and T. reesei paired with both A. inaequalis and N. punctiforme. A protocol of characterizing co-culture systems has been invented, including five quantitative characterization methods, i.e., optical density measurement, biomass dry weight measurement, resazurin assay, fungal plating on selective medium, and phycocyanin assay. Using this protocol, it was confirmed that the cyanobacterial and fungal growth in the coculture systems were significantly better than their axenic growth, demonstrating the importance of mutual interactions. The results demonstrated the potential of creating a stable phototrophic-heterotrophic system for self-sustained concrete repair, utilizing the capabilities of two species simultaneously and eliminating the need for exogenous nutrient supplies. The self-sustained production of CaCO3 precipitates by such co-culture systems can be tested on cracked concrete samples.