Abstract
Biocoatings immobilising viable bacteria within waterborne polymer coatings (i.e., synthetic latex) have garnered researchers’ interest in recent years. These biocoatings could be ready-to-use, sustainable alternatives for carbon capture to reduce climate change. The major challenge of biocoatings is the film formation which results in desiccation stress and low porosity, leading to reduced mass transfer and eventual cell death. Previous studies have included carbohydrates which created temporary pores and acted as osmoprotectants. In this study, comparisons of osmoprotectants glycerol, sucrose and trehalose and the hydrophilic phytoglycogen, were performed for the first time. Moreover, halloysite nanotubes were added to create stable pores. In an initial phase, lab-adapted E. coli were immobilised in the biocoatings. Adding halloysite significantly improved their survival after desiccation and rehydration, as shown by resazurin reduction assays, thus halloysite became a critical component of biocoatings. From the carbohydrates, only including trehalose to biocoatings along with halloysite showed significantly higher survival of E. coli. To create carbon capturing biocoatings, the cyanobacteria Synechococcus sp. PCC 7002, Synechocystis sp. PCC 6803 and Chroococcidiopsis cubana PCC 7433 were immobilised to compare their viability and oxygen evolution within the biocoatings. Synechococcus 7002 did not survive the film formation process. Synechocystis 6803 survived, as shown by an ATP assay, but only consumed oxygen for up to five days and were unable to perform photosynthesis. On the other hand, the extremophilic Chroococcidiopsis 7433 survived and carried out photosynthesis and carbon capture as shown by specific rates of oxygen evolution up to 0.4 gO2 gbiomass-1 day-1. Over a one-month period, no decrease of activity was observed. These extremophilic cyanobacteria are the ideal candidates for use in hard biocoatings, and their upscaling could result in carbon capture applications in human-made environments, wastewater treatment and biofuel
production.