Granular biofilms producing medium-chain carboxylic acids (MCCA) from carbohydrate-rich industrial feedstocks harbor highly streamlined communities converting sugars to MCCA either directly or via lactic acid as intermediate. We investigated the spatial organization and growth activity patterns of MCCA producing granular biofilms grown on an industrial side stream to test (i) whether key functional guilds (lactic acid producing Olsenella and MCCA producing Oscillospiraceae) stratified in the biofilm based on substrate usage, and (ii) whether spatial patterns of growth activity shaped the unique, lenticular morphology of these biofilms. First, three novel isolates (one Olsenella and two Oscillospiraceae species) representing over half of the granular biofilm community were obtained and used to develop FISH probes, revealing that key functional guilds were not stratified. Instead, the outer 150–500 µm of the granular biofilm consisted of a well-mixed community of Olsenella and Oscillospiraceae, while deeper layers were made up of other bacteria with lower activities. Second, nanoSIMS analysis of 15N incorporation in biofilms grown in normal and lactic acid amended conditions suggested Oscillospiraceae switched from sugars to lactic acid as substrate. This suggests competitive-cooperative interactions may govern the spatial organization of these biofilms, and suggests that optimizing biofilm size may be a suitable process engineering strategy. Third, growth activities were similar in the polar and equatorial biofilm peripheries, leaving the mechanism behind the lenticular biofilm morphology unexplained. Physical processes (e.g., shear hydrodynamics, biofilm life cycles) may have contributed to lenticular biofilm development. Together, this study develops an ecological framework of MCCA-producing granular biofilms that informs bioprocess development.
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16S rRNA gene sequences have been deposited to NCBI GenBank under accession numbers OP799682–OP799726.
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PC was supported by UGent Special Research Fund (BOF15/DOC/286) and the U.S. Department of Energy, Office of Science, Office of Biological & Environmental Research (#DE-SC0020356). RG is supported by the Special Research Fund of Ghent University (grant number BOF19/STA/044). GLC and VJO were supported by grants from the Department of Energy, Office of Science, Office of Biological and Environmental Research (#DE-SC0020373). VJO was also supported by the Life Sciences-Simons Collaboration on Principles of Microbial Ecosystems (PriME) Program from the Simons Foundation (Award 542393).
The authors declare no competing interests.
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Candry, P., Chadwick, G.L., Caravajal-Arroyo, J.M. et al. Trophic interactions shape the spatial organization of medium-chain carboxylic acid producing granular biofilm communities. ISME J 17, 2014–2022 (2023). https://doi.org/10.1038/s41396-023-01508-8