Cultivation-dependent effects of quorum sensing signals on a lactic acid and chain-elongating bacterium

Microbial chain elongation enables the conversion of organic waste into higher-value products and is therefore a promising process for circular biomanufacturing. However, the microbial interactions governing chain elongation communities remain poorly understood. While quorum sensing has been extensively studied in the context of pathogens and model organisms, research on the perception of quorum-sensing molecules by non-model organisms and their effects within microbial consortia has remained limited. Here, Lactiplantibacillus plantarum and Megasphaera elsdenii were selected as representatives of two key functional guilds in chain elongation communities, namely lactic acid bacteria and chain-elongating bacteria. The effects of different exogenous quorum sensing molecules were evaluated in pure cultures and co-cultures using microtiter plates and serum bottles. Both organisms exhibited distinct molecule-dependent responses for both growth and biofilm formation. Moreover, the response of M. elsdenii was highly dependent on the supplied substrate. Despite changes in growth and/or biofilm formation, product yield and product spectra remained largely unaffected. Importantly, responses observed in pure cultures did not predict co-culture behavior, and no clear response to the tested molecules was detected in the co-culture grown in serum bottles. These findings demonstrate that responses to quorum sensing molecules are strongly dependent on the signal, substrate, microbial context, and cultivation conditions. These results highlight the limited predictive power of pure-culture assays for microbial communication in interacting communities and emphasize the importance of studying signal perception under process-relevant cultivation conditions.