Microbial community analysis of EPS-overproducing mixed microbial cultures in glycerol- and VFA-fed bioreactors
Mixed microbial cultures offer a promising route for producing extracellular polymeric substances from wastewater-derived substrates, but the microbial communities involved in EPS overproduction remain insufficiently understood. This study investigated microbial community development in seven bioreactors operated under EPS-overproduction conditions, combining nitrogen limitation with short solids retention time. The reactors were operated with either glycerol- or volatile fatty acid-rich synthetic wastewater and differed in inoculum source, reactor configuration, substrate type, organic loading rate, and operational duration.  In glycerol-fed membrane bioreactors, EPS-overproduction conditions consistently stimulated EPS production and enriched communities containing both putative EPS-producing and EPS-degrading taxa. Recurrent putative EPS producers included Brevundimonas, Microbacterium/Microbacteriaceae, Pseudoxanthomonas, Novosphingobium, Asticcacaulis, and Derxia, while taxa such as Saprospiraceae, Pseudoclavibacter, Bdellovibrio, and Terrimonas were associated with EPS turnover. Direct start-up under nitrogen limitation resulted in comparable EPS yields, suggesting that prolonged acclimation was not required.  In VFA-fed systems, reactor configuration strongly influenced community assembly and process performance. The continuous stirred-tank reactor achieved higher COD removal and EPS yields than the membrane bioreactor, despite lower bacterial diversity. VFA-fed reactors enriched taxa potentially involved in both EPS and PHA metabolism, including Chryseobacterium, Flavobacterium, Brevundimonas, Pseudoxanthomonas, and Acinetobacter, together with polymer-degrading and predatory groups such as Microscillaceae, Kapabacteriales, Micavibrionales, and Bdellovibrio. Overall, EPS production appeared to be a community-level function supported by multiple EPS-producing taxa at moderate abundance rather than being linked to one dominant taxon. The findings highlight the ecological complexity of EPS-overproducing mixed microbial cultures and indicate that functional approaches beyond 16S rRNA gene profiling are needed to resolve the active roles of EPS producers, degraders, and polymer-turnover populations.
Mixed microbial cultures offer a promising route for producing extracellular polymeric substances from wastewater-derived substrates, but the microbial communities involved in EPS overproduction remain insufficiently understood. This study investigated microbial community development in seven bioreactors operated under EPS-overproduction conditions, combining nitrogen limitation with short solids retention time. The reactors were operated with either glycerol- or volatile fatty acid-rich synthetic wastewater and differed in inoculum source, reactor configuration, substrate type, organic loading rate, and operational duration.  In glycerol-fed membrane bioreactors, EPS-overproduction conditions consistently stimulated EPS production and enriched communities containing both putative EPS-producing and EPS-degrading taxa. Recurrent putative EPS producers included Brevundimonas, Microbacterium/Microbacteriaceae, Pseudoxanthomonas, Novosphingobium, Asticcacaulis, and Derxia, while taxa such as Saprospiraceae, Pseudoclavibacter, Bdellovibrio, and Terrimonas were associated with EPS turnover. Direct start-up under nitrogen limitation resulted in comparable EPS yields, suggesting that prolonged acclimation was not required.  In VFA-fed systems, reactor configuration strongly influenced community assembly and process performance. The continuous stirred-tank reactor achieved higher COD removal and EPS yields than the membrane bioreactor, despite lower bacterial diversity. VFA-fed reactors enriched taxa potentially involved in both EPS and PHA metabolism, including Chryseobacterium, Flavobacterium, Brevundimonas, Pseudoxanthomonas, and Acinetobacter, together with polymer-degrading and predatory groups such as Microscillaceae, Kapabacteriales, Micavibrionales, and Bdellovibrio. Overall, EPS production appeared to be a community-level function supported by multiple EPS-producing taxa at moderate abundance rather than being linked to one dominant taxon. The findings highlight the ecological complexity of EPS-overproducing mixed microbial cultures and indicate that functional approaches beyond 16S rRNA gene profiling are needed to resolve the active roles of EPS producers, degraders, and polymer-turnover populations.