Bioreactors hold great promise for treating graywater in an advanced life support system for space applications. However, questions remain regarding the reproducibility and reliability of biological systems for long-term use. Although there have been numerous studies on ground-based biological systems, most studies focus on a single reactor or a simple (single carbon) waste stream. There have been very few studies on microbial communities in replicate reactors using a nonsterile, complex waste stream. In this report, we describe the characterization of five replicate denitrifying reactors receiving a complex feed, including urine and limb washes from donors at Johnson Space Center over a 100-day period. Denitrifying conditions were employed because of the ease in adding a terminal electron acceptor to the bioreactor. Bacterial populations were tracked by 16S rRNA and nosZ genes T-RFLP analysis to target the total and denitrifying microbial communities. The results demonstrated reproducible biological communities with nearly identical performance that slowly changed with time and exhibited low variability with respect to the bacterial community (T-RFLP peak area) in all reactors. These results suggest that, when designed for replication, bioreactors are not stochastic systems exhibiting chaotic behavior, but are biological systems that can be highly reproducible and reliable.

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In their natural environment, bacteria and other microorganisms typically grow as surface-adherent biofilm communities. Cell signal processes, including quorum signaling, are now recognized as being intimately involved in the development and function of biofilms. In contrast to their planktonic (unattached) counterparts, bacteria within biofilms are notoriously resistant to many traditional antimicrobial agents and so represent a major challenge in industry and medicine. Although biofilms impact many human activities, they actually represent an ancient mode of bacterial growth as shown in the fossil record. Consequently, many aquatic organisms have evolved strategies involving signal manipulation to control or co-exist with biofilms. Here, we review the chemical ecology of biofilms and propose mechanisms whereby signal manipulation can be used to promote or control biofilms.