New insights to the difference in microbial composition and interspecies interactions between fouling layer and mixed liquor in a membrane bioreactor

Enhanced AHL-mediated quorum sensing accelerates the start-up of biofilm reactors by elevating the fitness of fast-growing bacteria in sludge and biofilm communities

Quorum sensing (QS)-based manipulations emerge as a promising solution for biofilm reactors to overcome challenges from inefficient biofilm formation and lengthy start-ups. However, the ecological mechanisms underlying how QS regulates microbial behaviors and community assembly remain elusive. Herein, by introducing different levels of N-acyl-homoserine lactones, we manipulated the strength of QS during the start-up of moving bed biofilm reactors and compared the dynamics of bacterial communities. We found that enhanced QS elevated the fitness of fast-growing bacteria with high ribosomal RNA operon (rrn) copy numbers in their genomes in both the sludge and biofilm communities. This led to notably increased extracellular substance production, as evidenced by strong positive correlations between community-level rrn copy numbers and extracellular proteins and polysaccharides (Pearson's r = 0.529-0.830, P < 0.001). Network analyses demonstrated that enhanced QS significantly promoted the ecological interactions among taxa, particularly cooperative interactions. Bacterial taxa with higher network degrees were more strongly correlated with extracellular substances, suggesting their crucial roles as public goods in regulating bacterial interactions and shaping network structures. However, the assembly of more cooperative communities in QS-enhanced reactors came at the cost of decreased network stability and modularity. Null model and dissimilarity-overlap curve analysis revealed that enhanced QS strengthened stochastic processes in community assembly and rendered the universal population dynamics more convergent. Additionally, these shaping effects were consistent for both the sludge and biofilm communities, underpinning the planktonic-to-biofilm transition. This work highlights that QS manipulations efficiently drive community assembly and confer specialized functional traits to communities by recruiting taxa with specific life strategies and regulating interspecific interactions. These ecological insights deepen our understanding of the rules governing microbial societies and provide guidance for managing engineering ecosystems.

Microbial tapestry of the Shulgan-Tash cave (Southern Ural, Russia): influences of environmental factors on the taxonomic composition of the cave biofilms

BACKGROUND

Cave biotopes are characterized by stable low temperatures, high humidity, and scarcity of organic substrates. Despite the harsh oligotrophic conditions, they are often inhabited by rich microbial communities. Abundant fouling with a wide range of morphology and coloration of colonies covers the walls of the Shulgan-Tash cave in the Southern Urals. This cave is also famous for the unique Paleolithic painting discovered in the middle of the last century. We aimed to investigate the diversity, distribution, and potential impact of these biofilms on the cave's Paleolithic paintings, while exploring how environmental factors influence the microbial communities within the cave.

RESULTS

The cave's biofilm morphotypes were categorized into three types based on the ultrastructural similarities. Molecular taxonomic analysis identified two main clusters of microbial communities, with Actinobacteria dominating in most of them and a unique "CaveCurd" community with Gammaproteobacteria prevalent in the deepest cave sections. The species composition of these biofilms reflects changes in environmental conditions, such as substrate composition, temperature, humidity, ventilation, and CO2 content. Additionally, it was observed that cave biofilms contribute to biocorrosion on cave wall surfaces.

CONCLUSIONS

The Shulgan-Tash cave presents an intriguing example of a stable extreme ecosystem with diverse microbiota. However, the intense dissolution and deposition of carbonates caused by Actinobacteria pose a potential threat to the preservation of the cave's ancient rock paintings.

Conductive materials enhance microbial salt-tolerance in anaerobic digestion of food waste: Microbial response and metagenomics analysis

Previous studies have shown that high salinity environments can inhibit anaerobic digestion (AD) of food waste (FW). Finding ways to alleviate salt inhibition is important for the disposal of the growing amount of FW. We selected three common conductive materials (powdered activated carbon, magnetite, and graphite) to understand their performance and individual mechanisms that relieve salinity inhibition. Digester performances and related enzyme parameters were compared. Our data revealed that under normal and low salinity stress conditions, the anaerobic digester ran steady without significant inhibitions. Further, the presence of conductive materials promoted conversion rate of methanogenesis. This promotion effect was highest from magnetite > powdered activated carbon (PAC) > graphite. At 1.5% salinity, PAC and magnetite are beneficial in maintaining high methane production efficiency while control and the graphite added digester acidified and failed rapidly. Additionally, metagenomics and binning were used to analyze the metabolic capacity of the microorganisms. Some species enriched by PAC and magnetite possessed higher cation transport capacities and were to accumulate compatible solutes. PAC and magnetite promoted direct interspecies electron transference (DIET) and syntrophic oxidation of butyrate and propionate. Also, the microorganisms had more energy available to cope with salt inhibition in the PAC and magnetite added digesters. Our data imply that the promotion of Na+/H+ antiporter, K+ uptake, and osmoprotectant synthesis or transport by conductive materials may be crucial for their proliferation in highly stressful environments. These findings will help to understand the mechanisms of alleviate salt inhibition by conductive materials and help to recover methane from high-salinity FW.

Nanomaterials in membrane bioreactors: Recent progresses, challenges, and potentials

The use of nanomaterials (NMs) in the fabrication and modification of membranes as well as the coupling of nanomaterial-based processes with membrane processes have been attracted many researchers today. The NMs due to a wide range of types, different chemistry, the possibility of various kinds of functionality, different properties like antibacterial activity, hydrophilicity, and large surface area were applied to enhance the membrane properties. In the membrane bioreactors (MBRs) as a highly successful process of membrane technology in wastewater treatment, the NMs have been applied for improving the efficiency of MBR process. This review assessed the application of NMs both as the modifiers of membrane and as the effective part of hybrid techniques with MBR system for wastewater treatment. The efficiency of NMs blended membranes in the MBR process has been reviewed in terms of antifouling and antibacterial improvement and removal performance of the pollutants. Novel kinds of NMs were recognized and discussed based on their properties and advantages. The NMs-based photocatalytic and electrochemical processes integrated with MBR were reviewed with their benefits and drawbacks. In addition, the effect of the presence of mobilized NPs in the sludge on MBR performance was surveyed. As a result of this review, it can be concluded that nanomaterials generally improve MBR performance. The high flux and antifouling properties can be obtained by adding nanomaterials with hydrophilic and antibacterial properties to the membrane, and further studies are required for photocatalytic NMs applications. In addition, this review shows that the low amounts of NMs in the membrane structure could have an effective influence on the MBR process. Besides, since many studies in the literature are carried out at the laboratory scale, it is thought that pilot and real-scale studies should be carried out to obtain more reliable data.

Chiral Inversion of 2-Arylpropionic Acid Enantiomers under Anaerobic Conditions

This work examined the chiral inversion of 2-arylpropionic acids (2-APAs) under anaerobic conditions and the associated microbial community. The anaerobic condition was simulated by two identical anaerobic digesters. Each digester was fed with the substrate containing 11 either pure (R)- or pure (S)-2-APA enantiomers. Chiral inversion was evidenced by the concentration increase of the other enantiomer in the digestate and the changes in the enantiomeric fraction between the two enantiomers. Both digesters showed similar and poor removal of 2-APAs (≤30%, except for naproxen) and diverse chiral inversion behaviors under anaerobic conditions. Four compounds exhibited (S → R) unidirectional inversion [flurbiprofen, ketoprofen, naproxen, and 2-(4-tert-butylphenyl)propionic acid], and the remaining seven compounds showed bidirectional inversion. Several aerobic and facultative anaerobic bacterial genera (Candidatus Microthrix, Rhodococcus, Mycobacterium, Gordonia, and Sphingobium) were identified in both digesters and predicted to harbor the 2-arylpropionyl-CoA epimerase (enzyme involved in chiral inversion) encoding gene. These genera presented at low abundances, <0.5% in the digester dosed with (R)-2-APAs and <0.2% in the digester dosed with (S)-2-APAs. The low abundances of these genera explain the limited extent of chiral inversion observed in this study.