Bioreactor Strategy Research Articles

Adaptive Laboratory Evolution and Carbon/Nitrogen Imbalance Promote High-Yield Ammonia Release in Saccharomyces cerevisiae

Ammonia, essential for fertilizers and energy storage, is mainly produced through the energy-demanding Haber–Bosch process. Microbial production offers a sustainable alternative, but natural yeast cells have not yet demonstrated success. This study aimed to enhance ammonia production in Saccharomyces cerevisiae by optimizing amino acid utilization through its deamination metabolism. Adaptive laboratory evolution is a method for rapidly generating desirable phenotypes through metabolic and transcriptional reorganization. We applied it to the efficiently fermenting S. cerevisiae strain CEN.PK113-7D using an unbalanced carbon/nitrogen medium to impose selective pressure. We selected several evolved strains with a 3–5-fold increase in amino acid utilization and ammonia secretion. The multi-step bioreactor strategy of the evolved strain AAV6, supplemented with concentrated nitrogen sources, resulted in the production of 1.36 g/L of ammonia, a value in line with levels produced by other microbial systems. This proof-of-concept study suggests that yeast-based processes can be adapted straightforwardly to ammonia production from high-protein waste derived from several sources.

A parallel bioreactor strategy to rapidly determine growth-coupling relationships for bioproduction: a mevalonate case study

BackgroundThe climate crisis and depleting fossil fuel reserves have led to a drive for ‘green’ alternatives to the way we manufacture chemicals, and the formation of a bioeconomy that reduces our reliance on petrochemical-based feedstocks. Advances in Synthetic biology have provided the opportunity to engineer micro-organisms to produce compounds from renewable feedstocks, which could play a role in replacing traditional, petrochemical based, manufacturing routes. However, there are few examples of bio-manufactured products achieving commercialisation. This may be partially due to a disparity between academic and industrial focus, and a greater emphasis needs to be placed on economic feasibility at an earlier stage. Terpenoids are a class of compounds with diverse use across fuel, materials and pharmaceutical industries and can be manufactured biologically from the key intermediate mevalonate.ResultsHere, we report on a method of utilising parallel bioreactors to rapidly map the growth-coupling relationship between the specific product formation rate, specific substrate utilisation rate and specific growth rate. Using mevalonate as an example product, a maximum product yield coefficient of 0.18 gp/gs was achieved at a growth rate (μ) of 0.34 h−1. However, this process also led to the formation of the toxic byproduct acetate, which can slow growth and cause problems during downstream processing. By using gene editing to knock out the ackA-pta operon and poxB from E. coli BW25113, we were able to achieve the same optimum production rate, without the formation of acetate.ConclusionsWe demonstrated the power of using parallel bioreactors to assess productivity and the growth-coupling relationship between growth rate and product yield coefficient of mevalonate production. Using genetic engineering, our resultant strain demonstrated rapid mevalonate formation without the unwanted byproduct acetate. Mevalonate production is quantified and reported in industrially relevant units, including key parameters like conversion efficiency that are often omitted in early-stage publications reporting only titre in g/L.

Semi-interpenetrating network hydrogels-based microcapsule for quorum quenching bacteria biocontainment to enhance biofouling control in membrane bioreactor

Microbial quorum quenching (QQ) has been proven to be a sustainable anti-biological fouling strategy for membrane bioreactors (MBR), but the long-term stability and practical application in MBR were uncertain. We reported a novel semi-interpenetrating network (SIPN) hydrogels-based design of QQ bacteria (Rhodococcus sp. BH4) encapsulation for both biofouling control and enhancement of organic pollutants removal in MBR. The microcapsule included the alginate core, chitosan thin intermediate compartment and SIPN (sodium alginate / polyacrylamide) shell, which exhibited near-perfect biocontainment, including preventing detectable QQ bacteria escape and improving mechanical strength. The QQ-microcapsules in the MBR demonstrated its significant anti-biofouling effect for treating synthetic wastewater (i.e., membrane fouling was delayed by 233%-280% compared to the control MBR membrane). Meanwhile, the efficiency of phosphorus removal was developed in QQ-microcapsule MBR because of the enhanced phosphorus removal triggered by the flocculation of polyacrylamide (PAM) fraction in SIPN. This promising QQ media brings the broad potential for biofouling control and long-term efficient operation in actual MBR wastewater treatment.

Growth kinetics of lead resistant Bacillus infantis isolated from battery industry waste

The current investigation presents an innovative approach to address the challenge of removing heavy metal lead from industrial waste through advanced biological remediation techniques. By amalgamating theoretical insights with empirically acquired data, this research endeavours to develop efficient bioreactor strategies suitable for large-scale applications. Initially, bacteria naturally endowed with lead resistance has been isolated from a native source. Extensive microbiological assessments, including a 16S rDNA study, verified the identity of the lead-resistant bacterial cells as Bacillus infantis 4352-1T. In order to evaluate the efficacy of Bacillus infantis 4352-1T for lead removal an attempt has been made to study the growth dynamics of Bacillus infantis 4352-1T cells in batch mode, using lead amended selective media. It has been observed that Monod's equation effectively defined the cell growth behaviour within the lead concentration range of 0.05–0.25 kg lead/m3. Notably, the experiment was also facilitated the derivation of essential intrinsic kinetic parameters, such as the maximum specific cell growth rate (0.0237 h−1) and substrate saturation constant (0.018 kg/m3). Beyond lead concentrations of 0.25 kg lead/m3, up to 0.43 kg lead/m3, it has also been observed the pronounced influence of substrate inhibition which is quantitatively elucidated by the Haldane equation.

Lactic Acid Fermentation of Carrageenan Hydrolysates from the Macroalga Kappaphycus alvarezii: Evaluating Different Bioreactor Operation Modes

Lactic acid is a molecule used abundantly in the food, cosmetic, and pharmaceutical industries. It is also the building block for polylactic acid, a biodegradable polymer which has gained interest over the last decade. Seaweeds are fast growing, environmentally friendly, and economically beneficial. The Rhodophyta, Kappaphycus alvarezii, is a carrageenan-rich alga, which can be successfully fermented into lactic acid using lactic acid bacteria. Lactobacillus pentosus is a versatile and robust bacterium and an efficient producer of lactic acid from many different raw materials. Bioreactor strategies for lactic acid fermentation of K. alvarezii hydrolysate were tested in 2-L stirred-tank bioreactor fermentations, operating at 37 °C, pH 6, and 150 rpm. Productivity and yields were 1.37 g/(L.h) and 1.17 g/g for the pulse fed-batch, and 1.10 g/(L.h) and 1.04 g/g for extended fed-batch systems. A 3.57 g/(L.h) production rate and a 1.37 g/g yield for batch fermentation operating with an inoculum size of 0.6 g/L was recorded. When applying fed-batch strategies, fermentation products reached 91 g/L with pulse feed and 133 g/L with constant continuous feed. For control and comparison, a simple batch of synthetic galactose-rich Man-Sharpe-Rugosa (MRS) media was fermented at the same conditions. A short study of charcoal regenerability is shown. A scheme for a third-generation lactic acid biorefinery is proposed, envisioning a future sustainable large-scale production of this important organic acid.

Bioreactor strategies for tissue-engineered osteochondral constructs: Advantages, present situations and future trends

The aim of osteochondral tissue engineering is to achieve the complex, functional and three-dimensional tissue regeneration under well defined, controlled and reproducible conditions in vitro. To achieve tissue-engineered products in vitro that incorporate rapidly in vivo with healthy tissue, it is essential to develop high-performance cell/scaffold culture systems that mimic the dynamics of the in vivo environment. Bioreactors could provide specific physicochemical culture environment, suitable mechanical stimulation and controlled condition for the development of osteochondral constructs in vitro. This review highlighted the multifunction of bioreactor in tissue engineering, and presented microenvironment and biomechanics of native osteochondral tissue, to illustrate the necessity of establishing osteochondral constructs by bioreactor. Then, we especially emphasized the advantages and limitations of various bioreactors. Furthermore, we systematically summarized and discussed the development of bioreactor-based production systems for bone, cartilage and osteochondral tissue engineering in recent years. Finally, we made a simple conclusion and offered perspectives of bioreactor‐based osteochondral tissue engineering. This review aims to serve as a reference for incorporating bioreactor strategies which could provide mechanical stimulation and physicochemical culture environment into the osteochondral construct culture regimens.

Enhancing quorum quenching media with 3D robust electrospinning coating: A novel biofouling control strategy for membrane bioreactors

Bacterial quorum quenching (QQ) is an effective strategy for controlling biofouling in membrane bioreactor (MBR) by interfering the releasing and degradation of signal molecules during quorum sensing (QS) process. However, due to the framework feature of QQ media, the maintenance of QQ activity and the restriction of mass transfer threshold, it has been difficult to design a more stable and better performing structure in a long period of time. In this research, electrospun fiber coated hydrogel QQ beads (QQ-ECHB) were fabricated by using electrospun nanofiber coated hydrogel to strengthen layers of QQ carriers for the first time. The robust porous PVDF 3D nanofiber membrane was coated on the surface of millimeter-scale QQ hydrogel beads. Biocompatible hydrogel entrapping quorum quenching bacteria (sp.BH4) was employed as the core of the QQ-ECHB. In MBR with the addition of QQ-ECHB, the time to reach transmembrane pressure (TMP) of 40 kPa was 4 times longer than conventional MBR. The robust coating and porous microstructure of QQ-ECHB contributed to keeping a lasting QQ activity and stable physical washing effect at a very low dosage (10g beads/5L MBR). Physical stability and environmental-tolerance tests also verified that the carrier can maintain the structural strength and keep the core bacteria stable when suffering long-term cyclic compression and great fluctuations in sewage quality.

Application of Encapsulated Quorum Quenching Strain Acinetobacter pittii HITSZ001 to a Membrane Bioreactor for Biofouling Control

Quorum quenching (QQ) is a novel anti-biofouling strategy for membrane bioreactors (MBRs) used in wastewater treatment. However, actual operation of QQ-MBR systems for wastewater treatment needs to be systematically studied to evaluate the comprehensive effects of QQ on wastewater treatment engineering applications. In this study, a novel QQ strain, Acinetobacter pittii HITSZ001, was encapsulated and applied to a MBR system to evaluate the effects of this organism on real wastewater treatment. To verify the effectiveness of immobilized QQ beads in the MBR system, we examined the MBR effluent quality and sludge characteristics. We also measured the extracellular polymeric substances (EPS) and soluble microbial products (SMP) in the system to determine the effects of the organism on membrane biofouling inhibition. Additionally, changes in microbial communities in the system were analyzed by high-throughput sequencing. The results indicated that Acinetobacter pittii HITSZ001 is a promising strain for biofouling reduction in MBRs treating real wastewater, and that immobilization does not affect the biofouling control potential of QQ bacteria.

Advances in In Vitro and In Vivo Bioreactor-Based Bone Generation for Craniofacial Tissue Engineering.

Craniofacial reconstruction requires robust bone of specified geometry for the repair to be both functional and aesthetic. While native bone from elsewhere in the body can be harvested, shaped, and implanted within a defect, using either an in vitro or in vivo bioreactors eliminates donor site morbidity while increasing the customizability of the generated tissue. In vitro bioreactors utilize cells harvested from the patient, a scaffold, and a device to increase mass transfer of nutrients, oxygen, and waste, allowing for generation of larger viable tissues. In vivo bioreactors utilize the patient's own body as a source of cells and of nutrient transfer and involve the implantation of a scaffold with or without growth factors adjacent to vasculature, followed by the eventual transfer of vascularized, mineralized tissue to the defect site. Several different models of in vitro bioreactors exist, and several different implantation sites have been successfully utilized for in vivo tissue generation and defect repair in humans. In this review, we discuss the specifics of each bioreactor strategy, as well as the advantages and disadvantages of each and the future directions for the engineering of bony tissues for craniofacial defect repair.

Engineering Burkholderia sacchari to enhance poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] production from xylose and hexanoate

Burkholderia sacchari LFM101 LMG19450T is a Brazilian bacterium isolated from sugarcane crops soil and a promising biotechnological platform for bioprocesses. It is an efficient producer of poly(3-hydroxybutyrate) from carbohydrates including xylose. In the present work, the expression of B. sacchari xylose consumption genes (xylA, xylB and tktA) was combined with the expression of Aeromonas sp. phaC (PHA synthase), aiming to increase both the growth rates in xylose and the 3-hydroxyhexanoate (3HHx) molar fractions in the produced PHA. Genes were cloned into pBBR1MCS-2 vectors and then expressed in the B. sacchari PHA- mutant LFM344. Maximum specific growth rates on xylose and PHA accumulation capacity of all recombinants were evaluated. In bioreactor experiments, up to 55.5 % CDW was accumulated as copolymer, hexanoate conversion to 3HHx raised from 2 % to 54 % of the maximum theoretical value, compared to wild type. 3HHx mol% ranged from 8 to 35, and molecular weights were between 111 and 220 kg/mol. Thermal analysis measurement showed a decrease in Tg and Tm values with higher 3HHx fraction, indicating improved thermomechanical characteristics. Recombinants construction and bioreactor strategies allowed the production of P(3HB-co-3HHx) with controlled monomeric composition from xylose and hexanoate, allowing its application in diverse fields, including the medical area.

Recirculating Anaerobic Dynamic Membrane Bioreactor Treatment of Municipal Wastewater

A recirculating anaerobic dynamic membrane bioreactor system was evaluated at the lab scale for the treatment of simulated and real municipal wastewater (MWW). The bioreactor contained a filtration structure with meshes to support the development of a biofilm or dynamic membrane through which bulk liquid was continuously recirculated. This approach aimed to overcome high fouling and dissolved methane oversaturation, challenges typical of mainstream anaerobic membrane bioreactor technologies. At hydraulic retention times ranging from 4 to10 h, the system achieved average effluent suspended solids levels of 20 mg/L (simulated MWW) and 22 mg/L (real MWW), while also achieving average chemical oxygen demand (COD) concentrations of 71 mg/L (simulated MWW) and 84 mg/L (real MWW). The system demonstrated minimal dissolved methane oversaturation, and the average total methane yield was 0.29 L CH4/g COD removed for simulated MWW and 0.18 L CH4/g COD removed for real MWW. The observed filtration resistance rate (approximately 1 × 108 m–1 h–1) was one to two orders of magnitude lower than those reported for MWW treatment by anaerobic membrane bioreactor approaches. Operation at low transmembrane pressure and high flux was possible without intervention to control fouling for over 450 days. If the lab-scale results reported here can be achieved at the full-scale level, the recirculating anaerobic dynamic membrane bioreactor will allow for net positive energy generation over a range of MWW characteristics (0.180 to 0.658 kWh/m3). Therefore, we conclude that the recirculating anaerobic dynamic membrane bioreactor strategy deserves further study as an emerging option for low-footprint, energy-positive treatment of dilute wastewaters like MWW.

Modeling mass transfer in stirred microbioreactors

A mechanistic in-silico approach for predicting mixing and mass transfer in a two-phase stirred tank bioreactor is presented. This fully transient approach, which is tailored to run on GPUs, makes a direct appeal to first principles turbulence theory. We investigate various approaches for predicting the convective mass transfer coefficient around bubbles. We then validate the free surface and bubble mass transfer coefficients against measured data over a range of microbioreactor operating conditions and then link these variations to the underlying fluid mechanics. The approach is designed to be general and requires no re-tuning between operating conditions. Additionally, the presented approach can be utilized as a digital scaleup and tech-transfer strategy for bioreactors used in the biopharmaceutical industry.

Optimizing a Fed-Batch High-Density Fermentation Process for Medium Chain-Length Poly(3-Hydroxyalkanoates) in Escherichia coli.

Production of medium chain-length poly(3-hydroxyalkanoates) [PHA] polymers with tightly defined compositions is an important area of research to expand the application and improve the properties of these promising biobased and biodegradable materials. PHA polymers with homopolymeric or defined compositions exhibit attractive material properties such as increased flexibility and elasticity relative to poly(3-hydroxybutyrate) [PHB]; however, these polymers are difficult to biosynthesize in native PHA-producing organisms, and there is a paucity of research toward developing high-density cultivation methods while retaining compositional control. In this study, we developed and optimized a fed-batch fermentation process in a stirred tank reactor, beginning with the biosynthesis of poly(3-hydroxydecanoate) [PHD] from decanoic acid by β-oxidation deficient recombinant Escherichia coli LSBJ using glucose as a co-substrate solely for growth. Bacteria were cultured in two stages, a biomass accumulation stage (37°C, pH 7.0) with glucose as the primary carbon source and a PHA biosynthesis stage (30°C, pH 8.0) with co-feeding of glucose and a fatty acid. Through iterative optimizations of semi-defined media composition and glucose feed rate, 6.0 g of decanoic acid was converted to PHD with an 87.5% molar yield (4.54 g L–1). Stepwise increases in the amount of decanoic acid fed during the fermentation correlated with an increase in PHD, resulting in a final decanoic acid feed of 25 g converted to PHD at a yield of 89.4% (20.1 g L–1, 0.42 g L–1 h–1), at which point foaming became uncontrollable. Hexanoic acid, octanoic acid, 10-undecenoic acid, and 10-bromodecanoic acid were all individually supplemented at 20 g each and successfully polymerized with yields ranging from 66.8 to 99.0% (9.24 to 18.2 g L–1). Using this bioreactor strategy, co-fatty acid feeds of octanoic acid/decanoic acid and octanoic acid/10-azidodecanoic acid (8:2 mol ratio each) resulted in the production of their respective copolymers at nearly the same ratio and at high yield, demonstrating that these methods can be used to control PHA copolymer composition.

Optimal fed-batch bioreactor operating strategies for the microbial production of lignocellulosic bioethanol and exploration of their economic implications: A step forward towards sustainability and commercialization

The enduring adoption of greener technologies from the biofuel manufacturing industries requires the balanced integration of multiple inter-disciplinary concerns (i.e., engineering, business, sustainability, societal) to make production processes more attractive to the industrial sector. From an engineering perspective, the commercial establishment of lignocellulosic bioethanol plants is still hindered by increased production cost. High product concentrations with improved yield and productivity at the fermentation stage seem to be inviolable condition to straightly compete with fossil-based and first-generation bioethanol facilities. This study proposes a model-based multi-objective dynamic optimization approach to systematically derive optimal operating policies for the fermentation bioreactor as a step forward towards enhancing the economic performance of lignocellulosic bioethanol plants. The economic benefit of the derived optimal bioreactor strategies is evaluated via a scalable economic index, linking for the first time the performance of the fermentation bioreactor to the economics of the entire production process. It is demonstrated that high values in productivity and substantial compromises in yield and final bioethanol concentration are conditions which favor economic feasibility with the achieved fermentation performance (3.32 g L−1 h−1, 0.399 g g−1, 106.0 g L−1) being comparable to first-generation bioethanol production. Finally, a global system analysis framework is employed to investigate the robustness of the optimal value of the economic index to the variability of key model parameters, illustrating the impact of model uncertainty on the process economic performance.

Time-lapsed imaging of nanocomposite scaffolds reveals increased bone formation in dynamic compression bioreactors

Progress in bone scaffold development relies on cost-intensive and hardly scalable animal studies. In contrast to in vivo, in vitro studies are often conducted in the absence of dynamic compression. Here, we present an in vitro dynamic compression bioreactor approach to monitor bone formation in scaffolds under cyclic loading. A biopolymer was processed into mechanically competent bone scaffolds that incorporate a high-volume content of ultrasonically treated hydroxyapatite or a mixture with barium titanate nanoparticles. After seeding with human bone marrow stromal cells, time-lapsed imaging of scaffolds in bioreactors revealed increased bone formation in hydroxyapatite scaffolds under cyclic loading. This stimulatory effect was even more pronounced in scaffolds containing a mixture of barium titanate and hydroxyapatite and corroborated by immunohistological staining. Therefore, by combining mechanical loading and time-lapsed imaging, this in vitro bioreactor strategy may potentially accelerate development of engineered bone scaffolds and reduce the use of animals for experimentation.

Fouling behavior and mechanism of hydrophilic modified membrane in anammox membrane bioreactor: Role of gel layer

Membrane hydrophilic modification has been applied as an effective antifouling strategy for aerobic and anaerobic heterotrophic membrane bioreactors (MBRs), while its antifouling performance remains unclear for anaerobic ammonium oxidation (anammox) MBR. Herein, hydrophilic membranes (Mh) modified from pristine nylon fabric meshes (Mp, pore size of 20 μm), were applied in long-term operation of an anammox MBR. Although the average flux of Mh was 90.7% higher than that of Mp (p < 0.05) filtered with model foulant (bovine serum albumin) in a dead-end filtration test, the average filtration cycle of Mh in the anammox MBR was 37.9% shorter than that of Mp filtered with synthesized wastewater, in spite of the comparable total nitrogen removal efficiency (over 80%) achieved. A thin and compact gel layer was formed on Mh by adsorption of hydrophilic polysaccharide and further gelation of protein and colloidal biomass. The bound water wrapped in the gel layer on Mh brought about 32.8% higher filtration resistance, and caused 81.3% higher contribution rate of the flux decline caused by concentration polarization, compared with Mp. Moreover, more microbial metabolites, especially protein (23.9% vs. 17.7%), was rejected by Mh than Mp, providing organic matters for the proliferation of heterotrophic bacteria, and leading to the decreased relative abundance of anammox bacteria (from 63.2% to 35.2%). We proposed the formation process of the gel layer and revealed the membrane fouling mechanism on Mh in the anammox MBR, providing significant theoretical foundation for the membrane fouling control of anammox MBR systems.

Stem Cells and Their Cardiac Derivatives for Cardiac Tissue Engineering and Regenerative Medicine.

Significance: Heart failure is among the leading causes of morbidity worldwide with a 5-year mortality rate of ∼50%. Therefore, major efforts are invested to reduce heart damage upon injury or maintain and at best restore heart function. Recent Advances: In clinical trials, acellular constructs succeeded in improving cardiac function by stabilizing the infarcted heart. In addition, strategies utilizing stem-cell-derived cardiomyocytes have been developed to improve heart function postmyocardial infarction in small and large animal models. These strategies range from injection of cell-laden hydrogels to unstructured hydrogel-based and complex biofabricated cardiac patches. Importantly, novel methods have been developed to promote differentiation of stem-cell-derived cardiomyocytes to prevascularized cardiac patches. Critical Issues: Despite substantial progress in vascularization strategies for heart-on-the-chip technologies, little advance has been made in generating vascularized cardiac patches with clinically relevant dimensions. In addition, proper electrical coupling between engineered and host tissue to prevent and/or eliminate arrhythmia remains an unresolved issue. Finally, despite advanced approaches to include hierarchical structures in cardiac tissues, engineered tissues do not generate forces in the range of native adult cardiac tissue. Future Directions: It involves utilizing novel materials and advancing biofabrication strategies to generate prevascularized three-dimensional multicellular constructs of clinical relevant size; inclusion of hierarchical structures, electroconductive materials, and biologically active factors to enhance cardiomyocyte differentiation for optimized force generation and vascularization; optimization of bioreactor strategies for tissue maturation. Antioxid. Redox Signal. 35, 143-162.

Porous shell quorum quenching balls for enhanced anti-biofouling efficacy and media durability in membrane bioreactors

Microbial quorum quenching (QQ) has been recognized as an effective anti-biofouling strategy for membrane bioreactors (MBRs), but long-term hydrogel QQ media durability is uncertain. In this study, we propose a new media design to enhance anti-biofouling efficacy and mechanical media stability. Mobile porous hard-shell balls to hold QQ sheets (named QQ balls) were found to be superior in QQ stability to both fixed and freely moving QQ sheets. Fouling mitigation by QQ balls was significant even at the lowest aeration intensity tested (51 s−1), in contrast to other QQ media. QQ balls saved substantive energy (~50%) at similar or lower fouling rates (2.8–3.2 kPa/d) compared to the others tested at the higher aeration intensity (72 s−1). QQ balls maintained their initial high level of QQ activity (~3.0 h−1) during long-term use (greater than160 d), whereas other types of QQ media did not (<1.3 h−1). The mechanical strength of free QQ media significantly deteriorated over time (~87–100% losses after 160-d use), but QQ balls prevented the active media from such damage. QQ media had no impacts on treatment efficiencies. A QQ media structure comprising a hard porous shell and inner active media encapsulating QQ bacteria is a promising QQ media architecture for sustainable MBR applications.

A salty start: Brackish water start-up as a microbial management strategy for nitrifying bioreactors with variable salinity

Nitrifying biofilms developed in brackish water are reported to be more robust to salinity changes than freshwater biofilms. This makes them a promising strategy for water treatment systems with variable salinity, such as recirculating aquaculture systems for Atlantic salmon. However, little is known about the time required for nitrification start-up in brackish water or the microbial community dynamics. To investigate the development of nitrifying biofilms at intermediate salinity, we compared the startup of moving bed biofilm reactors with virgin carriers in brackish- (12‰ salinity) and freshwater. After 60 days, the brackish water biofilm had half the nitrification capacity of the freshwater biofilm, with a less diverse microbial community, lower proportion of nitrifiers, and a significantly different nitrifying community composition. Nitrosomonas and Nitrosospira-like bacteria were the main ammonia oxidizers in the brackish water biofilms, whereas Nitrosomonas was dominant in freshwater biofilms. Nitrotoga was the dominant nitrite oxidizer in both treatments. Despite the lower nitrification capacity in the brackish water treatment, the low ammonia and nitrite concentration with rapidly increasing nitrate concentration indicated that complete nitrification was established in both reactors within 60 days. The results suggest that biofilms develop nitrification in brackish water in comparable time as in freshwater, and brackish start-up can be a strategy for bioreactors with varying salinity.

Isolation and characterization of novel indigenous facultative quorum quenching bacterial strains for ambidextrous biofouling control

Quorum quenching (QQ), the disruption of microbial communication, has proven to be effective as an innovative anti-biofouling strategy for membrane bioreactors (MBRs). However, QQ bacteria for anaerobic environments have not been extensively analyzed in previous research. This study thus investigated facultative QQ bacterial strains that exhibit potential for use in aerobic and anaerobic MBRs. Two novel QQ strains from the genus Pseudomonas (KS2 and KS10) were isolated from anaerobic digester sludge using signal molecules as the sole carbon source. The two QQ strains exhibited significant signal molecule degradation depending on the oxygen levels and demonstrated endogenous QQ activity, with KS2 producing lactonase and KS10 producing acylase. The QQ strains significantly reduced the formation of the biofilm generated by both Pseudomonas aeruginosa (PAO1) and real sludge. Facultative QQ strains have the potential to offer a more flexible option for effective biofouling control in both aerobic and anaerobic MBRs.