Conservation of acquired morphology and community structure in aged biofilms after facing environmental stress

Biofilms remember: Osmotic stress priming as a microbial management strategy for improving salinity acclimation in nitrifying biofilms

With increasing freshwater scarcity and greater use of seawater, fluctuating salinities are becoming common in water treatment systems. This can be challenging for salinity-sensitive processes like nitrification, especially in recirculating aquaculture systems (RAS), where maintaining nitrification efficiency is crucial for fish health. This study was undertaken to determine if prior exposure to seawater (priming) could improve nitrification in moving bed biofilm reactors (MBBR) under salinity increase from freshwater to seawater. The results showed that seawater-primed freshwater MBBRs had less than 10% reduction in nitrification activity and twice the ammonia oxidation capacity of the unprimed bioreactors after seawater transfer. The primed biofilms had different microbial community composition but the same nitrifying taxa, suggesting that priming promoted physiological adaptation of the nitrifiers. Priming may also have strengthened the extrapolymeric matrix protecting the nitrifiers. In MBBRs started up in brackish water (12‰ salinity), seawater priming had no significant impact on the nitrification activity and the microbial community composition. These bioreactors were inherently robust to salinity increase, likely because they were already primed to osmotic stress by virtue of their native salinity of 12‰. The results show that osmotic stress priming is an effective strategy for improving salinity acclimation in nitrifying biofilms and can be applied to water treatment systems where salinity variations are expected.

An innovative multistage anaerobic hythane reactor (MAHR): Metabolic flux, thermodynamics and microbial functions

Biohythane production from wastewater via anaerobic fermentation currently relies on two-stage physically separated biohydrogen and biomethane reactors, which requires closed monitoring, the implementation of a control system, and cost-intensive, complex operation. Herein, an innovative multistage anaerobic hythane reactor (MAHR) was reported via integrating two-stage fermentation into one reactor. MAHR was constructed using an internal down-flow packed bed reactor and an external up-flow sludge blanket to enhance microbial enrichment and thermodynamic feasibility of the associated bioreactions. The performance of MAHR was investigated for 160 d based on biogas production, metabolic flux and microbial structure in comparison to a typical anaerobic high-rate reactor (up-flow anaerobic sludge blanket (UASB)). A biohythane production with an optimized hydrogen volume ratio (10-20%) and a high methane content (75-80%) was achieved in the hythane zone (M_H) and methane zone (M_M) in MAHR, respectively. In addition, MAHR showed a stronger capability to accommodate a high organic loading rate (120 g COD/L/d), and it enhanced the conversion of organics leading to a methane production rate 66% higher than UASB. Thermodynamic analysis suggested that hydrogen extraction in M_H significantly decreased the hydrogen partial pressure (<0.1% vol) which favored acetogenesis in M_M. Metabolic flux and microbial function analysis further supported the superior performance of MAHR over UASB, which was primarily attributed to enhanced acetogenesis and acetoclastic methanogenesis.

Co-ensiling as a new technique for long-term storage of agro-industrial waste with low sugar content prior to anaerobic digestion

Biodegradable wastes produced seasonally need an upstream storage, because of the requirement for a constant feeding of anaerobic digesters. In the present article, the potential of co-ensiling biodegradable agro-industrial waste (sugar beet leaves) and lignocellulosic agricultural residue (wheat straw) to obtain a mixture with low soluble sugar content was evaluated for long-term storage prior to anaerobic digestion. The aim is to store agro-industrial waste while pretreating lignocellulosic biomass. The dynamics of co-ensiling was evaluated in vacuum-packed bags at lab-scale during 180 days. Characterization of the reaction by-products and microbial communities showed a succession of metabolic pathways. Even though the low initial sugars content was not sufficient to lower the pH under 4.5 and avoid undesirable fermentations, the methane potential was not substantially impacted all along the experiment. No lignocellulosic damages were observed during the silage process. Overall, it was shown that co-ensiling was effective to store highly fermentable fresh waste evenly with low sugar content and offers new promising possibilities for constant long-term supply of industrial anaerobic digesters.

Influence of Electric Fields on Biofouling of Carbonaceous Electrodes

Biofouling commonly occurs on carbonaceous capacitive deionization electrodes in the process of treating natural waters. Although previous work reported the effect of electric fields on bacterial mortality for a variety of medical and engineered applications, the effect of electrode surface properties and the magnitude and polarity of applied electric fields on biofilm development has not been comprehensively investigated. This paper studies the formation of a Pseudomonas aeruginosa biofilm on a Papyex graphite (PA) and a carbon aerogel (CA) in the presence and the absence of an electric field. The experiments were conducted using a two-electrode flow cell with a voltage window of ±0.9 V. The CA was less susceptible to biofilm formation compared to the PA due to its lower surface roughness, lower hydrophobicity, and significant antimicrobial properties. For both positive and negative applied potentials, we observed an inverse relationship between biofilm formation and the magnitude of the applied potential. The effect is particularly strong for the CA electrodes and may be a result of cumulative effects between material toxicity and the stress experienced by cells at high applied potentials. Under the applied potentials for both electrodes, high production of endogenous reactive oxygen species (ROS) was indicative of bacterial stress. For both electrodes, the elevated specific ROS activity was lowest for the open circuit potential condition, elevated when cathodically and anodically polarized, and highest for the ±0.9 V cases. These high applied potentials are believed to affect the redox potential across the cell membrane and disrupt redox homeostasis, thereby inhibiting bacterial growth.

The type of carbohydrates specifically selects microbial community structures and fermentation patterns

The impact on dark fermentation of seven carbohydrates as model substrates of lignocellulosic fractions (glucose, cellobiose, microcrystalline cellulose, arabinose, xylose, xylan and wheat straw) was investigated. Metabolic patterns and bacterial communities were characterized at the end of batch tests inoculated with manure digestate. It was found that hydrogen production was linked to the sugar type (pentose or hexose) and the degree of polymerisation. Hexoses produced less hydrogen, with a specific selection of lactate-producing bacterial community structures. Maximal hydrogen production was five times higher on pentose-based substrates, with specific bacterial community structures producing acetate and butyrate as main metabolites. Low hydrogen amounts accumulated from complex sugars (cellulose, xylan and wheat straw). A relatively high proportion of the reads was affiliated to Ruminococcaceae suggesting an efficient hydrolytic activity. Knowing that the bacterial community structure is very specific to a particular substrate offers new possibilities to design more efficient H₂-producing biological systems.