Microalgae-bacteria-based systems are an emerging and promising approach for wastewater treatment plants (WWTP), having nutrient and antibiotic resistance removal comparable to conventional technologies. Still, antibiotic-resistance genes and bacteria (ARG and ARB) can proliferate in microalga-bacteria aggregates (MABA), a concern to control. Different temperature regimes of MABA continuous anaerobic digestion (AD), thermophilic (55 °C), and mesophilic (35 °C) were evaluated in this study as a strategy to eliminate ARB and ARGs. Plate counting techniques and metagenomic-based analysis revealed that thermophilic temperature had a better performance, achieving ARB log reductions of 1.1 to 1.7 for various antibiotics and significantly reduced ARG abundance up to 19.5 ± 0.8 ppm. The microbiome selection, the mobilome restriction, and directed functionality to thermal stress resistance were the main mechanisms responsible for resistome reduction at thermophilic conditions. Thermophilic AD effectively manages antibiotic resistance in microalgae-bacteria aggregates, which has important implications for wastewater treatment and reduces environmental risks.
2,5-Furandicarboxylic acid (FDCA) is a high-value chemical extensively used in the production of bio-based polymers, but bioconversion of furan derivatives like 5-hydroxymethylfurfural (HMF) into FDCA remains challenging owing to substrate cytotoxicity. Here, we engineered an Mn(II)-oxidizing Pseudomonas sp. MB04B for efficient FDCA biosynthesis from HMF. We deleted 4.6 % of the MB04B genome to generate the engineered MB04C-6 chassis, then introduced two exogenous gene cassettes, PMP00-hmfH and PJ23119-hmfH'. Using the resulting MB04C-6/pHMF as a whole-cell catalyst, optimizing the reaction system, and incorporating CaCO3 increased the FDCA yield by approximately 63.4-fold compared to MB04C-6. We also enhanced the CRISPR-associated transposases system for single-step chromosomal integration of exogenous genes. The optimal chassis strain MB04S-HMF8, rapidly produced 97 mmol/L FDCA from 100 mmol/L HMF in 12 h, with an FDCA production rate of 1.26 g L-1h-1, showcasing its potential as a robust, cost-effective, and environmentally sustainable whole-cell biocatalyst for industrial-scale FDCA production.
Continuous high-intensity light exposure can inhibit anaerobic ammonium oxidation (anammox) bacteria activity, though the specific impacts on anammox reactor performance remain unclear. This study investigates the effects of long-term light stress on anammox sludge reactors and explores the use of tea polyphenols as an engineering interventions to mitigate photo oxidation damage. The results showed that the nitrogen removal efficiency (NRE) of the reactor rapidly deteriorated to 41.4 % under 10,000 lx light conditions. However, reactors supplemented with 1 mg·L-1 and 5 mg·L-1 tea polyphenols sustained NREs of 75.2 % and 82.5 %, respectively. The addition of tea polyphenols alleviated oxidative stress by scavenging reactive oxygen species such as ·OH and H2O2, and by enhancing the activities of antioxidant enzymes including total superoxide dismutase and glutathione peroxidase. Candidatus Kuenenia was negatively impacted by light, while unclassified_f__Brocadiaceae thrived under light stress. These findings provide insights for the development of stable nitrogen removal systems under light exposure.
Butanol is a more desirable second-generation biomass energy source. Acetone-butanol-ethanol (ABE) fermentation using Clostridium spp. is a promising method for butanol production. However, the toxicity of butanol to the producing strains leading to its low yield and the high cost of feedstock are the main obstacles limiting the ABE fermentation industry. In this study, to enhance the butanol tolerance and production in Clostridium beijerinckii D9, the strategies of metabolic engineering and process regulation were employed. With this effort, a recombinant strain D9/pykA was successfully developed. Furthermore, the effect of exogenous fermentation waste streams and their two-stage addition strategy on ABE fermentation was also investigated. Under the optimal condition, the highest butanol and total solvent production of 11.20 ± 0.58 g/L and 13.65 ± 0.51 g/L was achieved in C. beijerinckii D9/pykA, representing increases of 40.70 % and 37.05 %, respectively, compared to the original strain D9. Additionally, the results of the physiological mechanism revealed that the two-stage fermentation waste stream addition improved NADH synthesis and upregulated key genes involved in butanol biosynthesis, and thus enhancing the production. These insights could provide a foundation for further optimization of ABE fermentation processes and offer promising avenues for improving other similar research.
Abundant biomass, including industrial waste streams and second-generation (2G) and third-generation (3G) feedstocks, offers significant potential for sustainable bioconversion, nevertheless challenges such as fermentation inhibitors, CO2 losses and substrate selectivity of traditional microbial hosts hinder process efficiency. In this study, we address these challenges by exploring acetogenic bacteria as alternative microbial hosts. Using a newly established high-throughput method, acetogens were evaluated for their capacity to hydrolyse and metabolize variety of substrates derived from 2G and 3G feedstocks and industrial waste streams. Our findings demonstrate metabolic versatility of acetogens in converting biomass-derived substrates into a wide array of products while also exhibiting resilience to common fermentation inhibitors. These unique capabilities position acetogens as promising alternatives that could potentially outperform conventional production hosts in achieving 100% biomass valorization while underscoring the need for further research into critical areas, such as the utilization of mixed substrates under industrially relevant conditions.
The state-of-the-art, simple and scalable methods for lignin micro-/nano-particles recovery from agricultural biomasses were evaluated in this review. Being non-wood biomasses, these materials can be easily fibrillated, supporting the usage of mild soda or organic solvent pretreatment. Different approaches in particle recovery were compared to conclude that the bottom-up approach facilitates smaller particles towards the nano-size range whereas mechanical treatment can act as a supporting method to increase uniformity and reduce particle sizes after bottom-up precipitation. By combining with the pretreatment steps, direct one-pot lignin micro-/nano-particle recovery can be achieved using the lignin-containing black liquor or organosolv liquor. These lignin micro-/nano-particles can then be applied as high-value functional products in cosmetics, pharmaceuticals, environmental remediation, and energy sectors. The systematic evaluation of lignin micro-/nano-particles recovery from agricultural biomasses in this review can support the full utilization of these natural resources to aim towards a circular agriculture.
This study explored a sustainable alternative to the Haber-Bosch process by enhancing the production of the nitrogen-rich polymer cyanophycin (CGP) in the diazotrophic cyanobacterium Nostoc sp. PCC 7120. Applying UV-mutagenesis followed by canavanine selection, we isolate an initial mutant with enhanced CGP accumulation. Subsequently, a secondary selection under phosphorus-limited conditions was employed to decrease cellular ploidy, yielding stable mutants. Among these, strain 44 exhibited an improved CGP accumulation, achieving up to 34 % of cellular dry weight in batch cultures. Under continuous phosphorus-limited cultivation, this mutant demonstrated a CGP productivity of 63 mg L-1 day-1, approximately a fourfold improvement over the wild type. Genomic analysis of the mutants revealed mutations unrelated to known CGP biosynthetic pathways, suggesting that the observed enhancement in CGP may arise from complex, synergistic effects of multiple genetic changes. This integrative approach-combining mutagenesis, screening, and cultivation techniques-successfully increased CGP accumulation from atmospheric nitrogen over threefold compared to the wild-type.