Hemoglobin peroxidase reaction of hemoglobin efficiently catalyzes oxidation of benzo[a]pyrene

Efficient synthesis of high-active multi-subunit hemoglobins through balanced expression of globins and robust heme-supply in Saccharomyces cerevisiae

The biosynthesis of multi-subunit hemoglobins that can be used in artificial oxygen carriers, artificial foods and medical diagnostics has become a hot research issue. However, the imbalanced expression of different subunits and insufficient heme-supply limit the efficient production of multi-subunit hemoglobins. After the equalized synthesis of different globins through the regulation at transcriptional and translational levels, the improvement of heme-supply by relieving the feedback inhibition of heme on Hem1p and the enhancement of key rate-limiting enzymes in yeast, a robust platform for the expression of high-active hemoglobins was constructed. The synthesis of hemoglobins with high-activity were achieved, including human hemoglobin (174.2 mg/L, 61.7 % mol heme/mol Hb), porcine hemoglobin (203.9 mg/L, 72.1 % mol heme/mol Hb) and bovine hemoglobin (258.2 mg/L, 64.9 % mol heme/mol Hb). Therefore, the applied strategies can be broadly used in the production of other heteromultimeric and heme-binding proteins.

Synergism of endophytic microbiota and plants promotes the removal of polycyclic aromatic hydrocarbons from the Alfalfa rhizosphere

Endophytic bacteria can promote plant growth and accelerate pollutant degradation. However, it is unclear whether endophytic consortia (Consortium_E) can stabilize colonisation and degradation. We inoculated Consortium_E into the rhizosphere to enhance endophytic bacteria survival and promote pollutant degradation. Rhizosphere-inoculated Consortium_E enhanced polycyclic aromatic hydrocarbon (PAH) degradation rates by 11.5-13.1 % compared with sole bioaugmentation and plant treatments. Stable-isotope-probing (SIP) showed that the rhizosphere-inoculated Consortium_E had the largest number of degraders (8 amplicon sequence variants). Furthermore, only microbes from Consortium_E were identified among the degraders in bioaugmentation treatments, indicating that directly participated in phenanthrene metabolism. Interestingly, Consortium_E reshaped the community structure of degraders without significantly altering the rhizosphere community structure, and strengthened the core position of degraders in the network, facilitating close interactions between degraders and non-degraders in the rhizosphere, which were crucial for ensuring stable functionality. The synergistic effect between plants and Consortium_E significantly enhanced the upregulation of aromatic hydrocarbon degradation and auxiliary degradation pathways in the rhizosphere. These pathways showed a non-significant increasing trend in the uninoculated rhizosphere compared with the control, indicating that Consortium_E primarily promotes rhizosphere effects. Our results explore the Consortium_E bioaugmentation mechanism, providing a theoretical basis for the ecological restoration of contaminated soils.

Benzo[a]pyrene stress impacts adaptive strategies and ecological functions of earthworm intestinal viromes

The earthworm gut virome influences the structure and function of the gut microbiome, which in turn influences worm health and ecological functions. However, despite its ecological and soil quality implications, it remains elusive how earthworm intestinal phages respond to different environmental stress, such as soil pollution. Here we used metagenomics and metatranscriptomics to investigate interactions between the worm intestinal phages and their bacteria under different benzo[a]pyrene (BaP) concentrations. Low-level BaP (0.1 mg kg^-1) stress stimulated microbial metabolism (1.74-fold to control), and enhanced the antiphage defense system (n = 75) against infection (8 phage-host pairs). Low-level BaP exposure resulted in the highest proportion of lysogenic phages (88%), and prophages expressed auxiliary metabolic genes (AMGs) associated with nutrient transformation (e.g., amino acid metabolism). In contrast, high-level BaP exposure (200 mg kg^-1) disrupted microbial metabolism and suppressed the antiphage systems (n = 29), leading to the increase in phage-bacterium association (37 phage-host pairs) and conversion of lysogenic to lytic phages (lysogenic ratio declined to 43%). Despite fluctuating phage-bacterium interactions, phage-encoded AMGs related to microbial antioxidant and pollutant degradation were enriched, apparently to alleviate pollution stress. Overall, these findings expand our knowledge of complex phage-bacterium interactions in pollution-stressed worm guts, and deepen our understanding of the ecological and evolutionary roles of phages.

Experimentally and spectroscopically evidenced mechanistic study of butyl peroxyacid oxidative degradation of benzo[a]pyrene in soil

Benzo[a]pyrene (BaP) is a major indicator of soil contamination and categorized as a highly persistent, carcinogenic, and mutagenic polycyclic aromatic hydrocarbon. An advanced peroxyacid oxidation process was developed to reduce soil pollution caused by BaP originating from creosote spills from railroad sleepers. The pH, organic matter, particle size distribution of soil, and concentrations of BaP and heavy metals (Cd, Cu, Zn, Pb, and As) in the BaP-contaminated soils were estimated. A batch experiment was conducted to determine the effects of organic acid type, soil particle size, stirring speed, and reaction time on the peroxyacid oxidation of BaP in the soil samples. Additionally, the effect of the organic acid concentration on the peroxyacid degradation of BaP was investigated using an oxidizing agent in spiked soil with and without hydrogen peroxide. The results of the oxidation process indicated that BaP and heavy metal residuals were below acceptable Korean standards. A significant difference in the oxidative degradation of BaP was observed between the spiked and natural soil samples. The formation of a peroxyacid intermediate was primarily responsible for the enhanced BaP oxidation. Further, butyric acid could be reused thrice without losing the efficacy (<90%). The systematic peroxyacid oxidative degradation mechanism of BaP was also discussed. A qualitative analysis of the by-products of the BaP reaction was conducted, and their corresponding toxicities were determined for possible field applications. The findings conclude that the developed peroxyacid oxidation method has potential applications in the treatment of BaP-contaminated soils.