On-line adaptive metabolic flux analysis: Application to PHB production by mixed microbial cultures

Efficient remediation of Mn2+ and NH4+-N in co-contaminated water and soil by Acinetobacter sp. AL-6 synergized with grapefruit peel biochar: Performance and mechanism

Electrolysis manganese slag produced in industrial manganese production causes massive leachate containing heavy metal Mn²⁺ and inorganic NH₄⁺-N, which causes serious hazard to the water body and soil. A cost-effective alternative to address the multiple pollution is urgently needed. This study investigated the synergy of grapefruit peel biochar (BC) and strain AL-6 to remediate Mn²⁺ and NH₄⁺-N in sequencing batch bioreactor (SBR) and soil column. The results showed that, in SBR, under the condition of C/N 5, temperature 30°C, BC and strain AL-6 showed fabulous performance to remove Mn²⁺ (99.3%) and NH₄⁺-N (97.7%). The coexisting ions Mg²⁺ and Ca²⁺ had no effects on the removal of Mn²⁺ and COD, however, 23.3% removal efficiency of NH₄⁺-N was curtailed. Characterization found that the presence of MnCO₃ confirmed the adsorption of Mn²⁺ by functional groups action, and gas chromatography indicated that BC and strain AL-6 promoted the reduction of N₂O and organic carbon. In addition, BC and strain AL-6 helped to immobilize 799.41 mg L^-1 of Mn²⁺ and 320 mg L^-1 of NH₄⁺-N after 45 d in the soil column. And the determination of TOC, CEC, pH, Eh, soil enzymatic activity (catalase and urease), and microbial diversity and abundance confirmed that BC and strain AL-6 increased the soil fertility and bioavailability of pollutants. Totally, BC and strain AL-6 possess great potential to remediate Mn²⁺ and NH₄⁺-N pollution in water and soil.

Biochar Mitigates N2O Emission of Microbial Denitrification through Modulating Carbon Metabolism and Allocation of Reducing Power

To elucidate the direct effects of biochar on denitrification metabolism at the cellular level, the global response of model denitrifying soil bacterium (Paracoccus denitrificans) to biochar addition was investigated by physiological, proteomic, and metabolomics analyses. The enhancement effect on denitrification was positively correlated with its pyrolysis temperatures (300-500 °C) and dosages (0.1-1%), regardless of precursors [corn straw (CS) or wheat straw). Moreover, the stimulating effect of CS biochar made at 500 °C (CS-500) was mainly attributed to the bulk particles rather than the released soluble compounds. Without direct contact with cells, bulk CS-500 particles might directly modulate the carbon metabolism by the adsorption of extracellular metabolites. Since carbon flux to storage was shifted to oxidative catabolism and growth assimilation, more share of the produced reducing power was used for nitrogen reduction. Meanwhile, except for nitrate reductase, both protein expressions and enzyme activities of nitrite reductase, nitric oxide reductase, and nitrous oxide reductase were up-regulated. Accordingly, the accumulation of N₂O was reduced by 98% due to the optimized electron distribution among denitrifying enzymes. Eventually, the growth rate of Pc. denitrificans enhanced because of the improved energy utilization efficiency. These results updated the regulation mechanism of biochar on denitrification metabolism and N₂O mitigation.