Effect of iron and aeration on superoxide dismutase and catalase activity of PHB-producing Azotobacter chroococcum

Nitrogen removal in improved subsurface wastewater infiltration system: Mechanism, microbial indicators and the limitation of phosphorus

To enhance the nitrogen removal capacity, scrap iron filings and Si-Al porous clay mineral material (PCMW) was used to improve a subsurface wastewater infiltration system (SWIS). The results showed TN and NH₄⁺-N removal efficiencies of improved SWIS were 20.72% and 5.49% higher than those of the control SWIS, respectively. Based on the response of the removal performance, microbial community and function analysis of 16s rRNA amplicon sequencing results, the amending soil matrix substantially enriched the nitrogen removal bacteria (Rhizobiales_Incertae_Sedis and Gemmatimonadaceae), and significantly improved the activities of key enzymes (Hao, NasAB, NarGHI, NirK, NorBC, NirA and NirBD), particularly at co-occurrence zone of nitrification and denitrification (70-130 cm depth). The amending soil matrix not only extended the growth space of microbes, but also provided additional electrons and carbon sources for denitrifying bacteria by regulating the structure and function of the microbial community. In addition, amending soil matrix could enhance phosphate metabolism genes and phosphate solubilizing microbes in the denitrification zone by increasing the phosphorus source, thus strengthening nitrogen metabolism. Nitrospiraceae, Rhizobiales_Incertae_Sedis and Gemmatimonadaceae related to nitrogen removal and Bacillaceae with phosphate-solubilizing ability could be used as microbial indicators of nitrogen removal in SWISs. The reciprocal action of environmental on microbial characteristics exhibited microbial functional were related to DO, Fe²⁺, TOC, TP, TN, NH₄⁺-N and NO₃^--N. Those could be used as physicochemical and biological indicators for application and monitoring of SWIS. In conclusion, this study provided a low-cost and efficient enhancement approach for the application of SWIS in decentralized domestic sewage treatment, and furnished theoretical support for subsequent applications.

Self-cloning significantly enhances the production of catalase in Bacillus subtilis WSHDZ-01

The katA gene that encodes catalase (CAT) in Bacillus subtilis WSHDZ-01 was overexpressed in B. subtilis WB600 and B. subtilis WSHDZ-01. The CAT yield in both transformed strains was significantly improved compared to that in the wild-type WSHDZ-01 in shake flask culture. When cultured in a 3-L stirred tank reactor (STR), the recombinant CAT activity in B. subtilis WSHDZ-01 could be improved by 419 %, reaching up to 39,117 U/mL and was 8,149.4 U/mg dry cell weight, which is the highest activity reported in Bacillus sp. However, the recombinant CAT in B. subtilis WB600 cultured in a 3-L STR was not significantly improved by any of the common means for process optimization, and the highest CAT activity was 3,673.5 U/mg dry cell weight. The results suggest that self-cloning of the complete expression cassette in the original strain is a reasonable strategy to improve the yield of wild-type enzymes.