Study on the properties of denitrifying carbon sources from cellulose plants and their nitrogen removal mechanisms

Carbon sources of cellulose plants are the promising materials that enhancing the activities of denitrifying bacteria in the groundwater system. To further verify the denitrification performance of cellulose plants and the main factors of affecting the denitrifying system, six cellulose plants from agricultural wastes (wood chip, corn cob, rice husk, corn straw, wheat straw, and sugar cane) were selected for bioavailable organic matter leaching experiments, carbon denitrification experiments, functional bacteria identification, and analysis experiments. The results show that the extracts of cellulose plants contain a mixed carbon sources system including small molecular organic acids, sugars, nitrogen-containing organic components, and esters. The qPCR results showed that the denitrifying bacteria had obvious advantages compare to anaerobic ammonia-oxidizing bacteria during the stable period; the denitrification experiment showed that each of six cellulose plants removed more than 80% of nitrogen, and the denitrification rates reached 1.00–2.00 mg N cm−3·d−1. The supplement of cellulose plants promotes the metabolism rate of denitrifying bacteria, and the additional denitrifying bacteria have little effect on nitrate removal. In summary, the expected denitrification reaction occurred in the cellulose plant system, which is suitable as a carbon source material for water body nitrogen pollution remediation.

Investigation of Lipolytic-Secreting Bacteria from an Artificially Polluted Soil Using a Modified Culture Method and Optimization of Their Lipase Production

Compared to lipases from plants or animals, microbial lipases play a vital role in different industrial applications and biotechnological perspectives due to their high stability and cost-effectiveness. Therefore, numerous lipase producers have been investigated in a variety of environments in the presence of lipidic carbon and organic nitrogen sources. As a step in the development of cultivating the unculturable functional bacteria in this study, the forest soil collected from the surrounding plant roots was used to create an artificially contaminated environment for lipase-producing bacterial isolation. The ten strongest active bacterial strains were tested in an enzyme assay supplemented with metal ions such as Ca2+, Zn2+, Cu2+, Fe2+, Mg2+, K+, Co2+, Mn2+, and Sn2+ to determine bacterial tolerance and the effect of these metal ions on enzyme activity. Lipolytic bacteria in this study tended to grow and achieved a high lipase activity at temperatures of 35–40 °C and at pH 6–7, reaching a peak of 480 U/mL and 420 U/mL produced by Lysinibacillus PL33 and Lysinibacillus PL35, respectively. These potential lipase-producing bacteria are excellent candidates for large-scale applications in the future.

Insight Into Impacts of Sewage Discharge and River Self-Purification on Microbial Dynamics and Pathogenicity in River Ecosystem

Sewage directly discharge causes serious environmental problems. Here, the effects of treated and untreated sewage on the river ecosystem were investigated. The variations of microbial community structure, including infectious pathogenic bacteria and functional bacteria related to nitrogen, phosphorus, and COD metabolism were studied in detail. Bacterial diversity and richness were significantly decreased, while, Proteobacteria containing various infectious pathogens, such as Vibrio and Helicobacter, significantly increased after the discharge of raw sewage. Although the microbial structure was slightly restored and the abundance of most pathogenic bacteria was also slightly reduced through river self-purification, direct discharge of raw sewage caused severe and short-term irreversible damage to the river environment. Direct discharge also introduced various pollutants such as nitrogen, phosphorus, and COD, increasing the corresponding functional bacteria and their related genes. Furthermore, the high abundance of pathogenic bacteria of the drain outlet was mainly from raw sewage rather than bacteria reproduction caused by water deterioration according to the RDA analysis. With these results, direct discharge disturbed the ecological balance of the river. Therefore, more attention is needed to provide a hygienic situation for people and all sewage should be treated properly. In conclusion, all sewage should be treated properly before discharge into ecosystems to mitigate its negative impacts on receiving water bodies.

Role of Organic/Sulfide Ratios On DNRA Cultivation And The Microbial Community Structure of A Co-Driven Sequencing Biofilm Batch Reactor

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA), are two competing pathways in nitrate reducing process. In this study, a series of C/S ratios from 8:1 to 2:4 was investigated in a sequencing biofilm batch reactor (SBBR) to determine the role of reducers (sulfide and acetate) on their competition. The results showed the proportion of DNRA increased in high electron system, either in organic rich or in sulfide rich system. The highest DNRA ratio increased to 16.7% at the C/S ratio of 2:3. Excess electron donors, particularly sulfide, were favorable for DNRA in a limited nitrate environment. Moreover, a higher reductive environment (ORP <-400 mV) can be used as an indicator for the occurrence of DNRA. 16s RNA analysis demonstrated that Grobacter was the main functional bacteria of DNRA in the organic rich system, while Alphaproteobacteria and Desulfomicrobium were dominant DNRA bacteria in the sulfide rich system. DNRA cultivation could enrich nitrogen conversion pathways in conventional denitrification systems. This provides the great insight into nitrogen removal in high nitrogen containing sewage with low C/N.

A Novel Regulator Participating in Nitrogen Removal Process of Bacillus subtilis JD-014

Aerobic denitrification is considered as a promising biological method to eliminate the nitrate contaminants in waterbodies. However, the molecular mechanism of this process varies in different functional bacteria. In this study, the nitrogen removal characteristics for a newly isolated aerobic denitrifier Bacillus subtilis JD-014 were investigated, and the potential functional genes involved in the aerobic denitrification process were further screened through transcriptome analysis. JD-014 exhibited efficient denitrification performance when having sodium succinate as the carbon source with the range of nitrate concentration between 50 and 300 mg/L. Following the transcriptome data, most of the up-regulated differentially expressed genes (DEGs) were associated with cell motility, carbohydrate metabolism, and energy metabolism. Moreover, gene nirsir annotated as sulfite reductase was screened out and further identified as a regulator participating in the nitrogen removal process within JD-014. The findings in present study provide meaningful information in terms of a comprehensive understanding of genetic regulation of nitrogen metabolism, especially for Bacillus strains.