Growth, biofilm formation and atrazine degrading gene (trzN) expression of Arthrobacter sp. DNS10 cultured with montmorillonite, kaolinite and goethite

Microbial weathering of montmorillonite and its implication for Cd(II) immobilization

Interactions between silicate bacteria and silicates are very common in nature and hold great potential in altering their mutual physicochemical properties. But their interactions in regulating contaminants remediation involving performance and mechanisms are often overlooked. Here, we focused on the interactions between silicate bacteria (Paenibacillus polymyxa, PP; Bacillus circulans, BC) and a soil silicate montmorillonite (Mt), and their impact on Cd(II) immobilization. The obtained results showed that Mt greatly promoted the growth of the bacteria, resulting in a maximum 10.31 times increase in biomass production. In return, the bacteria strongly enhanced the Cd(II) adsorption on Mt, with adsorption capacities increased by 80.61%-104.45% in comparison to the raw Mt. Additionally, the bacteria-Mt interaction changed Cd(II) to a more stabilized state with a maximum reduction of 38.90%/g Mt in bioavailability. The enhancement of Cd(II) adsorption and immobilization on the bacterial modified Mt was caused by the following aspects: (1) the bacteria activities altered the aggregation state of Mt and made it better dispersed, thus more active sites were exposed; (2) the microbial activities brought about more rough and crumpled surface, as well as smaller Mt fragments; (3) a variety of microbial-derived functional groups were introduced onto the Mt surface, increasing its affinity for heavy metals; (4) the main Cd(II) immobilization mechanism was changed from ion exchange to the combination of ion exchange and functional groups induced adsorption. This work elucidates the potential ecological and evolutionary processes of silicate bacteria-soil clay mineral interactions, and bears direct implications for the clay-mediated bioremediation of heavy metals in natural environments.

Assessing microbial degradation potential of methylmercury in different types of paddy soil through short-term incubation

The neurotoxic methylmercury (MeHg) in paddy soils can accumulate in rice grains. Microbial demethylation is an important pathway of MeHg degradation in soil, but the effect of soil type on microbial degradation of MeHg remains unclear. Therefore, we investigated MeHg degradation in eight typical paddy soils and analyzed the associations between soil physiochemical properties and microbial degradation efficiencies of MeHg. Results showed that MeHg was significantly degraded in unsterilized paddy soils, and the microbial degradation efficiency ranged from 10.8% to 64.6% after a 30-day incubation. The high microbial degradation efficiency of MeHg was observed in the soils with high levels of clay content, whereas relatively low degradation efficiency was found in the red paddy soils. We identified that Paenibacillaceae was the most important microbial predictor of MeHg degradation and was positively correlated with the degradation efficiency in the soils. The abundances of these microbial taxa associated with MeHg degradation were positively correlated with clay content. In addition, Eh, pH, and SOC could influence microbial degradation of MeHg by regulating certain microbial communities. Our results indicate that soil type is crucial in driving MeHg degradation, which has important implications for the mitigation of MeHg pollution in various croplands.

Characterization of Biofilm Microbiome Formation Developed on Novel 3D-Printed Zeolite Biocarriers during Aerobic and Anaerobic Digestion Processes

Background: Aerobic or anaerobic digestion is involved in treating agricultural and municipal waste, and the addition of biocarriers has been proven to improve them further. We synthesized novel biocarriers utilizing zeolites and different inorganic binders and compared their efficiency with commercially available biocarriers in aerobic and anaerobic digestion systems. Methods: We examined BMP and several physicochemical parameters to characterize the efficiency of novel biocarriers on both systems. We also determined the SMP and EPS content of synthesized biofilm and measured the adherence and size of the forming biofilm. Finally, we characterized the samples by 16S rRNA sequencing to determine the crucial microbial communities involved. Results: Evaluating BMP results, ZSM-5 zeolite with bentonite binder emerged, whereas ZSM-5 zeolite with halloysite nanotubes binder stood out in the wastewater treatment experiment. Twice the relative frequencies of archaea were found on novel biocarriers after being placed in AD batch reactors, and >50% frequencies of Proteobacteria after being placed in WWT reactors, compared to commercial ones. Conclusions: The newly synthesized biocarriers were not only equally efficient with the commercially available ones, but some were even superior as they greatly enhanced aerobic or anaerobic digestion and showed strong biofilm formation and unique microbiome signatures.