Electroactive properties of EABs in response to long-term exposure to polystyrene microplastics/nanoplastics and the underlying adaptive mechanisms.

Given widespread presence of polystyrene (PS) microplastics/nanoplastics (MPs/NPs), the electroactive responses and adaptation mechanisms of electroactive biofilms (EABs) exposed long-term to PS-containing aquatic environments remain unclear. Therefore, this study investigated the impacts of PS MPs/NPs on electroactivity of EABs. Results found that EABs exhibited delayed formation upon initially exposure but displayed an increased maximum current density (Imax) after subsequent exposure for up to 55 days. Notably, EABs exposure to NH2PS NPs (EAB-NH2PSNPs) demonstrated a 50% higher Imax than the control, along with a 17.84% increase in viability and a 58.10% increase in biomass. The cytochrome c (c-Cyts) content in EAB-NH2PSNPs rose by 178.35%, benefiting the extracellular electron transfer (EET) of EABs. Moreover, bacterial community assembly indicated the relative abundance of electroactive bacteria increased to 87.56% in EAB-NH2PSNPs. The adaptability mechanisms of EABs under prolonged exposure to PS MPs/NPs predominantly operate by adjusting viability, EET, and bacterial community assembly, which were further confirmed a positive correlation with Imax through structural equation model. These findings provide deeper insights into long-term effects and mechanisms of MPs/NPs on the electroactive properties of EABs and even functional microorganisms in aquatic ecosystems.

[Community Structure Characteristics of nirS Denitrifying Bacteria of Spring Typical Parkland Waterbodies in Shijiazhuang City].

Four typical park water bodies located in the main urban area of Shijiazhuang city were selected to study the relationships between water quality and the community structure and diversity of nirS denitrifying bacteria. The results showed that the nitrogen concentration ranged from 4.43 to 13.83 mg·L-1 in four park water bodies, which exhibited notable nitrogen pollution characteristics. Based on the characteristic index analysis of three-dimensional fluorescence spectra, the four park water bodies all exhibited strong autochthonous components and low humus characteristics. The results of Illumina high-throughput sequencing indicated that most of the nirS denitrifying bacteria showed significant differences in dominant genus. The unclassified_Bacteria (53.52%), Pseudomonas (60.48%), and Rhodobacter (46.94%) were the dominant bacteria in Yuxi park, Shuishang park, and Chang'an park, respectively. In comparison, unclassified_Bacteria (36.19%) and unclassified_Proteobacteria (23.44%) were the dominant bacteria in Shiji park. Redundancy analysis showed that denitrification bacteria in Yuxi park were mainly affected by nitrate, total nitrogen, and dissolved oxygen; denitrification bacteria in Shuishang park were greatly affected by total phosphorus; denitrification bacteria in Chang 'an park were mainly affected by ammonia and nitrous nitrogen; and denitrification in Shiji park were mainly affected by total phosphorus, nitrite, and ammonia. Overall, the water quality and the community structure of nirS denitrification bacteria exhibited significant differences in park water bodies. Further research could contribute to the understanding of water quality characteristics and the denitrifying community structure of urban water systems, and develop efficient denitrifying bacterial agents.