PGN-202

Listeria monocytogenes is a highly adaptable foodborne pathogen that causes multiple foodborne illness outbreaks annually despite stringent food safety measures. The ubiquitous presence of L. monocytogenes in agricultural production environments provides easy routes of contamination to the human food production chain. The remarkable resilience of L. monocytogenes in harsh food processing and preservation conditions presents further challenges to controlling this pathogen in food and food processing plants. Furthermore, there is an increasing consumer demand for natural antimicrobials in food. Aspergillus oryzae is a food fermentation fungus with a generally recognized as safe status and is a workhorse in biotechnology applications. In this study, we examined the antimicrobial activity of Aspergillus oryzae fermentates and extracts toward L. monocytogenes, both in laboratory cultures and contaminated milk. Aspergillus oryzae-derived antimicrobials can be obtained in 2 culture conditions, which we term natural products 1 and 2 (NP1 and NP2). Laboratory cultures of L. monocytogenes were effectively and rapidly killed by both NP1 and NP2 extracts. In contaminated milk, the NP1 extract was bactericidal, whereas the NP2 extract was bacteriostatic. Nevertheless, the NP2 extract was heat stable, retaining antimicrobial activity even after boiling. Profiling L. monocytogenes transcriptional response to a subinhibitory level of NP2 fermentate, we observed significant shifts in amino acid metabolism and iron uptake, suggesting that these pathways can be tackled to increase the efficacy of NP2. Taken together, A. oryzae fermentates and extracts are promising candidates for natural antimicrobial treatments in food and food processing environments.

Ensuring the stability of soil organic carbon (SOC) is vital for effective long-term carbon storage in forest ecosystems. While nanoparticles (NPs) have shown the potential to enhance SOC stability and reduce cumulative carbon mineralization rates (CCMR) in agricultural soils, their effects on forest soils remain largely unexplored. This study addresses this gap through an incubation experiment that evaluated the impact of silicon nitride nanoparticles (Si₃N₄-NPs) at varying concentrations [control, 0 mg kg^-1 (NP₀); 50 mg kg^-1 (NP₁); 100 mg kg^-1 (NP₂)] on SOC stability, CCMR, enzymatic activities, and microbial diversity across three forest ecosystems in the Dinghushan region of Guangdong, China: coniferous forest (CF), mixed conifer-broadleaf forest (MCBF), and monsoon evergreen broadleaf forest (MEF). The results revealed that Si₃N₄-NP application at the NP₂ concentration significantly reduced CCMR by 40.82 % compared to the control (NP₀). Moreover, NP₂ substantially decreased the activities of key soil enzymes: β-glucosidase by 13.81 %, N-acetylglucosaminidase by 32.62 %, cellobiohydrolase by 59.12 %, and phenol oxidase by 26.40 %, relative to NP₀. The NP₂ treatment also enhanced total SOC retention by 24.62 % compared to NP₀. Within SOC fractions, NP₂ significantly impacted the less labile (C3) and non-labile (C4) fractions, which increased by 46.83 % and 57.84 %, respectively, compared to NP₀. Meanwhile, the very labile C (C1) and labile C (C2) fractions showed non-significant changes. Furthermore, the Si₃N₄-NP applications induced distinct shifts in bacterial (Actinobacteriota) and fungal (Ascomycota) microbiomes, which correlated significantly with CCMR and total SOC. These findings indicate that Si₃N₄-NPs improve SOC stability and reduce mineralization in forest soils. However, field-scale validation is essential to assess the long-term impacts of Si₃N₄-NPs on microbial communities and overall ecosystem functioning. This study highlights the significance of NP concentration and forest type in developing effective strategies for SOC management to mitigate climate change.