Volatile and Dissolved Organic Carbon Sources Have Distinct Effects on Microbial Activity, Nitrogen Content, and Bacterial Communities in Soil

Variability in Microbial Communities Driven by Particulate Matter on Human Facial Skin

Microbial communities are known to play an important role in maintaining ecological balance and can be used as an indicator for assessing environmental pollution. Numerous studies have revealed that air pollution can alter the structure of microbial communities, which may increase health risks. Nevertheless, the relationships between microbial communities and particulate matter (PM) caused by air pollution in terms of health risk assessment are not well understood. This study aimed to validate the influences of PM chemical compositions on microbial communities and assess the associated health risks. Our results, based on similarity analysis, revealed that the stability structure of the microbial communities had a similarity greater than 73%. In addition, the altered richness and diversity of microbial communities were significantly associated with PM chemical compositions. Volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) exerted a positive influence on microbial communities in different environmental variables. Additionally, a stronger linear correlation was observed between hydroxyl radicals (·OH) and the richness of microbial communities. All estimated health risks from PM chemical compositions, calculated under different environmental variables, significantly exceeded the acceptable level by a factor of more than 49. Cr and 1,2-Dibromoethane displayed dual adverse effects of non-carcinogenic and carcinogenic risks. Overall, the study provides insights into the fundamental mechanisms of the variability in microbial communities driven by PM, which may support the crucial role of PM chemical compositions in the risk of microorganisms in the atmospheric environment.

Arsenic stress on soil microbial nutrient metabolism interpreted by microbial utilization of dissolved organic carbon

In a 120-day microcosm incubation experiment, we investigated the impact of arsenic contamination on soil microbial nutrient metabolism, focusing on carbon cycling processes. Our study encompassed soil basal respiration, key enzyme activities (particularly, β-1,4-N-acetylglucosaminidase and phosphatases), microbial biomass, and community structure. Results revealed a substantial increase (1.21-2.81 times) in β-1,4-N-acetylglucosaminidase activities under arsenic stress, accompanied by a significant decrease (9.86%-45.20%) in phosphatase activities (sum of acid and alkaline phosphatases). Enzymatic stoichiometry analysis demonstrated the mitigation of microbial C and P requirements in response to arsenic stress. The addition of C-sources alleviated microbial C requirements but exacerbated P requirements, with the interference amplitude increasing with the complexity of the C-source. Network analysis unveiled altered microbial nutrient requirements and an increased resistance process of microbes under arsenic stress. Microbial carbon use efficiency (CUE) and basal respiration significantly increased (1.17-1.59 and 1.18-3.56 times, respectively) under heavy arsenic stress (500 mg kg-1). Arsenic stress influenced the relative abundances of microbial taxa, with Gemmatimonadota increasing (5.5-50.5%) and Bacteroidota/ Nitrospirota decreasing (31.4-47.9% and 31.2-63.7%). Application of C-sources enhanced microbial resistance to arsenic, promoting cohesion among microorganisms. These findings deepen our understanding of microbial nutrient dynamics in arsenic-contaminated areas, which is crucial for developing enzyme-based toxicity assessment systems for soil arsenic contamination.

Chitosan Modulates Volatile Organic Compound Emission from the Biocontrol Fungus Pochonia chlamydosporia

Fungal volatile organic compounds (VOCs) are responsible for fungal odor and play a key role in biological processes and ecological interactions. VOCs represent a promising area of research to find natural metabolites for human exploitation. Pochonia chlamydosporia is a chitosan-resistant nematophagous fungus used in agriculture to control plant pathogens and widely studied in combination with chitosan. The effect of chitosan on the production of VOCs from P. chlamydosporia was analyzed using gas chromatography-mass spectrometry (GC-MS). Several growth stages in rice culture medium and different times of exposure to chitosan in modified Czapek-Dox broth cultures were analyzed. GC-MS analysis resulted in the tentative identification of 25 VOCs in the rice experiment and 19 VOCs in the Czapek-Dox broth cultures. The presence of chitosan in at least one of the experimental conditions resulted in the de novo production of 3-methylbutanoic acid and methyl 2,4-dimethylhexanoate, and oct-1-en-3-ol and tetradec-1-ene in the rice and Czapek-Dox experiments, respectively. Other VOCs changed their abundance because of the effect of chitosan and fungal age. Our findings suggest that chitosan can be used as a modulator of the production of VOCs in P. chlamydosporia and that there is also an effect of fungal age and exposure time.

Allelopathic Effects of Amomum villosum Lour. Volatiles from Different Organs on Selected Plant Species and Soil Microbiota

Amomum villosum Lour. is a perennial herb of the Zingiberaceae family, which is widely distributed in Xishuangbanna, Yunnan Province in Southwest China. Large amounts of volatile components contained in this plant enter the surrounding atmosphere and soil through volatilization, foliar leaching, root exudation, and residue decomposition. However, the ecological role of these compounds is currently unclear. The aim of this study was to compare the differences in the composition of volatile oils from stems, leaves, and young fruits of A. villosum, identify chemicals that had allelopathic effects, and explore the effects of the oil on the diversity and composition of soil microbiomes. Volatile oils were obtained by steam distillation and characterized by gas chromatography−mass spectrometry, and then were tested for allelopathic activity using seedlings of Lactuca sativa L. and Lolium perenne L. as test species. The results showed that the oils from stems and leaves were rich in monoterpene hydrocarbons, unlike the oxygenated monoterpenes which dominated oils from young fruits. Leaves > stems > young fruits: this was the order of the allelopathic effects of volatile oils from various A. villosum organs. Among the four main chemical components in the oils, only α-pinene, which is abundant in leaves, had a stronger allelopathic action than the crude oils, implying that it might be a potential allelochemical. Experiments on soil microorganisms indicated that 3.0 mg/mL oil had the greatest effect on the structure of the soil fungal community. It can be concluded that A. villosum is capable of releasing allelochemicals which affect the growth of other plant species and the diversity and community structure of soil microorganisms.