Hyphospheric impacts of earthworms and arbuscular mycorrhizal fungus on soil bacterial community to promote oxytetracycline degradation.

A two-compartment microcosm was used to investigate the role of arbuscular mycorrhizal fungus (AMF) hyphae and earthworm in altering soil microbial community and OTC degradation. Treatments comprised OTC-contaminated hyphal compartments with or without AMF hyphae and with or without earthworms. Results indicated both AMF hyphae and earthworms accelerated OTC degradation; two degradation products were identified as 4-epi-oxytetracycline (EOTC) and 2-acetyl-2-decarboxamido-oxytetracycline (ADOTC). Q-PCR results indicated that both earthworms and AMF hyphae increased 16s rDNA gene, enhancing OTC degradation consequently. Illumina sequencing of the 16S rRNA genes showed that AMF hyphae and earthworm altered bacterial community. Earthworms stimulated the growth of class Anaerolineae, family Flavobacteriaceae, Genus Pseudomonas, reducing OTC residues. AMF hyphae significantly increased the abundance of family Pirellulaceae, genus Glycomyces, and Nonomuraea which had a negative correlation with EOTC, accelerating OTC degradation. When used together, AMF hyphae and earthworms enhanced OTC degradation by stimulating class Anaerolineae and family Flavobacteriaceae.

Improvement of the soil nitrogen content and maize growth by earthworms and arbuscular mycorrhizal fungi in soils polluted by oxytetracycline.

Interactions between earthworms (Eisenia fetida) and arbuscular mycorrhizal fungi (Rhizophagus intraradices, AM fungi) have been suggested to improve the maize nitrogen (N) content and biomass and were studied in soils polluted by oxytetracycline (OTC). Maize was planted and amended with AMF and/or earthworms (E) in the soil with low (1mgkg(-1) soil DM) or high (100mgkg(-1) soil DM) amounts of OTC pollution in comparison to soil without OTC. The root colonization, shoot and root biomass, shoot and root N contents, soil nitrogen forms, ammonia-oxidizing bacteria (AOB) and archaea (AOA) were measured at harvest. The results indicated that OTC decreased maize shoot and root biomass (p<0.05) by mediating the soil urease activity and AOB and AOA abundance, which resulted in a lower N availability for maize roots and shoots. There was a significant interaction between earthworms and AM fungi on the urease activity in soil polluted by OTC (p<0.05). Adding earthworms or AM fungi could increase the maize biomass and N content (p<0.05) in OTC polluted soil by increasing the urease activity and relieving the stress from OTC on the soil N cycle. AM fungi and earthworms interactively increased maize shoot and root biomass (p<0.05) in the OTC polluted soils through their regulation of the urease activity and the abundance of ammonia oxidizers, resulting in different soil NH4(+)-N and NO3(-)-N contents, which may contribute to the N content of maize shoots and roots. Earthworms and AM fungi could be used as an efficient method to relieve the OTC stress in agro-ecosystems.

[Effects of earthworm on soil microbes and biological fertility: A review].

Earthworms are considered as 'ecosystem engineers', as they affect soil microbial community and function by improving micro-habitat, increasing surface area of organic compound, feeding, and transporting microorganisms. Multi-scale cavities created through earthworm movements help improve soil porosity and aeration, thus supporting microbial growth and reproduction. Earthworms also break down complex organic compounds into microbe-accessible nutrients by means of feeding on, crushing, and mixing soil. This results in elevated mineralization and improvement of cycling of key soil nutrients including carbon, nitrogen, and phosphorus, overall enhancing the soil biological fertility.