With increasing efforts to reuse wastewater treatment plant (WWTP) products in agriculture, assessing their impact on soil-plant systems is crucial, while the effects of accompanying antibiotic residues on soil microbial communities have not yet been adequately studied. This study focuses on clarithromycin (CLR), highly present in wastewater, and investigates the CLR-degradation potential of plant-associated microorganisms. Phaseolus vulgaris plants were grown in raised beds filled with Haplic Cambisol and amended with or without WWTP products (treated wastewater, biosolid, or composted biosolid), as a source of CLR residues. The rhizosphere microbiomes after biosolid amendments was significantly enriched by Pseudomonadaceae as assessed by 16S rRNA metagenomics and cultures enriched by CLR revealed dominance of Proteobacteria. However, no degradation of CLR by microbial consortia or enrichment cultures was observed, suggesting the multiplication of CLR-resistant bacteria with other resistance mechanisms. Cultivation-based approach combined with antibiotic modulation assays and subsequent LC-MS analysis confirmed the complete CLR removal by seven phylogenetic groups of actinomycetes in vitro. The proportion of isolates indicated that the rhizosphere is a natural reservoir for CLR-inactivating microorganisms; however, the amendment of soils with WWTP products can significantly increase their abundance and diversity.
- Keywords
- Streptomyces, Antimicrobial resistance, Biodegradation, Macrolides, Micropollutants, Soil microbiome,
- MeSH
- Anti-Bacterial Agents * pharmacology MeSH
- Phaseolus * microbiology drug effects growth & development MeSH
- Phylogeny MeSH
- Clarithromycin * pharmacology metabolism MeSH
- Microbiota drug effects MeSH
- Wastewater * chemistry MeSH
- Soil Microbiology MeSH
- Rhizosphere * MeSH
- RNA, Ribosomal, 16S genetics MeSH
- Publication type
- Journal Article MeSH
- Names of Substances
- Anti-Bacterial Agents * MeSH
- Clarithromycin * MeSH
- Wastewater * MeSH
- RNA, Ribosomal, 16S MeSH
Streptomyces are of great interest in the pharmaceutical industry as they produce a plethora of secondary metabolites that act as antibacterial and antifungal agents. They may thrive on their own in the soil, or associate with other organisms, such as plants or invertebrates. Some soil-derived strains exhibit hemolytic properties when cultivated on blood agar, raising the question of whether hemolysis could be a virulence factor of the bacteria. In this work we examined hemolytic compound production in 23 β-hemolytic Streptomyces isolates; of these 12 were soil-derived, 10 were arthropod-associated, and 1 was plant-associated. An additional human-associated S. sp. TR1341 served as a control. Mass spectrometry analysis suggested synthesis of polyene molecules responsible for the hemolysis: candicidins, filipins, strevertene A, tetrafungin, and tetrin A, as well as four novel polyene compounds (denoted here as polyene A, B, C, and D) in individual liquid cultures or paired co-cultures. The non-polyene antifungal compounds actiphenol and surugamide A were also identified. The findings indicate that the ability of Streptomyces to produce cytolytic compounds (here manifested by hemolysis on blood agar) is an intrinsic feature of the bacteria in the soil environment and could even serve as a virulence factor when colonizing available host organisms. Additionally, a literature review of polyenes and non-polyene hemolytic metabolites produced by Streptomyces is presented.
- Keywords
- Actinomycetales, Streptomyces, hemolysis, polyene antibiotics, secondary metabolites, soil ecosystem, symbiosis,
- MeSH
- Anti-Bacterial Agents pharmacology metabolism MeSH
- Antifungal Agents pharmacology chemistry MeSH
- Virulence Factors metabolism MeSH
- Hemolysis MeSH
- Humans MeSH
- Polyenes pharmacology chemistry MeSH
- Streptomyces * chemistry MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Review MeSH
- Names of Substances
- Anti-Bacterial Agents MeSH
- Antifungal Agents MeSH
- Virulence Factors MeSH
- Polyenes MeSH
