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Steroids originating from bacterial bile acid degradation affect Caenorhabditis elegans and indicate potential risks for the fauna of manured soils

ABSTRACT: Bile acids are steroid compounds from the digestive tracts of vertebrates that enter agricultural environments in unusual high amounts with manure. Bacteria degrading bile acids can readily be isolated from soils and waters including agricultural areas. Under laboratory conditions, these bacteria transiently release steroid compounds as degradation intermediates into the environment. These compounds include androstadienediones (ADDs), which are C19-steroids with potential hormonal effects. Experiments with Caenorhabditis elegans showed that ADDs derived from bacterial bile acid degradation had effects on its tactile response, reproduction rate, and developmental speed. Additional experiments with a deletion mutant as well as transcriptomic analyses revealed that these effects might be conveyed by the putative testosterone receptor NHR-69. Soil microcosms showed that the natural microflora of agricultural soil is readily induced for bile acid degradation accompanied by the transient release of steroid intermediates. Establishment of a model system with a Pseudomonas strain and C. elegans in sand microcosms indicated transient release of ADDs during the course of bile acid degradation and negative effects on the reproduction rate of the nematode. This proof-of-principle study points at bacterial degradation of manure-derived bile acids as a potential and so-far overlooked risk for invertebrates in agricultural soils.

ORGANISM(S): Caenorhabditis elegans

PROVIDER: GSE126214 | GEO | 2019/02/08

REPOSITORIES: GEO

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Project description:Despite various efforts to develop tools to detect and compare the activity and catabolic potential and activity for pollutant degradation of microorganisms in environmental samples, an open-source, curated and reliable method is still required. Here we report on a customize normalization system that can be applied to any microarray design, allowing the assessment of reliability of signals and enabling cross-experiment comparisons. Probes for the underlying catabolic gene array were designed based on manually curated databases for catabolic key genes. Signals were assigned to the respective catabolic protein subfamily that allows to inferring the functions and substrate specificity. The placement of probes for critical degradation nodes and subsequent metabolic steps allows the retrieval of information on the metabolic net. Information on gene localization from genome surveys was correlated to signals of putative hosts to generate phylogenetic community information. Hence, this novel array system was validated using genomic DNA of genome sequenced bacterial strains hosting biodegradation functions and applied to genomic DNA and RNA extracted from environmental samples under aromatic pollution pressure. Catabolic microarray was optimized for detection and expression of catabolic genes involved in the degradation of pollutant compounds using genome genomic DNA of type strains: Burkholderia xenovorans LB400, Cupriavidus necator JMP134, Pseudomonas putida F1 and Sphingomonas wittichii RW1. Afterwards, this microarray was applied for environmental samples. For microcosm experiments, 200 ml of each groundwater were incubated in closed 1 l Erlenmeyer flasks at 20 degree C and 50 rpm. Second sets of 200 ml microcosms were supplemented with naphthalene (100 mg), which had above been identified as a contaminant present in both groundwaters in similar amounts. Naphthalene was supplied via the vapor phase and incubated under identical conditions as the control microcosms. After 4 days of incubations, 50 ml of each of the 4 microcosms were subjected to genomic DNA extraction and another 50 ml to RNA extraction.

Project description:Commensal microbes are exposed to enterohepatically circulated steroids such as bile acids and hormones in the gastrointestinal, vaginal, and urinary tracts. Since commensal microbes are exposed to these molecules exclusively in association with their host, we hypothesized that they may serve as effectors to identify and characterize genetic pathways involved in the commensal-host relationship. Host specific and some ingested steroids (phytoestrogens) are enterohepatically circulated through the lumen of the small intestine. Bile acid steroids are present at high concentrations, approximating 4 to 20 mM in the duodenum, and are released in bile from the common bile duct. Steroid hormones are secreted in bile at levels approximating 6 to 13 mg per day once conjugated to glucuronide or sulfate by the liver. Re-absorption of steroids by the terminal ileum is an incomplete process: for example, 200 to 600 mg of bile acid steroids per day in humans escape to the colon where complex microbial populations exist. We have shown that steroid hormones estradiol, progesterone, and hydrocortisone serve as strong substrates for the major RND- and MFS-type (except hydrocortisone) tripartite multidrug efflux systems, AcrAB-TolC and EmrAB-TolC respectively, even though such molecules fail to demonstrate antimicrobial properties in this bacterial background (Elkins and Mullis [2006] J. Bacteriol. 188:1191-1195). Although bile acids are subject to efflux, they are also known to directly interact with intracellular global regulators such as MarR (Prouty et al. [2004] Microbiol. 150:775-783) and Rob (Rosenberg et al., [2003] Mol. Microbiol. 48:1609-1619) consequently altering antimicrobial and bile resistance profiles. In our present study, whole-genome DNA microarrays of E. coli were used to determine what general effect steroids, both bile acid and hormones, may have on the transcriptome in relation to the human commensal environment. Keywords: Comparative Chemical Class Treatment

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Steroids originating from bacterial bile acid degradation affect Caenorhabditis elegans and indicate potential risks for the fauna of manured soils

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