Abstract

In this work, we have shown that Novosphingobium tardaugens NBRC 16725 (strain ARI-1), a bacterial strain that was isolated due to its capacity to mineralize the estrogenic endocrine compound 17β-estradiol, is also able to mineralize testosterone, the androgenic endocrine compound. Using in silico analysis, we predicted a new putative steroid degradation (SD) gene cluster in strain ARI-1, which resembles genes involved in testosterone degradation in Comamonas testosteroni and other testosterone degrading bacteria like Actinobacteria (like Rhodococcus and Mycobacteria genera) although with significant differences in gene organization. A whole transcriptomic analysis of N. tardaugens revealed that testosterone produces a limited induction of the genes of the SD cluster that show a high basal expression in its absence. The 3β/17β-hydroxysteroid dehydrogenase involved in the first metabolic step of testosterone degradation was identified by using genetic and biochemical approaches. The construction of knockout mutant strains in the genes of the SD cluster together with in silico analyses suggests the existence of gene redundancy in the genome of N. tardaugens. This work will expand the knowledge about the metabolic pathways and biotransformation capabilities of a Gram-negative bacterium that could become a new model system in the bacterial steroid degradation field.

Highlights

  • Endocrine disruptors (EDCs) are chemicals that interfere with the endocrine system and produce adverse effects in both humans and wildlife

  • TES-Ac generating as transient intermediate. Taken together all these together all these results reveal that N. tardaugens contains an efficient aerobic degradative pathway results that N. tardaugens contains an efficient aerobic degradative pathway for C-19 steroids

  • We have demonstrated that this strain is able to degrade steroids that can be considered as toxic EDCs, such as TES, TES-Ac, DHEA and other C-19 steroids, like AD and ADD (Figure 2)

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Summary

Introduction

Endocrine disruptors (EDCs) are chemicals that interfere with the endocrine system and produce adverse effects in both humans and wildlife. 17β-estradiol (E2) (estrogen) and testosterone (TES) (androgen), are the most ubiquitously sexual hormones found as pollutants in soil and water systems [2,3,4,5]. These compounds contaminate the waste water treatment plant effluents and occur at low concentration (ng/L to μg/L) [5,6]. Similar results were obtained in water treatment plants [4] This indicates that either a limited number of organisms can mineralize E2 [7,8,9,10,11,12,13,14] (Table S1) or that this compound is mineralized at lower rates compared to TES [15]

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