## 3 Microbiological Degradation of EDCs
In addition, 17\(\beta\)-estradiol is usually degraded faster while estrone and synthetic estrogens are decomposed slower [34; 47]. Moreover, [PERSON] et al. [37] noted the synergistic effect of mixture strains during 17\(\beta\)-estradiol degradation. While individual strains degraded to 86% of the hormone, the mixture of strains almost completely degraded 17\(\beta\)-estradiol. Synergy is caused by the cross-metabolism of strains, which allows better use of the intermediates. This is indicated by the analysis of intermediates in a mixed strain culture, which showed the appearance of two organic acids. These compounds were not identified during degradation of individual strains [37]. Due to the complicated, multi-ring structure of estrogens, they are degraded under aerobic conditions in different pathways, depending on which ring is cleaved first and in which position. Usually the first step of 17\(\beta\)-estradiol degradation is its dehydrogenation to estrone. This reaction is of great environmental significance as this reduces the total estrogenic activity due to the oxygenation of the phenol group of 17\(\beta\)-estradiol to ketone moiety [6; 10; 22; 35; 38]. [PERSON] et al. [38], during genome analysis of _Deinococcus actinosclerus_ SJTR1, found 18 genes encoding short-chain dehydrogenase/reductase (SDR), probably engaged in transformation 17\(\beta\)-estradiol to estrone. Estrone can be degraded in various pathways, during estrone metabolism by _Rhodococcus hagi_ BH2-1. [PERSON] et al. [48] identified two intermediates: 3-hydroxyandrosta-5,7,9(11)-trein-17-one and androsta-1,4,6-triene-3,17-dione, which were further metabolized. The mechanism of estrone degradation by cyanobacterial species is probably totally different. [PERSON] and [PERSON] [49] postulate that in this process lactose is engaged. One of the known degradation pathways of estrone is the 4,5-seco pathway with a characteristic metabolite--pyridinestrone acid--which has no estrogenic activity. This transformation pathway was observed in estrone-degrading alphaproteobacterial, e.g., in the _Novosphingobium_ sp. SLCC strain, which was isolated from the activated sludge of Dihua Sewage Treatment Plant in Taipei, and in the _Sphingomonas_ sp. strain KC8. In the first step of degradation, estrone is hydroxylated with estrone 4-hydroxylane and the resulting 4-hydroxyestrone is cleaved by 4-hydroxyestrone 4,5-dioxygenase. Analysis of the metabolites also showed that estratetraenol formed during degradation with the SLCC strain, which is a characteristic degradation product of 17\(\beta\)-estradiol in biological sewage treatment plants [12; 25]. 15 extradiol dioxygenase genes have been identified in the genome of the KC8 strain. The _oec_C cluster, which is responsible for the induction of active 4,5-dioxygenase, probably plays an important role in the catabolism of estrogens [25]. [PERSON] et al. [50] noted that a _meta_ cleavage product is converted by 2-oxoxacid oxidoreductase to 4-norestrogen-(10)-en-3-oyl-CoA. Further transformations include sequences of ester intermediate reactions leading to hydrolytic cleavage of the B ring. Hydrolysis by 2-hydroxycyclohexanecarboxylol-CoA dehydrogenase is facilitated by the deficiency of electrons on the carbonyl carbon of the B ring. The end product of the pathway is 9,17-dioxo-1,2,3,4,10,19-hexanoradirostan-5-oic acid (HIP) [50]. Similarly, 17\(\beta\)-estradiol degradation is carried out by the _Acinetobacter strain_ DSSKY-A-001. However, after cleavage of the ring to 4-(3\(\alpha\)-methyl-3,7-dodecane-6H-cyclopentadiene[\(\alpha\)]naphthalene-6-Subunit)-2-methoxy-3-butenoic acid, no re-closure of the ring to the heterocyclic end product- pyridinestrone acid was observed, as demonstrated in the typical 4,5-seco pathway. The obtained product is further oxidized to (\(Z\))-8-(7\(\alpha\)-methyl-1n-5-dioxo-octahydro-1\(H\)-in-4-yl)-2-0-6-dioxy-4-butenoic acid with the participation of the B ring cleaving oxygenase.