This review outlines information about the Gram-negative, aerobic bacterium Variovorax paradoxus. The genomes of these species have G+C contents of 66.5-69.4 mol%, and the cells form yellow colonies. Some strains of V. paradoxus are facultative lithoautotrophic, others are chemoorganotrophic. Many of them are associated with important catabolic processes including the degradation of toxic and/or complex chemical compounds. The degradation pathways or other skills related to the following compounds, respectively, are described in this review: sulfolane, 3-sulfolene, 2-mercaptosuccinic acid, 3,3'-thiodipropionic acid, aromatic sulfonates, alkanesulfonates, amino acids and other sulfur sources, polychlorinated biphenyls, dimethyl terephthalate, linuron, 2,4-dinitrotoluene, homovanillate, veratraldehyde, 2,4-dichlorophenoxyacetic acid, anthracene, poly(3-hydroxybutyrate), chitin, cellulose, humic acids, metal-EDTA complexes, yttrium, rare earth elements, As(III), trichloroethylene, capsaicin, 3-nitrotyrosine, acyl-homoserine lactones, 1-aminocyclopropane-1-carboxylate, methyl tert-butyl ether, geosmin, and 2-methylisoborneol. Strains of V. paradoxus are also engaged in mutually beneficial interactions with other plant and bacterial species in various ecosystems. This species comprises probably promising strains for bioremediation and other biotechnical applications. Lately, the complete genomes of strains S110 and EPS have been sequenced for further investigations.

The thioether 3,3-thiodipropionic acid can be used as precursor substrate for biotechnological synthesis of 3-mercaptopropionic acid-containing polythioesters. Therefore, the hitherto unknown catabolism of this compound was elucidated to engineer novel and improved polythioester biosynthesis pathways in the future. Bacteria capable of using 3,3-thiodipropionic acid as the sole source of carbon and energy for growth were enriched from the environment. From eleven isolates, TBEA3, TBEA6, and SFWT were morphologically and physiologically characterized. Their 16 S rDNAs and other features affiliated these isolates to the ␤-subgroup of the proteobacteria. Tn5::mob mutagenesis of isolate Variovorax paradoxus TBEA6 yielded ten mutants fully or partially impaired in growth on 3,3-thiodipropionic acid. Genotypic characterization of two 3,3-thiodipropionic acid-negative mutants demonstrated the involvement of a bacterial cysteine dioxygenase (EC 1.13.11.22) homologue in the further catabolism of the 3,3-thiodipropionic acid cleavage product 3-mercaptopropionic acid. Detection of 3-sulfinopropionate in the supernatant of one of these mutants during cultivation on 3,3-thiodipropionic acid as well as in vivo and in vitro enzyme assays using purified protein demonstrated oxygenation of 3-mercaptopropionic acid to 3-sulfinopropionate by this enzyme; cysteine and cysteamine were not used as substrate. Beside cysteine dioxygenase and cysteamine dioxygenase, this 3-mercaptopropionic acid dioxygenase is the third example for a thiol dioxygenase and the first report about the microbial catabolism of 3-mercaptopropionic acid. Insertion of Tn5::mob in a gene putatively coding for a family III acyl-CoAtransferase resulted in the accumulation of 3-sulfinopropionate during cultivation on 3,3-thiodipropionic acid, indicating that this compound is further metabolized to 3-sulfinopropionylCoA and subsequently to propionyl-CoA.The thioether 3,3-thiodipropionic acid (TDP) 2 and its ester are effective non-toxic antioxidants (1), and they are therefore widely used as antioxidant and stabilizer in food, for food packaging, and for various technical applications. Experiment with rats showed that TDP was rapidly adsorbed after oral intake and excreted in the urine (2). In technical applications esters of TDP are important stabilizers of polyolefins (1), and polymer-bound TDP is used to replace methyl sulfide for the reductive quenching of ozonolysis reactions (3). Recently, the biotechnological production of medium-and long-chain dialkyl 3,3-thiodipropionate antioxidants by a lipase-catalyzed esterification of 3,3-thiodipropionic acid in the absence of solvents was reported. In contrast to the chemical production of TDP ester, the biotechnological process does not require any materials with deleterious effects on health and environment (4). Another biotechnological process using TDP as primary product is the microbial production of polythioesters (PTEs) (5). In addition to 3-mercaptopropionic acid Ralstonia eutropha is able to use the organo sul...

The sucCD gene of Advenella mimigardefordensis strain DPN7 T encodes a succinyl coenzyme A (succinyl-CoA) synthetase homologue (EC 6.2.1.4 or EC 6.2.1.5) that recognizes, in addition to succinate, the structural analogues 3-sulfinopropionate (3SP) and itaconate as substrates. Accumulation of 3SP during 3,3-dithiodipropionic acid (DTDP) degradation was observed in Tn5::mob-induced mutants of A. mimigardefordensis strain DPN7T disrupted in sucCD and in the defined deletion mutant A. mimigardefordensis ⌬sucCD. These mutants were impaired in growth with DTDP and 3SP as the sole carbon source. Hence, it was proposed that the succinyl-CoA synthetase homologue in A. mimigardefordensis strain DPN7T activates 3SP to the corresponding CoA-thioester (3SP-CoA). The putative genes coding for A. mimigardefordensis succinyl-CoA synthetase (SucCD Am ) were cloned and heterologously expressed in Escherichia coli BL21(DE3)/pLysS. Purification and characterization of the enzyme confirmed its involvement during degradation of DTDP. 3SP, the cleavage product of DTDP, was converted into 3SP-CoA by the purified enzyme, as demonstrated by in vitro enzyme assays. The structure of 3SP-CoA was verified by using liquid chromatography-electrospray ionization-mass spectrometry. SucCD Am is Mg 2؉ or Mn 2؉ dependent and unspecific regarding ATP or GTP. In kinetic studies the enzyme showed highest enzyme activity and substrate affinity with succinate (V max ‫؍‬ 9.85 ؎ 0.14 mol min ؊1 mg ؊1 , K m ‫؍‬ 0.143 ؎ 0.001 mM). In comparison to succinate, activity with 3SP was only ca. 1.2% (V max ‫؍‬ 0.12 ؎ 0.01 mol min ؊1 mg ؊1 ) and the affinity was 6-fold lower (K m ‫؍‬ 0.818 ؎ 0.046 mM). Based on the present results, we conclude that SucCD Am is physiologically associated with the citric acid cycle but is mandatory for the catabolic pathway of DTDP and its degradation intermediate 3SP.3,3Ј-Dithiodipropionic acid (DTDP) is an organic disulfide and a precursor for the production of polythioesters (PTEs) by bacteria (25). Further applications for DTDP are thermodynamic studies (40), development of secondary batteries (52), amino acid analysis (53), and the construction of self-assembling monolayers (10). Microbial production of PTEs from simple carbon sources and inorganic sulfur is currently not possible. Knowledge of the catabolism of organic sulfur compounds in bacteria could provide a reasonable strategy to engineer strains suitable for PTE production. A first step in this direction was the isolation of bacteria able to utilize DTDP as the sole source of carbon and energy. Advenella mimigardefordensis strain DPN7T , a betaproteobacterium, found in mature compost in a waste management facility was one of the isolates (15,56

The biotechnological relevance of 3,3Ј-dithiodipropionic acid (DTDP) is its application as a precursor substrate for microbially synthesized polythioesters (PTEs) (36). Furthermore, this organic sulfur compound (OSC) is employed in electrochemical and thermodynamic studies (49), for development of secondary batteries (58), in amino acid analysis (59), and for construction of self-assembly monolayers (15). The chemical structure of DTDP is very similar to that of the disulfide amino acid cystine. The absence of amino groups in DTDP is the only difference, yielding a higher melting point of cystine (247 to 249°C) than of DTDP (152 to 157°C). The occurrence of DTDP in natural habitats has not been described, to our knowledge, although this OSC may well be formed, because it is the disulfide of two molecules of 3-mercaptopropionic acid (3MP) and an oxidative disulfide formation is not unlikely. 3MP, along with cysteine and glutathione, belongs to the most frequently detected thiols in natural aquatic environments (1, 69). However, it occurs only in nanomolar concentrations (24). 3MP was found as a central intermediate during catabolism of the marine alga osmolyte dimethylsulfoniopropionate (11,29,57,60,61,64) and also in freshwater habitats, as an anaerobic degradation product of sulfur-containing organic compounds, such as homocysteine and methionine (31,43). Furthermore, it is generated by abiotic reactions of dissolved sulfide with dissolved organic matter in hypolimnetic waters (24). Therefore, 3MP is not a xenobiotic, though it is chemically produced at the scale of several thousand tons for applications as a bisphenol A cocatalyst. Moreover, it is used as a convulsant for studies of experimental epilepsy (16, 53) and for gold nanoparticle arrays to form three-dimensional monolayers (68). During application as a precursor substrate in PTE production, the microbial utilization of 3MP has been demonstrated clearly (35,37,38,55). However, nothing is known about the pathway and the enzymes involved in the catabolism of 3MP or of its dimer, DTDP. Obviously, none of the PTE-producing microorganisms and only a few characterized strains utilize these two compounds as sole sources of carbon and energy (66). This is presumably due to the toxicity of these OSCs or of their intermediates during degradation (47).Most information regarding the catabolism of naturally occurring OSCs is available for cysteine and methionine and also for dimethyl sulfoxide, dimethylsulfoniopropionate, and dimethylsulfide as intermediates of the sulfur cycle (28,30,33,67). In addition, biodesulfurization of benzothiophenes (41) and of the fluorinated OSC bis-(3-pentafluorophenylpropyl)-sulfide (62) has been studied in detail. However, these OSCs are not related structurally to DTDP or 3MP.It is presently not possible to synthesize PTEs from simple carbon sources and inorganic sulfur sources. To establish mi-* Corresponding author. Mailing address:

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