NOVELTY - An isolated nucleic acid (I) which specifically hybridizes under stringent conditions with genome of Rhodococcus ruber CNCM accession number I-1889, is new.    USE - (I), (II) or (III) is useful for rendering a cell (e.g., bacterium, plant cell, fungus or yeast) able to cleave an ether fuel additive. (V), (VI) or (VII) is useful for identifying in a complex mixture the presence of a microorganism comprising at least part of the eth gene cluster able to confer to a bacterial strain the ability to cleave an ether fuel additive, which involves contacting the sample with (V), or (VII), or performing a DNA amplification with at least one (VI). The complex mixture is a sample of water, soil, sludge, sediment, dredge tailing, gas or chemical waste. (V) is useful for isolating a microorganism able to cleave an ether fuel additive which involves detecting the presence or absence in a sample, of a nucleic acid hybridizing under stringent conditions with (V). (XII) is useful for detecting a contamination by an ether fuel additive in an aqueous effluent, a soil, a sludge, a sediment, a dredge tailing, a gas or a chemical waste, involves contacting the components with (XII). (VIII), (IX) or (XI) is useful for depolluting aqueous effluent, a soil, a sludge, a sediment, a dredge tailing, a gas or a chemical waste, which involves contacting the components with (VIII), (IX) and (XI). The depolluting step takes place in a bioreactor, or optionally takes place in situ, by addition of (VIII), (IX) or (XI) to the contaminated medium. The bacteria are confined in biobarriers, biofilters, and/or biopiles. The method preferably involves additionally contacting the aqueous effluent, a soil, a sludge, a sediment, a dredge tailing, a gas or a chemical waste, to be decontaminated with other microorganisms capable of degrading the contaminant or its degradative by-products (all claimed).    DETAILED DESCRIPTION - An isolated nucleic acid (I) which specifically hybridizes under stringent conditions with genome of Rhodococcus ruber (Rr) CNCM accession number I-1889, and which does not hybridize under stringent conditions with the genome of bacterial cell derived from Rr I-1889 by chromosomal rearrangement resulting in a 14.3 kbp deletion including eth gene cluster and the loss of the ability to degrade ethyl tert-butyl ether (ETBE). (I) specifically hybridizes at least one of the nucleic acids having a fully defined sequence of 1239 (S4), 1203 (S5), 321 (S6), 312 (S7) or 4398 (S8) nucleotides (ethA, B, C, D or R open reading frames (ORFs), respectively) as given in specification, where the nucleic acid encodes a protein having a fully defined sequence of 412 (S9), 400 (S10), 106 (S11), 103 (S12) or 331 (S13) amino acids, respectively as given in specification or its functional variant.    INDEPENDENT CLAIMS are also included for the following:    (1) A nucleic acid (II) having the following properties:    (a) hybridizes stringent conditions with a nucleic acid having a fully defined sequence of 12342 nucleotides (S2) as given in the specification; or    (b) when transferred into a bacterial cell derived from Rr as deposited at the Collection Nationale de Cultures de Microorganisms (CNCM) under the accession number I-1889 by chromosomal rearrangement resulting in a 14.3 kbp deletion including the eth gene cluster, it confers to this bacterium the ability to cleave ether fuel additives;    (2) A vector (III) comprising (I) or (II);    (3) A recombinant Escherichia coli bacterium (IV) comprising (III), as deposited at the Collection Nationale de Cultures de Microorganismes (CNCM) on April 19,2001, under than name of E.coli K12 (pGT220) and the accession number 1-2662;    (4) A nucleic acid probe (V) for the detection or characterization of bacterial strains able to cleave ether fuel additives, which hybridizes under stringent conditions with a nucleic acid having a fully defined sequence of 23656 (S1) and/or 12342 (S2) and/or 8766 (S3) nucleotides as given in specification;    (5) A nucleic acid primer (VI) specifically hybridizing with (S1), where the primer can be used for the amplification of a DNA sequence included in (S1);    (6) An antibody (VII) specifically binding to a polypeptide having a sequence of (S9)-(S13);    (7) A cytochrome P-450 having a sequence of (S9) or its variant which catalyzes the oxidation of ETBE;    (8) A polypeptide of sequence (S10) (EthA), (S11) (EthC), (S12) (EthD) or (S13) (EthR), or their variants;    (9) A complex of at least two of the above mentioned polypeptides;    (10) A recombinant bacterium (VIII) derived from the strain of Rr as deposited at CNCM under accession I-1889 by deletion of or all or part of at least one copy of DNA fragment comprising a fully defined sequence of 5576 nucleotides as given in specification;    (11) A recombinant bacterium (IX) comprising (I) or (II) or (III);    (12) A biosensor (X) for detecting the presence in a sample, of a microorganism able to degrade ETBE, the biosensor comprising (I), (II), (V), (VI) or (VII);    (13) Isolating (M1) a microorganism able to cleave an ether fuel additive, involves detecting the presence or absence in a sample of the eth gene cluster included in (S3);    (14) A bacterium (XI) which is able to cleave an ether fuel additive, and which has been identified and/or isolated by (M1), or by using (V), (VII) or (VII);    (15) A recombinant bacterium (XII) comprising a reporter gene under the control of the eth promoter; and    (16) Microbial whole cell biosensor (XIII) for detecting the presence of contamination by an ether fuel additive in a complex mixture comprising (I).    DESCRIPTION OF DRAWING(S) - The figure shows the wild-type genetic organization of the 23.7 kbp region carrying the genes involved in the ETBE degradation (A) and restriction map of the 9.3-kbp BamHI fragment of the ETBE-negative mutant (B). The eth genes encode a transcriptional activator (EthR), a ferredoxin reductase (EthA), the ETBE-inducible cytochrome P-450 (EthB), a ferredoxin (EthC) and an ETBE-inducible unknown protein (EthD).