Mutagenic and toxic activity of environmental effluents from underground coal gasification experiments

Nucleotide sequences and regulational analysis of genes involved in conversion of aniline to catechol in Pseudomonas putida UCC22(pTDN1)

A 9,233-bp HindIII fragment of the aromatic amine catabolic plasmid pTDN1, isolated from a derivative of Pseudomonas putida mt-2 (UCC22), confers the ability to degrade aniline on P. putida KT2442. The fragment encodes six open reading frames which are arranged in the same direction. Their 5' upstream region is part of the direct-repeat sequence of pTDN1. Nucleotide sequence of 1.8 kb of the repeat sequence revealed only a single base pair change compared to the known sequence of IS1071 which is involved in the transposition of the chlorobenzoate genes (C. Nakatsu, J. Ng, R. Singh, N. Straus, and C. Wyndham, Proc. Natl. Acad. Sci. USA 88:8312-8316, 1991). Four open reading frames encode proteins with considerable homology to proteins found in other aromatic-compound degradation pathways. On the basis of sequence similarity, these genes are proposed to encode the large and small subunits of aniline oxygenase (tdnA1 and tdnA2, respectively), a reductase (tdnB), and a LysR-type regulatory gene (tdnR). The putative large subunit has a conserved [2Fe-2S]R Rieske-type ligand center. Two genes, tdnQ and tdnT, which may be involved in amino group transfer, are localized upstream of the putative oxygenase genes. The tdnQ gene product shares about 30% similarity with glutamine synthetases; however, a pUC-based plasmid carrying tdnQ did not support the growth of an Escherichia coli glnA strain in the absence of glutamine. TdnT possesses domains that are conserved among amidotransferases. The tdnQ, tdnA1, tdnA2, tdnB, and tdnR genes are essential for the conversion of aniline to catechol.

The characterization of the mutagenic activity of soil

The solvent extracts of non-agricultural soil were shown to cause a potent mutagenic response to Salmonella bacteria. The extract of soil from local sites had activities of 100,000-250,000 TA98 revertants per kg with S9 activation and 44,000-83,000 revertants per kg to TA100 with activation. The soil is mutagenic to both strains without S9, but at lower levels. Nitroreductase-deficient bacterial strains show that the soil extract may have mutagenic compound(s) containing a nitro group. The revertant numbers per gram of soil are lowest at the surface, increase at 4-10 cm and decrease in a linear fashion to a depth of 0.5 meter. HPLC fractionation shows that there is more than one separable component responsible for the mutagenicity of the soil. The source and consequences of the high levels of mutagenicity in 'ordinary soil' are unknown. Soil mutagens can be a significant complicating factor to those using the Ames/Salmonella assay for environmental sampling.