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SummaryDuring the course of experiments aimed at identifying genes with ribonuclease III (RNase III)-dependent expression in Escherichia coli, we found that steady state levels of bdm mRNA were dependent on cellular concentrations of RNase III. The half-lives of adventitiously overexpressed bdm mRNA and the activities of a transcriptional bdm'-'cat fusion were observed to be dependent on cellular concentrations of RNase III, indicating the existence of cis-acting elements in bdm mRNA responsive to RNase III. In vitro and in vivo cleavage analyses of bdm mRNA identified two RNase III cleavage motifs, one in the 5Ј-untranslated region and the other in the coding region of bdm mRNA, and indicated that RNase III cleavages in the coding region constitute a rate-determining step for bdm mRNA degradation. We also discovered that downregulation of the ribonucleolytic activity of RNase III is required for the sustained elevation of RcsB-induced bdm mRNA levels during osmotic stress and that cells overexpressing bdm form biofilms more efficiently. These findings indicate that the Rcs signalling system has an additional regulatory pathway that functions to modulate bdm expression and consequently, adapt E. coli cells to osmotic stress.

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Rhodococcus sp. strain DK17 was isolated from soil and analyzed for the ability to grow on o-xylene as the sole carbon and energy source. Although DK17 cannot grow on m-and p-xylene, it is capable of growth on benzene, phenol, toluene, ethylbenzene, isopropylbenzene, and other alkylbenzene isomers. One UV-generated mutant strain, DK176, simultaneously lost the ability to grow on o-xylene, ethylbenzene, isopropylbenzene, toluene, and benzene, although it could still grow on phenol. The mutant strain was also unable to oxidize indole to indigo following growth in the presence of o-xylene. This observation suggests the loss of an oxygenase that is involved in the initial oxidation of the (alkyl)benzenes tested. Another mutant strain, DK180, isolated for the inability to grow on o-xylene, retained the ability to grow on benzene but was unable to grow on alkylbenzenes due to loss of a meta-cleavage dioxygenase needed for metabolism of methyl-substituted catechols. Further experiments showed that DK180 as well as the wild-type strain DK17 have an ortho-cleavage pathway which is specifically induced by benzene but not by o-xylene. These results indicate that DK17 possesses two different ring-cleavage pathways for the degradation of aromatic compounds, although the initial oxidation reactions may be catalyzed by a common oxygenase. Gas chromatography-mass spectrometry and 300-MHz proton nuclear magnetic resonance spectrometry clearly show that DK180 accumulates 3,4-dimethylcatechol from o-xylene and both 3-and 4-methylcatechol from toluene. This means that there are two initial routes of oxidation of toluene by the strain. Pulsed-field gel electrophoresis analysis demonstrated the presence of two large megaplasmids in the wild-type strain DK17, one of which (pDK2) was lost in the mutant strain DK176. Since several other independently derived mutant strains unable to grow on alkylbenzenes are also missing pDK2, the genes encoding the initial steps in alkylbenzene metabolism (but not phenol metabolism) appear to be present on this approximately 330-kb plasmid.

Carboxydobacteria are a group of bacteria which are able to grow chemolithotrophically on carbon monoxide (CO) as the sole carbon and energy source under aerobic conditions (22,30 Microbiol. 1965Microbiol. , abstr. P108, 1965, and Actinoplanes, Microbispora, and Mycobacterium (4), have also been described.The facultatively chemolithotrophic bacterium Mycobacterium sp. strain JC1 (originally Acinetobacter sp. strain JC1 DSM 3803; reclassified by Song et al. [41]), is capable of growing aerobically not only on CO but also on methanol as a sole source of carbon and energy (8,39). This means that the bacterium is able to employ three distinct types of nutrition, chemoheterotrophy, chemolithotrophy, and methylotrophy, depending on substrate availability.Combined with these results, the facts that many mycobacterial species including Mycobacterium tuberculosis (10; GenBank accession no. AL123456), Mycobacterium avium (NCBI reference sequence [RefSeq] NC-002943), Mycobacterium bovis (NCBI RefSeq NC-002945), Mycobacterium leprae (9; GenBank accession no. AL450380), and Mycobacterium smegmatis (NCBI RefSeq NC-002974) have genes encoding amino acid sequences similar to those of Mycobacterium sp. strain JC1 CO dehydrogenase (CO-DH) (T. Song and Y. M. Kim, unpublished data), that Mycobacterium phlei is able to oxidize CO (4), and that Mycobacterium cuneatum (40), Mycobaterium gastri (18), and Mycobacterium ID-Y (36) are capable of growing on methanol raise the possibility that all known mycobacteria have an intrinsic ability to grow on CO and/or methanol as the sole carbon and energy source.In order to address this question, we examined several wellknown mycobacteria for the ability to grow on CO and/or methanol, and we found that all the mycobacteria tested grew well on each of these substrates as the sole source of carbon and energy, except that M. tuberculosis did not grow on methanol. We also present several enzymological backgrounds for the growth of the mycobacteria on CO and methanol. MATERIALS AND METHODSStrains and cultivation conditions. Mycobacterium sp. strain JC1 (DSM 3803) (3, 41), Mycobacterium flavescens (ATCC 14474), M. gastri (ATCC 15754), Mycobacterium neoaurum (ATCC 25795), Mycobacterium parafortuitum (ATCC 19686), Mycobacterium peregrinum (ATCC 14467), M. phlei (ATCC 11758), M. smegmatis mc 2 (ATCC 700084), M. tuberculosis H37Ra (ATCC 35835), and Mycobacterium vaccae (ATCC 15483) were used throughout this study. Cells were cultivated at 37°C under CO chemolithoautotrophy with a gas mixture of 30% CO-70% air in either standard mineral base (SMB) medium (SMB-CO) (21) or 0.47% (wt/vol) Middlebrook 7H9 medium (7H9-CO; Becton Dickinson, Cockeysville, Md.). For methylotrophic growth, cells were grown at 37°C in SMB medium supplemented with 1% (vol/vol) methanol (SMB-MeOH). For the methanol assimilation enzyme assay, Methylobacterium extorquens AM1 (NCIB 9133) and Methylobacillus sp. strain SK1 (DSM 8269) grown at 30°C in SMBMeOH were used as controls. Growth was measured with a spectrophotometer by determi...