Is toxin production by coryneform bacteria linked to their ability to utilize hydrocarbons?

Push-pull tests evaluating in situ aerobic cometabolism of ethylene, propylene, and cis-1,2-dichloroethylene

In situ aerobic cometabolic transformations of ethylene, propylene, and cis-1,2-dichloroethylene (c-DCE), by microorganisms stimulated on propane, were examined in groundwater contaminated with c-DCE and trichloroethylene (TCE). In situ measurements were performed by conducting field push-pull tests, which consisted of injecting site groundwater amended with a bromide tracer and combinations of propane, dissolved oxygen (DO), nitrate, ethylene, propylene, c-DCE, and TCE into existing monitoring wells and sampling the same wells over time. Mass balance and transformation rate calculations were performed after adjusting for dilution losses using measured tracer concentrations. Initial rates of propane utilization were very low; rates increased substantially following sequential additions of propane and DO. Evidence that propane and DO additions had stimulated organisms expressing a propane monoxygenase enzyme system and that had the capability to transform chlorinated aliphatic hydrocarbons (CAHs) included: (1) the transformation of injected ethylene and propylene to the cometabolic byproducts ethylene oxide and propylene oxide, (2) the transformation of c-DCE, and (3) the inhibition of these transformations in the presence of coinjected acetylene, a known monoxygenase mechanism-based inactivator. These results suggest that a series of push-pull tests performed with nontoxic chemical probes can be useful for detecting and monitoring in situ aerobic cometabolism of CAHs.

Push-pull tests for assessing in situ aerobic cometabolism

Three types of single-well push-pull tests were developed for use in assessing the feasibility of in situ aerobic cometabolism of chlorinated aliphatic hydrocarbons (CAHs). These included transport tests, biostimulation tests, and activity tests. Transport tests are conducted to evaluate the mobility of solutes used in subsequent tests. These included bromide or chloride (conservative tracers), propane (growth substrate), ethylene, propylene (CAH surrogates), dissolved oxygen (electron acceptor), and nitrate (a minor nutrient). Tests were conducted at an experimental wellfield of Oregon State University. At this site, extraction phase breakthrough curves for all solutes were similar, indicating apparent conservative transport of the dissolved gases and nitrate prior to biostimulation. Biostimulation tests were conducted to stimulate propane-utilizing activity of indigenous microorganisms and consisted of sequential injections of site ground water containing dissolved propane and oxygen. Biostimulation was detected by the increase in rates of propane and oxygen utilization after each injection. Activity tests were conducted to quantify rates of substrate utilization and to confirm that CAH-transforming activity had likely been stimulated. In particular, the transformation of injected CAH surrogates ethylene and propylene to the cometabolic byproducts ethylene oxide and propylene oxide provided evidence that activity of the monooxygenase enzyme system, responsible for aerobic cometabolic transformations of CAHs, had likely also been stimulated. Estimated zero-order transformation rates decreased in the order propane > ethylene > propylene. The series of push-pull tests developed and field tested in this study should prove useful for conducting rapid, low-cost feasibility assessments for in situ aerobic cometabolism of CAHs.

Gene cloning and characterization of multiple alkane hydroxylase systems in Rhodococcus strains Q15 and NRRL B-16531

The alkane hydroxylase systems of two Rhodococcus strains (NRRL B-16531 and Q15, isolated from different geographical locations) were characterized. Both organisms contained at least four alkane monooxygenase gene homologs (alkB1, alkB2, alkB3, and alkB4). In both strains, the alkB1 and alkB2 homologs were part of alk gene clusters, each encoding two rubredoxins (rubA1 and rubA2; rubA3 and rubA4), a putative TetR transcriptional regulatory protein (alkU1; alkU2), and, in the alkB1 cluster, a rubredoxin reductase (rubB). The alkB3 and alkB4 homologs were found as separate genes which were not part of alk gene clusters. Functional heterologous expression of some of the rhodococcal alk genes (alkB2, rubA2, and rubA4 [NRRL B-16531]; alkB2 and rubB [Q15]) was achieved in Escherichia coli and Pseudomonas expression systems. Pseudomonas recombinants containing rhodococcal alkB2 were able to mineralize and grow on C(12) to C(16) n-alkanes. All rhodococcal alkane monooxygenases possessed the highly conserved eight-histidine motif, including two apparent alkane monooxygenase signature motifs (LQRH[S/A]DHH and NYXEHYG[L/M]), and the six hydrophobic membrane-spanning regions found in all alkane monooxygenases related to the Pseudomonas putida GPo1 alkane monooxygenase. The presence of multiple alkane hydroxylases in the two rhodococcal strains is reminiscent of other multiple-degradative-enzyme systems reported in Rhodococcus.

Polyphasic microbial community analysis of petroleum hydrocarbon-contaminated soils from two northern Canadian communities

The cold-adapted bacterial communities in petroleum hydrocarbon-contaminated and non-impacted soils from two northern Canadian environments, Kuujjuaq, Que., and Alert, Nunavut, were analyzed using a polyphasic approach. Denaturing gradient gel electrophoresis (DGGE) separation of 16S rDNA PCR fragments from soil total community DNA revealed a high level of bacterial diversity, as estimated by the total number of bands visualized. Dendrogram analysis clustered the sample sites on the basis of geographical location. Comparison of the overall microbial molecular diversity suggested that in the Kuujjuaq sites, contamination negatively impacted diversity whereas in the Alert samples, diversity was maintained or increased as compared to uncontaminated controls. Extraction and sequencing analysis of selected 16S rDNA bands demonstrated a range of similarity of 86-100% to reference organisms, with 63.6% of the bands representing high G+C Gram-positive organisms in the order Actinomycetales and 36.4% in the class Proteobacteria. Community level physiological profiles generated using Biolog GN plates were analyzed by cluster analysis. Based on substrate oxidation rates, the samples clustered into groups similar to those of the DGGE dendrograms, i.e. separation based upon geographic origin. The coinciding results reached using culture-independent and -dependent analyses reinforces the conclusion that geographical origin of the samples, rather than petroleum contamination level, was more important in determining species diversity within these cold-adapted bacterial communities.

Analysis of the structural diversity of mycolic acids of Rhodococcus and Gordonia [correction of Gordonla] isolates from activated sludge foams by selective ion monitoring gas chromatography-mass spectrometry (SIM GC-MS)

A method using Selective Ion Monitoring (SIM) gas chromatography-mass spectrometry is described for analysis of mycolic acids which reveals a hitherto unrecognised chemical structural diversity among these in some members of the Mycolata. The structural interpretation of mass spectral data of mycolic acids from Rhodococcus spp and Gordonia [corrected] spp using SIM is discussed.

Bacterial adhesion to soil contaminants in the presence of surfactants

It has been proposed that addition of surfactants to contaminated soil enhances the solubility of target compounds; however, surfactants may simultaneously reduce the adhesion of bacteria to hydrophobic surfaces. If the latter mechanism is important for the biodegradation of virtually insoluble contaminants, then the use of surfactants may not be beneficial. The adhesion of a Mycobacterium strain and a Pseudomonas strain, isolated from a creosote-contaminated soil, to the surfaces of highly viscous non-aqueous-phase liquids (NAPLs) was measured. The NAPLs were organic material extracted from soils from two creosote-contaminated sites and two petroleum-contaminated sites. Cells suspended in media with and without surfactant were placed in test tubes coated with an NAPL, and the percentages of cells that adhered to the surface of the NAPL in the presence and absence of surfactant were compared by measuring optical density. Test tubes without NAPLs were used as controls. The presence of either Triton X-100 or Dowfax 8390 at a concentration that was one-half the critical micelle concentration (CMC) inhibited adhesion of both species of bacteria to the NAPLs. Both surfactants, when added at concentrations that were one-half the CMCs to test tubes containing previously adhered bacteria, also promoted the removal of the cells from the surfaces of the NAPL-coated test tubes. Neither surfactant was toxic to the bacteria. Further investigation showed that a low concentration of surfactant also inhibited the growth of both species on anthracene, indicating that the presence of a surfactant resulted in a reduction in the uptake of the solid carbon source.

Bacterial oxidation of propane

The bacterial metabolism of propane and the pathway(s) involved are poorly understood, as the relative importance of terminal versus subterminal oxidation of propane, via propan-1-ol and propan-2-ol, respectively, is still unclear. In the case of bacteria, the ability to oxidize propane appears to be confined mainly to the Gram-positive Corynebacterium - Nocardia - Mycobacterium - Rhodococcus complex. Studies on propane oxidation have been hampered by a lack of firm enzymological data; for example, to date there are no reports of a purified propane oxygenase system. However, oxygenase activity has been confirmed by the production of propan-1-ol and/or propan-2-ol, and more recently by the co-oxidation of propene to 1,2-epoxypropane in cell extracts of propane-grown cells. Here, we review the use of genetic, biochemical and immunological techniques to assess the role(s) of terminal and subterminal oxidation in the metabolism of propane by Rhodococcus rhodochrous PNKb1 and present a general overview of the topic.

Physicochemical Cell Surface and Adhesive Properties of Coryneform Bacteria Related to the Presence and Chain Length of Mycolic Acids

The presence and chain length of mycolic acids of bacteria of the genera Corynebacterium, Rhodococcus, Gordona, Mycobacterium , and Arthrobacter and of coryneform bacteria containing a type B peptidoglycan were related to the cell surface hydrophobicity of the bacteria, which in turn was related to adhesion of the cells to defined surfaces such as Teflon and glass. The origin of the overall negative charge of these bacteria is discussed.