Biomedical subjects

J O Ka

Publications and source records attributed to J O Ka.

8 recordsLinked to original sources

PubMed2001

Effects of low temperature and freeze-thaw cycles on hydrocarbon biodegradation in Arctic tundra soil.

Degradation of petroleum hydrocarbons was monitored in microcosms with diesel fuel-contaminated Arctic tundra soil incubated for 48 days at low temperatures (-5, 0, and 7 degrees C). An additional treatment was incubation for alternating 24-h periods at 7 and -5 degrees C. Hydrocarbons were biodegraded at or above 0 degrees C, and freeze-thaw cycles may have actually stimulated hydrocarbon biodegradation. Total petroleum hydrocarbon (TPH) removal over 48 days in the 7, 0, and 7 and -5 degrees C treatments, respectively, was 450, 300, and 600 microg/g of soil. No TPH removal was observed at -5 degrees C. Total carbon dioxide production suggested that TPH removal was due to biological mineralization. Bacterial metabolic activity, indicated by RNA/DNA ratios, was higher in the middle of the experiment (day 21) than at the start, in agreement with measured hydrocarbon removal and carbon dioxide production activities. The total numbers of culturable heterotrophs and of hydrocarbon degraders did not change significantly over the 48 days of incubation in any of the treatments. At the end of the experiment, bacterial community structure, evaluated by ribosomal intergenic spacer length analysis, was very similar in all of the treatments but the alternating 7 and -5 degrees C treatment.

Arctic Regions↗

PubMed1997

Diversity of oxygen and N-oxide regulation of nitrite reductases in denitrifying bacteria.

We examined alpha, beta and gamma Proteobacteria with Cu and heme-type dissimilatory nitrite reductases for patterns of nir regulation. Six of seven strains expressed nitrite reductase under aerobic growth conditions. In only one strain, G-179, was it stringently regulated by O2. Growth with NO-3 or NO-2 enhanced nitrite reductase production in four of seven strains under anaerobic growth conditions, but in only one strain, Pseudomonas aeruginosa PA01, under aerobic conditions. In this strain the nitrite reductase production was primarily regulated by an anr gene when grown under anaerobic conditions, but when grown under aerobic conditions it was regulated by both an anr gene and nitrogen oxide. Constitutive production of nitrite reductase was a common phenomenon rather than the exception among denitrifiers from the environment, which helps explain the prevalence of denitrifying enzymes in aerobic soils.

Aerobiosis↗

PubMed1995

Anaerobic activation of the entire denitrification pathway in Pseudomonas aeruginosa requires Anr, an analog of Fnr.

The Pseudomonas aeruginosa gene anr, which encodes a structural and functional analog of the anaerobic regulator Fnr in Escherichia coli, was mapped to the SpeI fragment R, which is at about 59 min on the genomic map of P. aeruginosa PAO1. Wild-type P. aeruginosa PAO1 grew under anaerobic conditions with nitrate, nitrite, and nitrous oxide as alternative electron acceptors. An anr deletion mutant, PAO6261, was constructed. It was unable to grow with these alternative electron acceptors; however, its ability to denitrify was restored upon the introduction of the wild-type anr gene. In addition, the activities of two enzymes in the denitrification pathway, nitrite reductase and nitric oxide reductase, were not detectable under oxygen-limiting conditions in strain PAO6261 but were restored when complemented with the anr+ gene. These results indicate that the anr gene product plays a key role in anaerobically activating the entire denitrification pathway.

Anaerobiosis↗

PubMed1995

Tracking microbial populations effective in reducing exposure.

Microbial ecology provides the link between basic biochemical and molecular studies on toxicity reduction by microbial metabolism and environmental studies that determine exposure. This link provides the ability to determine which microorganisms are responsible for the actual transformations in nature, thereby establishing how predictive the laboratory pathway, kinetic, regulatory, and enzyme mechanistic information is for nature. This information can be important to the rate of toxicant removal, the type and concentration of intermediate product(s), and the identification of conditions that limit effective toxicant removal. Nucleic acid-based methods now provide the main means to track important biodegrading populations. Examples of these methods are given that illustrate tracking a biodegrading microbe injected into an aquifer, following community succession in a toluene-degrading fluidized bed reactor, aiding the isolation from nature of novel biodegrading organisms, and rapidly characterizing the extent of microbial diversity in an aquifer stimulated to co-metabolize trichloroethene.

Biodegradation, Environmental↗

PubMed1994

Genetic and phenotypic diversity of 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading bacteria isolated from 2,4-D-treated field soils.

Forty-seven numerically dominant 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading bacteria were isolated at different times from 1989 through 1992 from eight agricultural plots (3.6 by 9.1 m) which were either not treated with 2,4-D or treated with 2,4-D at three different concentrations. Isolates were obtained from the most dilute positive most-probable-number tubes inoculated with soil samples from the different plots on seven sampling dates over the 3-year period. The isolates were compared by using fatty acid methyl ester (FAME) profiles, chromosomal patterns obtained by PCR amplification of repetitive extragenic palindromic (REP) sequences, and hybridization patterns obtained with probes for the tfd genes of plasmid pJP4 and a probe (Spa probe) that detects a distinctly different 2,4-D-degrading isolate, Sphingomonas paucimobilis (formerly Pseudomonas paucimobilis). A total of 57% of the isolates were identified to the species level by the FAME analysis, and these isolates were strains of Sphingomonas, Pseudomonas, or Alcaligenes species. Hybridization analysis revealed four groups. Group I strains, which exhibited sequence homology with tfdA, -B, -C, and -D genes, were rather diverse, as determined by both the FAME analysis and the REP-PCR analysis. Group II, which exhibited homology only with the tfdA gene, was a small group and was probably a subset of group I. All group I and II strains had plasmids. Hybridization analysis revealed that the tfd genes were located on plasmids in 75% of these strains and on the chromosome or a large plasmid in the other 25% of the strains. One strain exhibited tfdA and -B hybridization associated with a plasmid band, while tfdC and -D hybridized with the chromosomal band area. The group III strains exhibited no detectable homology to tfd genes but hybridized to the Spa probe. The members of this group were tightly clustered as determined by both the FAME analysis and the REP-PCR analysis, were distinctly different from group I strains as determined by the FAME analysis, and had very few plasmids; this group contained more of the 47 isolates than any other group. The group III strains were identified as S. paucimobilis. The group IV strains, which hybridized to neither the tft prove nor the Spa probe, were as diverse as the group I strains as determined by the FAME and REP-PCR analyses. Most of group IV strains could not be identified by the FAME analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

2,4-Dichlorophenoxyacetic Acid↗

PubMed1994

Use of gene probes to aid in recovery and identification of functionally dominant 2,4-dichlorophenoxyacetic acid-degrading populations in soil.

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was applied to soils in microcosms, and degradation was monitored after each of five repeated additions. Total DNAs were isolated from soil bacterial communities after each 2,4-D treatment. The DNA samples were analyzed on slot blots and Southern blots by using a tfdA gene probe subcloned from plasmid pJP4 and a Spa probe derived from a different 2,4-D-degrading isolate, a Sphingomonas paucimobilis strain. 2,4-D applied to soil was quickly degraded by indigenous microbial populations. As determined by slot blot analyses of DNA from a Michigan soil, the increase in hybridization signal in response to 2,4-D treatments was greater with the Spa probe than with the tfdA probe. In contrast, the DNA from a Saskatchewan soil exhibited an increase in hybridization signal with the tfdA probe. This indicated that a population with 2,4-D-degradative gene sequences different from the tfdA gene sequence was dominant in the Michigan site, but not in the Saskatchewan site. A Southern blot analysis of DNA from Michigan soil showed that the dominant 2,4-D-degrading population was S. paucimobilis 1443. A less dominant 2,4-D-degrading population was detected with the tfdA probe; further analysis revealed that this population was a Pseudomonas pickettii 712. These gene probe analyses revealed that an important population carrying out 2,4-D degradation was not detected when the canonical tfdA gene probe was used. After a series of new strains were isolated, we identified a probe to detect and identify the dominant members of this new group.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1994

Analysis of competition in soil among 2,4-dichlorophenoxyacetic acid-degrading bacteria.

Competition among indigenous and inoculated 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading bacteria was studied in a native Kansas prairie soil following 2,4-D additions. The soil was inoculated with four different 2,4-D-degrading strains at densities of 10(3) cells per g of soil; the organisms used were Pseudomonas cepacia DBO1(pJP4) and three Michigan soil isolates, strain 745, Sphingomonas paucimobilis 1443, and Pseudomonas pickettii 712. Following 2,4-D additions, total soil DNA was extracted and analyzed on Southern blots by using a tfdA gene probe which detected three of the strains and another probe that detected the fourth strain, S. paucimobilis 1443, which belongs to a different class of 2,4-D degraders. P. cepacia DBO1(pJP4), a constructed strain, outcompeted the other added strains and the indigenous 2,4-D-degrading populations. The S. paucimobilis population was the secondary dominant population, and strain 745 and P. pickettii were not detected. Relative fitness coefficients determined in axenic broth cultures predicted the outcome of competition in soil for some but not all strains. Lag time was shown to be a principal determinant of competitiveness among the strains, but the lag times were significantly reduced in mixed broth cultures, which changed the competitive outcome. Plasmids containing the genes for the 2,4-D pathway were important determinants of competitiveness since plasmid pKA4 in P. cepacia DBO1 resulted in the slower growth characteristic of its original host, P. pickettii, rather than the rapid growth observed when this strain harbors pJP4.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1994

Integration and excision of a 2,4-dichlorophenoxyacetic acid-degradative plasmid in Alcaligenes paradoxus and evidence of its natural intergeneric transfer.

A self-transmissible 2,4-dichlorophenoxyacetic acid (2,4-D)-degradative plasmid, pKA2, has been identified in a new 2,4-D-degrading strain, Alcaligenes paradoxus 2811P, isolated from agricultural soil. pKA2 occurred as a 42.9-kb plasmid in strain 2811P. A derivative strain, 2811C, was isolated from a stock culture in which the entire pKA2 plasmid was apparently integrated into the host chromosome without loss of the 2,4-D+ phenotype. This interpretation is based on the disappearance of a free plasmid DNA band, a shift in the tfdA-hybridizing band to the chromosome, loss of transmissibility of the 2,4-D+ trait, and appropriate shifts in Southern hybridization bands of plasmid DNA compared with whole-cell DNA. The integrated plasmid of strain 2811C was excised either precisely or imprecisely after continued transfer on 2,4-D-containing medium. This suggests that a chromosome-free plasmid cycle may occur to optimize fitness under conditions of specific resource fluctuation. Another new 2,4-D-degrading strain, Pseudomonas pickettii 712, which was isolated from the same field plot but at a different time, was found to carry a plasmid that is nearly identical to pKA2. The plasmid of this strain, pKA4, is 40.9 kb long and has features in common with pKA2, such as high self-transmissibility, hybridization only to the tfdA gene among the 2,4-D-metabolic genes of 2,4-D-degradative plasmid pJP4, and similar restriction endonuclease-generated fragments. Furthermore, the genetic homology between the two plasmids was high since all fragments of pKA2 hybridized to pKA4. These results suggest that these two plasmids are closely related and thus their occurrence in two genera in nature is the result of natural horizontal gene transfer.

2,4-Dichlorophenoxyacetic Acid↗