Biomedical subjects

M A Engelhardt

Publications and source records attributed to M A Engelhardt.

3 recordsLinked to original sources

PubMed2001

Isolation and characterization of a novel hydrocarbon-degrading, Gram-positive bacterium, isolated from intertidal beach sediment, and description of Planococcus alkanoclasticus sp. nov.

AIMS: Characterization of a bacterial isolate (strain MAE2) from intertidal beach sediment capable of degrading linear and branched alkanes. METHODS AND RESULTS: A Gram-positive, aerobic, heterotrophic bacterium (strain MAE2), that was capable of extensive degradation of alkanes in crude oil but had a limited capacity for the utilization of other organic compounds, was isolated from intertidal beach sediment. MAE2 had an obligate requirement for NaCl but could not tolerate high salt concentrations. It was capable of degrading branched and n-alkanes in crude oil from C11 to C33, but was unable to degrade aromatic hydrocarbons. Comparative 16S rRNA sequence analysis placed the isolate with members of the genus Planococcus. That finding was corroborated by chemotaxonomic and physiological data. The fatty acid composition of strain MAE2 was very similar to the type species of the genus Planococcus, P. citreus (NCIMB 1493T) and P. kocurii (NCIMB 629T), and was dominated by branched acids, mainly a15:0. However, the 16S rRNA of strain MAE2 had less than 97% sequence identity with the type strains of P. citreus (NCIMB 1439T), P. kocurii (NCIMB 629T) and two Planococcus spp. (strain MB6-16 and strain ICO24) isolated from Antarctic sea ice. This indicated that strain MAE2 represented a separate species from these planococci. Morphologically, the isolate resembled P. okeanokoites (NCIMB 561T) and P. mcmeekinii S23F2 (ATCC 700539T). The cellular fatty acid composition of P. okeanokoites and P. mcmeekinii was considerably different from strain MAE2, and the mol % G + C content of P. mcmeekinii was far lower than that of MAE2. CONCLUSION: On the basis of phenotypic and genotypic data, it is proposed that strain MAE2 is a new species of Planococcus, Planococcus alkanoclasticus sp. nov., for which the type strain is P. alkanoclasticus MAE2 (NCIMB 13489T). SIGNIFICANCE AND IMPACT OF THE STUDY: Planococcus species are abundant members of the bacterial community in a variety of marine environments, including some in sensitive Antarctic ecosystems. The occurrence of hydrocarbon-degrading Planococcus spp. is potentially of importance in controlling the impact of hydrocarbon contamination in sensitive marine environments.

Alkanes↗

PubMed2000

The P5abc peripheral element facilitates preorganization of the tetrahymena group I ribozyme for catalysis.

Phylogenetic comparisons and site-directed mutagenesis indicate that group I introns are composed of a catalytic core that is universally conserved and peripheral elements that are conserved only within intron subclasses. Despite this low overall conservation, peripheral elements are essential for efficient splicing of their parent introns. We have undertaken an in-depth structure-function analysis to investigate the role of one of these elements, P5abc, using the well-characterized ribozyme derived from the Tetrahymena group I intron. Structural comparisons using solution-based free radical cleavage revealed that a ribozyme lacking P5abc (E(DeltaP5abc)) and E(DeltaP5abc) with P5abc added in trans (E(DeltaP5abc).P5abc) adopt a similar global tertiary structure at Mg(2+) concentrations greater than 20 mM [Doherty, E. A., et al. (1999) Biochemistry 38, 2982-90]. However, free E(DeltaP5abc) is greatly compromised in overall oligonucleotide cleavage activity, even at Mg(2+) concentrations as high as 100 mM. Further characterization of E(DeltaP5abc) via DMS modification revealed local structural differences at several positions in the conserved core that cluster around the substrate binding sites. Kinetic and thermodynamic dissection of individual reaction steps identified defects in binding of both substrates to E(DeltaP5abc), with > or =25-fold weaker binding of a guanosine nucleophile and > or =350-fold weaker docking of the oligonucleotide substrate into its tertiary interactions with the ribozyme core. These defects in binding of the substrates account for essentially all of the 10(4)-fold decrease in overall activity of the deletion mutant. Together, the structural and functional observations suggest that the P5abc peripheral element not only provides stability but also positions active site residues through indirect interactions, thereby preferentially stabilizing the active ribozyme structure relative to alternative less active states. This is consistent with the view that peripheral elements engage in a network of mutually reinforcing interactions that together ensure cooperative folding of the ribozyme to its active structure.

Animals↗

PubMed1996

O brave new words...

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Biodegradation, Environmental↗