Characterisation of Structures in Salivary Secretion Film Formation. An Experimental Study with Atomic Force Microscopy

The purpose of the present study was to characterise the structure dynamics of pure salivary secretions retained on controlled surfaces with different surface energies in the early stage of salivary film formation. Germanium prisms prepared to have either low surface energy or medium surface energy were incubated in fresh secretions of either human parotid saliva (HPS) or human submandibular/sublingual saliva (HSMSLS) for 15, 90, and 180 min. After controlled rinsing with distilled water, the surfaces were air dried and thereafter imaged with atomic force microscopy (AFM). The amount of adsorbed material and the size of the structures detected increased with increased saliva exposure time. The film thicknesses varied from 10 to 150 nm, and both HPS and HSMSLS films contained structures with diameters varying from 40 nm to 2 μm. Some of these were clustered into special formations. The HPS films exhibited a more granular morphology than the HSMSLS films. Furthermore, branched lines were detected on the low surface energy germanium prisms incubated in saliva. The results indicate that exposure time, surface energy, and type of salivary secretion all are factors affecting the adsorption characteristics of salivary films.     

Mineralization of polycyclic aromatic hydrocarbons by a bacterium isolated from sediment below an oil field.

Microbiological analyses of sediments chronically exposed to petrogenic hydrocarbons resulted in the isolation of a gram-positive, rod-shaped bacterium which mineralized naphthalene (59.5% of the original amount), phenanthrene (50.9%), fluoranthene (89.7%), pyrene (63.0%), 1-nitropyrene (12.3%), 3-methylcholanthrene (1.6%), and 6-nitrochrysene (2.0%) to carbon dioxide when grown for 2 weeks in pure culture with organic nutrients. The bacterium tolerated salt concentrations up to 4% and grew well at 24 to 30 degrees C. The use of this bacterium may be an attractive alternative to existing physicochemical methods for the remediation of polycyclic aromatic hydrocarbons in the environment.     

Biodegradation of polycyclic aromatic hydrocarbons

The intent of this review is to provide an outline of the microbial degradation of polycyclic aromatic hydrocarbons. A catabolically diverse microbial community, consisting of bacteria, fungi and algae, metabolizes aromatic compounds. Molecular oxygen is essential for the initial hydroxylation of polycyclic aromatic hydrocarbons by microorganisms. In contrast to bacteria, filamentous fungi use hydroxylation as a prelude to detoxification rather than to catabolism and assimilation. The biochemical principles underlying the degradation of polycyclic aromatic hydrocarbons are examined in some detail. The pathways of polycyclic aromatic hydrocarbon catabolism are discussed. Studies are presented on the relationship between the chemical structure of the polycyclic aromatic hydrocarbon and the rate of polycyclic aromatic hydrocarbon biodegradation in aquatic and terrestrial ecosystems.     

Metabolism of benzonitrile and butyronitrile by Klebsiella pneumoniae.

A strain of Klebsiella pneumoniae that used aliphatic nitriles as the sole source of nitrogen was adapted to benzonitrile as the sole source of carbon and nitrogen. Gas chromatographic and mass spectral analyses of culture filtrates indicated that K. pneumoniae metabolized 8.4 mM benzonitrile to 4.0 mM benzoic acid and 2.7 mM ammonia. In addition, butyronitrile was metabolized to butyramide and ammonia. The isolate also degraded mixtures of benzonitrile and aliphatic nitriles. Cell extracts contained nitrile hydratase and amidase activities. The enzyme activities were higher with butyronitrile and butyramide than with benzonitrile and benzamide, and amidase activities were twofold higher than nitrile hydratase activities. K. pneumoniae appears promising for the bioremediation of sites contaminated with aliphatic and aromatic nitriles.     

Identification of a Carboxylic Acid Metabolite from the Catabolism of Fluoranthene by a Mycobacterium sp

A Mycobacterium sp. previously isolated from oil-contaminated estuarine sediments was capable of extensively mineralizing the high-molecular-weight polycyclic aromatic hydrocarbon fluoranthene. A carboxylic acid metabolite accumulated and was isolated by thin-layer and high-pressure liquid chromatographic analyses of ethyl acetate extracts from acidified culture media. The metabolite reached a maximum concentration of approximately 0.65% after 24 h of incubation. On the basis of comparisons with authentic compound in which we used UV and fluorescence spectrophotometry and R_f values, as well as mass spectral and proton and carbon nuclear magnetic resonance spectral analyses, the metabolite was identified as 9-fluorenone-1-carboxylic acid. This is the first report in a microbial system of a fluoranthene metabolite in which significant degradation of one of the aromatic rings has occurred.     

Mineralization of Polycyclic Aromatic Hydrocarbons by the White Rot Fungus Pleurotus ostreatus

The white rot fungus Pleurotus ostreatus was able to mineralize to (sup14)CO(inf2) 7.0% of [(sup14)C]catechol, 3.0% of [(sup14)C]phenanthrene, 0.4% of [(sup14)C]pyrene, and 0.19% of [(sup14)C]benzo[a]pyrene by day 11 of incubation. It also mineralized [(sup14)C]anthracene (0.6%) much more slowly (35 days) and [(sup14)C]fluorene (0.19%) within 15 days. P. ostreatus did not mineralize fluoranthene. The activities of the enzymes considered to be part of the ligninolytic system, laccase and manganese-inhibited peroxidase, were observed during fungal growth in the presence of the various polycyclic aromatic hydrocarbons. Although activity of both enzymes was observed, no distinct correlation to polycyclic aromatic hydrocarbon degradation was found.     

Degradation of a mixture of high‐molecular‐weight polycyclic aromatic hydrocarbons by a Mycobacterium strain PYR‐1

Mycobacterium sp. PYR‐1, which was previously shown to mineralize several individual polycyclic aromatic hydrocarbons (PAHs), simultaneously degraded phenanthrene, anthracene, fluoranthene, pyrene and benzo[a]pyrene in a six‐component synthetic mixture. Chrysene was not degraded significantly. When provided with a complex carbon source, Mycobacterium sp. PYR‐1 degraded greater than 74% of the total PAH mixture during 6 d of incubation. Mycobacterium sp. PYR‐1 appeared to preferentially degrade phenanthrene. No significant difference in degradation rates was observed between fluoranthene and pyrene. Anthracene degradation was slightly delayed but, once initiated, proceeded at a constant rate. Benzo[a]pyrene was degraded slowly. Degradation of a crude mixture of benzene‐soluble PAHs from contaminated sediments resulted in a 47% reduction of the material in 6 d compared with that of autoclaved controls. Experiments using an environmental microcosm test system indicated that mineralization rates of individual ¹⁴C‐labeled compounds were significantly lower in the mixtures than in equivalent doses of these compounds alone. Mineralization of the complete mixture was estimated conservatively to be between 49.7 and 53.6% and was nearly 50% in 30 d of incubation when all compounds were radiolabeled. These results strengthen the argument for the potential application of Mycobacterium sp. PYR‐1 for bioremediation of PAH‐contaminated wastes.     

Novel metabolites in phenanthrene and pyrene transformation by Aspergillus niger.

Aspergillus niger, isolated from hydrocarbon-contaminated soil, was examined for its potential to degrade phenanthrene and pyrene. Two novel metabolites, 1-methoxyphenanthrene and 1-methoxypyrene, were identified by conventional chemical techniques. Minor metabolites identified were 1- and 2-phenanthrol and 1-pyrenol. No 14CO2 evolution was observed in either [14C]phenanthrene or [14C]pyrene cultures.