Biomedical subjects

N A Assaf

Publications and source records attributed to N A Assaf.

3 recordsLinked to original sources

PubMed1998

Molecular identification of a Stenotrophomonas species used in the bioassay for erythromycin in aquaculture samples.

A bacterial strain isolated from aquaculture pond slurry, which was extremely sensitive to erythromycin, was used to detect erythromycin at levels as low as 0.05 micrograms ml-1 in aquaculture water, sediments and soil samples. Identification of the indicator organism was attempted by 16S rRNA sequencing, biochemical profile, fatty-acid analysis and polymerase chain reaction (PCR). GenBank comparison showed that the 16S rRNA sequence of the strain was similar to those of more than 20 copies of Xanthomonas and Stenotrophomonas. The position of the strain in a phylogenetic tree based on the 16S rRNA gene sequence comparison is in a cluster of Stenotrophomonas. The fatty-acid analysis also showed that the strain is similar to Stenotrophomonas maltophilia. However, the biochemical profile of the strain is most similar to Xanthomonas campestris, except that it can utilize maltose, which is similar to S. maltophilia. Polymerase chain reaction results showed that the strain is different from X. campestris, S. maltophilia and other Xanthomonas species tested. Based on these results, the authors named this strain as Stenotrophomonas sp. strain NCTR.

Aquaculture↗

PubMed1994

Accelerated biodegradation of atrazine by a microbial consortium is possible in culture and soil.

A mixed enrichment culture of microorganisms capable of accelerated mineralization of atrazine was isolated from soil treated with successive applications of the herbicide. Liquid cultures of this consortium, in the presence of simple carbon sources, mineralized 96% of the applied atrazine (0.56 mM) within 7 days. Atrazine mineralization in culture is initiated with the formation of the metabolite hydroxyatrazine. In soil treated with atrazine at a concentration of 0.14 mM (concentration is based on total soil mass), and then inoculated with the microbial consortium, the parent compound was completely transformed in 25 days. After 30 days of incubation, 60% of the applied atrazine was accounted for as 14CO2. As was found with the liquid cultures, hydroxyatrazine was the major metabolite. After 145 days, soil extractable hydroxyatrazine declined to zero and 86% of the applied atrazine was accounted for as 14CO2. No metabolites, other than hydroxyatrazine, were recovered from either the liquid culture or soil inoculated with the consortium. The use of the mixed microbial culture enhanced mineralization more than 20 fold as compared to uninoculated soil.

Atrazine↗

PubMed1993

Spheroplast formation and plasmid isolation from Rhodococcus spp.

The genus Rhodococcus comprises aerobic gram-positive actinomycetes that show considerable morphological and metabolic diversity and are known to be involved in the development of plant diseases and degradation of environmental pollutants. We describe a method for cell lysis and large plasmid DNA isolation from Rhodococcus by creating lysozyme susceptible cells by predigestion with the enzyme mutanolysin. Mutanolysin action resulted in the liberation of reducing sugars and free amino acids from the peptidoglycan layers of the cell wall. A 1-h predigestion with mutanolysin followed by a 0.5-h incubation with lysozyme resulted in spheroplast formation. Complete lysis of cells and efficient isolation of intact large plasmid DNA (108 kb) from wild-type Rhodococcus strains was confirmed.

Chromatography, High Pressure Liquid↗