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Isolation, characterization, and identification of Geobacillus thermodenitrificans HRO10, an α-amylase and α-glucosidase producing thermophile

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Thermophilic and amylolytic aerobic bacteria were isolated from soil through a selective enrichment procedure at 60 °C with starch as the carbon source. One of the isolates designated as HRO10 produced glucose aside from limit dextrin as the only hydrolysis product from starch and was characterized in detail. The starch-degrading enzymes produced by strain HRO10 were determined to be α-amylase and α-glucosidase. Whereas the α-amylase activity was detected exclusively in the culture supernatant, α-glucosidase occurred intracellular, extracellular, or on the surface of the bacteria depending on the growth phase. The optimum temperature and pH required for the growth of strain HRO10 were about 50 °C and pH 6.5 to 7.5. The strain used different carbohydrates as the carbon source, but the maximum production of α-amylase occurred when 1.0% (w/v) starch or dextrin was used. The use of organic vs. inorganic nitrogen favored the production of α-amylase in strain HRO10. The metal ions Li+, Mg2+, and Mn2+ stimulated the production of both enzymes. Identification of strain HRO10 by physiological and molecular methods including sequencing of the 16S rDNA showed that this strain belongs to the species Geobacillus thermodenitrificans. Biochemically, strain HRO10 differs from the type strain DSM 465 only in its ability to hydrolyze starch.Key words: thermophilic, amylolytic, α-amylase, α-glucosidase, Geobacillus thermodenitrificans.

Des bactéries aérobies thermophiles et amylolytiques ont été isolés du sol à travers une procédure d'enrichissement sélectif à 60 °C avec de l'amidon comme source de carbone. Un des isolats désigné comme HRO10 a produit, outre une quantité limitée de dextrine, du glucose comme seule produit d'hydrolyse de l'amidon et fut caractérisé en détail. Les enzymes de la dégradation de l'amidon produite par la souche HRO10 furent identifiés comme étant l'α-amylase et la α-glucosidase. Bien que l'activité α-amylase a été détectée exclusivement dans le surnageant de culture, la α-glucosidase fut décelée à l'intérieur, l'extérieur ou la surface la bactérie selon la phase de croissance. La température optimale et le pH requis pour la croissance de la souche HRO10 étaient d'environ 50 °C et de pH 6,5 à 7,5 respectivement. La souche a utilisé différents glucides comme sources de carbone mais la production maximale d'α-amylase fut atteinte lorsque 1,0 % (poids/vol.) d'amidon ou de dextrine fut utilisé. L'utilisation d'azote organique versus inorganique a favorisé la production d'α-amylase par la souche HRO10. Les ions métalliques Li+, Mg2+ et Mn2+ ont stimulé la production des deux enzymes. L'identification de la souche HRO10 par des méthodes physiologiques et moléculaires incluant le séquençage de l'ADNr 16S a démontré que cette souche appartenait à l'espèce Geobacillus thermodenitrificans. Au niveau biochimique, la souche HRO10 diffère de la souche type DSM 465 seulement dans sa capacité à hydrolyser l'amidon.Mots clés : thermophile, amylolytique, α-amylase, α-glucosidase, Geobacillus thermodenitrificans.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2005-08-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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