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Seasonal Changes in an Alpine Soil Bacterial Community in the Colorado Rocky Mountains. David A. Lipson, 2004.The period when the snowpack melts in late spring is a dynamic time for alpine ecosystems . The large winter microbial community begins to turn over rapidly, releasing nutrients to plants . Past studies have shown that the soil microbial community in alpine dry meadows of the Colorado Rocky Mountains changes in biomass, function, broad-level structure, and fungal diversity between winter and early summer . However, little specific information exists on the diversity of the alpine bacterial community or how it changes during this ecologically important period. We constructed clone libraries of 16S ribosomal DNA from alpine soil collected in winter, spring, and summer . We also cultivated bacteria from the alpine soil and measured the seasonal abundance of selected cultured isolates in hybridization experiments . The uncultured bacterial communities changed between seasons in diversity and abundance within taxa . The Acidobacterium division was most abundant in the spring . The winter community had the highest proportion of Actinobacteria and members of the Cytophaga/Flexibacter/Bacteroides (CFB) division . The summer community had the highest proportion of the Verrucomicrobium division and of ß-Proteobacteria . As a whole,  -Proteobacteria were equally abundant in all seasons,
although seasonal changes may have occurred within this group . A number
of sequences from currently uncultivated divisions were found,
including two novel candidate divisions . The cultured isolates belonged
to the
-, ß-, and
 -Proteobacteria,
the Actinobacteria, and the CFB groups . The only uncultured
sequences that were closely related to the isolates were from winter
and spring libraries . Hybridization experiments showed that
actinobacterial and ß-proteobacterial isolates were most
abundant during winter, while the
- and
-proteobacterial isolates tested did not vary significantly.
While the cultures and clone libraries produced generally distinct
groups of organisms, the two approaches gave consistent accounts of
seasonal changes in microbial
diversity .
Excision and Integration of Cassettes by an Integron Integrase of Nitrosomonas europaea. Grégory Léon, 2003.We found in the environmental strain Nitrosomonas europaea a chromosomal integron-like structure with an integrase gene, intINeu . We have tested the capacity of the IntINeu integrase to excise and integrate several resistance gene cassettes . The results allow us to consider IntINeu a new functional integron integrase . Conidial Hydrophobins of Aspergillus fumigatus. Sophie Paris, 2003.The surface of Aspergillus fumigatus conidia, the first structure recognized by the host immune system, is covered by rodlets . We report that this outer cell wall layer contains two hydrophobins, RodAp and RodBp, which are found as highly insoluble complexes . The RODA gene was previously characterized, and  rodA conidia do not display a rodlet layer (N . Thau, M . Monod, B . Crestani, C . Rolland, G . Tronchin, J . P . Latgé, and S . Paris, Infect . Immun . 62:4380-4388, 1994) . The RODB gene was cloned and disrupted . RodBp was highly homologous to RodAp and different from DewAp of A . nidulans .
rodB conidia had a rodlet layer similar to that of the wild-type conidia . Therefore, unlike RodAp, RodBp is not required for rodlet formation . The surface of
rodA conidia is granular; in contrast, an amorphous layer is present at the surface of the conidia of the
rodA
rodB double mutant . These data show that RodBp plays a role in the structure of the conidial cell wall . Moreover, rodletless mutants are more sensitive to killing by alveolar macrophages, suggesting that RodAp or the rodlet structure is involved in the resistance to host cells .
A New Bacterial Steroid Degradation Gene Cluster in Comamonas testosteroni TA441 Which Consists of Aromatic-Compound Degradation Genes for Seco-Steroids and 3-Ketosteroid Dehydrogenase Genes. Masae Horinouchi, 2003.In Comamonas testosteroni TA441, testosterone is degraded via aromatization of the A ring, which is cleaved by the meta-cleavage enzyme TesB, and further degraded by TesD, the hydrolase for the product of TesB . TesEFG, encoded downstream of TesD, are probably hydratase, aldolase, and dehydrogenase for degradation of 2-oxohex-4-enoicacid, one of the products of TesD . Here we present a new and unique steroid degradation gene cluster in TA441, which consists of ORF18, ORF17, tesI, tesH, ORF11, ORF12, and tesDEFG. TesH and TesI are 3-ketosteroid-  1-dehydrogenase and 3-ketosteroid-4(5 )-dehydrogenase, respectively, which work in the early steps of steroid degradation . ORF17 probably encodes the reductase component of 9-hydroxylase for 1,4-androstadiene-3,17-dione, which is the product of TesH in testosterone degradation . Gene disruption experiments showed that these genes are necessary for steroid degradation and do not have any isozymes in TA441 . By Northern blot analysis, these genes were shown to be induced when TA441 was incubated with steroids (testosterone and cholic acid) but not with aromatic compounds [phenol, biphenyl, and 3-(3-hydroxyphenyl)propionic acid], indicating that these genes function exclusively in steroid degradation .
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