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Endemic to the Namib Desert, Fairy Circles (FCs) are vegetation-free circular patterns surrounded and delineated by grass species. Since first reported the 1970''s, many theories have been proposed to explain their appearance, but none provide a fully satisfactory explanation of their origin(s) and/or causative agent(s). In this study, we have evaluated an early hypothesis stating that edaphic microorganisms could be involved in their formation and/or maintenance. Surface soils (0–5cm) from three different zones (FC center, FC margin and external, grass-covered soils) of five independent FCs were collected in April 2013 in the Namib Desert gravel plains. T-RFLP fingerprinting of the bacterial (16S rRNA gene) and fungal (ITS region) communities, in parallel with two-way crossed ANOSIM, showed that FC communities were significantly different to those of external control vegetated soil and that each FC was also characterized by significantly different communities. Intra-FC communities (margin and centre) presented higher variability than the controls. Together, these results provide clear evidence that edaphic microorganisms are involved in the Namib Desert FC phenomenon. However, we are, as yet, unable to confirm whether bacteria and/or fungi communities are responsible for the appearance and development of FCs or are a general consequence of the presence of the grass-free circles. 相似文献
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An antigen in the outer membrane protein (OMP) fraction of
Campylobacter jejuni was identified and characterized. Western blot
analysis demonstrated antigenic differences in this protein between two
congenic C. jejuni strains. Strain A74/C, which colonizes chickens,
expressed the antigen at 34 kDa, while strain A74/O, which poorly colonizes
chickens, expressed the antigen at 32 and 34 kDa. A genomic library was
constructed in λgt11 with DNA from A74/O and screened with antibody raised
against C. jejuni OMPs. A clone that possessed a 1.3-kb insert and
expressed an immunoreactive protein fused to β-galactosidase was isolated
and purified. DNA sequence analysis revealed the insert contained one open
reading frame 864 bases long. The deduced amino acid sequence demonstrated
56.3% similarity with Bacillus steorothermophilus glnH, a
glutamine-binding protein, and 54.0% similarity with C. jejuni
PEB1, a putative colonization adhesin. Southern hybridization, Northern
hybridization, and DNA sequence analyses of the congenic colonizing and
noncolonizing strains of C. jejuni failed to distinguish the two
strains and revealed only one copy of the gene. Post-translational
modification may be an alternate explanation for the antigenic differences
seen between the two strains.
Received: 15 October 1996 / Accepted: 3 December 1996 相似文献
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