Filtern
Dokumenttyp
Sprache
- Englisch (5)
Referierte Publikation
- ja (5)
Schlagworte
- A. versicolor (1)
- Actinomycetes (1)
- Aspergillus sydowii (1)
- Bacteria (1)
- Chad (1)
- Cyanobacteria (1)
- Cyclic Beta-(1,2)-glucans (1)
- Desert sand (1)
- Fungi-phototroph symbioses (1)
- Geobiology (1)
BacA of Sinorhizobium meliloti plays an essential role in the establishment of nitrogen-fixing symbioses with Medicago plants, where it is involved in peptide import and in the addition of very-long-chain fatty acids (VLCFA) to lipid A of lipopolysaccharide (LPS). We investigated the role of BacA in Rhizobium species strain NGR234 by mutating the bacA gene. In the NGR234 bacA mutant, peptide import was impaired, but no effect on VLCFA addition was observed. More importantly, the symbiotic ability of the mutant was comparable to that of the wild type for a variety of legume species. Concurrently, an acpXL mutant of NGR234 was created and assayed. In rhizobia, AcpXL is a dedicated acyl carrier protein necessary for the addition of VLCFA to lipid A. LPS extracted from the NGR234 mutant lacked VLCFA, and this mutant was severely impaired in the ability to form functional nodules with the majority of legumes tested. Our work demonstrates the importance of VLCFA in the NGR234-legume symbiosis and also shows that the necessity of BacA for bacteroid differentiation is restricted to specific legume-Rhizobium interactions.
Desert dust seeds distant lands and waters
with minerals as well as micro-organisms raising the
question of whether this ancient phenomenon also
spreads pathogens across the globe. Severe dust
storms require strong winds blowing over land-masses
that are largely devoid of vegetation, effectively
limiting the scope for winds to raise pathogens into
the air. Nevertheless, changing patterns of land-use,
often driven by belligerency, result in refugees
spreading to areas that were previously deemed barely
habitable. With the help of the International Committee
of the Red Cross, a number of sand/dust samples
were collected from the Republic of Chad, some near
refugee camps, others further removed from human
influence. In parallel studies, we documented the
micro-organisms present in these samples and used a
number of the isolates here to test the effect of
environmental constraints on their ability to survive
intercontinental flight. We also added traditional
pathogens to the palette of microbes and tested the
effects of UV irradiation, desiccation and temperature
on survival of both bacteria and fungi. A clear trend
was obvious—those microbes that are coloured or able
to form conidia or spores (in other words, those that
are native to deserts) were well able to resist the
imposed stresses. On the other hand, most pathogens
were more sensitive to stresses than the environmental
isolates. Toxin production in two species of Aspergillus
was also investigated. Short-term desiccation
(simulating environmental conditions during intercontinental
travel) of sand amended with fungal spores
containing sterigmatocystin leads to increased mycotoxin
contents, but significant mycotoxin production
was only possible under growth-permissive conditions,
e.g. at higher humidity. It thus seems likely that an ever-decreasing fraction of the initial pathogen load
survives as the dust recedes from its desert source and
that those organisms that land on other continents are
highly enriched in desert dwellers.
Life at the atmosphere-lithosphere boundary is an ancient terrestrial niche that is sparsely covered by thin subaerial biofilms. The microbial inhabitants of these biofilms (a) have adapted to all types of terrestrial/subaerial stresses (e.g., desiccation, extreme temperatures, low nutrient availability, intense solar radiation), (b) interact with minerals that serve as both a dwelling and a source of mineral nutrients, and (c) provoke weathering of rocks and soil formation. Subaerial communities comprise heterotrophic and phototrophic microorganisms that support each other's lifestyle. Major lineages of eubacteria associated with the early colonization of land (e.g., Actinobacteria, Cyanobacteria) are present in these habitats along with eukaryotes such as microscopic green algae and ascomycetous fungi. The subaerial biofilm inhabitants have adapted to desiccation, solar radiation, and other environmental challenges by developing protective, melanized cell walls, assuming microcolonial architectures and symbiotic lifestyles. How these changes occurred, their significance in soil formation, and their potential as markers of climate change are discussed below.
Three novel Gram-positive, aerobic, actinobacterial strains, CF5/2T, CF5/1 and CF7/1, were isolated in 2007 during environmental screening of arid desert soil in the Sahara desert, Chad. Results from riboprinting, MALDI-TOF protein spectra and 16S rRNA sequence analysis confirmed that all three strains belonged to the same species. Phylogenetic analysis of 16S rRNA sequences with the strains' closest relatives indicated that they represented a distinct species. The three novel strains also shared a number of physiological and biochemical characteristics distinct from previously named Geodermatophilus species. The novel strains' peptidoglycan contained meso-diaminopimelic acid; their main phospholipids were phosphatidylcholine, phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol and a small amount of phosphatidylglycerol; MK-9(H4) was the dominant menaquinone. The major cellular fatty acids were the branched-chain saturated acids iso-C16:0 and iso-C15:0. Galactose was detected as diagnostic sugar. Based on these chemotaxonomic results, 16S rRNA gene sequence analysis and DNA–DNA hybridization between strain CF5/2T and the type strains of Geodermatophilus saharensis, Geodermatophilus arenarius, Geodermatophilus nigrescens, Geodermatophilus telluris and Geodermatophilus siccatus, the isolates CF5/2T, CF5/1 and CF7/1 are proposed to represent a novel species, Geodermatophilus tzadiensis, with type strain CF5/2T = DSM 45416 = MTCC 11411 and two reference strains, CF5/1 (DSM 45415) and CF7/1 (DSM 45420).
Cyclic-β-glucans (CβG) consist of cyclic homo-polymers of glucose that are present in the periplasmic space of many Gram-negative bacteria. A number of studies have demonstrated their importance for bacterial infection of plant and animal cells. In this study, a mutant of Rhizobium (Sinorhizobium) sp. strain NGR234 (NGR234) was generated in the cyclic glucan synthase (ndvB)-encoding gene. The great majority of CβG produced by wild-type NGR234 are negatively charged and substituted. The ndvB mutation abolished CβG biosynthesis. We found that, in NGR234, a functional ndvB gene is essential for hypo-osmotic adaptation and swimming, attachment to the roots, and efficient infection of Vigna unguiculata and Leucaena leucocephala.