Rhizosphere bacterial communities associated with disease suppressiveness stages of take-all decline in wheat monoculture.

The decline of take-all disease (Gaeumannomyces graminis var. tritici), which may take place during wheat monocropping, involves plant-protecting, root-colonizing microorganisms. So far, however, most work has focused on antagonistic fluorescent pseudomonads. Our objective was to assess the changes in rhizobacterial community composition during take-all decline of field-grown wheat. The study was based on the development and utilization of a taxonomic 16S rRNA-based microarray of 575 probes, coupled with cloning-sequencing and quantitative PCR. Plots from one experimental field grown with wheat for 1 yr (low level of disease), 5 yr (high level of disease) or 10 yr (low level of disease, suppressiveness reached) were used. Microarray data discriminated between the three stages. The outbreak stage (5 yr) was mainly characterized by the prevalence of Proteobacteria, notably Pseudomonas (Gammaproteobacteria), Nitrosospira (Betaproteobacteria), Rhizobacteriaceae, Sphingomonadaceae, Phyllobacteriaceae (Alphaproteobacteria), as well as Bacteroidetes and Verrucomicrobia. By contrast, suppressiveness (10 yr) correlated with the prevalence of a broader range of taxa, which belonged mainly to Acidobacteria, Planctomycetes, Nitrospira, Chloroflexi, Alphaproteobacteria (notably Azospirillum) and Firmicutes (notably Thermoanaerobacter). In conclusion, take-all decline correlated with multiple changes in rhizobacterial community composition, far beyond the sole case of pseudomonads.

Modification of spatial distribution of 2,4-dichlorophenoxyacetic acid degrader microhabitats during growth in soil columns.

Bacterial processes in soil, including biodegradation, require contact between bacteria and substrates. Knowledge of the three-dimensional spatial distribution of bacteria at the microscale is necessary to understand and predict such processes. Using a soil microsampling strategy combined with a mathematical spatial analysis, we studied the spatial distribution of 2,4-dichlorophenoxyacetic acid (2,4-D) degrader microhabitats as a function of 2,4-D degrader abundance. Soil columns that allowed natural flow were percolated with 2,4-D to increase the 2,4-D degrader abundance. Hundreds of soil microsamples (minimum diameter, 125 microm) were collected and transferred to culture medium to check for the presence of 2,4-D degraders. Spatial distributions of bacterial microhabitats were characterized by determining the average size of colonized soil patches and the average number of patches per gram of soil. The spatial distribution of 2,4-D degrader microhabitats was not affected by water flow, but there was an overall increase in colonized patch sizes after 2,4-D amendment; colonized microsamples were dispersed in the soil at low 2,4-D degrader densities and clustered in patches that were more than 0.5 mm in diameter at higher densities. During growth, spreading of 2,4-D degraders within the soil and an increase in 2,4-D degradation were observed. We hypothesized that spreading of the bacteria increased the probability of encounters with 2,4-D and resulted in better interception of the degradable substrate. This work showed that characterization of bacterial microscale spatial distribution is relevant to microbial ecology studies. It improved quantitative bacterial microhabitat description and suggested that sporadic movement of cells occurs. Furthermore, it offered perspectives for linking microbial function to the soil physicochemical environment.

Relationship between spatial and genetic distance in Agrobacterium spp. in 1 cubic centimeter of soil.

The spatial and genetic unit of bacterial population structure is the clone. Surprisingly, very little is known about the spread of a clone (spatial distance between clonally related bacteria) and the relationship between spatial distance and genetic distance, especially at very short scale (microhabitat scale), where cell division takes place. Agrobacterium spp. Biovar 1 was chosen because it is a soil bacterial taxon easy to isolate. A total of 865 microsamples 500 microm in diameter were sampled with spatial coordinates in 1 cm(3) of undisturbed soil. The 55 isolates obtained yielded 42 ribotypes, covering three genomic species based on amplified ribosomal DNA restriction analysis (ARDRA) of the intergenic spacer 16S-23S, seven of which contained two to six isolates. These clonemates (identical ARDRA patterns) could be found in the same microsample or 1 cm apart. The genetic diversity did not change with distance, indicating the same habitat variability across the cube. The mixing of ribotypes, as assessed by the spatial position of clonemates, corresponded to an overlapping of clones. Although the population probably was in a recession stage in the cube (10(3) agrobacteria g(-1)), a high genetic diversity was maintained. In two independent microsamples (500 microm in diameter) at the invasion stage, the average genetic diversity was at the same level as in the cube. Quantification of the microdiversity landscape will help to estimate the probability of encounter between bacteria under realistic natural conditions and to set appropriate sampling strategies for population genetic analysis.

Combined use of a specific probe and PCAT medium to study Burkholderia in soil.

Due to its pathogenic traits and agricultural benefits, there is some challenge in detecting Burkholderia in the soil environment. In this perspective, an existing semi-selective medium, (PCAT), was combined with a Burkholderia specific molecular probe. Using the complete 16S rRNA sequences of all available Burkholderia species type strains, we selected the following sequence: 5'-ACCCTCTGTTCCGACCATTGTATGA-3'. The probe was validated against GenBank sequences, with dot blots and colony hybridization tests. A diversity study of all strains growing on a PCAT plate after plating a soil dilution (75 strains) was carried out with ARDRA analysis and colony hybridization tests. All the hybridizing strains belonged to genus Burkholderia. The major type of non-hybridizing isolates belonged to Pseudomonas (16S rRNA sequencing). Both tools were combined to compare the Burkholderia populations in a rhizosphere (maize) and a non-rhizosphere soil. Based on hybridizing PCAT isolates, we were able to show an increase in Burkholderia populations in the maize rhizosphere. This genus represented 2% and 16% of the total cultivable microflora in the non-rhizosphere and rhizosphere soils, respectively. Although PCAT was shown not to be appropriate to routinely enumerate Burkholderia populations in soil, it allowed environmental investigations at the genus level, when combined with a molecular specific probe.

High-resolution phylogenetic analysis of NO2--oxidizing Nitrobacter species using the rrs-rrl IGS sequence and rrl genes.

A high-resolution phylogenetic analysis of Nitrobacter strains and their neighbours was made using the rrs-rrl intergenic spacer sequence and the hypervariable part of the rrl gene. The phylogenetic tree obtained was consistent with that which was obtained previously but was much more discriminating, permitting the design of genus-specific primers.

Microscale diversity of the genus Nitrobacter in soil on the basis of analysis of genes encoding rRNA.

We looked at the diversity of [NO(2)](-) oxidizers at field scale by examining isolates at clump scale and in microsamples of soil (diameter, 50 microm). The genetic distances (as determined by amplified ribosomal DNA restriction analysis performed with Nitrobacter-specific primers) in a small clump of soil were as large as those between reference strains from large geographical areas. Diversity in individual microsamples was shown by serotyping.

Delayed NH3 and N2 O uptake by maize leaves.

15 N was used to give evidence of NH3 and N2 O absorption by maize leaves. A short-term labelling method (90 min) was chosen with high NH3 concentration (40 µ1 1-1 ) to assess uptake mechanisms. Two initial entry pathways were suggested for NH3 : fast uptake with immediate metabolism and fast storage with progressive metabolism. A storage compartment delayed NH3 absorption after exposure. Similar mechanisms might be involved in N2 O uptake.

[Occupational medicine otorhinolaryngologic analysis of employees of a district socialist agricultural facility within the scope of expanded public mass roentgen screening]. / Arbeitsmedizinisch-otorhinolaryngologische Analyse Beschäftigter der sozialistischen Landwirtschaft eines Kreises im Rahmen einer erweiterten Volksröntgenreihenuntersuchung.

For the purpose of registration of subjective complaints and pathological changes of the respiratory tract 1,023 employees of socialist agriculture were additionally examined in connection with an expanded x-ray-screening from the points of view of otorhinolaryngology and industrial medicine. The employees in industrial livestock breeding, especially in industrial poultry breeding, turned out to be the group with the most frequent complaints and pathological findings in the respiratory tract. The findings suggest, that chronic, non-specific changes develop on the basis of the summation of several noxious factors in industrial live-stock breeding. In conclusion of the examination recommendations for the optimization of the working conditions for employees in industrial livestock breeding are given from the points of view of industrial hygiene and occupational medicine.

[Quantitative determination of proteins in the contents of pseudocysts of the maxillary sinus]. / Quantitative Bestimmung von Proteinen im Inhalt von Pseudozysten des Sinus maxillaris.

The factors C 3c and C 4 of the complement system, the protease inhibitor alpha-1-antitrypsin (AAT) as well as the immunoglobulins IgA, IgG, IgM in the fluid of cysts of maxillary sinus were determined by means of single radial immunodiffusion. The concentration of these proteins was compared with the concentration in the serum obtained simultaneously. A decrease of C 3c, C 4 and AAT and an increase of IgA and IgG in fluid are indicators of active participation of the mucosa in defence processes.

[A sino-pulmonary syndrome in pneumonologic practice--alpha 1-antitrypsin deficiency in emphysema patients]. / Das Sino-Pulmonale-Syndrom in der Praxis der Pneumonologie--alpha 1-Antitrypsin-Mangel bei Emphysemkranken.

An illness in the arial of the paranasal sinuses was found in 43% of 120 persons with obstructive emphysema. In 40 cases the alpha 1-antitrypsin-concentration in serum was determined. The average of 1.73 +/- 0.19 g/1 was clearly lower than the 2.25 g/1 of normal-series. The clinical-therapeutic consequences and also the possible importance in work-medical examinations or expert-opinions of adequate occupational diseases will be pointed out.