Dissemination of Catabolic Plasmids among Desiccation-Tolerant Bacteria in Soil Microcosms

The dissemination of catabolic plasmids was compared to bioaugmentation by strain inoculation in microcosm experiments. When Rhodococcus erythropolis strain T902, bearing a plasmid with trichloroethene and isopropylbenzene degradation pathways, was used as the inoculum, no transconjugant was isolated but the strain remained in the soil. This plasmid had a narrow host range. Pseudomonas putida strain C8S3 was used as the inoculum in a second approach. It bore a broad host range conjugative plasmid harboring a natural transposon, RP4::Tn4371, responsible for biphenyl and 4-chlorobiphenyl degradation pathways. The inoculating population slowly decreased from its original level (10(6) colony-forming units [CFU]/g of dry soil) to approx 3 x 10(2) CFU/g of dry soil after 3 wk. Transconjugant populations degrading biphenyl appeared in constant humidity soil (up to 2 x 10(3) CFU/g) and desiccating soil (up to 10(4) CFU/g). The feasibility of plasmid dissemination as a bioaugmentation technique was demonstrated in desiccating soils. The ecologic significance of desiccation in bioaugmentation was demonstrated: it upset the microbial ecology and the development of transconjugants

Survival and preservation after freeze-drying process of thermoresistant acetic acid bacteria isolated from tropical products of Subsaharan Africa

Two thermoresistant acetic acid bacteria (TAAB) were previously isolated and selected for a sustainable development of vinegar fermentation in Subsaharan Africa. Their use as a starter culture in vinegar manufactures in such regions could reduce considerably water cooling expenses. For optimising biomass preservation, the effect of 20% w/w mannitol as cryoprotectant on the cells viability after freeze-drying process and during storage was evaluated. Results showed that freeze-dried cells could be conserved at 4 degrees C for at least 6 months without loss of viability. The main reasons were that cryoprotectant tends to lower the water activity (a(w)) and to maintain a temperature of product weaker than that of the glass transition temperature T-g. Furthermore, the heat resistance of freeze-dried cells during storage was all the more increased that strains were cryoprotected. In addition, intrinsically, an increase of saturated fatty acids with the temperature is the essential modification in the lipidome level of membrane cells when the fermentation occured at a temperature of 30 degrees C. Tolerance to heat during storage was significantly enhanced under such mechanisms. (c) 2006 Elsevier Ltd. All rights reserved

Différences morphologiques entre les sporidies aériennes et submergées du biofongicide Pseudozyma flocculosa CBS 16788

Pseudozyma flocculosa is a fungus very useful and highly efficient as a biocontrol agent against powdery mildew. The reproduction of this fungus occurs exclusively by asexual production of conidia or sporidia that are the most suitable form for agricultural use and seems to be the most resistant to storage conditions. Despite the advantages offered by P. flocculosa in biological control, the use of this fungus use remains largely limited compared to that of chemical fungicides, at least partly due to the difficulty to obtain sporidia resistant to adverse environmental stresses in submerged culture conditions. Under solid-state and submerged-state cultivation, P. flocculosa strain CBS 16788 produced different types of sporidia. The submerged sporidia (SS) appeared relatively uniform in size, which was 15, 4 ± 1,6 μm μm long, and 2,8 ± 0.8 μm wide. The aerial sporidia (AS) varied in shape and size, with a mean length of 8,2 ± 3 μm and width of 2,3 ± 0.6 μm. Under scanning and transmission electron microscopy, the cell wall of submerged sporidia was thinner than that of aerial spores, and the surface was smooth in contrast to the aerial sporidia that had a tendency to have verrucous, brittle surface characteristics. The thickness of the aerial sporidia wall is due to the presence of an outer layer rich in melanin. The sporidia germination was compared on YMPD (yeast extract, malt extract, soy peptone, dextrose and agar) coated coverslips. The aerial sporidia did not show germ tubes until 5 h of incubation, while the submerged sporidia showed many germ tubes after the same time. The resistance against the adverse environmental conditions in relation to the type of sporidia of P. flocculosa is discusse

Improving the growth and health of micropropagated strawberry by microbial inoculation

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Auto-fluorescence of cell wall of sporidia.

<p>A and B: AS recovered from 12-day-old cultures in solid-state fermentation. C and D: SS grown in liquid-state fermentation. Arrows show the sporidia hila.</p

SEM and TEM images of sporidia wall surface.

<p>A: aerial sporidia (AS) wall with ornament granules. B: submerged sporidia (SS) with a smooth wall surface. C: thick walls of AS, D: thin wall (white arrows) of SS with clear nucleus (N). E: thick walls of AS with an inner fibrous electron-lucent layer (SF) and an outer granular electron-dense layer (SD) showing a high affinity for the contrasting agents, F: hilum of sporogenesis (HS) of AS and G: Thin electron-lucent wall of SS.</p

SEM views of the three different populations of aerial sporidia.

<p>A: Large sporidia (P1), medium-sized sporidia (P2) with two scars (arrows) and small sporidia (P3) with one scar only. B: Flow cytometry analyses corresponding to the AS sample, revealed different morphotypic sub-populations (results were displayed on Forward Scatter Air/Forward Scatter Height (FSC-A/FSC-H) dot-plot on the basis of 40,000 events).</p

Fluorescence spectra obtained by SpectraMax M5 in the 300–440 nm wavelength range.

<p>MAS: melanin extracts from aerial sporidia, DOPA: sample containing a synthetic melanin (DOPA melanin) (0.5mg/ml), C-: reference sample without melanin. RFU: Relative fluorescence unit.</p

SEM images of <i>Pseudozyma flocculosa</i> sporidia.

<p>A: aerial sporidia produced by solid-state fermentation; B: submerged sporidia from the liquid-state fermentation.</p