42 research outputs found
Effect of bacterial inoculation, plant genotype and developmental stage on root-associated and endophytic bacterial communities in potato (Solanum tuberosum)
No full textBeneficial bacteria interact with plants by colonizing the rhizosphere and roots followed by further spread through the inner tissues, resulting in endophytic colonization. The major factors contributing to these interactions are not always well understood for most bacterial and plant species. It is believed that specific bacterial functions are required for plant colonization, but also from the plant side specific features are needed, such as plant genotype (cultivar) and developmental stage. Via multivariate analysis we present a quantification of the roles of these components on the composition of root-associated and endophytic bacterial communities in potato plants, by weighing the effects of bacterial inoculation, plant genotype and developmental stage. Spontaneous rifampicin resistant mutants of two bacterial endophytes, Paenibacillus sp. strain E119 and Methylobacterium mesophilicum strain SR1.6/6, were introduced into potato plants of three different cultivars (Eersteling, Robijn and Karnico). Densities of both strains in, or attached to potato plants were measured by selective plating, while the effects of bacterial inoculation, plant genotype and developmental stage on the composition of bacterial, Alphaproteobacterial and Paenibacillus species were determined by PCR-denaturing gradient gel-electrophoresis (DGGE). Multivariate analyses revealed that the composition of bacterial communities was mainly driven by cultivar type and plant developmental stage, while Alphaproteobacterial and Paenibacillus communities were mainly influenced by bacterial inoculation. These results are important for better understanding the effects of bacterial inoculations to plants and their possible effects on the indigenous bacterial communities in relation with other plant factors such as genotype and growth stage
The low-temperature induced viable-but-nonculturable state affects the virulence of Ralstonia solanacearum biovar 2
No full textvan Overbeek. L. S.. Bergervoet. J. H. W.. Jacobs, F. H. H.. and van Elsas. J. D. 2004. The low-ternperature-induced viable-but-nonculturable state 2. Phytopathology affects the virulence of Ralstonia solanacearum biovar 94:463-469. The physiology and virulence of Ralstonia solanacerum biovar 2 strain 1609. kept in water at 4 and 20degreesC, were studied. At 20degreesC. total cell and plate count (colony forming units: CFU) numbers were similar, between log 5.03 and log 5.55 CFU,and log 5.03 and log 5.51 cells per ml. at days 0 and 132. respectively. However, CFU in the Cultures kept at 4degreesC dropped from log 6.78 CFU/ml at day 0 to below detection after 84 days. The presence of catalase in the agar resulted in higher CFU. and at day 84. log, 1.95 CFU/ml still was detectable. No colonies were observed at day 125. The presence of viable-but-nonculturable (VBNC) cells in the 4degreesC Cultures was confirmed using SYTO9 viability staining. Viable Cell numbers were log 1.77 higher than CFU on plates with catalase. At day 84 and after 125 days, log 3.70 viable cells per ml still were I present. Shifts in subpopulations differing in viability were found by flow cytometric sorting of 4degreesC-treated cells stained with SYTO9 (healthy) and propidium iodide (PI, compromised). The SYTO9-stained cell fractions dropped from 99 to 39%, and the PI-stained fractions increased from 0.7 to 33.3% between days 0 and 125. At 20degreesC. the SYTO9-stained fraction remained stable at 99% until day 132, SYTO9-stained cells sorted from 4degreesC Cultures at day 100 were injected into tomato plants. Upon incubation for 30 days, these plants did not show wilting. However. more than log 4.19 CFU and log 8.17 cells were recovered from these plants. Cells from colonies isolated from the nonwilted plants did not regain their virulence as demonstrated by Subsequent injection into several mew, sets of tomato plants. Cells from 4degreesC cultures injected at day 125 were not able to cause wilting of, or proliferate in, tomato plants. The threat posed by VBNC R. solanacearum cells upon incubation at 4degreesC was thus ephemeral because cells lost their capacity to cause disease after 125 days
The low-temperature-induced viable-but-nonculturable state affects the virulence of Ralstonia solanacearum biovar 2
No full textvan Overbeek. L. S.. Bergervoet. J. H. W.. Jacobs, F. H. H.. and van Elsas. J. D. 2004. The low-ternperature-induced viable-but-nonculturable state 2. Phytopathology affects the virulence of Ralstonia solanacearum biovar 94:463-469.The physiology and virulence of Ralstonia solanacerum biovar 2 strain 1609. kept in water at 4 and 20degreesC, were studied. At 20degreesC. total cell and plate count (colony forming units: CFU) numbers were similar, between log 5.03 and log 5.55 CFU,and log 5.03 and log 5.51 cells per ml. at days 0 and 132. respectively. However, CFU in the Cultures kept at 4degreesC dropped from log 6.78 CFU/ml at day 0 to below detection after 84 days. The presence of catalase in the agar resulted in higher CFU. and at day 84. log, 1.95 CFU/ml still was detectable. No colonies were observed at day 125. The presence of viable-but-nonculturable (VBNC) cells in the 4degreesC Cultures was confirmed using SYTO9 viability staining. Viable Cell numbers were log 1.77 higher than CFU on plates with catalase. At day 84 and after 125 days, log 3.70 viable cells per ml still were I present. Shifts in subpopulations differing in viability were found by flow cytometric sorting of 4degreesC-treated cells stained with SYTO9 (healthy) and propidium iodide (PI, compromised). The SYTO9-stained cell fractions dropped from 99 to 39%, and the PI-stained fractions increased from 0.7 to 33.3% between days 0 and 125. At 20degreesC. the SYTO9-stained fraction remained stable at 99% until day 132, SYTO9-stained cells sorted from 4degreesC Cultures at day 100 were injected into tomato plants. Upon incubation for 30 days, these plants did not show wilting. However. more than log 4.19 CFU and log 8.17 cells were recovered from these plants. Cells from colonies isolated from the nonwilted plants did not regain their virulence as demonstrated by Subsequent injection into several mew, sets of tomato plants. Cells from 4degreesC cultures injected at day 125 were not able to cause wilting of, or proliferate in, tomato plants. The threat posed by VBNC R. solanacearum cells upon incubation at 4degreesC was thus ephemeral because cells lost their capacity to cause disease after 125 days.</p
Cultivation of hitherto-uncultured bacteria belonging to the Verrucomicrobia subdivision 1 from the potato (Solanum tuberosum L.) rhizosphere
No full textThe role of dominant bacterial groups in the plant rhizosphere, e.g., those belonging to the phyla Acidobacteria and Verrucomicrobia, has, so far, not been elucidated, and this is mainly due to the lack of culturable representatives. This study aimed to isolate hitherto-uncultured bacteria from the potato rhizosphere by a combination of cultivation approaches. An agar medium low in carbon availability (oligotrophic agar medium) and either amended with potato root exudates or catalase or left unamended was used with the aim to improve the culturability of bacteria from the potato rhizosphere. The colony forming unit numbers based on colonies and microcolonies were compared with microscopically determined fluorescence-stained cell numbers. Taxonomical diversity of the colonies was compared with that of library clones made from rhizosphere DNA, on the basis of 16S rRNA gene comparisons. The oligotrophic media amended or not with catalase or rhizosphere extract recovered up to 33.6% of the total bacterial numbers, at least seven times more than the recovery observed on R2A. Four hitherto-uncultured Verrucomicrobia subdivision 1 representatives were recovered on agar, but representatives of this group were not found in the clone library. The use of oligotrophic medium and its modifications enabled the growth of colony numbers, exceeding those on classical agar media. Also, it led to the isolation of hitherto-uncultured bacteria from the potato rhizosphere. Further improvement in cultivation will certainly result in the recovery of other as-yet-unexplored bacteria from the rhizosphere, making these groups accessible for further investigation, e.g., with respect to their possible interactions with plants
Assessment of Rice Root-Associated Bacteria
No full textDespite their importance, little is known about the putative interactions between rice plants and their associated bacteria. On the basis of plant-extracted DNA, molecular tools such as bacterium-specific PCR have been employed to assess the occurrence and prevalence of rice-associated bacteria. Here, we examine the coverage and usefulness of a well-consolidated primer (799f) used in these efforts. In addition, we discuss a recent study (Hardoim PR, Andreote FD, Reinhold-Hurek B, Sessitsch A, van Overbeek LS, van Elsas JD. Rice root-associated bacteria: insights into community structures across 10 cultivars. FEMS Microbiol Ecol 2011;77:154-164) that addressed the influence of the factors plant genotype, soil type, and nutrient use efficiency on the bacterial communities at the rice roots. In particular, total bacteria, Alpha- and Betaproteobacteria, Pseudomonas, and Actinobacteria communities were targeted. In silico analyses revealed that the great majority of plant-associated bacterial taxa are covered by primer 799f. Thus, a test for bacterial detection on the basis of primer pair 799f-1492r revealed true bacterial PCR-based denaturing gradient gel electrophoresis (PCR-DGGE) profiles, avoiding contamination with plastid DNA. In agreement with data presented in Chapter 18, we observed many conspicuous bands that occurred as commonalities across 10 rice cultivars. In contrast, the prevalence of cultivar-specific bands was limited. The bacterial communities associated with the rice roots were largely influenced by rice genotype, with Oryza sativa subspecies indica tending to select similar bacterial communities, whereas subspecies japonica and aromatica selected divergent community structures. The study demonstrated the essentiality of primer 799f, used in combination with primer 1492r, for the investigation of the rice-associated bacterial community.</p
Developmental trajectories and predictors of adolescents' use of sexually explicit Internet material
No full textIn deze studie onderzochten we of er verschillende ontwikkelingstrajecten bestaan in het gebruik van seksueel expliciet internetmateriaal (SEIM) van adolescenten en welke factoren voorspellend zijn voor deze trajecten. Een combinatie van latente klasseanalyse met groeicurves en multinominale regressieanalyse werd toegepast op 4-wave longitudinale gegevens van 441 adolescenten. Onder jongens waren vier ontwikkelingstrajecten in SEIM-gebruik te onderscheiden: ‘Stabiel geen/weinig gebruik’, ‘Sterk toenemend gebruik’, ‘Licht afnemend gebruik’ en ‘Stabiel veel gebruik’. Voor meisjes werd slechts één traject ‘Stabiel geen/weinig gebruik’ gevonden. Jongens in trajecten gekenmerkt door een hogere mate van SEIM-gebruik bleken bij de aanvang van de studie meer seksueel permissief en seksueel geïnteresseerd, zij communiceerden vaker met hun ouders over seks, konden vaker in privacy internetten en hadden een hogere realiteitsperceptie ten aanzien van seksuele media vergeleken met jongens in het traject ‘Stabiel geen/weinig gebruik’
Model Plants for Studying the Interaction between Methylobacterium mesophilicum and Xylella fastidiosa
No full textOver the last few years, endophytic bacterial communities associated with citrus have been studied as key components interacting with Xylella fastidiosa. In this study, we investigated the possible interaction between the citrus endophyte Methylobacterium mesophilicum SR1.6/6 and X. fastidiosa in model plants such as Catharanthus roseus (Madagaskar periwinkle) and Nicotiana clevelandii (Clevelands tobacco). The aim of this study was to establish the fate of M. mesophilicum SR1.6/6 after inoculation of C. roseus and N. clevelandii plants, using PCR-DGGE (polymerase chain reaction - denaturing gradient gel electrophoresis) and plating techniques. Shifts in the indigenous endophytic bacterial communities were observed in plants inoculated with strain SR1.6/6, using specific primers targeting ¿- and ß-Proteobacteria. Cells of strain SR1.6/6 were observed in a biofilm structure on the root and hypocotyl surfaces of in vitro seedlings inoculated with M. mesophilicum SR1.6/6. This emphasizes the importance of these tissues as main points of entrance for this organism. The results showed that C. roseus and N. clevelandii could be used as model plants to study the interaction between M. mesophilicum and X. fastidiosa.Key words: endophytic, Methylobacterium, model plants, DGG
Prevalence and characterization of ESBL- and AmpC-producing Enterobacteriaceae on retail vegetables
No full textIn total 1216 vegetables obtained from Dutch stores during 2012 and 2013 were analysed to determine the prevalence of 3rd-generation cephalosporin (3GC) resistant bacteria on soil-grown fresh produce possibly consumed raw. Vegetables grown conventionally and organically, from Dutch as well as foreign origin were compared. Included were the following vegetable types; blanched celery (n=192), bunched carrots (n=190), butterhead lettuce (n=137), chicory (n=96), endive (n=188), iceberg lettuce (n=193) and radish (n=120). Overall, 3GC-resistant Enterobacteriaceae were detected on 5.2% of vegetables. Based on primary habitat and mechanism of 3GC-resistance, these bacteria could be divided into four groups: ESBL-producing faecal species (Escherichia coli, Enterobacter spp.), AmpC-producing faecal species (Citrobacter freundii, Enterobacter spp.), ESBL-producing environmental species (Pantoea spp., Rahnella aquatilis, Serratia fonticola), and AmpC-producing environmental species (Cedecca spp., Hafnia alvei, Pantoea spp., Serratia plymuthica), which were detected on 0.8%, 1.2%, 2.6% and 0.4% of the vegetables analysed, respectively. Contamination with faecal 3GC-resistant bacteria was most frequently observed in root and bulb vegetables (average prevalence 4.4%), and less frequently in stem vegetables (prevalence 1.6%) and leafy greens (average prevalence 0.6%). In Dutch stores, only four of the included vegetable types (blanched celery, bunched carrots, endive, iceberg lettuce) were available in all four possible variants: Dutch/conventional, Dutch/organic, foreign/conventional, foreign/organic. With respect to these vegetable types, no statistically significant difference was observed in prevalence of 3GC-resistant Enterobacteriaceae between country of origin or cultivation type (5.2%, 5.7%, 5.7% and 3.3%, respectively). Vegetables consumed raw may be a source of dissemination of 3GC-resistant Enterobacteriaceae and their resistance genes to humans. The magnitude of the associated public health risk presumably depends on the types of bacteria that are ingested, i.e., faecal or environmental species, and may therefore be higher for root and bulb vegetables compared to leafy greens
The 125th anniversary of the first postulation of the soil origin of endophytic bacteria – a tribute to M.L.V. Galippe
No full textIn both managed and natural ecosystems, a wide range of various non-nodulating bacteria can thrive as endophytes in the plant interior, and some can be beneficial to their hosts (Hallmann and Berg 2007; Reinhold-Hurek and Hurek 2011). Colonizationmechanisms, the ecology and functioning of these endophytic bacteria as well as their interactions with plants have been investigated (Hardoim et al. 2008; Compant et al. 2010). Although the source of colonization can also be the spermosphere, anthosphere, caulosphere, and the phyllosphere,most endophytic bacteria are derived from the soil environment (Hallmann and Berg 2007; Compant et al. 2010)
