Effect of long-term vineyard monoculture on rhizosphere populations of pseudomonads carrying the antimicrobial biosynthetic genes phlD and/or hcnAB

The impact of repeated culture of perennial plants (i.e. in long-term monoculture) on the ecology of plant-beneficial bacteria is unknown. Here, the influence of extremely long-term monocultures of grapevine (up to 1603 years) on rhizosphere populations of fluorescent pseudomonads carrying the biosynthetic genes phlD for 2,4-diacetylphloroglucinol and/or hcnAB for hydrogen cyanide was determined. Soils from long-term and adjacent short-term monoculture vineyards (or brushland) in four regions of Switzerland were baited with grapevine or tobacco plantlets, and rhizosphere pseudomonads were studied by most probable number (MPN)-PCR. Higher numbers and percentages of phlD+ and of hcnAB+ rhizosphere pseudomonads were detected on using soil from long-term vineyards. On focusing on phlD, restriction fragment length polymorphism profiling of the last phlD-positive MPN wells revealed seven phlD alleles (three exclusively on tobacco, thereof two new ones). Higher numbers of phlD alleles coincided with a lower prevalence of the allele displayed by the well-studied biocontrol strain Pseudomonas fluorescens F113. The prevalence of this allele was 35% for tobacco in long-term monoculture soils vs. >60% in the other three cases. We conclude that soils from long-term grapevine monocultures represent an untapped resource for isolating novel biocontrol Pseudomonas strains when tobacco is used as bai

Antagonistic interactions between filamentous heterotrophs and the cyanobacterium Nostoc muscorum

Background: Little is known about interactions between filamentous heterotrophs and filamentous cyanobacteria. Here, interactions between the filamentous heterotrophic bacteria Fibrella aestuarina (strain BUZ 2) and Fibrisoma limi (BUZ 3) with an axenic strain of the autotrophic filamentous cyanobacterium Nostoc muscorum (SAG 25.82) were studied in mixed cultures under nutrient rich (carbon source present in medium) and poor (carbon source absent in medium) conditions. Findings: F. aestuarina BUZ 2 significantly reduced the cyanobacterial population whereas F. limi BUZ 3 did not. Physical contact between heterotrophs and autotroph was observed and the cyanobacterial cells showed some level of damage and lysis. Therefore, either contact lysis or entrapment with production of extracellular compounds in close vicinity of host cells could be considered as potential modes of action. The supernatants from pure heterotrophic cultures did not have an effect on Nostoc cultures. However, supernatant from mixed cultures of BUZ 2 and Nostoc had a negative effect on cyanobacterial growth, indicating that the lytic compounds were only produced in the presence of Nostoc. The growth and survival of tested heterotrophs was enhanced by the presence of Nostoc or its metabolites, suggesting that the heterotrophs could utilize the autotrophs and its products as a nutrient source. However, the autotroph could withstand and out-compete the heterotrophs under nutrient poor conditions. Conclusions: Our results suggest that the nutrients in cultivation media, which boost or reduce the number of heterotrophs, were the important factor influencing the outcome of the interplay between filamentous heterotrophs and autotrophs. For better understanding of these interactions, additional research is needed. In particular, it is necessary to elucidate the mode of action for lysis by heterotrophs, and the possible defense mechanisms of the autotrophs

Emergent multicellular life cycles in filamentous bacteria owing to density-dependent population dynamics

Filamentous bacteria are the oldest and simplest known multicellular life forms. By using computer simulations and experiments that address cell division in a filamentous context, we investigate some of the ecological factors that can lead to the emergence of a multicellular life cycle in filamentous life forms. The model predicts that if cell division and death rates are dependent on the density of cells in a population, a predictable cycle between short and long filament lengths is produced. During exponential growth, there will be a predominance of multicellular filaments, while at carrying capacity, the population converges to a predominance of short filaments and single cells. Model predictions are experimentally tested and confirmed in cultures of heterotrophic and phototrophic bacterial species. Furthermore, by developing a formulation of generation time in bacterial populations, it is shown that changes in generation time can alter length distributions. The theory predicts that given the same population growth curve and fitness, species with longer generation times have longer filaments during comparable population growth phases. Characterization of the environmental dependence of morphological properties such as length, and the number of cells per filament, helps in understanding the pre-existing conditions for the evolution of developmental cycles in simple multicellular organisms. Moreover, the theoretical prediction that strains with the same fitness can exhibit different lengths at comparable growth phases has important implications. It demonstrates that differences in fitness attributed to morphology are not the sole explanation for the evolution of life cycles dominated by multicellularity

Effect of long-term vineyard monoculture on rhizosphere populations of pseudomonads carrying the antimicrobial biosynthetic genes phlD and/or hcnAB

ISSN:0168-6496ISSN:1574-694

Fibrella aestuarina gen. nov., sp. nov., a filamentous bacterium of the family Cytophagaceae isolated from a tidal flat, and emended description of the genus Rudanella Weon et al. 2008

A gram-staining-negative, pink bacterium designated strain BUZ 2T, was isolated from coastal mud from the North Sea (Fedderwardersiel, Germany). Cells were rod-shaped and able to form multicellular filaments. Growth after 7 days was observed at 10-40 degrees C, at pH 6-8 and with 0-0.5 % NaCl. The phylogenetic tree based on 16S rRNA gene sequences indicated that strain BUZ 2T is a member of the family Cytophagaceae, its closest neighbours being Rudanella lutea 5715S-11T, Spirosoma linguale LMG 10896T and Spirosoma panaciterrae Gsoil 1519T (87.8 %, 86.4 % and 86.1 % 16S rRNA gene similarity, respectively). The major fatty acids were summed feature 3 (comprising C16:1omega7c and/or isoC15:0 2-OH), C16:1omega5c and isoC15:0. The predominant respiratory quinone was MK-7 and the major polar lipids were phosphatidylethanolamine and several unidentified aminophospholipids. The G+C content was 56.5 mol%. On the basis of this polyphasic study, we propose that strain BUZ 2T represents a novel genus and species, for which the name Fibrella aestuarina gen. nov., sp. nov. is proposed. The type strain is BUZ 2T (= DSMZ 22563T = CCUG 58136T). An emended description of the genus Rudanella is also proposed

Overview of carbon assimilation profiles for all strains.

<p>Profile of the strains presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065059#pone-0065059-g002" target="_blank">Figure 2</a> (four-tiered graph), listing the carbon substrates (BIOLOG 1) used by each isolate or equivalent class of bacterial isolates. The ordering of strains and the carbon substrates in the table was modified to match the graph in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065059#pone-0065059-g002" target="_blank">Figure 2</a>.</p

Enzyme profile analysis.

<p>(A) Principal component analysis based on Hamming distance of enzymatic profiles determined using API ZYM strips. The first two principal components explain 87% of the variance of the data. (B) Four-tiered graph linking bacteria and enzyme profiles. Links are to be followed from left to right. Bacteria showing similar enzymatic profiles (E1, E2, E3 E4, E5 and E6) group together. The number of enzymes produced by each equivalence class of bacteria and the number of bacteria classes that produce a certain enzyme are indicated at the right of the corresponding bacterial equivalence class and at the left of the corresponding enzyme equivalence class, respectively. The vertical positions of the bacterial classes correspond to their coefficient in the first principal component of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065059#pone-0065059-g001" target="_blank">Figure 1A</a>, though vertically-overlapping classes are separated from each other by a small distance to allow for an easy reading of the graph. Distances between the non-overlapping classes are preserved.</p

Carbon assimilation profile analysis.

<p>(A) Principal component analysis based on Hamming distance of carbon assimilation profiles measured with Biolog PM1. The first two principal components explain 84% of the variance of the data. (B) Four-tiered graph linking bacteria and carbon assimilation profiles. Bacteria showing similar carbon assimilation profiles group together (C1, C2, C3, C4, C5 and C6). This graph is constructed the same way as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065059#pone-0065059-g001" target="_blank">Figure 1B</a>. Here no two bacteria show identical profiles, hence they form single-member equivalence classes (each strain is linked to a unique node in the isolate equivalence class layer, second from the left). The vertical positions of the bacteria correspond to their coefficient in the first principal component of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065059#pone-0065059-g002" target="_blank">Figure 2A</a>, though vertically-overlapping bacteria are separated from each other by a small distance. Distances between the non-overlapping classes are preserved.</p