Miroslav Svercel

Candidatus Syngnamydia Venezia, a Novel Member of the Phylum Chlamydiae from the Broad Nosed Pipefish, Syngnathus typhle

Chlamydia are obligate intracellular bacteria and important pathogens of humans and animals. Chlamydia-related bacteria are also major fish pathogens, infecting epithelial cells of the gills and skin to cause the disease epitheliocystis. Given the wide distribution, ancient origins and spectacular diversity of bony fishes, this group offers a rich resource for the identification and isolation of novel Chlamydia. The broad-nosed pipefish (Syngnathus typhle) is a widely distributed and genetically diverse temperate fish species, susceptible to epitheliocystis across much of its range. We describe here a new bacterial species, Candidatus Syngnamydia venezia; epitheliocystis agent of S. typhle and close relative to other chlamydial pathogens which are known to infect diverse hosts ranging from invertebrates to humans.

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 2(T), 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 °C, at pH 6-8 and with 0-0.5 % NaCl. The phylogenetic tree based on 16S rRNA gene sequences indicated that strain BUZ 2(T) is a member of the family Cytophagaceae, its closest neighbours being Rudanella lutea 5715S-11(T), Spirosoma linguale LMG 10896(T) and Spirosoma panaciterrae Gsoil 1519(T) (87.8, 86.4 and 86.1 % sequence similarity, respectively). The major fatty acids were summed feature 3 (comprising C(16 : 1)ω7c and/or iso-C(15 : 0) 2-OH), C(16 : 1)ω5c and iso-C(15 : 0). The predominant respiratory quinone was MK-7 and the major polar lipids were phosphatidylethanolamine and several unidentified aminophospholipids. The DNA G+C content was 56.5 mol%. On the basis of this polyphasic study, we propose that strain BUZ 2(T) represents a novel genus and species, for which the name Fibrella aestuarina gen. nov., sp. nov. is proposed. The type strain of Fibrella aestuarina is BUZ 2(T) (=DSM 22563(T) =CCUG 58136(T)). An emended description of the genus Rudanella is also proposed.

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

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 bait.

Interspecies variation in survival and growth of filamentous heterotrophic bacteria in response to UVC radiation

Ultraviolet radiation is an important environmental constraint on the evolution of life. In addition to its harmful effects, ultraviolet radiation plays an important role in generating genetic polymorphisms and acting as a selective agent. Understanding how prokaryotes cope with high radiation can give insights on the evolution of life on Earth. Four representative filamentous bacteria from the family Cytophagaceae with different pigmentation were selected and exposed to different doses of UVC radiation (15-32,400Jm(-2)). The effect of UVC radiation on bacterial survival, growth and morphology were investigated. Results showed high survival in response to UVC for Rudanella lutea and Fibrisoma limi, whereas low survival was observed for Fibrella aestuarina and Spirosoma linguale. S. linguale showed slow growth recovery after ultraviolet exposure, R. lutea and F. limi showed intermediate growth recovery, while F. aestuarina had the fastest recovery among the four tested bacteria. In terms of survival, S. linguale was the most sensitive bacterium whereas R. lutea and F. limi were better at coping with UVC stress. The latter two resumed growth even after 2h exposure (∼10,800Jm(-2)). Additionally, the ability to form multicellular filaments after exposure was tested using two bacteria: one representative of the high (R. lutea) and one of the low (F. aestuarina) survival rates. The ability to elongate filaments due to cell division was preserved but modified. In R. lutea 10min exposure reduced the average filament length. The opposite was observed in F. aestuarina, where the 5 and 10min exposures increased the average filament length. R. lutea and F. limi are potential candidates for further research into survival and resistance to ultraviolet radiation stress.

Antagonistic interactions between filamentous heterotrophs and the cyanobacterium Nostoc muscorum

BackgroundLittle 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.FindingsF. 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.ConclusionsOur 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.

Use of a Four-Tiered Graph to Parse the Factors Leading to Phenotypic Clustering in Bacteria: A Case Study Based on Samples from the Aletsch Glacier

An understanding of bacterial diversity and evolution in any environment requires knowledge of phenotypic diversity. In this study, the underlying factors leading to phenotypic clustering were analyzed and interpreted using a novel approach based on a four-tiered graph. Bacterial isolates were organized into equivalence classes based on their phenotypic profile. Likewise, phenotypes were organized in equivalence classes based on the bacteria that manifest them. The linking of these equivalence classes in a four-tiered graph allowed for a quick visual identification of the phenotypic measurements leading to the clustering patterns deduced from principal component analyses. For evaluation of the method, we investigated phenotypic variation in enzyme production and carbon assimilation of members of the genera Pseudomonas and Serratia, isolated from the Aletsch Glacier in Switzerland. The analysis indicates that the genera isolated produce at least six common enzymes and can exploit a wide range of carbon resources, though some specialist species within the pseudomonads were also observed. We further found that pairwise distances between enzyme profiles strongly correlate with distances based on carbon profiles. However, phenotypic distances weakly correlate with phylogenetic distances. The method developed in this study facilitates a more comprehensive understanding of phenotypic clustering than what would be deduced from principal component analysis alone.