Plasmids are vessels of genetic exchange in microbial communities. They are known to transfer between different host organisms and acquire diverse genetic elements from chromosomes and/or other ...plasmids. Therefore, they constitute an important element in microbial evolution by rapidly disseminating various genetic properties among different communities. A paradigmatic example of this is the dissemination of antibiotic resistance (AR) genes that has resulted in the emergence of multiresistant pathogenic bacterial strains. To globally analyze the evolutionary dynamics of plasmids, we built a large graph in which 2,343 plasmids (nodes) are connected according to the proteins shared by each other. The analysis of this gene-sharing network revealed an overall coherence between network clustering and the phylogenetic classes of the corresponding microorganisms, likely resulting from genetic barriers to horizontal gene transfer between distant phylogenetic groups. Habitat was not a crucial factor in clustering as plasmids from organisms inhabiting different environments were often found embedded in the same cluster. Analyses of network metrics revealed a statistically significant correlation between plasmid mobility and their centrality within the network, providing support to the observation that mobile plasmids are particularly important in spreading genes in microbial communities. Finally, our study reveals an extensive (and previously undescribed) sharing of AR genes between Actinobacteria and Gammaproteobacteria, suggesting that the former might represent an important reservoir of AR genes for the latter.
Important evidence is reported on the antimicrobial and antagonistic properties of bacterial endophytes in Echinacea purpurea and their role in the modulation of plant synthesis of bioactive ...compounds. Here, endophytic fungi were isolated from E. purpurea, and the dual culture approach was applied to deepen insights into the complex plant–microbiome interaction network.
In vitro experiments were carried out to evaluate the species specificity of the interaction between host (E. purpurea) and non‐host (E. angustifolia and Nicotiana tabacum) plant tissues and bacterial or fungal endophytes isolated from living E. purpurea plants to test interactions between fungal and bacterial endophytes.
A higher tropism towards plant tissue and growth was observed for both fungal and bacterial isolates compared to controls without plant tissue. The growth of all fungi was significantly inhibited by several bacterial strains that, in turn, were scarcely affected by the presence of fungi. Finally, E. purpurea endophytic bacteria were able to inhibit mycelial growth of the phytopathogen Botrytis cinerea.
Bacteria and fungi living in symbiosis with wild Echinacea plants interact with each other and could represent a potential source of bioactive compounds and a biocontrol tool.
Bacteria and fungi living in symbiosis with wild Echinacea plants interact at cellular level with each other and could represent a new source of bioactive compounds and a biocontrol tool.
The Antarctic bacterium
Pseudoalteromonas haloplanktis
TAC125 is a model organism of cold-adapted bacteria. The interest in the study of this psychrophilic bacterium stems from its capability either ...as a non-conventional system for production of recombinant protein and as a rich source of bioactive compounds. To further explore the biotechnological ability of
P. haloplanktis
TAC125, we have developed a synthetic medium, containing D-gluconate and L-glutamate (GG), which allows the bacterium to grow even at subzero temperatures.
P. haloplanktis
TAC125 growing in GG medium at low temperature displays growth kinetic parameters which confirm its spectacular adaptation to cold environment and subzero lifestyle, paving the way to the definition of the underlying molecular strategies. Moreover, in this paper, we report the setup of a finely regulated gene expression system inducible by D-galactose to produce recombinant protein in GG synthetic medium at temperatures as low as −2.5 °C. Thanks to the combination of the novel medium and the new expression system, we obtained for the first time the production of a recombinant protein at subzero temperature, thus providing an innovative strategy for the recombinant production of “difficult” proteins.
Many bacteria produce a wide range of volatile info-chemicals compounds (mVOCs) that constitute an important regulatory factor in the interrelationships among different organisms in microbial ...ecosystems. It has been shown that Antarctic bacteria isolated from three different sponge species, by producing mVOCs, are able to inhibit specifically the growth of
Burkholderia cepacia
complex (Bcc) strains (i.e. opportunistic pathogens of cystic fibrosis patients) as demonstrated by cross-streaking inhibition assays. This study reports a metabolomics approach to investigate the volatile profile of both the Antarctic sponge-associated
Pseudoalteromonas
sp. TB41 (P-sp-TB41) and
Burkholderia cenocepacia
strain LMG16654 (Bc-LMG16654) under aerobic conditions. Solid phase micro extraction (SPME) in head space of biological samples allowed an in vivo sampling of mVOCs with minimal specimen disturbance. The SPME fiber was termically desorbed in the injection port of gas chromatography–mass spectrometer (GC–MS) system setted in EI scan mode. The raw data were processed using both an automated mass spectra deconvolution and identification system and a metabolomic approach, which allowed a selection of 30 compounds presumably responsible for the inhibition of Bc-LMG16654 growth. The results obtained from samples prepared under cross-streaking conditions also suggest that the presence of Bc-LMG16654 cells neither interferes with the production of mVOCs nor induces the synthesis of different mVOCs. The employing of mass spectrometry played a key role in tuning the experimental system and in the evaluation of results. The use of this approach to study the interaction, in aerobic condition, among other Antarctic bacteria and Bcc and the possibility to extend this approach to other pathogen-antagonist relationship, is currently in progress.
A Pseudomonas 2,4-diacetylphloroglucinol (DAPG)-producing population that occurred naturally on the roots, in rhizosphere soil of Zea mays and in the nonrhizosphere soil was investigated in order to ...assess the microbial diversity at five stages of plant growth. A total of 1,716 isolates were obtained, and 188 of these isolates were able to produce DAPG. DAPG producers were isolated at each stage of plant growth, indicating that the maize rhizosphere is colonized by natural DAPG producers throughout development. The frequency of DAPG producers was very low in the first stage of plant growth and increased over time. An analysis of the level of biodiversity of the DAPG producers at the species level was performed by comparing the AluI restriction patterns of the 16S ribosomal DNAs (rDNAs) amplified by PCR from 167 isolates. This comparison allowed us to cluster the isolates into four amplified rDNA restriction analysis (ARDRA) groups, and the main group (ARDRA group 1) contained 89.8% of the isolates. The diversity of the 150 isolates belonging to ARDRA group 1 was analyzed by the random amplified polymorphic DNA (RAPD) technique. An analysis of RAPD patterns by a molecular variance method revealed that there was a high level of genetic diversity in this population and that the genetic diversity was related to plant age. Finally, we found that some of the DAPG producers, which originated from all stages of plant growth, had the same genotype. These DAPG producers could be exploited in future screening programs for biocontrol agents.
Lipids are an important nutritional component of the avian egg. A review of the literature was completed to determine the fatty acid compositions in egg yolk from some avian species. Additionally, ...the nutritional influence of lipid and lipoprotein content on the plasma of male participants during 30‐day feeding was discussed. The ostrich eggs had the highest unsaturated fatty acid and the lowest cholesterol content in relation to other avian species. Ostrich had a higher proportion of 18:3n‐3 (p < 0.01) compared with other species. Chicken yolk numerically contained much higher levels of 22:6n‐3 than those found in turkeys, quails and geese, but the amount of 22:6n‐3 in ostrich egg was lower by comparison with other species (p < 0.01). After the storage of eggs at the room temperature, there was a notable loss of vitamin E (vitE) in the yolks of all species and this decrease was marginal (p < 0.01) in ostrich compared with other species. There were significant (p < 0.05) increases in plasma low‐density lipoprotein (LDL) level in all male subjects. Plasma high‐density lipoprotein (HDL) level decreased (p < 0.05) only in men who were fed chicken or ostrich eggs daily. Consumption of different species’ eggs had no influence on the total male plasma cholesterol and triglyceride levels. LDL‐C:HDL‐C ratio increased (p < 0.05) after goose and turkey egg consumption. Consumption of one egg/month by healthy human subjects had no effect on serum total cholesterol and triglyceride. The LDL‐C:HDL‐C ratio (which is a strong predictor of coronary heart disease risk) increased, although non‐significantly, by consuming chicken, quail and ostrich eggs.
A Burkholderia cepacia population naturally occurring in the rhizosphere of Zea mays was investigated in order to assess the degree of root association and microbial biodiversity at five stages of ...plant growth. The bacterial strains isolated on semiselective PCAT medium were mostly assigned to the species B. cepacia by an analysis of the restriction patterns produced by amplified DNA coding for 16S rRNA (16S rDNA) (ARDRA) with the enzyme AluI. Partial 16S rDNA nucleotide sequences of some randomly chosen isolates confirmed the ARDRA results. Throughout the study, B. cepacia was strictly associated with maize roots, ranging from 0.6 to 3.6% of the total cultivable microflora. Biodiversity among 83 B. cepacia isolates was analyzed by the random amplified polymorphic DNA (RAPD) technique with two 10-mer primers. An analysis of RAPD patterns by the analysis of molecular variance method revealed a high level of intraspecific genetic diversity in this B. cepacia population. Moreover, the genetic diversity was related to divergences among maize root samplings, with microbial genetic variability markedly higher in the first stages of plant growth; in other words, the biodiversity of this rhizosphere bacterial population decreased over time
Aims: The aim of this study was to investigate the lipolytic activity of cold‐adapted Antarctic marine bacteria and, furthermore, the combined effect of some environmental factors on this enzymatic ...process.
Methods and Results: Strains were assayed for lipolytic activity on a basal medium amended with seven individual fatty acid esters. A significant activity was observed for 148 isolates (95·5% of the total screened). The interactive effect of pH, temperature and NaCl concentration on the substrates was tested for six representative isolates, identified as Pseudoalteromonas, Psychrobacter and Vibrio. Differences between strains according to NaCl and pH tolerances were observed. Only one strain degraded the substrate more efficiently at 4°C than at 15°C.
Conclusions: Our findings demonstrate that the lipolytic activity of Antarctic marine bacteria is rather variable, depending on culture conditions, and occurs in a wide range of salt concentration and pH.
Significance and Impact of the Study: Isolation and characterization of bacteria that are able to efficiently remove lipids at low temperatures will provide insight into the possibility to use cold‐adapted bacteria as a source of exploitable enzymes. Moreover, research on the interactive effects of salt concentration, pH and temperature will be useful to understand the true enzyme potentialities for industrial applications.
In this paper we report the identification and characterization of a DNA region containing putative nif genes and belonging to a Burkholderia endosymbiont of the arbuscular mycorrhizal fungus ...Gigaspora margarita. A genomic library of total DNA extracted from the fungal spores was also representative of the bacterial genome and was used to investigate the prokaryotic genome. Screening of the library with Azospirillum brasilense nifHDK genes as the prokaryotic probes led to the identification of a 6,413-bp region. Analysis revealed three open reading frames encoding putative proteins with a very high degree of sequence similarity with the two subunits (NifD and NifK) of the component I and with component II (NifH) of nitrogenase from different diazotrophs. The three genes were arranged in an operon similar to that shown by most archaeal and bacterial diazotrophs. PCR experiments with primers designed on the Burkholderia nifHDK genes and Southern blot analysis demonstrate that they actually belong to the genome of the G. margarita endosymbiont. They offer, therefore, the first sequence for the nif operon described for Burkholderia. Reverse transcriptase PCR experiments with primers designed on the Burkholderia nifH and nifD genes and performed on total RNA extracted from spores demonstrate that the gene expression was limited to the germination phase. A phylogenetic analysis performed on the available nifK sequences placed the endosymbiotic Burkholderia close to A. brasilense.