Bacterial isolates from the bryozoan Membranipora membranacea: influence of culture media on isolation and antimicrobial activity

From specimens of the bryozoan Membranipora membranacea collected in the Baltic Sea, bacteria were isolated on four different media, which significantly increased the diversity of the isolated groups. All isolates were classified according to 16S rRNA gene sequence analysis and tested for antimicrobial properties using a panel of five indicator strains and six different media. Each medium featured a unique set of isolated phylotypes, and a phylogenetically diverse collection of isolates was obtained. A total of 96 isolates were assigned to 49 phylotypes and 29 genera. Only one-third of the members of these genera had been isolated previously from comparable sources. The isolates were affiliated with Alpha- and Gammaproteobacteria, Bacilli, and Actinobacteria. A comparable large portion of up to 22 isolates, i.e., 15 phylotypes, probably represent new species. Likewise, 47 isolates (approximately 50%) displayed antibiotic activities, mostly against grampositive indicator strains. Of the active strains, 63.8 % had antibiotic traits only on one or two of the growth media, whereas only 12.7 % inhibited growth on five or all six media. The application of six different media for antimicrobial testing resulted in twice the number of positive hits as obtained with only a single medium. The use of different media for the isolation of bacteria as well as the variation of media considered suitable for the production of antibiotic substances significantly enhanced both the number of isolates obtained and the proportion of antibiotic active cultures. Thus the approach described herein offers an improved strategy in the search for new antibiotic compounds.     

Interaction between PGPR and PGR for water conservation and plant growth attributes under drought condition

Drought is one of the key restraints to agricultural productivity worldwide and is expected to increase further. Drought stress accompanied by reduction in precipitation pose major challenges to future food safety. Strategies should be develop to enhance drought tolerance in crops like chickpea and wheat, in order to enhance their growth and yield. Drought tolerance strategies are costly and time consuming however, recent studies specify that plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) can help plants to withstand under harsh environmental condition and enable plants to cope with drought stress. PGPR can act as biofertilizer and bioenhancer for different legumes and non-legumes. The use of PGPR and symbiotic microorganisms, may be valuable in developing strategies to assist water conservation in plants. The use of PGPR has been confirmed to be an ecologically sound way of enhancing crop yields by facilitating plant growth through direct or indirect mechanism. The mechanisms of PGPR for water conservation include secretion of exopolysaccharides, biofilm formation, alternation in phytohormone content, improvement in sugar concentration, enhancing availability of micro- and macronutrients and changes in plant functional traits. Similarly, plant growth regulators (PGRs) are specially noticed in actively growing tissues under stress conditions and have been associated in the control of cell division, embryogenesis, root formation, fruit development and ripening, and reactions to biotic and abiotic stresses and upholding water conservation status in plants. Previous studies also suggest that plant metabolites interact with plant physiology under stress condition and impart drought tolerance. Metabolites like, sugars, amino acids, organic acid and polyols play a key role in drought tolerance of crop plants grown under stress condition. It is concluded from the present study that PGRs in combination with PGPR consortium can be an effective formulation to promote plant growth and maintenance of plant turgidity under drought stress. This review is a compilation of the effect of drought stress on crop plants and described interactions between PGPR/PGRs and plant development, knowledge of water conservation and stress release strategies of PGPR and PGRs and the role of plant metabolites in drought tolerance of crop plants. This review also bridges the gaps that summarizes the mechanism of action of PGPR for drought tolerance of crop plants and sustainability of agriculture and applicability of these beneficial rhizobacteria in different agro-ecosystems under drought stress.     

Drought- and frost-induced accumulation of soluble carbohydrates during accelerated senescence in <Emphasis Type="Italic">Quercus pubescens</Emphasis>

Key message

Different environmental conditions affect tree senescence by different patterns of carbohydrate concentrations and have specific impact on the dissection of the photosynthetic apparatus.

Abstract

A proactive cultivation of Mediterranean broadleaf species, including oaks, has been suggested to fill possible temporal and spatial gaps in forestry created by Climate Change in Central Europe in the future. Climate can affect trees in several different ways, e.g., by modulating the course of leaf senescence. Senescence-associated processes, like regulation of carbohydrates and changes in chlorophyll fluorescence under drought stress conditions were studied with leaf tissue of drought-tolerant downy oak (Quercus pubescens). Two months of consistent drought stress in a frost-free greenhouse led to significantly earlier senescence and significant increased amounts of soluble sugars in the leaves of the drought-stressed group in comparison to a well-watered control group. Similar sugar accumulation was observed in trees outdoors, after exposure to frost. In contrast to monocarpic plants the accumulation of free sugars is neither triggering leaf senescence, nor is it a side effect of age-depending changes in Q. pubescens. Instead, sugar accumulation is induced by abiotical factors, like drought and frost. Furthermore, we suggest that the senescence process in the absence of drought stress or frost depends on the source status of the leaf, which, in term, is a function of light (through photosynthesis) and night temperature (through respiration). Contents of the storage metabolite starch decreased during late summer in all three groups. Drought-stressed plants showed a decline of the connectivity of photosystem II antenna, reflected as the L-band in the chlorophyll fluorescence induction curves, and stronger correlations between the declines in the capacity of photosynthetic dark reactions and electron transport-associated chlorophyll fluorescence parameters. We conclude that the disassembly of single parts of the photosynthetic apparatus during leaf senescence is a uniform process, but the onset of this process depends on abiotical environmental factors.

     

Vascular endothelial growth factor-induced secretion of fibronectin is ERK dependent

In severe asthma, cytokines and growth factors contribute to the proliferation of smooth muscle cells and blood vessels, and to the increased extracellular matrix deposition that constitutes the process of airway remodeling. Vascular endothelial growth factor (VEGF), which regulates vascular permeability and angiogenesis, also modulates the function of nonendothelial cell types. In this study, we demonstrate that VEGF induces fibronectin secretion by human airway smooth muscle (ASM) cells. In addition, stimulation of ASM with VEGF activates ERK, but not p38MAPK, and fibronectin secretion is ERK dependent. Both ERK activation and fibronectin secretion appear to be mediated through the VEGF receptor flt-1, as evidenced by the effects of the flt-1-specific ligand placenta growth factor. Finally, we demonstrate that ASM cells constitutively secrete VEGF, which is increased in response to PDGF, transforming growth factor-beta, IL-1beta, and PGE(2). We conclude that ASM-derived VEGF, through modulation of the extracellular matrix, may play an important role in airway remodeling seen in asthma.     

Cloning, expression, and purification of recombinant bovine rotavirus hemagglutinin, VP8*, in Escherichia coli

Rotavirus VP8* subunit is the minor trypsin cleavage product of the spike protein VP4, which is the major determinant of the viral infectivity and neutralization. To study the structure-function relationship of this fragment and to obtain type-specific reagents, substantial amounts of this protein are needed. Thus, full-length VP8* cDNA, including the entire trypsin cleavage-encoding region in gene 4, was synthesized and amplified by RT-PCR from total RNA purified from bovine rotavirus strain C486 propagated in MA104 cell culture. The extended VP8* cDNA (VP8ext) was cloned into the pGEM-T Easy plasmid and subcloned into the Escherichia coli expression plasmid pET28a(+). The correspondent 30 kDa protein was overexpressed in E. coli BL21(DE3)pLysS cells under the control of the T7 promoter. The identity and the antigenicity of VP8ext were confirmed on Western blots using anti-His and anti-rotavirus antibodies. Immobilized Ni-ion affinity chromatography was used to purify the expressed protein resulting in a yield of 4 mg of VP8ext per liter of induced E. coli culture. Our results indicate that VP8ext maintained its native antigenicity and specificity, providing a good source of antigen for the production of P type-specific immune reagents. Detailed structural analysis of pure recombinant VP8 subunit should allow a better understanding of its role in cell attachment and rotavirus tropism. Application of similar procedure to distinct rotavirus P serotypes should provide valuable P serotype-specific immune reagents for rotavirus diagnostics and epidemiologic surveys.     

Leaf yellowing and anthocyanin accumulation are two genetically independent strategies in response to nitrogen limitation in Arabidopsis thaliana

For the first time in Arabidopsis thaliana, this work proposes the identification of quantitative trait loci (QTLs) associated with leaf senescence and stress response symptoms such as yellowing and anthocyanin-associated redness. When Arabidopsis plants were cultivated under low nitrogen conditions, we observed that both yellowing of the old leaves of the rosette and whole rosette redness were promoted. Leaf yellowing is a senescence symptom related to chlorophyll breakdown. Redness is a symptom of anthocyanin accumulation related to whole plant ageing and nutrient limitation. In this work, Arabidopsis is used as a model system to dissect the genetic variation of these parameters by QTL mapping in the 415 recombinant inbred lines of the Bay-0xShahdara population. Fifteen new QTLs and two epistatic interactions were described in this study. The yellowing of the rosette, estimated by visual notation and image processing, was controlled by four and five QTLs, respectively. The visual estimation of redness allowed us to detect six QTLs among which the major one explained 33% of the total variation. Two main QTLs were confirmed in near-isogenic lines (heterogenous inbred family; HIF), thus confirming the relevance of the visual notation of these traits. Co-localizations between QTLs for leaf yellowing, redness and nitrogen use efficiency described in a previous publication indicate complex interconnected pathways involved in both nitrogen management and senescence- and stress-related processes. No co-localization between QTLs for leaf yellowing and redness has been found, suggesting that the two characters are genetically independent.