Bacterial phytopathogens living on the surface or within plant tissues may experience oxidative stress because of the triggered plant defense responses. Although it has been suggested that polyamines ...can defend bacteria from this stress, the mechanism behind this action is not entirely understood. In this study, we investigated the effects of oxidative stress on the polyamine homeostasis of the plant pathogen Pseudomonas syringae and the functions of these compounds in bacterial stress tolerance. We demonstrated that bacteria respond to H
O
by increasing the external levels of the polyamine putrescine while maintaining the inner concentrations of this compound as well as the analogue amine spermidine. In line with this, adding exogenous putrescine to media increased bacterial tolerance to H
O
. Deletion of arginine decarboxylase (speA) and ornithine decarboxylate (speC), prevented the synthesis of putrescine and augmented susceptibility to H
O
, whereas targeting spermidine synthesis alone through deletion of spermidine synthase (speE) increased the level of extracellular putrescine and enhanced H
O
tolerance. Further research demonstrated that the increased tolerance of the ΔspeE mutant correlated with higher expression of H
O
-degrading catalases and enhanced outer cell membrane stability. Thus, this work demonstrates previously unrecognized connections between bacterial defense mechanisms against oxidative stress and the polyamine metabolism.
Abstract
Endophytic bacterial communities of tomato leaves were analyzed by 16S-rRNA gene pyrosequencing and compared to rhizosphere communities. Leaf endophytes mainly comprised five phyla, among ...which Proteobacteria was the most represented (90%), followed by Actinobacteria (1,5%), Planctomycetes (1,4%), Verrucomicrobia (1,1%), and Acidobacteria (0,5%). Gammaproteobacteria was the most abundant class of Proteobacteria (84%), while Alphaproteobacteria and Betaproteobacteria represented 12% and 4% of this phylum, respectively. Rarefaction curves for endophytic bacteria saturated at 80 OTUs, indicating a lower diversity as compared to rhizosphere samples (> 1700 OTUs). Hierarchical clustering also revealed that leaf endophytic communities strongly differed from rhizospheric ones. Some OTUs assigned to Bacillus, Stenotrophomonas, and Acinetobacter, as well as some unclassified Enterobacteriaceae were specific for the endophytic community, probably representing bacteria specialized in colonizing this niche. On the other hand, some OTUs detected in the leaf endophytic community were also present in the rhizosphere, probably representing soil bacteria that endophytically colonize leaves. As a whole, this study describes the composition of the endophytic bacterial communities of tomato leaves, identifying a variety of genera that could exert multiple effects on growth and health of tomato plants.
A culture-independent approach was used to analyze the structure and diversity of bacterial communities that endophytically colonize leaves of cultivated tomato.
This work aimed to characterize potentially endophytic culturable bacteria from leaves of cultivated tomato and analyze their potential for growth promotion and biocontrol of diseases caused by ...Botrytis cinerea and Pseudomonas syringae. Bacteria were obtained from inner tissues of surface-disinfected tomato leaves of field-grown plants. Analysis of 16S rRNA gene sequences identified bacterial isolates related to Exiguobacterium aurantiacum (isolates BT3 and MT8), Exiguobacterium spp. (isolate GT4), Staphylococcus xylosus (isolate BT5), Pantoea eucalypti (isolate NT6), Bacillus methylotrophicus (isolate MT3), Pseudomonas veronii (isolates BT4 and NT2), Pseudomonas rhodesiae (isolate BT2) and Pseudomonas cichorii (isolate NT3). After seed inoculation, BT2, BT4, MT3, MT8, NT2 and NT6 were re-isolated from leaf extracts. NT2, BT2, MT3 and NT6 inhibited growth of Botrytis cinerea and Pseudomonas syringae pv. tomato in vitro, produced antimicrobial compounds and reduced leaf damage caused by B. cinerea. Some of these isolates also promoted growth of tomato plants, produced siderophores, the auxin indole-3-acetic and solubilized inorganic phosphate. Thus, bacterial communities of leaves from field-grown tomato plants were found to harbor potentially endophytic culturable beneficial bacteria capable of antagonizing pathogenic microorganisms and promoting plant growth, which could be used as biological control agents and biofertilizers/biostimulators for promotion of tomato plant growth.
Abstract
As compared to eukaryotes, bacteria have a reduced tRNA gene set encoding between 30 and 220 tRNAs. Although in most bacterial phyla tRNA genes are dispersed in the genome, many species from ...distinct phyla also show genes forming arrays. Here, we show that two types of arrays with distinct evolutionary origins exist. This work focuses on long tRNA gene arrays (L-arrays) that encompass up to 43 genes, which disseminate by horizontal gene transfer and contribute supernumerary tRNA genes to the host. Although in the few cases previously studied these arrays were reported to be poorly transcribed, here we show that the L-array of the model cyanobacterium Anabaena sp. PCC 7120, encoding 23 functional tRNAs, is largely induced upon impairment of the translation machinery. The cellular response to this challenge involves a global reprogramming of the transcriptome in two phases. tRNAs encoded in the array are induced in the second phase of the response, directly contributing to cell survival. Results presented here show that in some bacteria the tRNA gene set may be partitioned between a housekeeping subset, which constantly sustains translation, and an inducible subset that is generally silent but can provide functionality under particular conditions.
Graphical Abstract
Graphical Abstract
Workflow diagram describing the characterization of the role of the Anabaena tRNA-encoding operon.
Freshwaters are among the most vulnerable ecosystems to climate warming, with projected temperature increases over the coming decades leading to significant losses of aquatic biodiversity. ...Experimental studies that directly warm entire natural ecosystems in the tropics are needed, for understanding the disturbances on aquatic communities. Therefore, we conducted an experiment to test the impacts of predicted future warming on density, alpha diversity, and beta diversity of freshwater aquatic communities, inhabiting natural microecosystems—Neotropical tank bromeliads. Aquatic communities within the tanks bromeliads were experimentally exposed to warming, with temperatures ranging from 23.58 to 31.72°C. Linear regression analysis was used to test the impacts of warming. Next, distance‐based redundancy analysis was performed to assess how warming might alter total beta diversity and its components. This experiment was conducted across a gradient of habitat size (bromeliad water volume) and availability of detrital basal resources. A combination of the highest detritus biomass and higher experimental temperatures resulted in the greatest density of flagellates. However, the density of flagellates declined in bromeliads with higher water volume and lower detritus biomass. Moreover, the combination of the highest water volume and high temperature reduced density of copepods. Finally, warming changed microfauna species composition, mostly through species substitution (βrepl component of total beta‐diversity). These findings indicate that warming strongly structures freshwater communities by reducing or increasing densities of different aquatic communities groups. It also enhances beta‐diversity, and many of these effects are modulated by habitat size or detrital resources.
Effects of warming on structure of aquatic communities.
To succeed in plant invasion, phytopathogenic bacteria rely on virulence mechanisms to subvert plant immunity and create favorable conditions for growth. This process requires a precise regulation in ...the production of important proteins and metabolites. Among them, the family of compounds known as polyamines have attracted considerable attention as they are involved in important cellular processes, but it is not known yet how phytopathogenic bacteria regulate polyamine homeostasis in the plant environment. In the present study, we performed a meta-analysis of publicly available transcriptomic data from experiments conducted on bacteria to begin delving into this topic and better understand the regulation of polyamine metabolism and its links to pathogenicity. We focused our research on
, an important phytopathogen that causes disease in many economically valuable plant species. Our analysis discovered that polyamine synthesis, as well as general gene expression activation and energy production are induced in the early stages of the disease. On the contrary, synthesis of these compounds is inhibited whereas its transport is upregulated later in the process, which correlates with the induction of virulence genes and the metabolism of nitrogen and carboxylic acids. We also found that activation of plant defense mechanisms affects bacterial polyamine synthesis to some extent, which could reduce bacterial cell fitness in the plant environment. Furthermore, data suggest that a proper bacterial response to oxidative conditions requires a decrease in polyamine production. The implications of these findings are discussed.
Key message
Oxalotrophic
Stenotrophomonas
isolated from tomato rhizosphere are able to protect plants against oxalate-producing pathogens by a combination of actions including induction of plant ...defence signalling callose deposition and the strengthening of plant cell walls and probably the degradation of oxalic acid.
Oxalic acid plays a pivotal role in the virulence of the necrotrophic fungi
Botrytis cinerea
and
Sclerotinia sclerotiorum
. In this work, we isolated two oxalotrophic strains (OxA and OxB) belonging to the bacterial genus
Stenotrophomonas
from the rhizosphere of tomato plants. Both strains were capable to colonise endophytically
Arabidopsis
plants and protect them from the damage caused by high doses of oxalic acid. Furthermore, OxA and OxB protected
Arabidopsis
from
S. sclerotiorum
and
B. cinerea
infections. Bacterial inoculation induced the production of phenolic compounds and the expression of
PR
-
1
. Besides, both isolates exerted a protective effect against fungal pathogens in
Arabidopsis
mutants affected in the synthesis pathway of salicylic acid (
sid2
-
2
) and jasmonate perception (
coi1
). Callose deposition induced by OxA and OxB was required for protection against phytopathogens. Moreover,
B. cinerea
and
S. sclerotiorum
mycelial growth was reduced in culture media containing cell wall polysaccharides from leaves inoculated with each bacterial strain. These findings suggest that cell walls from
Arabidopsis
leaves colonised by these bacteria would be less susceptible to pathogen attack. Our results indicate that these oxalotrophic bacteria can protect plants against oxalate-producing pathogens by a combination of actions and show their potential for use as biological control agents against fungal diseases.
Assessing the effectiveness of protected areas for sustaining species and identifying priority sites for their conservation is vital for decision making, particularly for freshwater fishes in South ...America, the global centre of freshwater fish diversity. Several conservation planning studies have used threatened freshwater fishes or species that are vulnerable to climate change as conservation targets, but none has included both in priority‐setting analysis.
The objectives of this study were to identify gaps in the coverage of the existing protected areas in representing the endemic freshwater fishes of the Tropical Andes region, and to identify conservation priority areas that adequately cover threatened species and species vulnerable to climate change.
Data on 648 freshwater fishes from the Tropical Andes were used to identify gaps in the protected area coverage, and to identify conservation priority sites under three scenarios: (i) prioritize threatened species; (ii) prioritize species that are vulnerable to climate change; and (iii) prioritize both threatened species and species vulnerable to climate change.
A total of 571 species (88% of all species) were not covered by any protected areas; most of them are restricted to ≤10 catchments. To represent both threatened species and species vulnerable to climate change in the third scenario, 635 catchments were identified as priority areas, representing 26.5% of the study area. The number of irreplaceable catchments for this scenario is 475, corresponding to 22.5% of the total area.
The results of this study could be crucial for designing strategies for the effective protection of native fish populations in the Tropical Andes, and for planning proactive climate adaptation. It is hoped that the identification of priority areas, particularly irreplaceable catchments, will help to guide conservation and management decisions in the Andean region.
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