Burkholderia is a diverse and dynamic genus, containing pathogenic species as well as species that form complex interactions with plants. Pathogenic strains, such as B. pseudomallei and B. mallei, ...can cause serious disease in mammals, while other Burkholderia strains are opportunistic pathogens, infecting humans or animals with a compromised immune system. Although some of the opportunistic Burkholderia pathogens are known to promote plant growth and even fix nitrogen, the risk of infection to infants, the elderly, and people who are immunocompromised has not only resulted in a restriction on their use, but has also limited the application of non-pathogenic, symbiotic species, several of which nodulate legume roots or have positive effects on plant growth. However, recent phylogenetic analyses have demonstrated that Burkholderia species separate into distinct lineages, suggesting the possibility for safe use of certain symbiotic species in agricultural contexts. A number of environmental strains that promote plant growth or degrade xenobiotics are also included in the symbiotic lineage. Many of these species have the potential to enhance agriculture in areas where fertilizers are not readily available and may serve in the future as inocula for crops growing in soils impacted by climate change. Here we address the pathogenic potential of several of the symbiotic Burkholderia strains using bioinformatics and functional tests. A series of infection experiments using Caenorhabditis elegans and HeLa cells, as well as genomic characterization of pathogenic loci, show that the risk of opportunistic infection by symbiotic strains such as B. tuberum is extremely low.
Despite efforts to control toxigenic
species, wilt and head-blight infections are destructive and economically damaging diseases that have global effects. The utilization of biological control agents ...in disease management programs has provided an effective, safe, and sustainable means to control
-induced plant diseases. Among the most widely used microbes for biocontrol agents are members of the genus
. These species influence plant and fungal pathogen interactions by a number of mechanisms such as competing for essential nutrients, antagonizing pathogens by producing fungitoxic metabolites, or inducing systemic resistance in plants. The multivariate interactions among plant-biocontrol agent-pathogen are the subject of this study, in which we survey the advances made regarding the research on the
interaction and focus on the principles and mechanisms of action among plant-growth promoting
species. In particular, we highlight their use in limiting and controlling
spread and infestations of economically important crops. This knowledge will be useful to define strategies for exploiting this group of beneficial bacteria for use as inoculants by themselves or in combination with other microbes for enhanced crop protection.
is a complex genus of ascomycete fungi that consists of plant pathogens of agricultural relevance. Controlling
infection in crops that leads to substantial yield losses is challenging. These economic ...losses along with environmental and human health concerns over the usage of chemicals in attaining disease control are shifting focus toward the use of biocontrol agents for effective control of phytopathogenic
spp. In the present study, an analysis of the plant-growth promoting (PGP) and biocontrol attributes of four bacilli (
30N-5,
11,
237, and
30VD-1) has been conducted. The production of cellulase, xylanase, pectinase, and chitinase in functional assays was studied, followed by
gene analysis of the PGP-related and biocontrol-associated genes. Of all the bacilli included in this study,
30VD-1 (30VD-1) demonstrated the most effective antagonism against
spp. under
conditions. Additionally, 100 μg/ml of the crude 1-butanol extract of 30VD-1's cell-free culture filtrate caused about 40% inhibition in radial growth of
spp. Pea seed bacterization with 30VD-1 led to considerable reduction in wilt severity in plants with about 35% increase in dry plant biomass over uninoculated plants growing in
-infested soil. Phase contrast microscopy demonstrated distortions and abnormal swellings in
hyphae on co-culturing with 30VD-1. The results suggest a multivariate mode of antagonism of 30VD-1 against phytopathogenic
spp., by producing chitinase, volatiles, and other antifungal molecules, the characterization of which is underway.
Chitin is an important component of the exteriors of insects and fungi. Upon degradation of chitin by a number of organisms, severe damage and even death may occur in pathogens and pests whose ...external surfaces contain this polymer. Currently, chemical fungicides and insecticides are the major means of controlling these disease-causing agents. However, due to the potential harm that these chemicals cause to the environment and to human and animal health, new strategies are being developed to replace or reduce the use of fungal- and pest-killing compounds in agriculture. In this context, chitinolytic microorganisms are likely to play an important role as biocontrol agents and pathogen antagonists and may also function in the control of postharvest rot. In this review, we discuss the literature concerning chitin and the basic knowledge of chitin-degrading enzymes, and also describe the biocontrol effects of chitinolytic microorganisms and their potential use as more sustainable pesticides and fungicides in the field.
Severe gonadal steroid deficiency induces bone loss in adult men; however, the specific roles of androgen and estrogen deficiency in hypogonadal bone loss are unclear. Additionally, the threshold ...levels of testosterone and estradiol that initiate bone loss are uncertain.
One hundred ninety-eight healthy men, ages 20-50, received goserelin acetate, which suppresses endogenous gonadal steroid production, and were randomized to treatment with 0, 1.25, 2.5, 5, or 10 grams of testosterone gel daily for 16 weeks. An additional cohort of 202 men was randomized to receive these treatments plus anastrozole, which suppresses conversion of androgens to estrogens. Thirty-seven men served as controls and received placebos for goserelin and testosterone. Changes in bone turnover markers, bone mineral density (BMD) by dual-energy x-ray absorptiometry (DXA), and BMD by quantitative computed tomography (QCT) were assessed in all men. Bone microarchitecture was assessed in 100 men.
As testosterone dosage decreased, the percent change in C-telopeptide increased. These increases were considerably greater when aromatization of testosterone to estradiol was also suppressed, suggesting effects of both testosterone and estradiol deficiency. Decreases in DXA BMD were observed when aromatization was suppressed but were modest in most groups. QCT spine BMD fell substantially in all testosterone-dose groups in which aromatization was also suppressed, and this decline was independent of testosterone dose. Estradiol deficiency disrupted cortical microarchitecture at peripheral sites. Estradiol levels above 10 pg/ml and testosterone levels above 200 ng/dl were generally sufficient to prevent increases in bone resorption and decreases in BMD in men.
Estrogens primarily regulate bone homeostasis in adult men, and testosterone and estradiol levels must decline substantially to impact the skeleton.
ClinicalTrials.gov, NCT00114114.
AbbVie Inc., AstraZeneca Pharmaceuticals LP, NIH.
Rhizobia form specialized nodules on the roots of legumes (family Fabaceae) and fix nitrogen in exchange for carbon from the host plant. Although the majority of legumes form symbioses with members ...of genus Rhizobium and its relatives in class Alphaproteobacteria, some legumes, such as those in the large genus Mimosa, are nodulated predominantly by betaproteobacteria in the genera Burkholderia and Cupriavidus. The principal centers of diversity of these bacteria are in central Brazil and South Africa. Molecular phylogenetic studies have shown that betaproteobacteria have existed as legume symbionts for approximately 50 million years, and that, although they have a common origin, the symbiosis genes in both subclasses have evolved separately since then. Additionally, some species of genus Burkholderia, such as B. phymatum, are highly promiscuous, effectively nodulating several important legumes, including common bean (Phaseolus vulgaris). In contrast to genus Burkholderia, only one species of genus Cupriavidus (C. taiwanensis) has so far been shown to nodulate legumes. The recent availability of the genome sequences of C. taiwanensis, B. phymatum, and B. tuberum has paved the way for a more detailed analysis of the evolutionary and mechanistic differences between nodulating strains of alpha- and betaproteobacteria. Initial analyses of genome sequences have suggested that plant-associated Burkholderia spp. have lower G+C contents than Burkholderia spp. that are opportunistic human pathogens, thus supporting previous suggestions that the plant- and human-associated groups of Burkholderia actually belong in separate genera.
A rapidly increasing human population coupled with climate change and several decades of over-reliance on synthetic fertilizers has led to two pressing global challenges: food insecurity and land ...degradation. Therefore, it is crucial that practices enabling both soil and plant health as well as sustainability be even more actively pursued. Sustainability and soil fertility encompass practices such as improving plant productivity in poor and arid soils, maintaining soil health, and minimizing harmful impacts on ecosystems brought about by poor soil management, including run-off of agricultural chemicals and other contaminants into waterways. Plant growth promoting bacteria (PGPB) can improve food production in numerous ways: by facilitating resource acquisition of macro- and micronutrients (especially N and P), modulating phytohormone levels, antagonizing pathogenic agents and maintaining soil fertility. The PGPB comprise different functional and taxonomic groups of bacteria belonging to multiple phyla, including
, and
, among others. This review summarizes many of the mechanisms and methods these beneficial soil bacteria use to promote plant health and asks whether they can be further developed into effective, potentially commercially available plant stimulants that substantially reduce or replace various harmful practices involved in food production and ecosystem stability. Our goal is to describe the various mechanisms involved in beneficial plant-microbe interactions and how they can help us attain sustainability.
Burkholderia
comprises more than 60 species of environmental, clinical, and agro-biotechnological relevance. Previous phylogenetic analyses of 16S rRNA,
recA
,
gyrB
,
rpoB
, and
acdS
gene sequences ...as well as genome sequence comparisons of different
Burkholderia
species have revealed two major species clusters. In this study, we undertook a multilocus sequence analysis of 77 type and reference strains of
Burkholderia
using
atpD
,
gltB
,
lepA
, and
recA
genes in combination with the 16S rRNA gene sequence and employed maximum likelihood and neighbor-joining criteria to test this further. The phylogenetic analysis revealed, with high supporting values, distinct lineages within the genus
Burkholderia
. The two large groups were named A and B, whereas the
B. rhizoxinica
/
B. endofungorum
, and
B. andropogonis
groups consisted of two and one species, respectively. The group A encompasses several plant-associated and saprophytic bacterial species. The group B comprises the
B. cepacia
complex (opportunistic human pathogens), the
B. pseudomallei
subgroup, which includes both human and animal pathogens, and an assemblage of plant pathogenic species. The distinct lineages present in
Burkholderia
suggest that each group might represent a different genus. However, it will be necessary to analyze the full set of
Burkholderia
species and explore whether enough phenotypic features exist among the different clusters to propose that these groups should be considered separate genera.
Micromonospora species have long been recognized as important sources of antibiotics and also for their unusual spores. However, their involvement in plant-microbe associations is poorly understood ...although several studies demonstrate that
Micromonospora species function in biocontrol, plant growth promotion, root ecology, and in the breakdown of plant cell wall material. Our knowledge of this generally understudied group of actinomycetes has been greatly advanced by the increasing number of reports of their associations with plants, by the deployment of DNA cloning and molecular systematics techniques, and by the recent application of whole genome sequencing. Efforts to annotate the genomes of several
Micromonospora species are underway. This information will greatly augment our knowledge of these versatile microorganisms.
sensu lato is a large and complex group, containing pathogenic, phytopathogenic, symbiotic and non-symbiotic strains from a very wide range of environmental (soil, water, plants, fungi) and clinical ...(animal, human) habitats. Its taxonomy has been evaluated several times through the analysis of 16S rRNA sequences, concantenated 4⁻7 housekeeping gene sequences, and lately by genome sequences. Currently, the division of this group into
,
, and
is strongly supported by genome analysis. These new genera broadly correspond to the various habitats/lifestyles of
s.l., e.g., all the plant beneficial and environmental (PBE) strains are included in
(which also includes all the N₂-fixing legume symbionts) and
, while most of the human and animal pathogens are retained in
sensu stricto. However, none of these genera can accommodate two important groups of species. One of these includes the closely related
and
, which are both symbionts of the fungal phytopathogen
. The second group comprises the
-nodulating bacterium
, the phytopathogen
, and the soil bacteria
and
. In order to clarify their positions within
sensu lato, a phylogenomic approach based on a maximum likelihood analysis of conserved genes from more than 100
sensu lato species was carried out. Additionally, the average nucleotide identity (ANI) and amino acid identity (AAI) were calculated. The data strongly supported the existence of two distinct and unique clades, which in fact sustain the description of two novel genera
gen. nov. and
gen. nov. The newly proposed combinations are
comb. nov.,
comb. nov.,
comb. nov.,
comb. nov.,
comb. nov., and
comb. nov. Given that the division between the genera that comprise
s.l. in terms of their lifestyles is often complex, differential characteristics of the genomes of these new combinations were investigated. In addition, two important lifestyle-determining traits-diazotrophy and/or symbiotic nodulation, and pathogenesis-were analyzed in depth i.e., the phylogenetic positions of nitrogen fixation and nodulation genes in
via-à-vis other
were determined, and the possibility of pathogenesis in
and
was tested by performing infection experiments on plants and the nematode
. It is concluded that (1)
and
genes fit within the wider
-nodulating
but appear in separate clades and that
genes are basal to the free-living
s.l. strains, while with regard to pathogenesis (2) none of the
and
strains tested are likely to be pathogenic, except for the known phytopathogen
.
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