In many legumes, roots that are exposed to light do not form nodules. Here, we report that blue light inhibits nodulation in Lotus japonicus roots inoculated with Mesorhizobium loti. Using RNA ...interference, we suppressed the expression of the phototropin and cryptochrome genes in L. japonicus hairy roots. Under blue light, plants transformed with an empty vector did not develop nodules, whereas plants exhibiting suppressed expression of cry1 and cry2 genes formed nodules. We also measured rhizobial growth to investigate whether the inhibition of nodulation could be caused by a reduced population of rhizobia in response to light. Although red light had no effect on rhizobial growth, blue light had a strong inhibitory effect. Rhizobial growth under blue light was partially restored in signature-tagged mutagenesis (STM) strains in which LOV-HK/PAS- and photolyase-related genes were disrupted. Moreover, when Ljcry1A and Ljcry2B-silenced plants were inoculated with the STM strains, nodulation was additively increased. Our data show that blue light receptors in both the host plant and the symbiont have a profound effect on nodule development. The exact mechanism by which these photomorphogenetic responses function in the symbiosis needs further study, but they are clearly involved in optimizing legume nodulation.
Variovorax species catabolize a wide range of natural and industrial products and have been shown to be integral rhizosphere inhabitants. Here, we report the complete genomes of V. paradoxus 2u118 ...and V. sp. SPNA7, which were isolated from alfalfa root nodules and possess plant growth-promoting properties.
Purpose
Studying the legume nodule microbiome is important for understanding the development and nutrition of the plants inhabited by the various microbes within and upon them. We analyzed the ...microbiomes of these underground organs from both an important crop plant (
Medicago sativa
) and a related legume (
M. polymorpha
) using metagenomic and culture-based techniques to identify the main cultivatable contributors to plant growth enhancement.
Methods
Using high-throughput sequencing, culturing, and
in planta
techniques, we identified and analyzed a broad population of the bacterial taxa within
Medicago
nodules and the surrounding soil.
Results
Fifty-one distinct bacterial strains were isolated and characterized from nodules of both
Medicago
species and their growth-promoting activities were studied. Sequencing of 16S rRNA gene amplicons showed that in addition to
Ensifer
, the dominant genus, a large number of Gram-positive bacteria belonging to the Firmicutes and Actinobacteria were also present. After performing ecological and plant growth-promoting trait analyses, selecting the most promising strains, and then performing in planta assays, we found that strains of
Bacillus
and
Micromonospora
among others could play important roles in supporting the growth, health, and productivity of the host plant.
Conclusion
To our knowledge, the comparison of the biodiversity of the microbiota of undomesticated vs. cultivated
Medicago
roots and nodules is novel and shows the range of potential Plant Growth-Promoting Bacteria that could be used for plants of agricultural interest. These and other nodule-isolated microbes could also serve as inoculants with rhizobia with the goal of replacing synthetic fertilizers and pesticides for sustainable agriculture.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract Background Spirituality is a patient need that requires special attention from the Pain and Palliative Care Service team. This quality improvement project aimed to provide spiritual ...assessment for all new outpatients with serious life-altering illnesses. Measures Percentage of new outpatients receiving spiritual assessment (Faith, Importance/Influence, Community, Address/Action in care, psychosocial evaluation, chaplain consults) at baseline and postinterventions. Intervention Interventions included encouraging clinicians to incorporate adequate spiritual assessment into patient care and implementing chaplain covisits for all initial outpatient visits. Outcomes The quality improvement interventions increased spiritual assessment (baseline vs. postinterventions): chaplain covisits (25.5% vs. 50%), Faith, Importance/Influence, Community, Address/Action in care completion (49% vs. 72%), and psychosocial evaluation (89% vs. 94%). Conclusions/Lessons Learned Improved spiritual assessment in an outpatient palliative care clinic setting can occur with a multidisciplinary approach. This project also identifies data collection and documentation processes that can be targeted for improvement.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Investigations of Rhizobium biofilm formation Fujishige, Nancy A; Kapadia, Neel N; De Hoff, Peter L ...
FEMS microbiology ecology,
20/May , Volume:
56, Issue:
2
Journal Article, Conference Proceeding
Peer reviewed
Open access
Abstract
The development of nitrogen-fixing nodules of the Rhizobium-legume symbiosis, especially the early stages of root hair deformation and curling, infection thread formation, and nodule ...initiation, has been well studied from a genetic standpoint. In contrast, the factors important for the colonization of surfaces by rhizobia, including roots–an important prerequisite for nodule formation–have not been as thoroughly investigated. We developed conditions for analyzing the ability of two fast-growing rhizobia, Sinorhizobium meliloti and Rhizobium leguminosarum bv. viciae, to produce biofilms on abiotic surfaces such as glass, plastic microtiter plates, sand and soil as a prelude to characterizing the genes important for aggregation and attachment. Factors involved in adherence to abiotic surfaces are likely to be used in rhizobial attachment to legume root cells. In this report, we show that S. meliloti exopolysaccharide-deficient mutants as well as exopolysaccharide overproducers exhibit reduced biofilm phenotypes that show parallels with their nodulation abilities. We also investigated two flagella-less S. meliloti mutants and found them to have reduced biofilming capabilities. To investigate whether there was a symbiotic phenotype, we tested one of the Fla− mutants on two different S. meliloti hosts, alfalfa and white sweetclover, and found that nodule formation was significantly delayed on the latter.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Soil degradation is an ecological disturbance, usually human‐caused, that negatively affects the vegetation and climate of an ecosystem, particularly arid and semiarid environments. These degraded ...soils can be restored by using native perennial plants inoculated with specific microorganisms. We studied the changes in root growth and the rhizosphere bacterial community of mesquite seedlings (Prosopis articulata) after inoculation with the endophytic bacteria Bacillus pumilus ES4, over 3 cycles of growth in the same soil under desert climatic conditions, and found that inoculation significantly enhanced root biomass during the growth cycles but not shoot biomass or root and shoot lengths. Fluorescent in situ hybridization analysis demonstrated that B. pumilus colonized the root cap, apical meristem, and elongation zone, forming small colonies, on roots from soil‐grown mesquite. Inoculation also significantly changed the bacterial community structure of rhizophere and nonrhizosphere (without plants) soils based on denaturing gradient gel electrophoresis profiles. The changes were highly stable, and the bacterial community structure was maintained throughout the experimental period and not affected by plant replacement. The 16S rRNA pyrosequencing confirmed the changes on structure of bacterial community and revealed an impact on the top taxonomic levels analyzed. The rhizospheres of inoculated plants showed a significant increase in the abundance of Proteobacteria and Acidobacteria coupled with a concomitant decrease in Actinobacteria, whereas an opposite response was observed in nonrhizospheric degraded soils. Overall, inoculation with B. pumilus reduced bacterial diversity but increased the Rhizobium population in the soil. The class Bacilli, despite B. pumilus inoculum, showed minimal variation.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Two strains, 30N-5 and 30VD-1, identified as Bacillus simplex and B. subtilis, were isolated from the rhizospheres of two different plants, a Podocarpus and a palm, respectively, growing in the ...University of California, Los Angeles (UCLA) Mildred E. Mathias Botanical Garden. B. subtilis is a well-known plant-growth promoting bacterial species, but B. simplex is not. B. simplex 30N-5 was initially isolated on a nitrogen-free medium, but no evidence for nitrogen fixation was found. Nevertheless, pea plants inoculated with B. simplex showed a change in root architecture due to the emergence of more lateral roots. When Pisum sativum carrying a DR5::GUSA construct, an indicator for auxin response, was inoculated with either B. simplex 30N-5 or its symbiont Rhizobium leguminosarum bv. viciae 128C53, GUS expression in the roots was increased over the uninoculated controls. Moreover, when pea roots were coinoculated with either B. simplex 30N-5 or B. subtilis 30VD-1 and R. leguminosarum bv. viciae 128C53, the nodules were larger, clustered, and developed more highly branched vascular bundles. Besides producing siderophores and solubilizing phosphate, the two Bacillus spp., especially strain 30VD-1, exhibited anti-fungal activity towards Fusarium. Our data show that combining nodulating, nitrogen-fixing rhizobia with growth-promoting bacteria enhances plant development and strongly supports a coinoculation strategy to improve nitrogen fixation, increase biomass, and establish greater resistance to fungal disease.
Swarming motility and biofilm formation are opposite, but related surface-associated behaviors that allow various pathogenic bacteria to colonize and invade their hosts. In Sinorhizobium meliloti, ...the alfalfa endosymbiont, these bacterial processes and their relevance for host plant colonization are largely unexplored. Our previous work demonstrated distinct swarming abilities in two S. meliloti strains (Rm1021 and GR4) and revealed that both environmental cues (iron concentration) and bacterial genes (fadD, rhb, rirA) play crucial roles in the control of surface motility in this rhizobial species. In the current study, we investigate whether these factors have an impact on the ability of S. meliloti to establish biofilms and to colonize host roots.
We found that strain GR4, which is less prone to translocate on solid surfaces than strain Rm1021, is more efficient in developing biofilms on glass and plant root surfaces. High iron conditions, known to prevent surface motility in a wild-type strain of S. meliloti, promote biofilm development in Rm1021 and GR4 strains by inducing the formation of more structured and thicker biofilms than those formed under low iron levels. Moreover, three different S. meliloti mutants (fadD, rhb, and rirA) that exhibit an altered surface translocation behavior compared with the wild-type strain, establish reduced biofilms on both glass and alfalfa root surfaces. Iron-rich conditions neither rescue the defect in biofilm formation shown by the rhb mutant, which is unable to produce the siderophore rhizobactin 1021 (Rhb1021), nor have any impact on biofilms formed by the iron-response regulator rirA mutant. On the other hand, S. meliloti FadD loss-of-function mutants do not establish normal biofilms irrespective of iron levels.
Our studies show that siderophore Rhb1021 is not only required for surface translocation, but also for biofilm formation on glass and root surfaces by strain Rm1021. In addition, we present evidence for the existence of control mechanisms that inversely regulate swarming and biofilm formation in S. meliloti, and that contribute to efficient plant root colonization. One of these mechanisms involves iron levels and the iron global regulator RirA. The other mechanism involves the participation of the fatty acid metabolism-related enzyme FadD.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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