Optimization of plant hormonal balance by microorganisms prevents plant heavy metal accumulation.

Heavy metal contamination is a threat to global food safety. Reducing heavy metal uptake in plants is a promising way to make plants safer, yet breeding the right set of traits can be tedious. We test whether microorganisms are able to impact the plant's hormonal balance hereby helping to manage plant heavy metal uptake. We focus on ethylene, a plant hormone regulating plant stress tolerance and nutrition. We grew three phylogenetically distinct plants, Rumex palustris, Alcea aucheri and Arabidopsis thaliana, on a cadmium-spiked soil. Plants roots were coated with the bacterium Pseudomonas putida UW4, which degrades the precursor of ethylene, or an isogenic ACC deaminase-deficient mutant lacking this ability. We followed ethylene concentrations, plant growth and cadmium uptake. Wildtype bacteria reduced shoot cadmium concentration by up to 35% compared to the control, while the mutant increased cadmium concentration. This effect was linked to ethylene, which was consistently positively correlated with cadmium concentration. We therefore propose that bacteria modulating plant hormonal balance may offer new possibilities to improve specific aspects of plant phenotype, in the present context reducing heavy metal. They may thus pave the way for new strategies to improve food safety in a context of the widespread soil contamination.

Changes in root-exudate-induced respiration reveal a novel mechanism through which drought affects ecosystem carbon cycling.

Root exudates play an important role in ecosystem response to climate change, but the functional consequences of drought-induced changes in the quality of root exudates are unknown. Here, we addressed this knowledge gap in a unique experimental approach. We subjected two common grassland species that differ widely in their growth strategies and root systems, the grass Holcus lanatus and the forb Rumex acetosa, to 2 wk of drought. We collected root exudates and soils at the end of the drought and after 2 wk of recovery and readded all root exudates to all soils in a fully reciprocal set-up to measure root-exudate-induced respiration. We found that soil treatment was unimportant for determining root-exudate-induced respiration. By contrast, root exudates collected from plants that had experienced drought clearly triggered more soil respiration than exudates from undroughted plants. Importantly, this increased respiration compensated for the lower rates of root exudation in droughted plants. Our findings reveal a novel mechanism through which drought can continue to affect ecosystem carbon cycling, and a potential plant strategy to facilitate regrowth through stimulating microbial activity. These findings have important implications for understanding plant and ecosystem response to drought.

Fusariumins C and D, two novel antimicrobial agents from Fusarium oxysporum ZZP-R1 symbiotic on Rumex madaio Makino.

Bioassay-guided fractionation of the crude extract of fermentation broth of one symbiotic strain Fusarium oxysporum ZZP-R1 derived from coastal plant Rumex madaio Makino, one traditional Chinese medicine used as a treatment of inflammation and toxication, yielded two novel compounds, fusariumins C (1) and D (2). Chemical structures of 1 and 2 were respectively determined as one meroterpene with cyclohexanone moiety and a sesquiterpene ester with a conjugated triene and an unusual oxetene ring by a combination of spectroscopic methods, including 1D and 2D NMR, mass spectrometry, and optical rotation analysis, as well as by comparison with literature data. Bioassay results indicated that compound 1 displayed potent activity against Staphyloccocus aureus with an MIC value of 6.25 µM, and compound 2 had a moderate inhibitory effect on S. aureus with an MIC value of 25.0 µM. It was the first report that phytochemical investigation of Fusarium strain from R. madaio Makino led to isolation of new antimicrobial agents.

The improvement of bioactive secondary metabolites accumulation in Rumex gmelini Turcz through co-culture with endophytic fungi

Abstract Aspergillus sp., Fusarium sp., and Ramularia sp. were endophytic fungi isolated from Rumex gmelini Turcz (RGT), all of these three strains could produce some similar bioactive secondary metabolites of their host. However the ability to produce active components degraded significantly after cultured these fungi alone for a long time, and were difficult to recover. In order to obtain more bioactive secondary metabolites, the co-culture of tissue culture seedlings of RGT and its endophytic fungi were established respectively, and RGT seedling was selected as producer. Among these fungi, Aspergillus sp. showed the most significant enhancement on bioactive components accumulation in RGT seedlings. When inoculated Aspergillus sp. spores into media of RGT seedlings that had taken root for 20 d, and made spore concentration in co-culture medium was 1 × 104 mL-1, after co-cultured for 12 d, the yield of chrysophaein, resveratrol, chrysophanol, emodin and physcion were 3.52-, 3.70-, 3.60-, 4.25-, 3.85-fold of the control group. The extreme value of musizin yield was 0.289 mg, which was not detected in the control groups. The results indicated that co-culture with endophytic fungi could significantly enhance bioactive secondary metabolites production of RGT seedlings.

The improvement of bioactive secondary metabolites accumulation in Rumex gmelini Turcz through co-culture with endophytic fungi.

Aspergillus sp., Fusarium sp., and Ramularia sp. were endophytic fungi isolated from Rumex gmelini Turcz (RGT), all of these three strains could produce some similar bioactive secondary metabolites of their host. However the ability to produce active components degraded significantly after cultured these fungi alone for a long time, and were difficult to recover. In order to obtain more bioactive secondary metabolites, the co-culture of tissue culture seedlings of RGT and its endophytic fungi were established respectively, and RGT seedling was selected as producer. Among these fungi, Aspergillus sp. showed the most significant enhancement on bioactive components accumulation in RGT seedlings. When inoculated Aspergillus sp. spores into media of RGT seedlings that had taken root for 20d, and made spore concentration in co-culture medium was 1×104mL-1, after co-cultured for 12d, the yield of chrysophaein, resveratrol, chrysophanol, emodin and physcion were 3.52-, 3.70-, 3.60-, 4.25-, 3.85-fold of the control group. The extreme value of musizin yield was 0.289mg, which was not detected in the control groups. The results indicated that co-culture with endophytic fungi could significantly enhance bioactive secondary metabolites production of RGT seedlings.

Ecosystem services and plant physiological status during endophyte-assisted phytoremediation of metal contaminated soil.

Mining sites shelter a characteristic biodiversity with large potential for the phytoremediation of metal contaminated soils. Endophytic plant growth-promoting bacteria were isolated from two metal-(hyper)accumulator plant species growing in a metal contaminated mine soil. After characterizing their plant growth-promoting traits, consortia of putative endophytes were used to carry out an endophyte-assisted phytoextraction experiment using Noccaea caerulescens and Rumex acetosa (singly and in combination) under controlled conditions. We evaluated the influence of endophyte-inoculated plants on soil physicochemical and microbial properties, as well as plant physiological parameters and metal concentrations. Data interpretation through the grouping of soil properties within a set of ecosystem services was also carried out. When grown together, we observed a 41 and 16% increase in the growth of N. caerulescens and R. acetosa plants, respectively, as well as higher values of Zn phytoextraction and soil microbial biomass and functional diversity. Inoculation of the consortia of putative endophytes did not lead to higher values of plant metal uptake, but it improved the plants' physiological status, by increasing the content of chlorophylls and carotenoids by up to 28 and 36%, respectively, indicating a reduction in the stress level of plants. Endophyte-inoculation also stimulated soil microbial communities: higher values of acid phosphatase activity (related to the phosphate solubilising traits of the endophytes), bacterial and fungal abundance, and structural diversity. The positive effects of plant growth and endophyte inoculation on soil properties were reflected in an enhancement of some ecosystem services (biodiversity, nutrient cycling, water flow regulation, water purification and contamination control).

Azorhizobium oxalatiphilum sp. nov., and emended description of the genus Azorhizobium.

A gram-negative, motile, non-spore-forming rod, designated NS12(T), was isolated from macerated petioles of Rumex sp. after enrichment with oxalate. On the basis of 16S rRNA gene sequence similarity, strain NS12(T) was phylogenetically related to the genera Azorhizobium and Xanthobacter in the class Alphaproteobacteria. Strain NS12(T) was most closely related to Azorhizobium doebereinerae BR 5401(T) and Azorhizobium caulinodans ORS 571(T) (98.3 and 97.3 % 16S rRNA gene sequence similarity, respectively). Membership of the genus Xanthobacter was excluded by phenotypic characterization. The whole-cell fatty acid compositions of the isolate was typical of members of the genus Azorhizobium with C18 : 1ω7c, cyclo-C19 : 0ω8c, 11-methyl-C18 : 1ω7c and C16 : 0 as the main components. The results of DNA-DNA hybridization and physiological tests allowed the genotypic and phenotypic differentiation of strain NS12(T) from the two members of the genus Azorhizobium. Therefore it is concluded that the isolate represents a novel species of the genus Azorhizobium, for which the name Azorhizobium oxalatiphilum sp. nov. is proposed. The type strain is NS12(T) ( = DSM 18749(T) = CCM 7897(T)). The description of the genus Azorhizobium is also emended.

Rhizosphere and non-rhizosphere bacterial community composition of the wild medicinal plant Rumex patientia.

To investigate bacterial communities between rhizosphere and non-rhizosphere soils of the wild medicinal plant Rumex patientia of Jilin, China, small subunit rRNAs (16S rDNA) from soil metagenome were amplified by polymerase chain reaction using primers specific to the domain bacteria and analysed by cloning and sequencing. The relative proportion of bacterial communities in rhizosphere soils was similar to non-rhizosphere soils in five phylogenetic groups (Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi and Planctomycetes). But there were differences in five other phylogenetic groups (Firmicutes, Bacteroidetes, Gemmatimonadetes, Verrucomicrobia and Unclassified bacteria). Over 97.24 % of the sequenced clones were found to be unique to rhizosphere and non-rhizosphere soils, while 2.76 % were shared by both of them. Our results indicate that there are differences in the composition and proportion of bacterial communities between rhizosphere and non-rhizosphere soils. Furthermore, the unique bacterial clones between rhizosphere and non-rhizosphere soils of the wild medicinal plant R. patientia have obvious differences.

Phytohabitans flavus sp. nov., Phytohabitans rumicis sp. nov. and Phytohabitans houttuyneae sp. nov., isolated from plant roots, and emended description of the genus Phytohabitans.

An actinomycete strain, designated K09-0627(T), was isolated from the roots of an orchid collected in Okinawa Prefecture, Japan. Two actinomycete strains K11-0047(T) and K11-0057(T) were isolated from the roots of Rumex acetosa and Houttuynia cordata collected in Kanagawa Prefecture, Japan. 16S rRNA gene sequence analyses indicated that the isolates belonged to the genus Phytohabitans, and that they were closely related to each other and to Phytohabitans suffuscus K07-0523(T). The DNA-DNA relatedness values between the three isolates and Phytohabitans suffuscus were below 70%. On the basis of phylogenetic analysis, DNA-DNA relatedness values and phenotypic characteristics, the strains should be classified as novel species in the genus Phytohabitans, for which the names Phytohabitans flavus sp. nov. (type strain, K09-0627(T)=JCM 17387(T)=NBRC 107702(T)=DSM 45551(T)), Phytohabitans rumicis sp. nov. (type strain, K11-0047(T)=JCM 17829(T)=NBRC 108638(T)=BCC 48146(T)) and Phytohabitans houttuyneae sp. nov. (type strain, K11-0057(T)=JCM 17830(T)=NBRC 108639(T)=BCC 48147(T)) are proposed.

Arbuscular mycorrhizal fungi do not enhance nitrogen acquisition and growth of old-field perennials under low nitrogen supply in glasshouse culture.

Arbuscular mycorrhizal fungi (AMF) are known to promote plant growth when phosphorus is limiting, but the role of AMF in plant growth under nitrogen (N) limiting conditions is unclear. Here, we manipulated N (control vs inorganic and organic forms) and AMF species (control vs four AMF species) for five old-field perennials grown individually in a glasshouse under N-limiting conditions. We found that AMF were at best neutral and that some AMF species depressed growth for some plant species (significant plant-fungus interaction). Native plant species growth was strongly depressed by all but one AMF species; exotic plant species were less sensitive to AMF. We found no evidence of plant N preferences. Both natives and exotics were able to acquire more N with N addition, but only exotics grew more with added N. Our results suggest that AMF do not promote plant N acquisition at low N supply, and our results are consistent with other research showing that AMF can act as a parasitic carbon drain when phosphorus availability is relatively high.

[Seasonal dynamics in a yeast population on the Oxalis acetosella L. leaves]. / Sezonnaia dinamika drozhzhevogo naseleniia list'ev Oxalis acetosella L.

Analysis of an epiphytic yeast population on the leaves of the evergreen common wood sorrel Oxalis acetosella L. throughout a year showed that the density and the species composition of this population underwent regular seasonal changes. There were almost no yeasts on the young spring leaves. However, the yeast population on the mature leaves tended to increase in the autumn, reaching a maximum after the formation of continuous snow cover. Then the yeast population on the leaves tended to decrease, reaching a minimum in the spring. The species diversity of the yeasts was maximum in the autumn. The population of the epiphytic yeast species Cystofilobasidium capitatum, Rhodotorula fujisanensis, Leucosporium scottii, and Cryptococcus flavus peaked in the autumn. On the other hand, the population of the widespread epiphytic species Cryptococcus laurentii on the wood sorrel leaves peaked in January. The relative abundance of the red-pigmented phytobionts Rhodotorula glutinis and Sporobolomyces roseus virtually did not change throughout the year. The relative abundance of the euribiotic species Cryptococcus albidus showed irregular monthly variations. The data obtained show that the epiphytic microbial population of various plants can be comprehensively studied only by analyzing this population throughout the vegetative period of the plants.