Bacterial endophytes enhance phytostabilization in soils contaminated with uranium and lead

The combined use of plants and bacteria is a promising approach for the remediation of polluted soil. In the current study, the potential of bacterial endophytes in partnership with Leptochloa fusca (L.) Kunth was evaluated for the remediation of uranium (U)- and lead (Pb)-contaminated soil. L. fusca was vegetated in contaminated soil and inoculated with three different endophytic bacterial strains, Pantoea stewartii ASI11, Enterobacter sp. HU38, and Microbacterium arborescens HU33, individually as well as in combination. The results showed that the L. fusca can grow in the contaminated soil. Bacterial inoculation improved plant growth and phytoremediation capacity: this manifested in the form of a 22–51% increase in root length, 25–62% increase in shoot height, 10–21% increase in chlorophyll content, and 17–59% more plant biomass in U- and Pb-contaminated soils as compared to plants without bacterial inoculation. Although L. fusca plants showed potential to accumulate U and Pb in their root and shoot on their own, bacterial consortia further enhanced metal uptake capacity by 53–88% for U and 58–97% for Pb. Our results indicate that the combination of L. fusca and endophytic bacterial consortia can effectively be used for the phytostabilization of both U- and Pb-contaminated soils.     

Root bacterial endophytes confer drought resistance and enhance expression and activity of a vacuolar H+-pumping pyrophosphatase in pepper plants

It has been previously shown that the transgenic overexpression of the plant root vacuolar proton pumps H⁺-ATPase (V-ATPase) and H⁺-PPase (V-PPase) confer tolerance to drought. Since plant-root endophytic bacteria can also promote drought tolerance, we hypothesize that such promotion can be associated to the enhancement of the host vacuolar proton pumps expression and activity. To test this hypothesis, we selected two endophytic bacteria endowed with an array of in vitro plant growth promoting traits. Their genome sequences confirmed the presence of traits previously shown to confer drought resistance to plants, such as the synthesis of nitric oxide and of organic volatile organic compounds. We used the two strains on pepper (Capsicuum annuum L.) because of its high sensitivity to drought. Under drought conditions, both strains stimulated a larger root system and enhanced the leaves' photosynthetic activity. By testing the expression and activity of the vacuolar proton pumps, H⁺-ATPase (V-ATPase) and H⁺-PPase (V-PPase), we found that bacterial colonization enhanced V-PPase only. We conclude that the enhanced expression and activity of V-PPase can be favoured by the colonization of drought-tolerance-inducing bacterial endophytes.     

Identification and characterization of bacterial endophytes of rice

We isolated seven different bacteria from rice seedlings grown from surface sterilized seeds. Three were associated with the rice seed husk and the other four were growing endophytically within the seed. Microscopic studies revealed that the endophytes were concentrated in the root stele region. Some of the bacteria exhibited strong anti-fungal activity against Rhizoctonia solani, Pythium myriotylum, Guamannomyces graminis and Heterobasidium annosum.     

Impact of dust exposure on mixed bacterial cultures and during eukaryotic cell co-culture infections

On a daily basis, humans, and their colonizing microbiome, are exposed to both indoor and outdoor dust, containing both deleterious organic and inorganic contaminants, through dermal contact, inhalation, and ingestion. Recent studies evaluating the dust exposure responses of opportunistic pathogens, such as Escherichia coli and Pseudomonas aeruginosa, revealed significant increases in biofilm formation following dust exposure. In this study, the effects of dust exposure on mixed bacterial cultures as well as HT-29 co-cultures were evaluated. As it was observed in pure, single bacterial cultures earlier, neither indoor nor outdoor dust exposure (at concentrations of 100 μg/mL) influenced the growth of mixed bacterial liquid cultures. However, when in paired mixed cultures, dust exposure increased sensitivity to oxidative stress and significantly enhanced biofilm formation (outdoor dust). More specifically, mixed cultures (E. coli-Klebsiella pneumoniae, K. pneumoniae-P. aeruginosa, and E. coli-P. aeruginosa) exhibited increased sensitivity to 20 and 50 mM of H2O2 in comparison to their pure, single bacterial culture counterparts and significantly enhanced biofilm production for each mixed culture. Finally, bacterial proliferation during a eukaryotic gut cell (HT29) co-culture was significantly more robust for both K. pneumoniae and P. aeruginosa when exposed to both house and road dust; however, E. coli only experienced significantly enhanced proliferation, in HT29 co-culture, when exposed to road dust. Taken together, our findings demonstrate that bacteria respond to dust exposure differently when in the presence of multiple bacterial species or when in the presence of human gut epithelial cells, than when grown in isolation.     

Properties of bacterial endophytes and their proposed role in plant growth

Bacterial endophytes live inside plants for at least part of their life cycle. Studies of the interaction of endophytes with their host plants and their function within their hosts are important to address the ecological relevance of endophytes. The modulation of ethylene levels in plants by bacterially produced 1-aminocyclopropane-1-carboxylate deaminase is a key trait that enables interference with the physiology of the host plant. Endophytes with this capacity might profit from association with the plant, because colonization is enhanced. In turn, host plants benefit by stress reduction and increased root growth. This mechanism leads to the concept of 'competent' endophytes, defined as endophytes that are equipped with genes important for maintenance of plant-endophyte associations. The ecological role of these endophytes and their relevance for plant growth are discussed here.     

Strategies to enhance production of microalgal biomass and lipids for biofuel feedstock

ABSTRACT

Microalgae have enormous potential as feedstock for biofuel production compared with other sources, due to their high areal productivity, relatively low environmental impact, and low impact on food security. However, high production costs are the major limitation for commercialization of algal biofuels. Strategies to maximize biomass and lipid production are crucial for improving the economics of using microalgae for biofuels. Selection of suitable algal strains, preferably from indigenous habitats, and further improvement of those ‘platform strains’ using mutagenesis and genetic engineering approaches are desirable. Conventional approaches to improve biomass and lipid productivity of microalgae mainly involve manipulation of nutritional (e.g. nitrogen and phosphorus) and environmental (e.g. temperature, light and salinity) factors. Approaches such as the addition of phytohormones, genetic and metabolic engineering, and co-cultivation of microalgae with yeasts and bacteria are more recent strategies to enhance biomass and lipid productivity of microalgae. Improvement in culture systems and the use of a hybrid system (i.e. a combination of open ponds and photobioreactors) is another strategy to optimize algal biomass and lipid production. In addition, the use of low-cost substrates such as agri-industrial wastewater for the cultivation of microalgae will be a smart strategy to reduce production costs. Such systems not only generate high algal biomass and lipid productivity, but are also useful for bioremediation of wastewater and bioremoval of waste CO₂. The aim of this review is to highlight the advances in the use of various strategies to enhance production of algal biomass and lipids for biofuel feedstock.     

Enumeration of bacterial cell numbers by amplified firefly bioluminescence without cultivation

We recently developed a novel bioluminescent enzymatic cycling assay for ATP and AMP with the concomitant use of firefly luciferase and pyruvate orthophosphate dikinase (PPDK), where AMP and pyrophosphate produced from ATP by firefly luciferase were converted back into ATP by PPDK. Background luminescence derived from contaminating ATP and AMP in the reagent was reduced using adenosine phosphate deaminase which degrades ATP, ADP, and AMP, resulting in constant and highly amplified bioluminescence with low background luminescence. To detect bacterial cells without cultivation, we applied the above bioluminescent enzymatic cycling reagent to rapid microbe detection system. ATP spots (0.31-5.0 amol/spot) at the level of a single bacterial cell were detected with 5 min signal integration, signifying that integrated luminescence was amplified 43 times in comparison to traditional ATP bioluminescence. Consequently, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Lactobacillus brevis in beer were detected without cultivation. Significant correlation was observed between the number of signal spots obtained using this novel system and the colony-forming units observed with the conventional colony-counting method (R(2)=0.973).     

Survey of indigenous bacterial endophytes from cotton and sweet corn

The genotypic diversity of indigenous bacterial endophytes within stems and roots of sweet corn (Zea mays L.) and cotton (Gossypium hirsutum L.) was determined in field trials throughout one growing season. Strains were isolated from surface-disinfested tissues and identified by fatty acid analysis. Gram-negative bacteria comprised 70.5% of the endophytic bacteria and 27 of the 36 genera identified. The most frequently isolated groups from sweet corn roots, were Burkholderia pickettii and Enterobacter spp.; from sweet corn stems, Bacillus megaterium. Bacterial genera present in sweet corn roots were also generally present in sweet corn stems. However, Burkholderia gladioli, Burkholderia solanacearum and Enterobacter cloacae were isolated much more frequently from sweet corn roots than stems, whereas Methylobacterium spp. were found more frequently in sweet corn stems than roots. Agrobacterium radiobacter, Serratia spp. and Burkholderia solanacearum, were the most frequently isolated groups from cotton roots; and Bacillus megaterium and Bacillus pumilus from cotton stems. Acinetobacter baumannii and Arthrobacter spp. were present in cotton stems but not in cotton roots. There were 14 taxonomic groups present in cotton roots that were not in cotton stems; all but one were Gram-negative. These included, Agrobacterium radiobacter, Bacillus megaterium, Bacillus pumilus, Enterobacter asburiae, Pseudomonas chlororaphis, Serratia spp. and Staphylococcus spp. Rhizobium japonicum and Variovorax paradoxus were isolated, almost exclusively, from the roots of both crops. Bacterial taxa present in both sweet corn and cotton early in the season were generally present late in the season. The diversity of bacteria was greater in roots than stems for each crop.     

Mapping QTLs for chlorophyll content and chlorophyll fluorescence in wheat under heat stress

Heat stress, one of the major abiotic stresses in wheat, affects chlorophyll fluorescence and chlorophyll content and thereby photosynthesis. To identify quantitative trait loci (QTLs) associated with these traits under terminal heat stress, 251 recombinant inbred lines (RILs) derived from a cross HD 2808/HUW510 were phenotyped. Using composite interval mapping, 40 QTLs were identified; 17 were related to conditions after timely sowing and 23 to heat stress after late sowing. The various parameters of chlorophyll fluorescence were associated with 23 QTLs, which were located on chromosomes 1A, 2A, 3A, and 2D and explained 3.67 to 18.04 % of phenotypic variation, whereas chlorophyll content was associated with 17 QTLs on chromosomes 2A, 2B, 2D, 5B, and 7A explaining 3.49 to 31.36 % of phenotypic variation. Most of the identified QTLs were clustered on chromosome 2D followed by 2A and 1A. The QTL Qchc.iiwbr-2A for chlorophyll content linked with marker gwm372 was stable over conditions and explained 3.81 to 18.05 % of phenotypic variation. In addition, 7 epistatic QTL pairs were also detected which explained 1.67 to 11.0 % of phenotypic variance. These identified genomic regions can be used in marker assisted breeding after validation for heat tolerance in wheat.     

Biodiversity and antimicrobial potential of bacterial endophytes from halophyte Salicornia brachiata

Extreme natural habitats like halophytes, marsh land, and marine environment are suitable arena for chemical ecology between plants and microbes having environmental impact. Endophytes are an ecofriendly option for the promotion of plant growth and to serve as sustainable resource of novel bioactive natural products. The present study, focusing on biodiversity of bacterial endophytes from Salicornia brachiata, led to isolation of around 336 bacterial endophytes. Phylogenetic analysis of 63 endophytes revealed 13 genera with 27 different species, belonging to 3 major groups: Firmicutes, Proteobacteria, and Actinobacteria. 30% endophytic isolates belonging to various genera demonstrated broad-spectrum antibacterial and antifungal activities against a panel of human, plant, and aquatic infectious agents. An endophytic isolate Bacillus amyloliquefaciens 5NPA-1, exhibited strong in-vitro antibacterial activity against human pathogen Staphylococcus aureus and phytopathogen Xanthomonas campestris. Investigation through LC–MS/MS-based molecular networking and bioactivity-guided purification led to the identification of three bioactive compounds belonging to lipopeptide class based on ¹H-, ¹³C-NMR and MS analysis. To our knowledge, this is the first report studying bacterial endophytic biodiversity of Salicornia brachiata and the isolation of bioactive compounds from its endophyte. Overall, the present study provides insights into the diversity of endophytes associated with the plants from the extreme environment as a rich source of metabolites with remarkable agricultural applications and therapeutic properties.

     

玉米叶绿素含量的QTL定位

为了探讨玉米叶绿素含量的遗传规律, 以A150-3-2×Mo17杂交组配的189个F2单株作为作图群体, 构建了具有112个标记位点的玉米分子遗传图谱, 于喇叭口期和开花期分别进行了玉米叶绿素a含量(chla), 叶绿素b含量(chlb), 其他叶绿素含量(chlc)和叶绿素总含量(chlz)4个性状的测定, 并进行QTL分析。在喇叭口期和开花期共检测到32个QTL, 分布在除第6和10染色体以外的其他染色体上。在喇叭口期检测到24个QTL, 分布于第1、2、3、5、7、8和9染色体上, 叶绿素a、叶绿素b、其他叶绿素和叶绿素总含量各检测到6个QTL, 在同一区间内检测到的4个性状的QTL之间的距离在0~2 cM之间。喇叭口期检测到控制叶绿素a、叶绿素b、其他叶绿素和叶绿素总含量的4个主效QTL位于第5染色体上的umc1098~bnlg557区间, 分别可解释表型变异的11.63%、10.3%、10.77%和11.51%。开花期检测到8个QTL, 分布于第4和5染色体上。其中叶绿素a、叶绿素b、其他叶绿素和叶绿素总含量各2个QTL。标记umc1098和bnlg557之间同时存在控制喇叭口期4个叶绿素含量性状的QTL和开花期控制叶绿素a和叶绿素b的QTL。标记umc2308和bnlg386之间只存在控制开花期4个叶绿素含量性状的QTL。     

Involvement of chlorophyllase in chlorophyll metabolism in olive varieties with high and low chlorophyll content

Olive fruits of the Arbequina variety are differentiated from those of Hojiblanca and Picual by the differing presence of 13²-OH-chlorophyll a and of dephytylated chlorophyll derivatives during the life cycle of the fruit. During the fruit growth stage, which coincides with chlorophyll synthesis, chlorophyllase (EC: 3.1.1.14) is present in the three varieties but only yields chlorophyllides in Arbequina. The presence of oxidized catabolites of chlorophyll a in fruits of the Arbequina variety during this same period confirms the activity of oxidative enzyme systems. The low synthesis of chlorophylls in the fruits of the Arbequina variety is associated with the fact that, during the natural biosynthetic turnover, the catabolic pathway is more potentiated than the anabolic one. In the ripening phase, in the Hojiblanca and Picual fruits, chlorophyllase activity was measured but the absence of chlorophyllides showed that this enzyme remains latent and that oxidative enzymes are the ones taking part in the chlorophyll disappearance. In the Arbequina variety, both chlorophyllase and oxidative enzymes are responsible for the chlorophyll degradation.     

New approach in studies of microalgal cell lysis

A new approach to the studies of the microalgal cell lysis by utilizing a combination of two complementary methods is presented. Delayed fluorescence (DF) is a measure of the living algal biomass, detecting only cells with active photosynthesis. Thermal lens spectrometry (TLS) detects the total pigment amount released from lysed cells. Both methods select for photosynthetic organisms, reducing possible background from other sources (e.g. heterotrophic bacteria, zooplankton, and abiotic substances). The DF/TLS method was tested with a laboratory Skeletonema costatum culture exposed to a geometric dilution series of the lysing factor poly- APS. The exposure resulted in similar EC₅0 values for DF intensity, TLS and dissolved esterase activity of 0.8±0.2, 1.77±0.35, and 1.25±0.1 mg poly-APS l⁻¹, respectively. The combined DF/TLS method enabled a rapid evaluation of the living vs. dead cells without any sample pretreatment or manipulation.     

High resolution retrieval of leaf chlorophyll content over Himalayan pine forest using Visible/IR sensors mounted on UAV and radiative transfer model

Forests play an essential role towards net primary productivity, biological cycles and provide habitat to flora & fauna. To monitor key physiological activities in forest canopies such as photosynthesis, respiration, transpiration, spatially-explicit and precise information of the biochemical (biological) variables such as Leaf Chlorophyll Content (LCC) is required. While lookup-table (LUT)-based Radiative Transfer Model (RTM) inversion against optical remote sensing imagery is regarded as a physically sound and robust approach for retrieving biochemical and biophysical variables, regularization procedures are required to offset the problem of ill-posedness. To optimize the RTM inversion of LCC over a sub-tropical pine forest plantation, in the Western Himalaya, we investigated the role of: (1) cost functions (CFs), (2) added noise, and (3) multiple finest solutions in LUT inversion. Principal CFs were evaluated belonging to three categories: information measures, M-estimates, and minimal contrast approaches. The inversion approaches were applied to a LUT produced by the coupled leaf-canopy model known as PROSAIL RTM and tested in contrast field spectral data obtained from reflectance data derived from UAV (Unmanned Aerial Vehicle) images taken over the canopies of covered pine forests. The Bhattacharyya divergence, an information measure, outperformed all other CFs in LCC inversion, with R² of 0.94, RMSE of 6.20 μg/cm² and NRMSE of 12.27% during the validation. The optimized inversion strategy was subsequently applied to a UAV-acquired multispectral image at an 8.2 cm pixel resolution for detailed landscape forest LCC mapping. The associated residuals as provided by the LUT-based inversion provided insights in the spatial consistency of the LCC map.     

Diabetes-related changes in cAMP response element-binding protein content enhance smooth muscle cell proliferation and migration

We hypothesized that diabetes and glucose-induced reactive oxygen species lead to depletion of cAMP response element-binding protein (CREB) content in the vasculature. In primary cultures of smooth muscle cells (SMC) high medium glucose decreased CREB function but increased SMC chemokinesis and entry into the cell cycle. These effects were blocked by pretreatment with the antioxidants. High glucose increased intracellular reactive oxygen species detected by CM-H(2)DCFA. SMC exposed to oxidative stress (H(2)O(2)) demonstrated a 3.5-fold increase in chemokinesis (p < 0.05) and accelerated entry into cell cycle, accompanied by a significant decrease in CREB content. Chronic oxidative challenge similar to the microenvironment in diabetes (glucose oxidase treatment) decreases CREB content (40-50%). Adenoviral-mediated expression of constitutively active CREB abolished the increase in chemokinesis and cell cycle progression induced by either high glucose or oxidative stress. Analysis of vessels from insulin resistant or diabetic animals indicates that CREB content is decreased in the vascular stroma. Treatment of insulin-resistant animals with the insulin sensitizer rosiglitazone restores vessel wall CREB content toward that observed in normal animals. In summary, high glucose and oxidative stress decrease SMC CREB content increase chemokinesis and entry into the cell cycle, which is blocked by antioxidants or restoration of CREB content. Thus, decreased vascular CREB content could be one of the molecular mechanisms leading to increased atherosclerosis in diabetes.     

Rapid,nondestructive measurement of chlorophyll content in leaves with nonuniform chlorophyll distribution

A practical microcomputerized video image analysis method is described for quantifying leaf chlorophyll content without extraction. Chlorophyll concentration is estimated from densimetric measurements of whole, intact leaves. Direct comparison with conventional extraction measurements on Epipremnum aureum, a variegated species, verified the image analysis technique's accuracy. The inherent advantages with regard to the nondestructive and convenient nature of the measurement, and suitability for leaves with irregular chlorophyll distribution, are discussed.     

Positioning cell wall synthetic complexes by the bacterial morphogenetic proteins MreB and MreD

In Caulobacter crescentus, intact cables of the actin homologue, MreB, are required for the proper spatial positioning of MurG which catalyses the final step in peptidoglycan precursor synthesis. Similarly, in the periplasm, MreC controls the spatial orientation of the penicillin binding proteins and a lytic transglycosylase. We have now found that MreB cables are required for the organization of several other cytosolic murein biosynthetic enzymes such as MraY, MurB, MurC, MurE and MurF. We also show these proteins adopt a subcellular pattern of localization comparable to MurG, suggesting the existence of cytoskeletal‐dependent interactions. Through extensive two‐hybrid analyses, we have now generated a comprehensive interaction map of components of the bacterial morphogenetic complex. In the cytosol, this complex contains both murein biosynthetic enzymes and morphogenetic proteins, including RodA, RodZ and MreD. We show that the integral membrane protein, MreD, is essential for lateral peptidoglycan synthesis, interacts with the precursor synthesizing enzymes MurG and MraY, and additionally, determines MreB localization. Our results suggest that the interdependent localization of MreB and MreD functions to spatially organize a complex of peptidoglycan precursor synthesis proteins, which is required for propagation of a uniform cell shape and catalytically efficient peptidoglycan synthesis.     

Degradation and dechlorination of low-chlorinated biphenyls by a three-membered bacterial co-culture

A Pseudomonas sp. strain, designated CPE1, was found to be capable of completely mineralizing 4-chlorobiphenyl via 4-chlorobenzoate and of partially dechlorinating 3,4-dichlorobiphenyl in the presence of biphenyl. A three-membered bacterial consortium, designated ECO3, prepared by combining CPE1 with two chlorobenzoate (CBA)-degrading strains, was capable of extensively degrading and dechlorinating all the monochlorinated biphenyls and several dichlorinated biphenyls in the presence of bipheny. Both CPE1 and ECO3 were capable of co-metabolizing several low-chlorinated biphenyl congeners of Fenclor 42 in the presence of biphenyl; however, only in ECO3 cultures were high degradation rates and chloride release observed. The higher rate of degradation and mineralization of some polychlorinated biphenyls (PCBs) of Fenclor 42 due to the concerted action of ECO3 members both on PCBs and CBAs suggested that the removal of CBAs from the culture medium may favour PCB degradation, and, therefore, that CBAs may be ivollved in the regulation of the degradation process of several chlorinated biphenyl congeners.Correspoeence to: F. Fava