Enhanced biomass and steviol glycosides in <Emphasis Type="Italic">Stevia rebaudiana</Emphasis> treated with phosphate-solubilizing bacteria and rock phosphate

Biofertilizers offer alternative means to promoting cultivation of medicinal plants less dependent on chemical fertilizers. Present study was aimed at evaluating the potential of phosphate-solubilizing bacteria (PSB) Burkholderia gladioli MTCC 10216, B. gladioli MTCC 10217, Enterobacter aerogenes MTCC 10208 and Serratia marcescens MTCC 10238 for utilizing Mussoorie rock phosphate (MRP) to enhance plant growth, and stevioside (ST) and rebaudioside-A (R-A) contents of Stevia rebaudiana. The solubilization of MRP by PSB strains varied from 1.4 to 15.2 μg ml⁻¹, with the highest solubilization by Enterobacter aerogenes 10208. The PSB treatment increased the growth and ST and R-A contents of plants. Plant growth and stevioside contents were more pronounced with plants treated with a mixture of strains and grown in MRP amended soil compared to the unamended soil. The increment in shoot length (47.8%), root length (17.4%), leaf dry weight (164%), stem dry weight (116%), total shoot biomass (136%) resulted in enhanced productivity of ST (291%) and R-A (575%) in plants inoculated with mixture of PSB as compared to the uninoculated plants. The soils of PSB treated plants contained more available P than the soils of uninoculated plants (increase of 86–576%). PSB inoculated plants also recorded higher P content (64–273% increase) compared to uninoculated plants. The PSB strains differed in the extent of rhizosphere colonization, carbon source utilization pattern and whole cell fatty acids methyl esters composition.     

Isolation of Phosphate Solubilizing Bacteria from Maize Rhizosphere and Their Potential for Rock Phosphate Solubilization–Mineralization and Plant Growth Promotion

Phosphate solubilizing bacteria (PSB) play a significant role in plant P nutrition by their effect on soil P dynamics and their subsequent ability to make P available to plants via solubilization and mineralization processes. This study aimed to evaluate the effect of separate and combined use of indigenous PSB, poultry manure (PM) and compost on solubilization and mineralization of rock phosphate (RP) and their subsequent effect on growth and P accumulation of maize (Zea mays L.). A group of fifty seven bacteria were isolated from the rhizosphere/rhizoplane of maize that had been grown in soils collected from varying altitudes (655–2,576 m) of the mountain region of Rawalakot, Azad Jammu and Kashmir, Pakistan. After screening, the capacity of eleven isolates to solubilize mineral phosphate was quantitatively evaluated using insoluble Ca₃(PO₄)₂ in culture medium as a time course study through spectrometer. The growth hormone producing (IAA) capacity of the isolates was also determined. Furthermore, five potential isolates were tested for their ability to increase P release capacity (mineralization) of insoluble RP in an incubation study. The effect of PSB inoculation on maize was determined in a completely randomized greenhouse experiment where root and shoot biomass and P accumulation in plants were assessed. The P solubilization index of selected isolates varied from 1.94 to 3.69, while the P solubilization efficiency ranged between 94.1% and 269.0%. The isolates MRS18 and MRS27 displayed the highest values. The P solubilization in the liquid medium was maximum at 6 and 9 days of incubation ranging between 9.91 and 44.04 µgmL^?1 and the isolates MRS27 and MRS34 exhibited the highest solubilization. Six isolates showed additional capability of producing IAA ranging between 2.66 and 28.41 µgmL^?1. Results of the incubation study indicated that P release capacity (P mineralization) of RP-amended soil varied between 6.0 and 11.8 µgPg^?1 that had been significantly increased to 30.6–36.3 µgPg^?1 (maximum value) when PSB were combined with RP. The combined application of PSB and organic amendments (PM, compost) with RP further increased P mineralization by releasing a maximum of 37.7 µgPg^?1 compared with separate application of RP (11.8 µgPg^?1) and organic amendments (21.5 and 16.5 µgPg^?1). The overall effect of PSB (as a group) with RP over RP alone on maize growth showing a relative increase in shoot length 21%, shoot fresh weight 42%, shoot dry weight 24%, root length 11%, root fresh weight 59%, root dry weight 35% and chlorophyll content 32%. This study clearly indicates that use of PSB, and organic amendments with insoluble RP could be a promising management strategy to enhance P availability in soil pool and improve plant growth in intensive cropping systems.     

Effect of Silicon and Phosphate-Solubilizing Bacteria on Improved Phosphorus (P) Uptake Is Not Specific to Insoluble P-Fertilized Sorghum (Sorghum bicolor L.) Plants

In the research, the single-and dual effects of phosphate-solubilizing bacteria (PSB) (B0, Pseudomonas sp. FA1, and Bacillus simplex UT1) and silicon (Si) (0, 150, 300, and 600 mg kg⁻¹ used as silicic acid) on P uptake by sorghum (Sorghum bicolor L.) plant fertilized with soluble or insoluble P (rock phosphate—RP) were studied via a perlite-potted experiment. Moreover, the effects of various treatments on morphological (shoot and root dry weight), nutritional (the uptake of Si and K) and physiological parameters (activity of catalase, superoxide dismutase, and peroxidase enzymes) of this plant were also measured. When grown in RP-fertilized medium compared with those grown in soluble P-fertilized medium, both shoot biomass and root biomass of sorghum plants were noticeably diminished. The PSB strains and Si levels independently improved all the aforementioned parameters. Use of Si and PSB strains to sorghum plants grown in soluble P or insoluble P medium significantly augmented P use efficiency. Silicon not only augmented the uptake of P from sparingly soluble-P source (RP), but also augmented uptake of P from water-soluble P source. Both B. simplex UT1 and Pseudomonas sp. FA1 indicated a meaningful betterment in sorghum plant dry matter and uptake of P (and K and Si) under both soluble and insoluble P fertilization conditions with Pseudomonas sp. FA1 being more efficacious than B. simplex UT1. But, the dual use of the PSB with Si resulted in the greatest increase in sorghum plant P uptake and other measured growth indices. Application of 600 mg Si kg⁻¹ and Pseudomonas sp. FA1 significantly augmented the P shoot concentration of sorghum plant fertilized with RP to an sufficient level (> 0.3%) in the range of P-fertilized sorghum plants. Therefore, in addition to PSB utilization, Si should be considered as soil amendment in agricultural soils inadequate in plant-available Si as a means of sustainable agriculture with respect to possible savings of scarce P resources.

     

The Interactive Effect of Selenium and Farmyard Manure on Soil Microbial Activities,Yield and Selenium Accumulation by Wheat (Triticum aestivum L.) Grains

This study assessed the interactive effect of selenium (Se) and farmyard manure (FYM) on soil microbial activities, growth, yield, and Se accumulation by wheat grains. Preliminarily, the effect of Se (0–250 µg kg^?1 soil) and FYM (0–12.5 g kg^?1 soil) was assessed on soil microflora. Selenium exhibited an adverse impact on soil microflora; respiration was decreased at?≥?10 µg kg^?1 soil while dehydrogenase and urease activities were decreased at?≥?125 µg kg^?1 soil. At 250 µg Se kg^?1 soil, respiration, dehydrogenase and urease activities were decreased by 81, 40 and 35%, respectively, on unamended soil, and by 9, 47 and 22%, respectively, on FYM-amended soil. The subsequent plant experiments were conducted with same Se and FYM rates; one was harvested 42 days after sowing and other at crop maturity. The application of 125 µg Se kg^?1 and 12.5 g FYM kg^?1 soil improved seedling biomass by 12.6 and 22%, respectively, while their combined use lacked synergistic effect. Similarly, at maturity Se and FYM increased grain yield while their combined effect was not synergistic. The Se-induced suppression in microbial activities was not related to yield which was improved (11% at the highest rate in unamended soil) by Se application. Selenium application increased grain Se content in a rate-dependent manner, it increased from 0 to 1025 µg kg^?1 by applying 250 µg Se kg^?1 soil. Moreover, FYM application decreased Se accumulation in grains. It is concluded that FYM application increased soil microbial activities and yield but reduced grain Se accumulation in wheat on Se-applied soil.

     

Antimicrobial activity and cytotoxicity trait of a bioactive peptide purified from Lactococcus garvieae subsp. bovis BSN307T

A bioactive peptide of 8595 Da was purified from the cell free supernatant of Lactococcus garvieae subsp. bovis BSN307^T. MALDI MS/MS peptide mapping and the data base search displayed no significant similarity to any reported antimicrobial peptide of LAB. This peptide at a dose concentration of 200 µg ml⁻¹ inhibited the growth of both Gram-positive and Gram-negative bacteria by 58–89% and a dose of 500 µg ml⁻¹ scavenged 50% of DPPH-free radicals generated. Interestingly, cytotoxicity assay demonstrated that 17 µg ml⁻¹ of peptide selectively inhibited 50% proliferation of mammalian cancer cell lines HeLa and MCF-7 whereas normal H9c2 cells remained unaffected. Fluorescent microscopic analysis after DAPI nuclear staining of HeLa cells showed characteristics of apoptosis and activation of caspase-3 was ascertained by caspase-3 fluorescence assay.     

Antifungal activity of streptavidin C1 and C2 against pathogens causing Fusarium wilt

Fusarium wilt is caused by the soil-inhabiting fungus Fusarium oxysporum ff. spp. and is one of the most devastating plant diseases, resulting in losses and decreasing the quality and safety of agricultural crops. We recently reported the structures and biochemical properties of two biotin-binding proteins, streptavidin C1 and C2 (isolated from Streptomyces cinnamonensis strain KPP02129). In the present study, the potential of the biotin-binding proteins as antifungal agent for Fusarium wilt pathogens was investigated using recombinant streptavidin C1 and C2. The minimum inhibitory concentration of streptavidin C2 was found to be 16 µg ml^–1 for inhibiting the mycelial growth of F. oxysporum f.sp. cucumerinum and F. oxysporum f.sp. lycopersici, while that of streptavidin C1 was found to be 64 µg ml^–1. Compared with the nontreated control soil, the population density of F. oxysporum f.sp. lycopersici in the soil was reduced to 49·5% and 39·6% on treatment with streptavidin C1 (500 µg ml^–1) and C2 (500 µg ml^–1), respectively. A greenhouse experiment revealed that Fusarium wilt of tomato plants was completely inhibited on soil drenching using a 50-ml culture filtrate of the streptavidin-producing strain KPP02129.     

Antibiofilm and antifungal activities of medium-chain fatty acids against Candida albicans via mimicking of the quorum-sensing molecule farnesol

Candida biofilms are tolerant to conventional antifungal therapeutics and the host immune system. The transition of yeast cells to hyphae is considered a key step in C. albicans biofilm development, and this transition is inhibited by the quorum-sensing molecule farnesol. We hypothesized that fatty acids mimicking farnesol might influence hyphal and biofilm formation by C. albicans. Among 31 saturated and unsaturated fatty acids, six medium-chain saturated fatty acids, that is, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid and lauric acid, effectively inhibited C. albicans biofilm formation by more than 75% at 2 µg ml⁻¹ with MICs in the range 100–200 µg ml⁻¹. These six fatty acids at 2 µg ml⁻¹ and farnesol at 100 µg ml⁻¹ inhibited hyphal growth and cell aggregation. The addition of fatty acids to C. albicans cultures decreased the productions of farnesol and sterols. Furthermore, down-regulation of several hyphal and biofilm-related genes caused by heptanoic or nonanoic acid closely resembled the changes caused by farnesol. In addition, nonanoic acid, the most effective compound diminished C. albicans virulence in a Caenorhabditis elegans model. Our results suggest that medium-chain fatty acids inhibit more effectively hyphal growth and biofilm formation than farnesol.     

Inhibition and eradication of Salmonella Typhimurium biofilm using P22 bacteriophage,EDTA and nisin

Abstract

P22 phage >10⁵ PFU ml^?1 could be used to inhibit Salmonella Typhimurium biofilm formation by 55–80%. Concentrations of EDTA >1.25?mM and concentrations of nisin >1,200?µg ml^?1 were also highly effective in reducing S. Typhimurium biofilm formation (≥96% and ≥95% reductions were observed, respectively). A synergistic effect was observed when EDTA and nisin were combined whereas P22 phage in combination with nisin had no synergistic impact on biofilm formation. Triple combination of P22 phage, EDTA and nisin could be also used to inhibit biofilm formation (≥93.2%) at a low phage titer (10² PFU ml^?1), and low EDTA (1.25?mM) and nisin (9.375?µg ml^?1) concentrations. A reduction of 70% in the mature biofilm was possible when 10⁷ PFU ml^?1 of P22 phage, 20?mM of EDTA and 150?μg ml^?1 of nisin were used in combination. This study revealed that it could be possible to reduce biofilm formation by S. Typhimurium by the use of P22 phage, EDTA and nisin, either alone or in combination. Although, removal of the mature biofilm was more difficult, the triple combination could be successfully used for mature biofilm of S. Typhimurium.     

Micropropagation,berberine content and antitumor activity of Jeffersonia dubia (Maxim.) Benth et Hook

An efficient micropropagation protocol was developed for Jeffersonia dubia using sucker explants. High frequency of multiple shoot formation was induced when the sucker explants were cultured on Chu’s (N6) medium with different concentrations of thidiazuron (TDZ) plus 0.54 µM α-naphthaleneacetic acid (NAA). The maximum frequency of shoot formation (96.2 %) was obtained on N6 medium with 2.27 µM TDZ plus 0.54 µM NAA. The highest mean number of shoots per explant (13.6) was obtained in temporary immersion system using an immersion frequency of 30 s every 30 min. The highest frequency of rooting (100 %), number of roots per shoot (5.8), and root length (6.3) was observed in half-strength N6 medium supplemented with 2.69 µM NAA. The regenerated plantlets (30 days old) were successfully acclimatized in the greenhouse with 98 % survival rate. The berberine content and cytotoxicity were higher in in vitro-developed calli and shoots than in leaves of field-grown plants. The greatest content of berberine was found in shoots (1381 μg g⁻¹) followed by calli (1092 μg g⁻¹) and leaves of field-grown plants (92 μg g⁻¹). At 1000 μg mL⁻¹ concentration, growth inhibition rate of berberine, callus, shoot, and leaf (in vivo) extracts were 68.4, 57.1, 54.2, and 17.7 %, respectively.

     

Effect of Abiotic Stress on Phosphate Solubilization by Biocontrol Fungus <Emphasis Type="Italic">Trichoderma</Emphasis> sp.

This study was undertaken to explore the role of Trichoderma sp. in phosphate (P) solubilization and antagonism against fungal phytopathogens. All fungal isolates (SE₆, KT₆, KT₂₈, and BRT₁₁) and a standard culture of T. harzianum (Th-std) were able to antagonize two fungal phytopathogens (Sclerotium rolfsii and Rhizoctonia solani) of chickpea (Cicer arietinum L.) wilt complex. Transmission electron microscopic studies (TEM) further confirmed ultra-cytological changes in the sclerotia of S. rolfsii parasitized by Trichoderma sp. All fungal cultures exhibited production of NH₃ and siderophore, but only BRT₁₁, SE₆, and Th-std could produce HCN. Among all the cultures tested, isolate KT₆ was found to be most effective for solubilization of ferric phosphate releasing 398.4 μg ml⁻¹ phosphate while isolates BRT₁₁ and SE₆ showed more potential for tricalcium phosphate (TCP) solubilization releasing 449.05 and 412.64 μg ml⁻¹ phosphate, respectively, in their culture filtrates. Part of this study focused on the influence of abiotic stress conditions such as pH, temperature, and heavy metal (cadmium) on phosphate (TCP) solubilizing efficiency. Two selected cultures KT₆ and T. harzianum retained their P solubilizing potential at varying concentrations of cadmium (0–1000 μg ml⁻¹). Isolate KT₆ and standard culture of T. harzianum released 278.4 and 287.6 μg ml⁻¹ phosphate, respectively, at 1000 μg ml⁻¹cadmium. Maximum solubilization of TCP was obtained at alkaline pH and at 28°C temperature. Isolate BRT₁₁ was found most alkalo-tolerant releasing 448.0 μg ml⁻¹ phosphate at pH 9.     

Development and characterization of a carvacrol nanoemulsion and evaluation of its antimicrobial activity against selected food-related pathogens

Carvacrol has been recognized as an efficient growth inhibitor of food pathogens. However, carvacrol oil is poorly water-soluble and can be oxidized, decomposed or evaporated when exposed to the air, light, or heat. To overcome these limitations, a carvacrol nanoemulsion was developed and its antimicrobial activity against food pathogens evaluated in this study. The nanoemulsion containing 3% carvacrol oil, 9% surfactants (HLB 11) and 88% water, presented good stability over a period of 90 days. In general, the carvacrol nanoemulsion (MIC: 256 µg ml⁻¹ for E. coli and Salmonella spp., 128 µg ml⁻¹ for Staphylococcus aureus and Pseudomonas aeruginosa) exhibited improved antimicrobial activity compared to the free oil. The carvacrol nanoemulsion additionally displayed bactericidal activity against Escherichia coli, P. aeruginosa and Salmonella spp. Therefore, the results of this study indicated that carvacrol oil nanoemulsions can potentially be incorporated into food formulations, wherein their efficacy for the prevention and control of microbial growth could be evaluated.     

Nanoparticles combined with cefixime as an effective synergistic strategy against Salmonella enterica typhi

Enteric fever caused by Salmonella typhi has been the most crucial health issue in rural people, especially in Southeast Asia and Africa. Another disease, Salmonellosis, caused by a large group of bacteria of the genus Salmonella, cause substantial economic loss resulting from mortality and morbidity. Higher concentration and repeated use of antibiotics to treat these diseases will likely develop antibiotic resistance among the microbes. The nanoparticle has good penetration power and can kill microbes. Combining two strategies by using nanoparticles with antibiotics kills microbes and reduces the chances of the development of antibiotics resistance. Silver, Nickel, Copper, and Zinc oxide Nanoparticles were chemically synthesized and characterized in this study. Silver nanoparticles at a concentration of 10 µg/ml inhibit all the strains under study.In comparison, silver nanoparticles (16.90 µg/ml), Nickel nanoparticles (83 µg ml^?1), Copper nanoparticles (249 µg ml^?1), and Zinc oxide (1614 µg ml^?1) along with 50 µg/ml cefixime gave maximum zone of inhibition of 35 mm, 19 mm, 31 mm and 23 mm respectively. The antimicrobial assay showed that silver nanoparticles presented good antibacterial performance against all multi-drug-resistant pathogenic Salmonella sp alone as well as in combinations. The present study proved that silver nanoparticles at the lowest concentration along with cefixime could be a possible alternative to control the multi-drug-resistant pathogens.     

Tolerance to Zinc Deficiency in Rice Correlates with Zinc Uptake and Translocation

To study variation in zinc efficiency (ZE) among current Chinese rice genotypes, a pot experiment was conducted with 15 aerobic and 8 lowland rice genotypes. Aerobic rice is currently bred by crossing lowland with upland rice genotypes, for growth in an aerobic cultivation system, which is saving water and producing high yields. A Zn deficient clay soil was used in our screening. Zn deficiency resulted in a marked decrease in shoot dry matter production of most genotypes after 28 days of growth. Genotypes were ranked according to their tolerance to Zn deficiency based on ZE, expressed as the ratio of shoot dry weight at Zn deficiency over that at adequate Zn supply. Substantial genotypic variation in ZE (50–98%) was found among both lowland and aerobic genotypes. ZE correlated significantly (P < 0.05) with Zn uptake (R ² = 0.34), Zn translocation from root to shoot (R ² = 0.19) and shoot Zn concentration (R ² = 0.27). The correlation with seed Zn content was insignificant. In stepwise multiple regression analyses, variation in Zn uptake and Zn translocation explained 53% of variation in ZE. Variation in Zn uptake could be explained only for 32% by root surface area. These results indicate that Zn uptake may be an important determinant of ZE and that mechanisms other than root surface area are of major importance in determining Zn uptake by rice.     

Interstrains comparison of the antimicrobial effect and mode of action of a Vietnamese Cinnamomum cassia essential oil from leaves and its principal component against Listeria monocytogenes

The antibacterial activity of a Cinnamomum cassia essential oil (EO) and of its main component trans-cinnamaldehyde (90% w/w) was examined against five Listeria monocytogenes strains. The minimal inhibitory concentrations (MICs) of C. cassia EO against the five L. monocytogenes strains were identical (250 µg ml⁻¹), while the minimal bactericidal concentrations (MBCs) ranged between 800 and 1200 µg ml⁻¹. In order to study if this EO and trans-cinnamaldehyde altered the five strains at the membrane level, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured in presence of different concentrations (1/2MIC, MIC, 2MIC) of these antibacterial agents. A concentration-dependent increase of fluorescence anisotropy of DPH in their presence reflecting a rigidification of the membrane was observed for the five strains. This modification of the membrane fluidity was associated with a perturbation of the selective membrane permeability, as a perturbation of the gradient between intracellular and extracellular pH was also observed.     

Influence of the KDEL signal,DMSO and mannitol on the production of the recombinant antibody 14D9 by long-term <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> cell suspension culture

We have established two transgenic cell suspension culture lines of Nicotiana tabacum that express the catalytic antibody 14D9 as a secretory product (sec-Ab) or as a KDEL-tagged product in the endoplasmic reticulum (Ab-KDEL), respectively. After 3 years of culture, the performance improved to a production level of 0.15 ± 0.03 μg ml⁻¹ on the seventh day of culture for the sec-Ab line and 0.48 ± 0.05 μg ml⁻¹ on the third day for Ab-KDEL line. Analysis of the effect of osmotic stress using mannitol (90 g l⁻¹) as an osmolite revealed that there was a 12-fold increase in antibody yield (1.96 ± 0.20 μg ml⁻¹) on the seventh day of culture in line sec-Ab and a fivefold increase (2.31 ± 0.18 μg ml⁻¹) on the seventh day for line Ab-KDEL. The concentration of the antibody in the culture medium was not significant. Dimethyl sulfoxide used as a permeabilizing agent was not effective in increasing 14D9 yield, but it did cause distinctive cell damage at all concentrations tested.     

Biodiesel synthesis from Chlorella vulgaris under effect of nitrogen limitation,intensity and quality light: estimation on the based fatty acids profiles

Cultures under nitrogen limitation for Chlorella vulgaris were kept under different light quality (white, blue, yellow and violet) at 70 and 140 µE m^?2 s^?1; to evaluate the effect on fatty acids profiles and biodiesel quality. The results showed a maximum biomass and cell density at 140 µE m^?2 s^?1 of: white light (0.69 g L^?1 and 6.5?×?10⁶ cells mL^?1, respectively) and blue light (0.65 g L^?1 and 8.0?×?10⁶ cells mL^?1, respectively); compared to violet and yellow light. The chlorophyll concentration (µg mg^?1 biomass dry weight) at 70 µE m^?2 s^?1 were in the order of light: white (25.61)?>?violet (17.10)?>?yellow (11.68)?>?blue (11.40) and, at 140 µE m^?2 s^?1 were: violet (23.64)?>?white (10.20)?>?yellow (9.66)?>?blue (7.99), suggesting the violet light stimulates the increase of chlorophyll a at higher intensity. The maximum lipid content (% w/w) were present under blue light (43.11), yellow (70.92) and violet (83.87) at 140 µE m^?2 s^?1. The different wavelengths did not have a negative effect on the quality of the biodiesel, however; violet light presented greater productivity and the indicators such as CFPP were related to the oxidative stability value and low PUFA content, leading biodiesel to good oxidative stability.

     

Chromium Reduction,Plant Growth–Promoting Potentials,and Metal Solubilizatrion by <Emphasis Type="Italic">Bacillus sp</Emphasis>. Isolated from Alluvial Soil

The plant growth–promoting potentials, production of siderophore and solubilization of insoluble phosphorus (P) and zinc and lead by the chromium (vi) -reducing Bacillus species, PSB 1, PSB 7, and PSB 10, was assessed both in the presence and absence of chromium under in vitro conditions. The Bacillus strains tolerated chromium up to the concentration of 500 (PSB1), 400 (PSB7), and 550 μg ml⁻¹ (PSB10), respectively, on nutrient agar plates. Bacillus sp. PSB 10 reduced Cr (vi) by 87% at pH 7, which was followed by Bacillus sp. PSB 1 (83%) and PSB 7 (74%) in nutrient broth after 120 h of incubation. A concentration of 50 μg ml⁻¹ of Cr (vi) was completely reduced by Bacillus sp. PSB 1 and PSB 10 (after 100 h) and PSB 7 (after 120 h). The Bacillus strains PSB 1, PSB 7, and PSB 10 produced 19.3, 17.7, and 17.4 μg ml⁻¹ of indole acetic acid, respectively, in luria bertani broth at 100 μg ml⁻¹ of tryptophan, which consistently decreased with an increase in chromium concentration. The Bacillus strains were positive for siderophore, HCN, and ammonia both in the absence and presence of chromium. The Bacillus strains solubilized 375 (PSB 1), 340 (PSB 7), and 379 (PSB 10) μg ml⁻¹ P, respectively, in Pikovskaya broth devoid of chromium. In contrast, chromium at 150 μg ml⁻¹ reduced the amount of P solubilized by 17 (PSB 1), 15 (PSB 7), and 9% (PSB 10) compared to control. The tested bacterial strains solubilized a considerable amount of zinc and lead in nutrient broth both in the absence and presence of chromium. Generally, the chromium reduction and the plant growth–promoting potentials of chromium-reducing Bacillus were strongly correlated at the tested concentration of chromium. The present observations demonstrated that the chromium-reducing, metal-solubilizing, and plant growth–promoting potentials of the Bacillus strains PSB1, PSB 7, and PSB10 were not adversely affected by the chromium application and, hence, may be applied for raising the productivity of crops under metal-contaminated soils.     

Investigation of the Cytotoxicity of Antimicrobial Peptide P40 on Eukaryotic Cells

The in vitro cytotoxicity of the antimicrobial peptide P40 was investigated. The food grade bacteriocin nisin was also analyzed for comparison. VERO cells were treated with different concentrations (0.02–2.5 μg ml⁻¹) of nisin and P40, and cell viability and plasma membrane integrity were checked by MTT, neutral red uptake (NRU), and lactate dehydrogenase (LDH) assays. In MTT and NRU assays the EC₅₀ to the purified peptide P40 were 0.30 and 0.51 μg ml⁻¹, while values found to nisin were 0.35 and 0.79 μg ml⁻¹, respectively. In the LDH assay, the EC₅₀ was 0.57 and 0.62 μg ml⁻¹ for P40 and nisin, respectively. The peptide P40 revealed higher hemolytical activity (19%) when compared to nisin (4.9%) at the highest concentration tested (2.5 μg ml⁻¹). Relatively few studies about the cytotoxicity of antimicrobial peptides are available. The determination of the cytotoxicity of antimicrobial peptides is an essential step to warrant their safe use.     

Repellency and toxicity of a CO2-derived cedarwood oil on hard tick species (Ixodidae)

The repellency and toxicity of a CO₂-derived cedarwood oil (CWO) was evaluated against actively questing unfed nymphs of four species of hard ticks: Amblyomma americanum (L.), Dermacentor variabilis (Say), Ixodes scapularis Say, and Rhipicephalus sanguineus (Latreille). Using a vertical climb bioassay for repellency, nymphs of these species avoided a CWO-treated filter paper in proportional responses to treatment concentrations. At 60 min of exposure, I. scapularis nymphs were most sensitive with 50% repellency concentration (RC₅₀) of 19.8 µg cm^?2, compared with RC₅₀ of 30.8, 83.8 and 89.6 µg cm^?2 for R. sanguineus, D. variabilis and A. americanum, respectively. Bioassays determined the lethal concentration for 50% (LC₅₀) and 90% (LC₉₀) mortality of nymphs exposed to CWO in treated vials after 24- and 48-h exposure. After 24 h exposure, the LC₅₀ values were 1.25, 3.45 and 1.42 µg cm^?2 and LC₉₀ values were 2.39, 7.59 and 4.14 µg cm^?2 for D. variabilis, I. scapularis and R. sanguineus, respectively, but had minimal effect on A. americanum. After 48 h exposure, the LC₅₀ values were 4.14, 0.78, 0.79 and 0.52 µg cm^?2, and LC₉₀ values were 8.06, 1.48, 1.54 and 1.22 µg cm^?2 for A. americanum, D. variabilis, I. scapularis and R. sanguineus, respectively. The repellency of CWO on tick species decreased with time. The repellency and toxicity bioassays demonstrated concentration-dependent responses of tick nymphs to the oil, indicating the potential of the CO₂-derived cedarwood oil be developed as an eco-friendly repellent and/or acaricide.

     

Interaction between C4 barnyard grass and C3 upland rice under elevated CO2: Impact of mycorrhizae

Atmospheric CO₂ enrichment may impact arbuscular mycorrhizae (AM) development and function, which could have subsequent effects on host plant species interactions by differentially affecting plant nutrient acquisition. However, direct evidence illustrating this scenario is limited. We examined how elevated CO₂ affects plant growth and whether mycorrhizae mediate interactions between C₄ barnyard grass (Echinochloa crusgalli (L.) Beauv.) and C₃ upland rice (Oryza sativa L.) in a low nutrient soil. The monocultures and combinations with or without mycorrhizal inoculation were grown at ambient (400 ± 20 μmol mol^?1) and elevated CO₂ (700 ± 20 μmol mol^?1) levels. The ¹⁵N isotope tracer was introduced to quantify the mycorrhizally mediated N acquisition of plants. Elevated CO₂ stimulated the growth of C₃ upland rice but not that of C₄ barnyard grass under monoculture. Elevated CO₂ also increased mycorrhizal colonization of C₄ barnyard grass but did not affect mycorrhizal colonization of C₃ upland rice. Mycorrhizal inoculation increased the shoot biomass ratio of C₄ barnyard grass to C₃ upland rice under both CO₂ concentrations but had a greater impact under the elevated than ambient CO₂ level. Mycorrhizae decreased relative interaction index (RII) of C₃ plants under both ambient and elevated CO₂, but mycorrhizae increased RII of C₄ plants only under elevated CO₂. Elevated CO₂ and mycorrhizal inoculation enhanced ¹⁵N and total N and P uptake of C₄ barnyard grass in mixture but had no effects on N and P acquisition of C₃ upland rice, thus altering the distribution of N and P between the species in mixture. These results implied that CO₂ stimulation of mycorrhizae and their nutrient acquisition may impact competitive interaction of C₄ barnyard grass and C₃ upland rice under future CO₂ scenarios.