Resistance and resilience of soil biological indicators: A case study with multi-walled carbon nanotube

Soil ecosystem is experiencing stresses due to climate change, and soil inhabitants try to demonstrate their inherent resistance and resilience against those stresses. Application of nanomaterials as agricultural inputs could bring shifts in resistance and resilience patterns of soil microbes and associated enzymes, especially under short-term heat stress. With this background, the impacts of multi-walled carbon nanotube (MWCNT) on the resistance and resilience of soil biological indicators were evaluated. An incubation experiment was conducted with varied MWCNT concentrations (0, 50, 100, 250, and 500 mg kg^-1 soil) for 90 d after 24-h heat stress at 48 ±2 ℃ to assess the impacts of MWCNT on soil enzyme activities and microbial populations vis-à-vis their resistance and resilience indices under short-term exposure to heat stress. Enzyme activities were reduced after exposure to heat stress. Resistance indices of enzyme activities were enhanced by MWCNT application on day 1 after heat stress, whereas there was no recovery of enzyme activities after 90-d incubation. Like soil enzyme activities, resistance index values of soil microbial populations followed the similar trend and were improved by MWCNT application. Multi-walled carbon nanotube has the potential to improve resistance indices of soil enzyme activities and microbial populations under heat stress, although they could not recover to their original state during periodical incubation after heat stress. This study helps to understand the relative changes of biological indicators under MWCNT and their ability to withstand heat stress.     

Chromosomal and nucleolar RNA synthesis in root tips during mitosis

Comparative rates of RNA synthesis in chromatin and nucleolar fractions during mitosis in root-tip cells of Allium and Nigella were studied by pulse-labeling of cells with tritiated cytidine. Although the rate of RNA synthesis decreases in the condensing chromosomes during prophase, it remains normal in the nucleolar fraction as long as nucleoli are maintained. RNA synthesis stops in mitotic cells lacking distinct nucleoli. In the late telophase or very early interphase cells, RNA synthesis resumes at a faster rate in the pronucleolar bodies than in the chromatin.     

Enhanced Lead Uptake by an Association of Plant and Earthworm Bioaugmented with Bacteria

Lead (Pb) is recorded as the second most hazardous pollutant of the environment. Previous cases of Pb bioremediation has been reported using single biosystem, but very few reports are available in biological approaches using multi-biosystems to achieve an enhanced bioremoval of Pb. The present study evaluated the capacity of a unique association of Pennisetum purpureum, a hyperaccumulator plant, and Lumbricus terrestris (earthworm) bioaugmented with a Pb-resistant bacterium, obtained from an industrially contaminated site and identified as isolate VITMVCJ1 Klebsiella variicola, to bioremediate Pb. The Pb-resistant gene was amplified in the bacterial isolate VITMVCJ1. The study was conducted for 60 d. Results verified that the bioaugmentation process enhanced 1) root and shoot length of the plants, 2) chlorophyll content of the plants, and 3) biofilm-producing ability of the microbes from the rhizosphere region of the plants. The total phenolic and flavonoid contents were found to be lower in the plants in the bioaugmented setup. The study also observed a reduction in the toxic effects of Pb on earthworm and plant. The earthworm was used to assess the Pb-induced stress syndrome after exposure to sublethal concentrations of Pb in the soil. A reduction in the content of malondialdehyde, a potential biomarker, on exposure to Pb demonstrated the role of the inoculum to alleviate heavy metal-induced stress in earthworms. All three symbionts accumulated Pb; Pb was accumulated mainly in the root of the plant, and poorly in the shoot of the plant and body mass of the earthworm. The bioaugmentation system exhibited stable and excellent uptake of Pb from the contaminated soils. The results of the present study suggest the positive effect of the synergistic association of the plant and earthworm with appropriate microbes for the bioremoval of Pb.     

海洋细菌生物膜用于生物修复陆地生态系统中土壤多环芳烃污染

Polycyclic aromatic hydrocarbons(PAHs) in soil retain for a quite long period due to their hydrophobicity and aggregation properties. Biofilm-forming marine bacterial consortium(named as NCPR), composed of Stenotrophomonas acidaminiphila NCW702,Alcaligenes faecalis NCW402, Pseudomonas mendocina NR802, Pseudomonas aeruginosa N6P6, and Pseudomonas pseudoalcaligenes NP103, was used for the bioremediation of PAHs in a soil microcosm. Phenanthrene and pyrene were used as reference PAHs. Parameters that can affect PAH degradation, such as chemotaxis, solubility of PAHs in extracellular polymeric substances(EPS), and catechol2,3-dioxygenase(C23O) activity, were evaluated. P. aeruginosa N6P6 and P. pseudoalcaligenes NP103 showed chemotactic movement towards both the reference PAHs. The solubility of both the PAHs was increased with an increase in EPS concentration(extracted from all the 5 selected isolates). Significantly(P 0.001) high phenanthrene(70.29%) and pyrene(55.54%) degradation was observed in the bioaugmented soil microcosm. The C23O enzyme activity was significantly(P 0.05) higher in the bioaugmented soil microcosm with phenanthrene added at 173.26 ± 2.06 nmol min~(-1) mg~(-1) protein than with pyrene added at 61.80 ± 2.20 nmol min~(-1) mg~(-1) protein. The C23O activity and gas chromatography-mass spectrometer analyses indicated catechol pathway of phenanthrene metabolism. However, the metabolites obtained from the soil microcosm added with pyrene revealed both the catechol and phthalate pathways for pyrene degradation.     

Earthworm (Eudrillus euginae) multiplication through variable substrates

Three hundred adult healthy earthworms ( Eudrillus euginae ) ranging length and weight from 14–29 cm (mean 21.5 ± 6.8 cm) to 1.6–3.0 g (mean 2.55 ± 1.1 g), respectively, were cultured in three different substrate for 70 days. The substrates were soil alone, (control T-1), cow ( Bos taurus ) dung and water hyacinth ( Eichhornia crassipes ) (1 : 1 T-2), and partially dried neem ( Azadirachta indica ) leaves with kitchen waste (1 : 1 T-3). The earthworms were grown in these substrates in a wooden chamber (0.8 m × 0.5 m × 0.2 m) and these were subjected to monitoring for various growth patterns (length, biomass, number) at every fortnight (five observations) interval. The observations showed that T-2 was the best among the three treatments used. There was significant difference ( P  < 0.05) between the mean values of growth efficiency in food conversion among the treatments. However, there was no significant difference ( P  > 0.05) between the mean values of survival rate of earthworm among different treatments.     

Effects of dietary vitamin C on immunity, growth and survival of Indian major carp Labeo rohita, fingerlings

An 8‐week feeding trial was conducted to evaluate the efficacy of dietary l ‐ascorbic acid (AA) dosages on immunity, growth and survival of the fingerlings of Labeo rohita. AA was supplemented at 0, 100, 200 and 500 mg kg⁻¹ basal diets. Each diet was fed for 8 weeks to duplicate groups of fingerlings of rohu with initial body weight of 35 ± 5 g. Selected biochemical and haematological analyses were evaluated every second week. At the end of the feeding trial of 56 days, fish were divided into two subgroups under each major treatment group for challenge with two pathogens, Aeromonas hydrophila and Edwardsiella tarda. The mortality (%) and agglutinating antibody titre were recorded on 28th day postchallenge. Non‐specific immune parameters like superoxide anion production, lysozyme activity and complement activity increased independently of the levels of AA in the diet. Whereas phagocytic ratio, phagocytic indices, lymphokine production indices and serum bactericidal activity were better in the group of fish fed with 200 mg AA kg⁻¹ feed for 42 days. However, growth parameters such as specific growth rate, feed conversion ratio and survival were better in the group of fish fed with the highest level of AA through feed for 56 days. These data indicated that elevated levels of dietary AA could be recommended for optimum immunity, growth and survival of fingerlings of L. rohita.