Studies on litter characterization using 13C NMR and assessment of microbial activity in natural forest and plantation crops’ (teak and rubber) soil ecosystems of Kerala, India

The leaf litter is the major source of soil organic matter in natural and many plantation crop ecosystems. Quantity and quality of organic matter in a soil ecosystem is of utmost importance in regulating the soil health. Hence assessment of quality of organic matter input, viz., litter is important and is attempted in this study. The leaf litter of rubber (Hevea brasiliensis), pueraria (Pueraria phaseoloides), mucuna (Mucuna bracteata), teak (Tectona grandis) and forest (mixed species) were analyzed using solid state ¹³C nuclear magnetic resonance (NMR) to study the relative abundance of different carbon compounds present. The spectra revealed that litter of all species studied contain relatively larger amounts of polysaccharides compared to other C containing compounds. Also it could be observed that the alkyl-C to O-alkyl-C ratio of rubber litter was much higher compared to that of others. Aromatics and carbonyl compounds were also present in all litter species. The resource quality based on alkyl-C to O-alkyl-C ratio of the litter samples studied can be arranged in the order pueraria > teak > mucuna > forest > rubber. The respiration rate, substrate induced respiration rate and biomass-C (Cmic) of the litter samples were estimated. It could be observed that litter associated microbial activity decreased as alkyl-C to O-alkyl-C ratio increased. Resource quality derived from the NMR spectra and the litter biological properties were complementary. Soil samples (0–15 cm) from the five soil ecosystems (rubber, pueraria, mucuna, teak and forest) were analyzed for respiration rate, substrate induced respiration rate, Cmic, total-C and total-N. The forest soil had higher respiration rate, total-C and total-N compared to cultivated soil systems. Pueraria, mucuna and teak soils were comparable for their biological properties while rubber soil recorded comparatively lower microbial activity.     

Production of Bacillus thuringiensis Berliner var. kurstaki Grown in Alternative Media

Agro - industrial residues and by - products available in southeastern Brazil were used as ingredients for low - cost culture media for liquid fermentation of Bacillus thuringiensis var. kurstaki. Highest spore yield was obtained with a medium containing cheese whey , soya bean milk and molasses (WSM) . Crystals and spores were produced in all media and potency of the final product was highest for nutrient broth + yeast extract medium (NBY) . There was no correlation between the number of spores in the fermented media and the potency of the preparations . Considering all three factors , the potencies , costs and yields of the final products , lowest relative cost was obtained with BMM medium ( Bombyx mori pupae + molasses) . NBY and WSM had intermediate relative cost approximately nine times higher than BMM . The cost analysis suggests that BMM medium should be preferred for local production of B. thuringiensis var . kurstaki in comparison to other media tested . The results also demonstrate the importance of considering yields , cost and potency of the B. thuringiensis preparations in selecting the production medium .     

Competition for nitrate between denitrifying Pseudomonas stutzeri and nitrate ammonifying enterobacteria

Abstract Competition for nitrate between nitrate ammonifying enterobacteria and a denitrifying pseudomonad was studied in electron acceptor-limited chenostats. In pure cultures, using different carbon and energy sources, the C/N-ratio needed for denitrification is far lower than that required for nitrate ammonification. In mixed cultures of Citrobacter freundii and Pseudomonas stutzeri , competing for nitrate with l -lactate as electron donor, the nitrate ammonifying organism dominated at dilution rates of D ≤ 0.14 h⁻¹. Competition for both nitrate and l -lactate at a dilution rate of D = 0.05 h⁻¹ always resulted in the coexistence of both species. Using glucose as additional carbon source, the final ratio of nitrate ammonifying and denitrifying organism depended on the C/N-ratio as well as on the dilution rate. The results of the study are discussed with respect to field data.     

The Protozoan-Metazoan Trophic Link In Pelagic Ecosystems

ABSTRACT The evidence for a qualitatively and quantitatively important trophic link between planktonic Protozoa and higher order metazoan consumers is reviewed. the available data are obtained primarily, but not exclusively, from laboratory studies of calanoid copepod consumers and tintinnid ciliate prey from marine estuarine and nearshore environments. the data indicates that the protozoan-metazoan link is of similar magnitude and importance in the pelagic ecosystems of freshwaters. It is proposed that planktonic Protozoa constitute a high quality, nitrogen-rich food in the diets of their metazoan consumers. Implications of die trophic link to the consumers, prey, and ecosystem are discussed.     

Response of a solutivory chain to a nutrient pulse

A microbial community model is proposed that accounts for byproducts of one strain being nutrients for another and for cells passing in and out of states of torpor. It is shown that such models can sustain the propagation of a nutrient pulse as observed, for example, in methanogenesis.This work was supported in part by NSF Grant DMS9206677 and in part by NSF STC Center in Microbial Ecology, Michigan State University.     

Stoichiometric analysis of dissolved organic carbon flux into storage and growth in aerobic granules culture

This study attempted to address a fundamental question of whether metabolic behaviors of aerobic granules are different from their counterparts, such as activated sludge and biofilms. A series of respirometric experiments were carried out using mature aerobic granules with mean sizes of 0.75–3.4 mm. Results suggested that metabolism of aerobic granules comprised three consecutive phases: (i) conversion of external dissolved organic carbon to a poly-β-hydroxybutyrate-like substance; (ii) growth of aerobic granules on the stored poly-β-hydroxybutyrate-like substance derived from phase I, and (iii) subsequent endogenous metabolism of aerobic granules. The stoichiometric analysis revealed that the conversion yields of external dissolved organic carbon to the poly-β-hydroxybutyrate-like substance, the growth yields of biomass on storage, and the overall growth yields of biomass on external dissolved organic carbon were not significantly correlated to the sizes of aerobic granules, i.e., the metabolism of aerobic granules would be size independent. The conversion coefficients and growth rates of aerobic granules were found to be comparable with those reported in the activated sludge and biofilms cultures, indicating that there would not be significant difference in the metabolisms of aerobic granules over activated sludge and biofilms. This information will be useful for modeling and designing aerobic granular sludge processes.     

Microbiological production of tocopherols: current state and prospects

Tocopherols are antioxidants that prevent various diseases caused by oxidative stress. Tocochromanols comprise four isoforms of tocopherols and four isoforms of tocotrienols but α-tocopherol is the most abundant and active isoform in human and animal tissues. Tocopherols are used as dietary supplements for human, as food preservatives, in manufacture of cosmetics, and for fortification of animal feed. Only photosynthetic cells are known to accumulate detectable concentrations of tocopherols. Tocopherols can be extracted and purified or concentrated from vegetable oils and other higher plant materials. However, the concentrations in these higher plant materials are very low and there are high proportions of the less-active homologues of tocopherols. Among the many strains of photosynthetic microorganisms known to accumulate tocopherols, Euglena gracilis is promising for commercial production of α-tocopherol. The growth rate and α-tocopherol contents are relatively high and α-tocopherol comprise more than 97% of all the tocopherols accumulated by Euglena gracilis. Although a lot of work has been done to increase the contents and composition of tocopherols in higher plants through genetic and metabolic engineering, work on genetic modification of microorganisms for increased tocopherol accumulation is scarce. Many cultivation systems have been investigated for efficient production of tocopherol by Euglena gracilis. However, those that involve heterotrophic metabolism are more promising. Bubble columns and flat-plate photobioreactors are more suitable for commercial production of tocopherols, than the tubular, internally illuminated, and open-air photobioreactors.     

Aerobic microbial activity in fresh and aged bottom ashes from municipal solid waste incineration (MSWI)

Although mostly mineral, municipal solid waste incineration (MSWI) bottom ashes also contain organic matter that may support heterogeneous microbial activities. The objective of the present study was to evaluate the potential influence of such activities on the physico-chemical properties of the waste with respect to the release of contaminants into water. Fresh and aged MSWI bottom ashes originating from the same incineration plant were studied. Respirometry assays were carried out under various experimental conditions, where the microbial flora was quantitatively and qualitatively analyzed before and after the incubations. The leaching behavior of the waste was studied before and after the incubations to determine the effects of microbial activities.Relatively high O₂ consumption and CO₂ production were observed during incubation, particularly with the fresh waste which contained more organic matter and was less carbonated than the aged one. Cell counts and DGGE molecular profiles indicated the presence of an abundant and diversified microbial biomass in both aged and fresh waste. Incubations resulted in a reduction of the dissolved fraction of organic carbon in the leaching tests and a modification of the leaching patterns of many metallic species (Al, Cr, Cu, Fe, Pb and Zn). This influence on the leaching behavior was particularly significant with the fresh waste. It was mostly explained by the pH decrease due to the carbonation of the bottom ash resulting from the CO₂ generated by the microbial respiration.     

A method to distinguish microbial acclimation from reduced growth rates in perturbed ecosystems

Abstract Predicting variations in microbial growth rates (μ) in Nature requires a method that will detect departures from optimal μ, determine the time scale at sub-optimal μ, and measure the restoration or reversibility toward optimal μ. Isotopic flux measurements are equivocal because of uncertainties in their relationship to μ, particularly in non-steady state condictions. After perturbing a natural microbial community and a clone of the phytoplankter Selenastrum capricornutum with two different toxicants, we examined the kinetics of the adenylate energy charge, and followed changes in biomass over time with the total adenylate and chlorophyll a concentrations. We determined that exposure to cadmium resulted in a reduction in μ; reversible within a short time, whereas exposure to the industrial effluent caused an exponential loss of adenylates and complete inhibition of growth. Upon perturbing a microbiol community, the study of adenylate energy charge kinetics detects departures from optimal μ, measures their duration and reversibility.