Analytical modelling of bacterial migration and accumulation with rate-limited sorption in discrete fractures

An analytical model for bacterial accumulation in a discrete fractllre has been developed. The transport and accumlllation processes incorporate into the model include advection, dispersion, rate-limited adsorption, rate-limited desorption, irreversible adsorption, attachment, detachment, growth and first order decay botl1 in sorbed and aqueous phases. An analytical solution in Laplace space is derived and nlln1erically inverted. The model is implemented in the code BIOFRAC vvhich is written in Fortran 99. The model is derived for two phases, Phase I, where adsorption-desorption are dominant, and Phase II, where attachment-detachment are dominant. Phase I ends yvhen enollgh bacteria to fully cover the substratllm have accllillulated. The model for Phase I vvas verified by comparing to the Ogata-Banks solution and the model for Phase II was verified by comparing to a nonHomogenous version of the Ogata-Banks solution. After verification, a sensitiv"ity analysis on the inpllt parameters was performed. The sensitivity analysis was condllcted by varying one inpllt parameter vvhile all others were fixed and observing the impact on the shape of the clirve describing bacterial concentration verSllS time. Increasing fracture apertllre allovvs more transport and thus more accllffilliation, "Vvhich diminishes the dllration of Phase I. The larger the bacteria size, the faster the sllbstratum will be covered. Increasing adsorption rate, was observed to increase the dllration of Phase I. Contrary to the aSSllmption ofllniform biofilm thickness, the accllffilliation starts frOll1 the inlet, and the bacterial concentration in aqlleous phase moving towards the olitiet declines, sloyving the accumulation at the outlet. Increasing the desorption rate, redllces the dliration of Phase I, speeding IIp the accllmlilation. It was also observed that Phase II is of longer duration than Phase I. Increasing the attachment rate lengthens the accliffililation period. High rates of detachment speeds up the transport. The grovvth and decay rates have no significant effect on transport, althollgh increases the concentrations in both aqueous and sorbed phases are observed. Irreversible adsorption can stop accllillulation completely if the vallIes are high.

Trading nitrogen for carbon: Nitrogen and carbon translocation in a plant/fungal (Metarhizium spp.) symbiosis

While nitrogen is critical for all plants, they are unable to utilize organically bound nitrogen in soils. Therefore, the majority of plants obtain useable nitrogen through nitrogen fixing bacteria and the microbial decomposition of organic matter. In the majority of cases, symbiotic microorganisms directly furnish plant roots with inorganic forms of nitrogen. More than 80% of all land plants form intimate symbiotic relationships with root colonizing fungi. These common plant/fungal interactions have been defined largely through nutrient exchange, where the plant receives limiting soil nutrients, such as nitrogen, in exchange for plant derived carbon. Fungal endophytes are common plant colonizers. A number of these fungal species have a dual life cycle, meaning that they are not solely plant colonizers, but also saprophytes, insect pathogens, or plant pathogens. By using 15N labeled, Metarhizium infected, wax moth larvae (Galleria mellonella) in soil microcosms, I demonstrated that the common endophytic, insect pathogenic fungi Metarhizium spp. are able to infect living soil borne insects, and subsequently colonize plant roots and furnish ts plant host with useable, insect-derived nitrogen. In addition, I showed that another ecologically important, endophytic, insect pathogenic fungi, Beauveria bassiana, is able to transfer insect-derived nitrogen to its plant host. I demonstrated that these relationships between various plant species and endophytic, insect pathogenic fungi help to improve overall plant health. By using 13C-labeled CO2, added to airtight plant growth chambers, coupled with nuclear magnetic resosnance spectroscopy, I was able to track the movement of carbon from the atmosphere, into the plant, and finally into the root colonized fungal biomass. This indicates that Metarhizium exists in a symbiotic partnership with plants, where insect nitrogen is exchanged for plant carbon. Overall these studies provide the first evidence of nutrient exchange between an insect pathogenic fungus and plants, a relationship that has potentially useful implications on plant primary production, soil health, and overall ecosystem stability.

Carbon metabolism in transgenic roots with altered levels of hexokinase and triosephosphate isomerase and growing under different nitrogen status

Ce projet a pour but d’évaluer la capacité de la voie des pentoses phosphates (VPP) dans les racines transgéniques de pomme de terre (Solanum tuberosum) modifiées pour exprimer différents niveaux de l'hexokinase (HK) et de la triosephosphate isomérase cytosolique (cTPI). Dans les racines, la VPP alimente la voie de l’assimilation de l’azote en equivalents réducteurs et permet donc la biosynthèse des acides aminés. Le glucose-6-phosphate produit par l’HK est consommé par la partie oxydative de la VPP catalysée par la glucose-6-phosphate déshydrogénase (G6PDH) et la 6-phosphogluconate déshydrogénase (6PGDH). Les changements dans l'expression de HK et cTPI peuvent affecter le fonctionnement de la VPP et les mécanismes qui sont liés à l’utilisation des équivalents réducteurs produits par la VPP, comme l'assimilation de l’azote et la synthèse des acides aminés. Afin d’évaluer l’effet des manipulations génétiques de l’HK et de la cTPI sur l’assimilation de l’azote, nous avons cultivé les racines transgéniques sur des milieux contenant des concentrations élevées (7 mM) ou basses (0,7 mM) de nitrate d’ammonium comme source d’azote. Les résultats montrent que la culture sur un milieu riche en azote induit les activités G6PDH et 6PGDH. Les données montrent que la capacité de la VPP est plus grande avec des niveaux élevés en HK ou en cTPI. Nous avons aussi pu démontrer une plus grande activité spécifique de l’HK dans les conditions pauvres en azote. Ces données ont été complémentées par des mesures des pools d’acides aminés dans les racines transgéniques cultivées sur différents niveaux d’azote. Aucune tendance notable des pools d’acides aminés n’a été remarquée dans les racines modifiées pour leur contenu en HK suggèrant que la manipulation de HK n’affecte pas l'assimilation de l’azote. Dans les racines transgéniques modifiées pour la cTPI, les ratios Gln/Glu et Asn/Asp sont plus élevés chez les clones antisens, indiquant une assimilation de l’azote plus élevée. Ces résultats ont démontré l'activation de l'assimilation de l’azote chez les clones antisens cTPI dans les conditions élevées et basses d’azote alors que la manipulation de l’HK n’affecte pas l’assimilation de l’azote.

Étude de la sorption et de la désorption de neuf contaminants émergents dans les boues usées

Des études de sorption/désorption ont été effectuées pour neuf contaminants émergents sélectionnés (caféine, sulfaméthoxazole, déséthylatrazine, carbamazépine, atrazine, estradiol, éthinylestradiol, noréthindrone et diclofénac) dans les boues usées provenant de trois systèmes différents. Les contaminants incluent une variété de classes de composés (pesticides, hormones et pharmaceutiques) qui possèdent des propriétés physicochimiques différentes. L’objectif de ces travaux est de modéliser leur comportement dans une station d’épuration, en présence d’une phase particulaire et d’une phase aqueuse, et du même coup, de mieux comprendre leur devenir lors de leur rejet dans l’environnement. Le coefficient octanol-eau (log Kow) permet de bien interpréter les résultats et nous permet de classer les composés selon deux types de comportements observés : les composés avec un log Kow inférieur à 3 montrent peu ou pas de sorption alors que les composés avec un log Kow supérieur à 3 montrent une sorption variant de 30 à 90 % durant les premières minutes, suivi d’une sorption lente durant les heures suivantes. Une augmentation du contenu organique favorise la sorption des composés hydrophobes alors qu’un changement de pH peut modifier la charge à la surface des particules et également la charge des analytes. Les résultats ont montré que seul le diclofénac était sensible aux variations de pH étudiés. Dans une telle situation, il est nécessaire d’utiliser le facteur d’hydrophobicité corrigé en fonction du pH (log Dow). Le coefficient de distribution solide-eau (log Kd) a été déterminé pour chaque composé à la fin de chaque expérience de sorption et se situe entre -0.3 et 2.6. Avec l’augmentation de l’hydrophobicité, la désorption diminue avec le temps et avec l’étape de rinçage. Pour simuler le relargage dans les systèmes aquatiques, les facteurs de rinçage ont été déterminés pour estimer le nombre de rinçages qui seraient nécessaire pour désorber 50 et 99 % de la concentration initialement sorbée. Les bilans de masse ont été effectués après chaque expérience dans le but de ne pas surestimer les capacités de sorption d’un composé et se situent entre 7 et 25 % pour l’estradiol, la noréthindrone et le sulfaméthoxazole et entre 44 et 103 % pour l’éthinylestradiol, l’atrazine, la déséthylatrazine, la carbamazépine, la caféine et le diclofénac.

Studies on lipid production of microalgae under mixotrophic growth, utilizing glycerol as a carbon source, combined with nitrogen starvation

Rampant increases in oil prices and detrimental effects of fossil fuels on the environment have been the main impetus for the development of environmentally friendly and sustainable energy sources. Amongst the many possibilities, microalgae have been proposed as a new alternative energy source to fossil fuels, as their growth is both sustainable and ecologically safe. By definition, microalgae are unicellular photosynthetic microorganisms containing chlorophyll a. These organisms are capable of producing large quantities of oils, surpassing that of traditional oil-seed crops, which can be transformed, through chemical processes, into biofuels such as biodiesel or bio-gasoline. Thus, recent research has gone into discovering high lipid producing algal strains, optimising growth media for increased lipid production and developing metabolic engineering to make microalgae a source of biofuel that is competitive to more traditional sources of biofuel and even to fossil fuel. In this context, the research reported here focused on using a mixotrophic growth mode as a way to increase lipid production for certain strains of microalgae. In addition, nitrogen starvation combined with mixotrophy was studied to analyse its effects on lipid production. Mixotrophy is the parallel usage of two trophic modes, in our case photoautotrophy and heterotrophy. Consequently, 12 algal strains were screened for mixotrophic growth, using glycerol as a carbon source. Glycerol is a waste product of the current biodiesel industry; it is a cheap and abundant carbon source present in many metabolic pathways. From this initial screening, several strains were chosen for subsequent experiments involving nitrogen starvation. Nitrogen starvation has been shown to induce lipid accumulation. The results obtained show that a mixotrophic growth mode, using glycerol as a carbon source, enhances lipid production for certain strains. Moreover, lipid enhancement was shown for nitrogen starvation combined with mixotrophic growth mode. This was dependant on time spent under nitrogen starvation and on initial concentrations of the nitrogen source.

Synthesis and Transformations of a Few Nitrogen and Oxygen Heterocycles

Department of Applied Chemistry, Cochin University of Science and Technology

Optimization of carbon and nitrogen sources and growth factors for the production of an aquaculture probiotic (Pseudomonas MCCB 103) using response surface methodology

Aim: To develop a new medium for enhanced production of biomass of an aquaculture probiotic Pseudomonas MCCB 103 and its antagonistic phenazine compound, pyocyanin. Methods and Results: Carbon and nitrogen sources and growth factors, such as amino acids and vitamins, were screened initially in a mineral medium for the biomass and antagonistic compound of Pseudomonas MCCB 103. The selected ingredients were further optimized using a full-factorial central composite design of the response surface methodology. The medium optimized as per the model for biomass contained mannitol (20 g l)1), glycerol (20 g l)1), sodium chloride (5 g l)1), urea (3Æ3 g l)1) and mineral salts solution (20 ml l)1), and the one optimized for the antagonistic compound contained mannitol (2 g l)1), glycerol (20 g l)1), sodium chloride (5Æ1 g l)1), urea (3Æ6 g l)1) and mineral salts solution (20 ml l)1). Subsequently, the model was validated experimentally with a biomass increase by 19% and fivefold increase of the antagonistic compound. Conclusion: Significant increase in the biomass and antagonistic compound production could be obtained in the new media. Significance and Impact of the Study: Media formulation and optimization are the primary steps involved in bioprocess technology, an attempt not made so far in the production of aquaculture probiotics.

High resolution optogalvanic study in nitrogen discharge

Doppler limited high resolution spectrum in the wavelength region 17224 to 17236 cm−1 of the first positive system (B 3Π g −A 3Σ u + ) of the N2 molecule is recorded by optogalvanic spectroscopic technique using a single mode ring dye laser. It is observed that the intensity and line width of the rotational line increase with the discharge current. Dependence of the collision broadening coefficient on the current was also evaluated.

Carbon/Nitrogen Ratio Optimization and Periphyton Development on the Production and Sustainability of Penaeus Monodon(Fabricius)in Extensive Culture System

Controlling the inorganic nitrogen by manipulating carbon / nitrogen ratio is a method gaining importance in aquaculture systems. Nitrogen control is induced by feeding bacteria with carbohydrates and through the subsequent uptake of nitrogen from the water for the synthesis of microbial proteins. The relationship between addition of carbohydrates, reduction of ammonium and the production of microbial protein depends on the microbial conversion coefficient. The carbon / nitrogen ratio in the microbial biomass is related to the carbon contents of the added material. The addition of carbonaceous substrate was found to reduce inorganic nitrogen in shrimp culture ponds and the resultant microbial proteins are taken up by shrimps. Thus, part of the feed protein is replaced and feeding costs are reduced in culture systems.The use of various locally available substrates for periphyton based aquaculture practices increases production and profitability .However, these techniques for extensive shrimp farming have not so far been evaluated. Moreover, an evaluation of artificial substrates together with carbohydrate source based farming system in reducing inorganic nitrogen production in culture systems has not yet been carried-out. Furthermore, variations in water and soil quality, periphyton production and shrimp production of the whole system have also not been determined so-far.This thesis starts with a general introduction , a brief review of the most relevant literature, results of various experiments and concludes with a summary (Chapter — 9). The chapters are organised conforming to the objectives of the present study. The major objectives of this thesis are, to improve the sustainability of shrimp farming by carbohydrate addition and periphyton substrate based shrimp production and to improve the nutrient utilisation in aquaculture systems.