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Persistent and susceptible bacteria with individual deaths  [PDF]
Fabio Zucca
Mathematics , 2012,
Abstract: The aim of this paper is to study two models for a bacterial population subject to antibiotic treatments. It is known that some bacteria are sensitive to antibiotics. These bacteria are in a state called persistence and each bacterium can switch from this state to a non-persistent (or susceptible) state and back. Our models extend those introduced in [6] by adding a (random) natural life cycle for each bacterium and by allowing bacteria in the susceptible state to escape the action of the antibiotics with a fixed probability 1-p (while every bacterium in a persistent state survives with probability 1). In the first model we "inject" the antibiotics in the system at fixed, deterministic times while in the second one the time intervals are random. We show that, in order to kill eventually the whole bacterial population, these time intervals cannot be "too large". The maximum admissible length is increasing with respect to p and it decreases rapidly when p<1.
Efficiency of Chlorella minutissima microalgae in the treatment of swine-waste enriched with urea
Jo?o Bosco Rozas Rodrigues,Paulo Belli Filho
Biotemas , 2004,
Abstract: The increasing process of pig breeding and the lack of adequate technologies to treat the residue originating from this activity in Brazil has been causing considerable environmental degradation and a threat to water resources. The utilization of microalgae to treat rural farming residue has been widely used in several countries with success. This presents many advantages, such as reducing polluting agents and providing a high biological and economic value of the produced algal biomass. The present work was developed with the microalgae Chlorella minutissima, with the objective of testing the process on a medium scale, under semi-controlled conditions, verifying the effect of urea addition and the pH control. The effects of these treatments on algal growth efficiency and on the capaciy to remove polluting agents were observed experimentally. The results showed that the growth efficiency of the microalgae Chlorella minutissima, cultivated in residues 20cm deep at a cod concentration of 280mg/L was not influenced by added urea or pH control. The use of these algae in a mixed culture (algae and bacteria) reduced the COD, turbidity, total solids, volatile total solids, total suspended solids, ammnonia, orthophosphate and total phosphate.
Interacción bacteria-microalga en el ambiente marino y uso potencial en acuicultura Microalgae and bacteria interaction in the aquatic environment and their potential use in aquaculture  [cached]
Revista chilena de historia natural , 2003,
Abstract: El presente estudio tiene como objetivo revisar el conocimiento generado sobre el rol que juegan las interacciones bacteria-microalga en ambientes marinos y dulceacuícolas, definiendo las posibles aplicaciones que puede tener el conocimiento de estas interacciones en el manejo de las aguas costeras y sistemas acuícolas. Los antecedentes proporcionados en este análisis permiten sugerir que bacterias y/o microalgas, constituyen una alternativa para el control de proliferaciones de bacterias y fitoplancton causantes de efectos da inos en ambientes naturales y sistemas cerrados de cultivo. Además, las interacciones específicas entre bacteria-microalga permitiría la optimización de sistemas productivos en la industria acuícola. Sin embargo, los mecanismos de estas interacciones son pobremente entendidos. Futuras investigaciones debieran ser dirigidas a comprender el modo de acción de las interacciones bacteria-microalga a nivel molecular The objective of this survey is to review the knowledge generated with respect to the role of bacteria-microalgae interaction play in marine and fresh environments, and to define the possible application of these microorganisms on the management of costal water and aquaculture systems. This review proposes that bacteria and/or microalgae are an alternative to control the proliferation of bacteria and phytoplankton that cause damages in natural environments or in closed culture systems. Also, the knowledge of specific interactions between bacteria and microalgae will allow the optimization of productive systems in aquaculture. However, until date the mechanisms involved in these interactions are poorly understood. Therefore, future investigations should be directed towards understanding the mode of action of such interactions at a molecular level
Nitrogen turnover in a tidal flat sediment: assimilation and dissimilation by bacteria and benthic microalgae  [PDF]
K. D?hnke,A. Moneta,B. Veuger,K. Soetaert
Biogeosciences Discussions , 2012, DOI: 10.5194/bgd-9-6987-2012
Abstract: In a short-term (24 h) 15N-labeling experiment, we investigated reactive nitrogen cycling in a tidal flat sediment, focusing on the relative importance of assimilatory versus dissimilatory processes and the role of benthic microalgae therein. 15N-labeled ammonium and nitrate were added separately to homogenized sediment, and 15N was subsequently traced into sediment and dissolved inorganic nitrogen (DIN) pools. Integration of results in a N-cycle model allowed us to quantify rates for the major assimilatory and dissimilatory processes in the sediment. Overall, results indicate that the balance between assimilation and dissimilation in this tidal mudflat was mainly dependent on the nitrogen source. Nitrate was utilized almost exclusively dissimilatory via denitrification, whereas ammonium was rapidly assimilated, with about a quarter of this assimilation due to benthic microalgae (BMA). Benthic microalgae significantly affect assimilation of ammonium, because in the absence of BMA activity the sediments turns from a net ammonium sink to a net source. Nitrification rates were initially very high, but declined rapidly suggesting that nitrification rates are low in undisturbed sediments, and that in a dynamic environment like tidal flats, intense and fast nitrification/denitrification of ammonium is common. The driving mechanisms for assimilation or dissimilation accordingly appear to be ruled to a large extent by external physical forcing, with the entire system being capable of rapid shifts following environmental changes.
An Overview of Biocement Production from Microalgae  [cached]
Dessy Ariyanti,Noer Abyor Handayani,Hadi Hadiyanto
International Journal of Science and Engineering , 2011, DOI: 10.12777/ijse.v2i2.1265
Abstract: The invention of microorganism’s involvement in carbonate precipitation, has lead the exploration of this process in the field of construction engineering. Biocement is a product innovation from developing bioprocess technology called biocementation. Biocement refers to CaCO3 deposit that formed due to microorganism activity in the system rich of calcium ion. The primary role of microorganism in carbonate precipitation is mainly due to their ability to create an alkaline environment (high pH and DIC increase) through their various physiological activities. Three main groups of microorganism that can induce the carbonate precipitation: (i) photosynthetic microorganism such as cyanobacteria and microalgae; (ii) sulphate reducing bacteria; and (iii) some species of microorganism involved in nitrogen cycle. Microalgae are photosynthetic microorganism and utilize urea using urease or urea amidolyase enzyme, based on that it is possible to use microalgae as media to produce biocement through biocementation. This paper overviews biocement in general, biocementation, type of microorganism and their pathways in inducing carbonate precipitation and the prospect of microalgae to be used in biocement production. Keywords— Biocement, Biocementation, Microalgae, CaCO3 precipitation
Light-Dependant Biostabilisation of Sediments by Stromatolite Assemblages  [PDF]
David M. Paterson, Rebecca J. Aspden, Pieter T. Visscher, Mireille Consalvey, Miriam S. Andres, Alan W. Decho, John Stolz, R. Pamela Reid
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003176
Abstract: For the first time we have investigated the natural ecosystem engineering capacity of stromatolitic microbial assemblages. Stromatolites are laminated sedimentary structures formed by microbial activity and are considered to have dominated the shallows of the Precambrian oceans. Their fossilised remains are the most ancient unambiguous record of early life on earth. Stromatolites can therefore be considered as the first recognisable ecosystems on the planet. However, while many discussions have taken place over their structure and form, we have very little information on their functional ecology and how such assemblages persisted despite strong eternal forcing from wind and waves. The capture and binding of sediment is clearly a critical feature for the formation and persistence of stromatolite assemblages. Here, we investigated the ecosystem engineering capacity of stromatolitic microbial assemblages with respect to their ability to stabilise sediment using material from one of the few remaining living stromatolite systems (Highborne Cay, Bahamas). It was shown that the most effective assemblages could produce a rapid (12–24 h) and significant increase in sediment stability that continued in a linear fashion over the period of the experimentation (228 h). Importantly, it was also found that light was required for the assemblages to produce this stabilisation effect and that removal of assemblage into darkness could lead to a partial reversal of the stabilisation. This was attributed to the breakdown of extracellular polymeric substances under anaerobic conditions. These data were supported by microelectrode profiling of oxygen and calcium. The structure of the assemblages as they formed was visualised by low-temperature scanning electron microscopy and confocal laser microscopy. These results have implications for the understanding of early stromatolite development and highlight the potential importance of the evolution of photosynthesis in the mat forming process. The evolution of photosynthesis may have provided an important advance for the niche construction activity of microbial systems and the formation and persistence of the stromatolites which came to dominate shallow coastal environments for 80% of the biotic history of the earth.
Stabilisation of Quantum Computations by Symmetrisation  [PDF]
Adriano Barenco,Andre` Berthiaume,David Deutsch,Artur Ekert,Richard Jozsa,Chiara Macchiavello
Physics , 1996,
Abstract: We propose a method for the stabilisation of quantum computations (including quantum state storage). The method is based on the operation of projection into $\cal SYM$, the symmetric subspace of the full state space of $R$ redundant copies of the computer. We describe an efficient algorithm and quantum network effecting $\cal SYM$--projection and discuss the stabilising effect of the proposed method in the context of unitary errors generated by hardware imprecision, and nonunitary errors arising from external environmental interaction. Finally, limitations of the method are discussed.
Selenium Utilization Strategy by Microalgae  [PDF]
Hiroya Araie,Yoshihiro Shiraiwa
Molecules , 2009, DOI: 10.3390/molecules14124880
Abstract: The diversity of selenoproteins raises the question of why so many life forms require selenium. Selenoproteins are found in bacteria, archaea, and many eukaryotes. In photosynthetic microorganisms, the essential requirement for selenium has been reported in 33 species belonging to six phyla, although its biochemical significance is still unclear. According to genome databases, 20 species are defined as selenoprotein-producing organisms, including five photosynthetic organisms. In a marine coccolithophorid, Emiliania huxleyi (Haptophyta), we recently found unique characteristics of selenium utilization and novel selenoproteins using 75Se-tracer experiments. In E. huxleyi, selenite, not selenate, is the main substrate used and its uptake is driven by an ATP-dependent highaffinity, active transport system. Selenite is immediately metabolized to low-molecular mass compounds and partly converted to at least six selenoproteins, named EhSEP1–6. The most (EhSEP2) and second-most abundant selenoproteins (EhSEP1) are disulfide isomerase (PDI) homologous protein and thioredoxin reductase (TR) 1, respectively. Involvement of selenium in PDI is unique in this organism, while TR1 is also found in other organisms. In this review, we summarize physiological, biochemical, and molecular aspects of selenium utilization by microalgae and discuss their strategy of selenium utilization.
Microalgae for Stabilizing Biogas Production from Cassava Starch Wastewater  [cached]
B Budiyono,T.D. Kusworo
International Journal of Waste Resources , 2012, DOI: 10.12777/ijwr.v2i1.24
Abstract: The rapid growing of Indonesian population is emerging several critical national issues i.e. energy, food, environmental, water, transportation, as well as law and human right. As an agricultural country, Indonesia has abundant of biomass wastes such as agricultural wastes include the cassava starch wastes. The problem is that the effluent from cassava starch factories is released directly into the river before properly treatment. It has been a great source of pollution and has caused environmental problems to the nearby rural population. The possible alternative to solve the problem is by converting waste to energy biogas in the biodigester. The main problem of the biogas production of cassava starch effluent is acid forming-bacteria quickly produced acid resulting significantly in declining pH below the neutral pH and diminishing growth of methane bacteria. Hence, the only one of the method to cover this problem is by adding microalgae as biostabilisator of pH. Microalgae can also be used as purifier agent to absorb CO2.The general objective of this research project was to develop an integrated process of biogas production and purification from cassava starch effluent by using biostabilisator agent microalgae. This study has been focused on the used of urea, ruminant, yeast, microalgae, the treatment of gelled and ungelled feed for biogas production, pH control during biogas production using buffer Na2CO3, and feeding management in the semi-continuous process of biogas production. The result can be concluded as follows: i) The biogas production increased after cassava starch effluent and yeast was added, ii) Biogas production with microalgae and cassava starch effluent, yeast, ruminant bacteria, and urea were 726.43 ml/g total solid, iii) Biogas production without microalgae was 189 ml/g total solid. Keywords: microalgae, ruminant bacteria, bioga, cassava effluent, biodigester
Microalgae as bioreactors for bioplastic production
Franziska Hempel, Andrew S Bozarth, Nicole Lindenkamp, Andreas Klingl, Stefan Zauner, Uwe Linne, Alexander Steinbüchel, Uwe G Maier
Microbial Cell Factories , 2011, DOI: 10.1186/1475-2859-10-81
Abstract: In this study, we report on introducing the bacterial PHB pathway of R. eutropha H16 into the diatom Phaeodactylum tricornutum, thereby demonstrating for the first time that PHB production is feasible in a microalgal system. Expression of the bacterial enzymes was sufficient to result in PHB levels of up to 10.6% of algal dry weight. The bioplastic accumulated in granule-like structures in the cytosol of the cells, as shown by light and electron microscopy.Our studies demonstrate the great potential of microalgae like the diatom P. tricornutum to serve as solar-powered expression factories and reveal great advantages compared to plant based production systems.About 140 million tons of plastic are consumed every year worldwide, which necessitates the processing of approximately 150 million tons of fossil fuels and directly causes immense amounts of waste that can take thousands of years to naturally deteriorate, if it degrades at all [1]. Consequently, bioplastics are a feasible alternative in that they are not based on fossil resources and can easily be biodegraded. So far, however, production costs for petroleum-derived polymers still remain lower than biodegradable alternatives, which is a hindrance to commercial development and retail of environmentally friendly alternatives.Poly-(R)-3-hydroxybutyrate (PHB) is an aliphatic polyester with thermoplastic properties, which is naturally produced by certain bacteria as storage compound and is 100% biodegradable [1-5]. PHB is synthesized from acetyl-CoA by the action of three enzymes: a ketothiolase, an acetoacetyl-CoA reductase and a PHB synthase [6]. Under optimal conditions bacteria such as Ralstonia eutropha H16 can produce up to 80% PHB of cellular dry weight, and some companies have specialized on commercial PHB production (e.g. Metabolix Inc., Micromidas Inc.). Nevertheless, costs for PHB production by bacterial fermentation are still very high, which brought plants into focus as photosynthesis fueled low-cost pr
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