957 research outputs found
The role of the motility of Methylobacterium in bacterial interactions in drinking water
Bacterial motility is one important factor that affects biofilm formation. In drinking water there are key bacteria in aggregation, whose biology acts to enhance the formation of biofilms. However, it is unclear whether the motility of these key bacteria is an important factor for the interactions between bacteria in drinking water, and, subsequently, in the formation of aggregates, which are precursors to biofilms. Thus, the role of the motility of one of these key bacteria, the Methylobacterium strain DSM 18358, was investigated in the interactions between bacteria in drinking water. The motility of pure Methylobacterium colonies was initially explored; if it was affected by the viscosity of substrate, the temperature, the available energy and the type of substrate. Furthermore, the role of Methylobacterium in the interactions between mixed drinking water bacteria was investigated under the mostly favourable conditions for the motility of Methylobacterium identified before. Overall, the motility of Methylobacterium was found to play a key role in the communication and interactions between bacteria in drinking water. Understanding the role of the motility of key bacteria in drinking water might be useful for the water industry as a potential tool to control the formation of biofilms in drinking water pipes
Nanoparticle transport in saturated porous medium using magnetic resonance imaging
Transport study of nanoparticle (NP) through matrix flow dominated aquifer sand and soils have significant influence in natural systems. To quantify the transport behaviour, magnetic resonance imaging (MRI) was used to image the iron oxide based nanoparticle, Molday ION (carboxyl terminated) through saturated sandstone rock core. T2-weighted images were acquired and the changes in image intensity were calibrated to get a quantitative concentration profiles at various time intervals. These profiles were evaluated through CXTFIT transport model to estimate the transport parameters. These parameters are estimated at various points along the length of the column while classical breakthrough curve analysis cannot provide these details. NPâsurface interactions were investigated using DLVO (DerjaguinâLandauâVerweyâOverbeek) theory. The dispersion coefficients (2.55â1.21Â ĂÂ 10â7Â m2/s) were found to be decrease with distance, deposition rate constant k (6.70â9.13Â ĂÂ 10â4Â (1/s)) and fast deposition rate constant kfast (4.32â8.79Â ĂÂ 10â2Â (1/s)) were found to be increase with distance. These parameter variations over length will have a scaling up impact in developing transport models for environmental remediation and risk assessment schemes
Productivity of Florida Springs: Second semi-annual report to the Biology Division, Office of Naval Research progress from February 1, 1953 to June 30, 1953
During this second six months emphasis has been laid on developing a complete understanding of the metabolism of the Silver Springs ecosystem as an example of a community apparently in a steady state. Variation in phosphates, uptake of nitrates, and importance of boron have been estimated. Fluctuation of some major elements has been estimated. Examination of stomach contents has permitted trophic classifications of dominant species and the standing crops have been estimated for these species by number and by dry weight. From these a pyramid of mass has been constructed. Special attention has been paid to bacteria using 3 methods for comparison of Silver Springs with lakes and estimation of the standing crop. The oxygen gradient method has been repeated at half hourly intervals. A carbon-dioxide gradient method has also been used to check the oxygen and to obtain a photosynthetic quotient. Black and light Bell jar experiments have been initiated to obtain checks on the other production measurement and to obtain a community respiration rate. An approximate balance has resulted from estimates of production , respiration , and downstream loss. A flow rate diagram has been constructed to clarify definitions of efficiency and their relationship to a steady state system. Mr. Sloan has statistically verified the increase of insect number and variety away from the boils and demonstrated the reliability of quantitative dipping for aquatic insects. Plans for the third half year include detained and comparative study of the dominant algae and further estimates of rates of growth of all community components. (29pp.
A keystone Methylobacterium strain in biofilm formation in drinking water
The structure of biofilms in drinking water systems is influenced by the interplay between
biological and physical processes. Bacterial aggregates in bulk fluid are important in seeding biofilm
formation on surfaces. In simple pure and co-cultures, certain bacteria, including Methylobacterium,
are implicated in the formation of aggregates. However, it is unclear whether they help to form
aggregates in complex mixed bacterial communities. Furthermore, different flow regimes could affect
the formation and destination of aggregates. In this study, real drinking water mixed microbial
communities were inoculated with the Methylobacterium strain DSM 18358. The propensity of
Methylobacterium to promote aggregation was monitored under both stagnant and flow conditions.
Under stagnant conditions, Methylobacterium enhanced bacterial aggregation even when it was
inoculated in drinking water at 1% relative abundance. Laminar and turbulent flows were developed
in a rotating annular reactor. Methylobacterium was found to promote a higher degree of aggregation
in turbulent than laminar flow. Finally, fluorescence in situ hybridisation images revealed that
Methylobacterium aggregates had distinct spatial structures under the different flow conditions.
Overall, Methylobacterium was found to be a key strain in the formation of aggregates in bulk water
and subsequently in the formation of biofilms on surfaces
Space Station Ground Data Management System
KSC is planning a Space Station Ground Data Management System (GDMS) for support of functional interface verification, integration and test of Space Station modules and elements. This computer system, planned for initial operational support in 1992, currently is entering a definition and prototyping stage. This paper provides an overview of the GDMS system concept. It synqpsizes system functional capabilities, and discusses software and hardware architectural approaches currently under evaluation. It identifies programmatic constraints and their influence upon the concept, as well as specific technical issues planned for study or evaluation via prototyping
The active microbial community more accurately reflects the anaerobic digestion process: 16S rRNA (gene) sequencing as a predictive tool
Background:
Amplicon sequencing methods targeting the 16S rRNA gene have been used extensively to investigate microbial community composition and dynamics in anaerobic digestion. These methods successfully characterize amplicons but do not distinguish micro-organisms that are actually responsible for the process. In this research, the archaeal and bacterial community of 48 full-scale anaerobic digestion plants were evaluated on DNA (total community) and RNA (active community) level via 16S rRNA (gene) amplicon sequencing.
Results:
A significantly higher diversity on DNA compared with the RNA level was observed for archaea, but not for bacteria. Beta diversity analysis showed a significant difference in community composition between the DNA and RNA of both bacteria and archaea. This related with 25.5 and 42.3% of total OTUs for bacteria and archaea, respectively, that showed a significant difference in their DNA and RNA profiles. Similar operational parameters affected the bacterial and archaeal community, yet the differentiating effect between DNA and RNA was much stronger for archaea. Co-occurrence networks and functional prediction profiling confirmed the clear differentiation between DNA and RNA profiles.
Conclusions:
In conclusion, a clear difference in active (RNA) and total (DNA) community profiles was observed, implying the need for a combined approach to estimate community stability in anaerobic digestion
The price of corporate social responsibility: the case of black economic empowerment transactions in South Africa
Since the demise of apartheid in South Africa, corporations have been encouraged to participate in the governmental goal of increasing corporate ownership by the black majority population. One vehicle that has arisen to help facilitate an increase in corporate ownership has been black economic empowerment (BEE) transactions. BEE transactions are essentially private placements of equity. Firms that have taken this socially activist position of selling portions of their equity, usually at a substantial discount, to black empowerment groups have received positive media attention in the name of âgood corporate citizenship.â ; This study investigates the market performance of these BEE transactions, specifically addressing three questions. The first question is whether BEE transactions create or destroy wealth. To address this question we use an event study methodology to calculate the cumulative abnormal returns (CARs) associated with public announcements of BEE transactions. The second question is whether specific types of BEE transactions did better or worse than others. We address this question by analyzing the cross-sectional variation in the CARs associated with public announcements of BEE transactions. The third question is whether firms that engage in BEE transactions experience negative post-announcement price performance. This last question is motivated by popular press accounts of the exploitation of black empowerment groups by white-owned South African corporations. To address this question, we test whether BEE transactions have benefited white corporate South Africa at the expense of the participating black empowerment groups.
Productivity of Florida Springs: first semi-annual report to Biology Division, Office of Naval Research, progress from June 1, 1952 to January 31, 1953
Work has begun on studying the factors responsible for productivity
in the Florida springs, which are nearly constant temperature, constant
chemical, steady state giant laboratories. Progress has been made on five
aspects: qualitative description, quantitative description, completion
of knowledge of chemical factors, measurement of productivity , development
of productivity theory.
Measurement of the primary productivity in Silver Springs and Green
Cove Springs by two new methods: the raising of organisms in cages, and the
measurement of night & day differences in oxygen downstream agree roughly.
Production in these springs is greater than previous production figures reported
for marine, fresh water, and land areas. Instantaneous measures of production
show large variations with season, time of day, cloud cover. Production
estimates range from 11,000 lbs per acre per year to 70,000 lbs. glucose per
acre per year during daylight hours.
Essential stability of the springs environment has been shown with
respect to temperature, phosphorus, and plant cover. A correlation of species
number with lack of stability has been shown with insects. Quantitative
studies have shown very large plant base to pyramids of mass. Correlation
of marine invasion with chlorinity has been shown. The essential aspects of
pH regulated phosphorus geochemistry in Florida have been outlined. Some
theoretical ideas on productivity have been evolved. Mapping of sessile
organisms in springs and taxonomic identification of dominants are half
completed. Plans for second six months include measurement of herbivore
and carnivore production rates and completion of food chain efficiency
determinations in Silver Springs as a preparation for subsequent
comparisons between springs. (34pp.
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