Physical Constraints to Aquatic Plant Growth in New Zealand Lakes

The nature of aquatic plant communities often defines benthic habitat within oligotrophic and mesotrophic lakes and lake management increasingly recognizes the importance of maintaining plant diversity in order to sustain biological diversity and capacity within lakes. We have developed simple statistical relationships between key physical and vegetation variables that define the habitat requirements, or “habitat-templates”, of key vegetation types to facilitate management of plant communities in New Zealand lakes. Statistical relationships were derived from two datasets. The first was a multi-lake dataset to determine the effects of water level fluctuation and water clarity. The second dataset was from a comprehensive shoreline survey of Lake Wanaka, which allowed us to examine within-lake variables such as beach slope and wave action. Sufficient statistical relationships were established to develop a habitat template for each of the major species or assemblages. The relationships suggested that the extent and diversity of shallow-growing species was related to a combination of the extent of water level fluctuation and wave exposure. (PDF contains 9 pages.

Efficient data mappings for parity-declustered data layouts

AbstractThe joint demands of high performance and fault tolerance in a large array of disks can be satisfied by a parity-declustered data layout. Such a data layout is generated by partitioning the data on the disks into stripes and choosing a part of each stripe to hold redundant information. Thus the data layout can be represented as a table of stripes. The data mapping problem is the problem of translating a data address into a disk identifier and an offset on that disk. Recent work has yielded mappings that compute disks and offsets directly from data addresses without the need to store tables. In this paper, we show that parity-declustered data layouts based on commutative rings yield mappings with improved computational efficiency and wider applicability

P. fluorescens biofilm control using bacteriophage ΦS1

Pseudomonas fluorescens biofilms contribute to the spoilage of dairy industry products due to the proteolytic activity of some Pseudomonas fluorescens strains. The eradication of these biofilms is difficult using the traditional chemical biocides due to the low removal action of these agents. Additionally chemical control leaves inactivated cells attached to the surface that tends to provide an ideal environment for further bacterial adhesion and growth. Bacteriophages can be seen as good alternative biofilm control agents due to their high specificity, efficacy against biocide resistant bacteria and because they are innocuous to the environment. The use of the bacteriophage phi-S1 as control agent of P. fluorescens biofilms at early stages of formation and in the mature stage was investigated in this work. Phage infection of attached cells was studied using a parallel plate flow cell mounted on an inverted microscope and with an automatic image analysis system that enables in situ and real time enumeration of cells. After phage infection the recolonization of the surfaces was also assessed with this system. The results obtained showed that phage infection caused a removal of about 93.5 ± 1.51% of the adhered cells. Additionally P. fluorescens recolonization of the surfaces was no longer possible due to the adsorption of phages (assessed by EDS) that remained on the glass surfaces after being washed during one hour with buffer. Five days old biofilms and planktonic cells in different growth phases were infected with phage (with initial MOI of 0.5). The infection was monitored by measuring the amount of cell lysis, PFU release and decrease in biomass. The results obtained revealed that although the rate of cell lysis and PFU release was lower in biofilms than those in exponential planktonic cultures (p<0.05, ANOVA), the decrease in the biomass after 200 minutes was approximately the same of infection and about 85.27 ± 1.41%. This work demonstrated that phages are important tools to be considered in industrial control of biofilms because they are able to cause significant biomass reduction of early stages and mature biofilms and prevent cell recolonization of the surfaces

Prevention of P. fluorescens adhesion to surfaces using bacteriophage ΦS1

The presence of biofilms in industrial settings is problematic as bacteria are responsible for several losses including product spoilage. Biofilms are difficult to eradicate and their removal and destruction has been for long attempted using chemical biocides. These agents usually yield very low biofilm removal amounts, have negative environmental impacts and the emergence of biocide-resistant bacteria represents one of the major drawback on their use. Therefore there is an increase interest in the utilization of bacteriophages (phages). Phages are specific for a host or a range of hosts, active against biocide-resistant bacteria and considered innocuous to the environment. This work focuses on the use of bacteriophage ΦS1 to prevent P. fluorescens biofilm formation. Glass and stainless steel surfaces were coated with a suspension of 10^9 PFUmlˉ¹ prior to bacterial attachment. The results obtained showed, that P. fluorescens were no longer able to adhere to these surfaces. Moreover, after several washings of the surface the remaining attached phages (10³ PFUmlˉ¹) were still able to prevent biofilm formation on the surfaces

Bacteriophage Ф S1 infection of Pseudomonas fluorescens planktonic cells versus biofilms

This communication focuses on the efficacy of a specific lytic phage, phage Ф S1, as a control agent of Pseudomonas fluorescens biofilms. The effect of phage infection temperature and the host growth temperature were evaluated. The results obtained showed that the phage infection process was temperature dependent and that the optimum temperature of infection of planktonic cells and biofilms was 26ºC. At this temperature, bacteriophage Ф S1, at a multiplicity of infection (MOI) of 0.5 infected both planktonic cells and biofilms causing a biomass reduction of about 85% in both cases.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI) - POCTI/BIO/35683/99

Pseudomonas fluorescens infection by bacteriophage ФS1 : the influence of temperature, host growth phase and media

The influence of host growth temperature, phase and media, together with the effect of infection temperature on bacteriophage ФS1 infection of Pseudomonas fluorescens were examined. The rates of cell lysis and phage release were determined and showed that the efficacy of phage infection was optimal with host cells grown and infected at 26 ºC. The host physiological state also affected these rates. Infection was dependent on the presence of cell wall proteins with molecular weights of 17.5 ± 1 and 99 ± 5 kDa.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência, Tecnologia, Inovação” (POCTI) - POCTI/BIO/35683/99

Spectral function of spinless fermions on a one-dimensional lattice

We study the spectral function of interacting one-dimensional fermions for an integrable lattice model away from half-filling. The divergent power-law singularity of the spectral function near the single-particle or single-hole energy is described by an effective x-ray edge type model. At low densities and for momentum near the zone boundary, we find a second divergent singularity at higher energies which is associated with a two-particle bound state. We use the Bethe ansatz solution of the model to calculate the exact singularity exponents for any momentum and for arbitrary values of chemical potential and interaction strength in the critical regime. We relate the singularities of the spectral function to the long-time decay of the fermion Green's function and compare our predictions with numerical results from the time-dependent density matrix renormalization group (tDMRG). Our results show that the tDMRG method is able to provide accurate time decay exponents in the cases of power-law decay of the Green's function. Some implications for the line shape of the dynamical structure factor away from half-filling are also discussed. In addition, the spectral weight of the Luttinger liquid result for the dynamical structure factor of the Heisenberg model at zero field is compared with the exact two-spinon contribution.Comment: 30 pages, 18 figure

GSK3-mediated raptor phosphorylation supports amino acid-dependent Q2 mTORC1-directed signalling

The mammalian or mechanistic target of rapamycin (mTOR) complex 1 (mTORC1) is a ubiquitously expressed multimeric protein kinase complex that integrates nutrient and growth factor signals for the co-ordinated regulation of cellular metabolism and cell growth. Herein, we demonstrate that suppressing the cellular activity of glycogen synthase kinase-3 (GSK3), by use of pharmacological inhibitors or shRNA-mediated gene silencing, results in substantial reduction in amino acid (AA)-regulated mTORC1-directed signalling, as assessed by phosphorylation of multiple downstream mTORC1 targets. We show that GSK3 regulates mTORC1 activity through its ability to phosphorylate the mTOR-associated scaffold protein raptor (regulatory-associated protein of mTOR) on Ser(859). We further demonstrate that either GSK3 inhibition or expression of a S859A mutated raptor leads to reduced interaction between mTOR and raptor and under these circumstances, irrespective of AA availability, there is a consequential loss in phosphorylation of mTOR substrates, such as p70S6K1 (ribosomal S6 kinase 1) and uncoordinated-51-like kinase (ULK1), which results in increased autophagic flux and reduced cellular proliferation