|
|
Cominetti, R., Correa, J., & Olver, N. (2022). Long-Term Behavior of Dynamic Equilibria in Fluid Networks. Oper. Res., 70(1), 516–526.
Abstract: A fluid queuing network constitutes one of the simplest models in which to study flow dynamics over a network. In this model we have a single source-sink pair, and each link has a per-time-unit capacity and a transit time. A dynamic equilibrium (or equilibrium flow over time) is a flow pattern over time such that no flow particle has incentives to unilaterally change its path. Although the model has been around for almost 50 years, only recently results regarding existence and characterization of equilibria have been obtained. In par-ticular, the long-term behavior remains poorly understood. Our main result in this paper is to show that, under a natural (and obviously necessary) condition on the queuing capacity, a dynamic equilibrium reaches a steady state (after which queue lengths remain constant) in finite time. Previously, it was not even known that queue lengths would remain bounded. The proof is based on the analysis of a rather nonobvious potential function that turns out to be monotone along the evolution of the equilibrium. Furthermore, we show that the steady state is characterized as an optimal solution of a certain linear program. When this program has a unique solution, which occurs generically, the long-term behavior is completely predictable. On the contrary, if the linear program has multiple solutions, the steady state is more difficult to identify as it depends on the whole temporal evolution of the equilibrium.
|
|
|
|
De la Iglesia, R., Valenzuela-Heredia, D., Andrade, S., Correa, J., & Gonzalez, B. (2012). Composition dynamics of epilithic intertidal bacterial communities exposed to high copper levels. FEMS Microbiol. Ecol., 79(3), 720–727.
Abstract: Copper has a dual role for organisms, both as micronutrient and toxic element. Copper mining activities have an enormous ecological impact because of the extraction process and the consequent release of copper-containing waste materials to the environment. In northern Chile, mainly in the Chanaral coastal area, this phenomenon is clearly evident. The released waste material has caused a strong modification of the area, and copper enrichment of beaches and rocky shores has provoked a decrease in the richness and diversity of many species of macroorganisms. However, the effects that copper enrichment has on microbial (e.g. bacterial epilithic) communities associated with the rocky shore environment are poorly understood. Using a culture-independent molecular approach, field sampling and laboratory microcosm experiments, we determined the effects of copper enrichment on bacterial communities inhabiting the rocky shore environment. Field samples showed a strong effect of copper on the structure of the natural bacterial epilithic communities, and microcosm experiments demonstrated rapid changes in bacterial community when copper is added, and reversibility of this effect within 48 h after copper is removed.
|
|
|
|
De la Iglesia, R., Valenzuela-Heredia, D., Pavissich, J. P., Freyhoffer, S., Andrade, S., Correa, J. A., et al. (2010). Novel polymerase chain reaction primers for the specific detection of bacterial copper P-type ATPases gene sequences in environmental isolates and metagenomic DNA. Lett. Appl. Microbiol., 50(6), 552–562.
Abstract: Aims: In the last decades, the worldwide increase in copper wastes release by industrial activities like mining has driven environmental metal contents to toxic levels. For this reason, the study of the biological copper-resistance mechanisms in natural environments is important. Therefore, an appropriate molecular tool for the detection and tracking of copper-resistance genes was developed. Methods and Results: In this work, we designed a PCR primer pair to specifically detect copper P-type ATPases gene sequences. These PCR primers were tested in bacterial isolates and metagenomic DNA from intertidal marine environments impacted by copper pollution. As well, T-RFLP fingerprinting of these gene sequences was used to compare the genetic composition of such genes in microbial communities, in normal and copper-polluted coastal environments. New copper P-type ATPases gene sequences were found, and a high degree of change in the genetic composition because of copper exposure was also determined. Conclusions: This PCR based method is useful to track bacterial copper-resistance gene sequences in the environment. Significance and Impact of the Study: This study is the first to report the design and use of a PCR primer pair as a molecular marker to track bacterial copper-resistance determinants, providing an excellent tool for long-term analysis of environmental communities exposed to metal pollution.
|
|
|
|
Hengst, M. B., Andrade, S., Gonzalez, B., & Correa, J. A. (2010). Changes in Epiphytic Bacterial Communities of Intertidal Seaweeds Modulated by Host, Temporality, and Copper Enrichment. Microb. Ecol., 60(2), 282–290.
Abstract: This study reports on the factors involved in regulating the composition and structure of bacterial communities epiphytic on intertidal macroalgae, exploring their temporal variability and the role of copper pollution. Culture-independent, molecular approaches were chosen for this purpose and three host species were used as models: the ephemeral Ulva spp. (Chlorophyceae) and Scytosiphon lomentaria (Phaeophyceae) and the long-living Lessonia nigrescens (Phaeophyceae). The algae were collected from two coastal areas in Northern Chile, where the main contrast was the concentration of copper in the seawater column resulting from copper-mine waste disposals. We found a clear and strong effect in the structure of the bacterial communities associated with the algal species serving as host. The structure of the bacterial communities also varied through time. The effect of copper on the structure of the epiphytic bacterial communities was significant in Ulva spp., but not on L. nigrescens. The use of 16S rRNA gene library analysis to compare bacterial communities in Ulva revealed that they were composed of five phyla and six classes, with approximately 35 bacterial species, dominated by members of Bacteroidetes (Cytophaga-Flavobacteria-Bacteroides) and alpha-Proteobacteria, in both non-polluted and polluted sites. Less common groups, such as the Verrucomicrobiae, were exclusively found in polluted sites. This work shows that the structure of bacterial communities epiphytic on macroalgae is hierarchically determined by algal species > temporal changes > copper levels.
|
|
|
|
Tapia, J. E., Gonzalez, B., Goulitquer, S., Potin, P., & Correa, J. A. (2016). Microbiota Influences Morphology and Reproduction of the Brown Alga Ectocarpus sp. Front. Microbiol., 7, 14 pp.
Abstract: Associated microbiota play crucial roles in health and disease of higher organisms. For macroalgae, some associated bacteria exert beneficial effects on nutrition, morphogenesis and growth. However, current knowledge on macroalgae microbiota interactions is mostly based on studies on green and red seaweeds. In this study, we report that when cultured under axenic conditions, the filamentous brown algal model Ectocarpus sp. loses its branched morphology and grows with a small ball like appearance. Nine strains of periphytic bacteria isolated from Ectocarpus sp. unialgal cultures were identified by 16S rRNA sequencing, and assessed for their effect on morphology, reproduction and the metabolites secreted by axenic Ectocarpus sp. Six of these isolates restored morphology and reproduction features of axenic Ectocarpus sp. Bacteria-algae co-culture supernatants, but not the supernatant of the corresponding bacterium growing alone, also recovered morphology and reproduction of the alga. Furthermore, colonization of axenic Ectocarpus sp. with a single bacterial isolate impacted significantly the metabolites released by the alga. These results show that the branched typical morphology and the individuals produced by Ectocarpus sp. are strongly dependent on the presence of bacteria, while the bacterial effect on the algal exometabolome profile reflects the impact of bacteria on the whole physiology of this alga.
|
|
