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A S Fernandez

Publications and source records attributed to A S Fernandez.

7 recordsLinked to original sources
PubMed2000

Parallel processing of substrate correlates with greater functional stability in methanogenic bioreactor communities perturbed by glucose.

Parallel processing is more stable than serial processing in many areas that employ interconnected activities. This hypothesis was tested for microbial community function using two quadruplicate sets of methanogenic communities, each set having substantially different populations. The two communities were maintained at a mean cell residence time of 16 days and a mean glucose loading rate of 0.34 g/liter-day in variable-volume reactors. To test stability to perturbation, they were subjected to an instantaneous glucose pulse that resulted in a 6.8-g/liter reactor concentration. The pattern of accumulated products in response to the perturbation was analyzed for various measures of functional stability, including resistance, resilience, and reactivity for each product. A new stability parameter, "moment of amplification envelope," was used to compare the soluble compound stability. These parameters indicated that the communities with predominantly parallel substrate processing were functionally more stable in response to the perturbation than the communities with predominantly serial substrate processing. The data also indicated that there was good replication of function under perturbed conditions; the degrees of replication were 0.79 and 0.83 for the two test communities.

Bioreactors↗
PubMed2000

Flexible community structure correlates with stable community function in methanogenic bioreactor communities perturbed by glucose.

Methanogenic bioreactor communities were used as model ecosystems to evaluate the relationship between functional stability and community structure. Replicated methanogenic bioreactor communities with two different community structures were established. The effect of a substrate loading shock on population dynamics in each microbial community was examined by using morphological analysis, small-subunit (SSU) rRNA oligonucleotide probes, amplified ribosomal DNA (rDNA) restriction analysis (ARDRA), and partial sequencing of SSU rDNA clones. One set of replicated communities, designated the high-spirochete (HS) set, was characterized by good replicability, a high proportion of spiral and short thin rod morphotypes, a dominance of spirochete-related SSU rDNA genes, and a high percentage of Methanosarcina-related SSU rRNA. The second set of communities, designated the low-spirochete (LS) set, was characterized by incomplete replicability, higher morphotype diversity dominated by cocci, a predominance of Streptococcus-related and deeply branching Spirochaetales-related SSU rDNA genes, and a high percentage of Methanosaeta-related SSU rRNA. In the HS communities, glucose perturbation caused a dramatic shift in the relative abundance of fermentative bacteria, with temporary displacement of spirochete-related ribotypes by Eubacterium-related ribotypes, followed by a return to the preperturbation community structure. The LS communities were less perturbed, with Streptococcus-related organisms remaining prevalent after the glucose shock, although changes in the relative abundance of minor members were detected by morphotype analysis. A companion paper demonstrates that the more stable LS communities were less functionally stable than the HS communities (S. A. Hashsham, A. S. Fernandez, S. L. Dollhopf, F. B. Dazzo, R. F. Hickey, J. M. Tiedje, and C. S. Criddle, Appl. Environ. Microbiol. 66:4050-4057, 2000).

Anaerobiosis↗
PubMed1998

Expression of the Emx-1 and Dlx-1 homeobox genes define three molecularly distinct domains in the telencephalon of mouse, chick, turtle and frog embryos: implications for the evolution of telencephalic subdivisions in amniotes.

Homologies between vertebrate forebrain subdivisions are still uncertain. In particular the identification of homologs of the mammalian neocortex or the dorsal ventricular ridge (DVR) of birds and reptiles is still a matter of dispute. To get insight about the organization of the primordia of the main telencephalic subdivisions along the anteroposterior axis of the neural tube, a fate map of the dorsal prosencephalon was obtained in avian chimeras at the 8- to 9-somite stage. At this stage, the primordia of the pallium, DVR and striatum were located on the dorsal aspect of the prosencephalon and ordered caudorostrally along the longitudinal axis of the brain. Expression of homeobox-containing genes of the Emx, Dlx and Pax families were used as markers of anteroposterior developmental subdivisions of the forebrain in mouse, chick, turtle and frog. Their expression domains delineated three main telencephalic subdivisions in all species at the onset of neurogenesis: the pallial, intermediate and striatal neuroepithelial domains. The fate of the intermediate subdivisions diverged, however, between species at later stages of development. Homologies between forebrain subdivisions are proposed based on the conservation and divergence of these gene expression patterns.

Animals↗
PubMed1997

Protective effect against Rhodococcus equi infection in mice of IgG purified from horses vaccinated with virulence associated protein (VapA)-enriched antigens.

IgG was purified from horses immunized with repeated doses of virulence associated (VapA) enriched antigens extracted with Triton X-114 from the surface of a virulent strain of R. equi. This IgG were administered to mice immunosuppressed by prior treatment with indomethacin. Mice administered the higher dose were completely protected against intraperitoneal infection with R. equi; mice given the lower dose were partially protected. By contrast, mice administered concentrated nonimmune equine IgG were not protected. This study demonstrates that VapA may be an important antigen involved in humoral protective immunity in R. equi infections caused by foal virulent strains.

Actinomycetales Infections↗
PubMed1996

Use of a virulence-associated protein based enzyme-linked immunosorbent assay for Rhodococcus equi serology in horses.

An enzyme-linked immunosorbent assay (ELISA) was developed against Rhodococcus equi using Triton X-114 detergent extracted whole cell material, in which the virulence associated protein (VapA) predominated. Enzymelinked immunosorbent assay titres corresponded to antibody reacting with VapA on Western blots. There was considerable variation in antibody titres of nonimmunised mares and in the time when the colostrally derived antibody of their foals had declined to low or undetectable titres. In general, antibodies in foals declined to their lowest levels at age 4-8 weeks. Seroconversion occurred in foals age 8-10 weeks, but the precise time depended on maternal titre and the month in which the foal was born. Foals reaching age 8 weeks in late summer showed more marked seroconversion than foals born earlier. The ELISA was used to follow the response to immunisation with the same Triton X-114 extracted material. Six mares immunised before parturition with the antigen in aluminium hydroxide adjuvant developed high titres, up to > 102,400 and transferred them to their foals through colostrum. Their foals responded to immunisation with 0.5-1.0 mg antigen 3, 5, 7 and 9 weeks after birth. Antibody titres following immunisation with similar dosage reached up to > 102,400 in a separate group of foals of nonimmunised mares. Nonvaccinated control foals seroconverted at age 6-8 weeks. The VapA based ELISA is useful to follow the course of natural infection with R. equi or immunisation with VapA based antigen.

Actinomycetales Infections↗
PubMed1987

Effect of bovine non-agglutinating antibodies on the blood clearance of 131I-labelled Brucella abortus strain 45/20.

Non-agglutinating anti-Brucella abortus S45/20 antibodies were isolated and purified from sera of immunized cattle by means of immunoadsorption and ion-exchange chromatography (DEAE-Sephadex A-50). They corresponded to the IgG1 isotype as shown by immunoelectrophoresis using monospecific anti-IgG1 and anti-bovine gamma globulin sera. These antibodies failed to agglutinate the antigen. They were detected by the anti-bovine gamma globulin test, showing higher titres than those of agglutinating antibodies during the whole period of the experiment. Blood clearance of 131I-S45/20 in mice, was slower in those groups which had received non-agglutinating antibodies than in the control group.

Agglutination Tests↗