Complex pattern formation by Pseudomonas strain KC in response to nitrate and nitrite.
(9/2155)
Pattern formation by enteric bacteria growing on semi-solid agar plates has recently been described, and in this paper a similar phenomenon is reported in an environmental isolate, Pseudomonas strain KC. This organism reproducibly formed complex patterns on 3-mm-thick, semi-solid agar (0.25%, w/v) mineral medium motility plates containing either 5 mM 2-oxoglutarate or 5 mM glycerol, and 2 mM NO2- or 3 mM NO3-. When the plates were inoculated at the centre and incubated in air at 30 degrees C, a growth zone formed that migrated slowly (<0.5 mm h(-1)) and uniformly outward. Within 24 h, a dense outer growth ring formed which then coalesced into discrete aggregates (approx. 0.5 mm in diameter) with uniform spacing; these aggregates moved radially at approximately 0.7 mm h(-1) and maintained their density and spacing, to form a spoke-like pattern. Microscopic observations revealed that cells within an intact aggregate were very motile, but did not appear to leave the aggregate. Pattern formation did not occur if the NO2- or NO3- concentration was altered, if the agar layer was thicker or thinner, if the plates were incubated under strictly denitrifying conditions, or if carbon sources that were chemoattractants, e.g. acetate, were used. Five other species of pseudomonads were tested under identical conditions, and none formed patterns. Oxygen microelectrode studies indicated that there was little or no oxygen within the aggregates. The growth of strain KC was progressively inhibited in imposed diffusion gradients of NO2- or NO3- of which NO2- was the more potent inhibitor. These results suggest that pattern formation by strain KC may reflect an adaptive response to adverse environmental conditions. (+info)
In vivo transcription of the Escherichia coli oxyR regulon as a function of growth phase and in response to oxidative stress.
(10/2155)
Simultaneous expression of seven genes in Escherichia coli was measured by a reverse transcription-multiplex PCR fluorescence procedure. Genes studied were (i) oxyR (transcriptional regulator); (ii) katG, dps, gorA, and ahpCF (controlled by OxyR); (iii) sodA (controlled by SoxRS); and (iv) trxA (not related to OxyR or SoxRS). Except for trxA, transcription of all genes was activated during the course of growth of wild-type bacteria, though notable variations were observed with respect to both the time and extent of activation. Whereas oxyR, katG, dps, and gorA were activated during exponential growth, ahpCF and sodA were stimulated in stationary phase. Maximal induction ranged from 4.6- to 86.5-fold, for gorA and dps, respectively. Treatment with H2O2 stimulated expression of the genes (katG, dps, ahpCF, and gorA) previously identified as members of the OxyR regulon, except for oxyR itself. Induction by H2O2 was a remarkably rapid and reversible process that took place in an OxyR-dependent and sigmaS-independent manner. NaCl induced expression of the genes controlled by OxyR, including the oxyR locus. This transcriptional up-regulation was preserved in a strain with the DeltaoxyR::kan mutation, but it was abolished (ahpCF) or significantly reduced (oxyR and dps) in a strain with the rpoS::Tn10 mutation, potentially reflecting positive transcriptional regulation of the oxyR regulon by sigmaS. Expression of trxA was not increased either by H2O2 stress or by a shift to high-osmolarity conditions. (+info)
Bioenergetic aspects of halophilism.
(11/2155)
Examination of microbial diversity in environments of increasing salt concentrations indicates that certain types of dissimilatory metabolism do not occur at the highest salinities. Examples are methanogenesis for H2 + CO2 or from acetate, dissimilatory sulfate reduction with oxidation of acetate, and autotrophic nitrification. Occurrence of the different metabolic types is correlated with the free-energy change associated with the dissimilatory reactions. Life at high salt concentrations is energetically expensive. Most bacteria and also the methanogenic Archaea produce high intracellular concentrations of organic osmotic solutes at a high energetic cost. All halophilic microorganisms expend large amounts of energy to maintain steep gradients of NA+ and K+ concentrations across their cytoplasmic membrane. The energetic cost of salt adaptation probably dictates what types of metabolism can support life at the highest salt concentrations. Use of KCl as an intracellular solute, while requiring far-reaching adaptations of the intracellular machinery, is energetically more favorable than production of organic-compatible solutes. This may explain why the anaerobic halophilic fermentative bacteria (order Haloanaerobiales) use this strategy and also why halophilic homoacetogenic bacteria that produce acetate from H2 + CO2 exist whereas methanogens that use the same substrates in a reaction with a similar free-energy yield do not. (+info)
Comparative fitness of multi-dideoxynucleoside-resistant human immunodeficiency virus type 1 (HIV-1) in an In vitro competitive HIV-1 replication assay.
(12/2155)
We examined whether human immunodeficiency virus type 1 (HIV-1) fitness was altered upon the acquisition of a set or subset of five mutations (A62V, V75I, F77L, F116Y, and Q151M) in the pol gene, which confers resistance to multiple dideoxynucleosides (MDR), as well as the zidovudine resistance-associated mutation T215Y, using a competitive HIV-1 replication assay in a setting of an HXB2D genetic background. Target H9 cells were exposed to a 50:50 mixture of paired infectious molecular clones, and HIV-1 in the culture supernatant was transmitted to new cultures every 7 to 10 days. The polymerase-encoding region of the virus was sequenced at various time points, and the relative proportion of the two viral populations was determined. In the absence of drugs, the comparative order for replicative fitness was HIV-162/75/77/116/151 > HIV-177/116/151 > HIV-1151 > wild-type HIV-1 (HIV-1wt) > HIV-175/77/116/151 > HIV-1151/215 > HIV-1215. In the presence of zidovudine or didanosine, the order was HIV-162/75/77/116/151 > HIV-177/116/151 > HIV-175/77/116/151 > HIV-1151 > HIV-1215. HIV-1215S(TCC), a putative intermediate infectious clone for HIV-1215, replicated comparably to HIV-1wt, while two putative intermediates for HIV-1151 [HIV-1151L(CTG) and HIV-1151K(AAG)] replicated much less efficiently than HIV-1wt and HIV-1151, suggesting that for HIV-1151 to develop, two base substitutions are likely to occur concurrently or within a short interval. These data may illustrate the molecular basis by which HIV-1151 emerges much less frequently than HIV-1215. The present data also demonstrate that several MDR HIV-1 variants are more fit than HIV-1wt in the absence of drugs and that resistance-associated mutations and drug pressure are critical variates for HIV-1 fitness. (+info)
Shift of clinical human immunodeficiency virus type 1 isolates from X4 to R5 and prevention of emergence of the syncytium-inducing phenotype by blockade of CXCR4.
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The emergence of X4 human immunodeficiency virus type 1 (HIV-1) strains in HIV-1-infected individuals has been associated with CD4(+) T-cell depletion, HIV-mediated CD8(+) cell apoptosis, and an impaired humoral response. The bicyclam AMD3100, a selective antagonist of CXCR4, selected for the outgrowth of R5 virus after cultivation of mixtures of the laboratory-adapted R5 (BaL) and X4 (NL4-3) HIV strains in the presence of the compound. The addition of AMD3100 to peripheral blood mononuclear cells infected with X4 or R5X4 clinical HIV isolates displaying the syncytium-inducing phenotype resulted in a complete suppression of X4 variants and a concomitant genotypic change in the V2 and V3 loops of the envelope gp120 glycoprotein. The recovered viruses corresponded genotypically and phenotypically to R5 variants in that they could no longer use CXCR4 as coreceptor or induce syncytium formation in MT-2 cells. Furthermore, the phenotype and genotype of a cloned R5 HIV-1 virus converted to those of the R5X4 virus after prolonged culture in lymphoid cells. However, these changes did not occur when the infected cells were cultured in the presence of AMD3100, despite low levels of virus replication. Our findings indicate that selective blockade of the CXCR4 receptor prevents the switch from the less pathogenic R5 HIV to the more pathogenic X4 HIV strains, a process that heralds the onset of AIDS. In this article, we show that it could be possible to redirect the evolution of HIV so as to impede the emergence of X4 strains or to change the phenotype of already-existing X4 isolates to R5. (+info)
Effects of egg-adaptation on the receptor-binding properties of human influenza A and B viruses.
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Propagation of human influenza viruses in embryonated chicken eggs (CE) results in the selection of variants with amino acid substitutions near the receptor-binding site of the hemagglutinin (HA) molecule. To evaluate the mechanisms by which these substitutions enable human virus growth in CE, we studied the binding of 10 human influenza A (H1N1, H3N2) and B strains, isolated and propagated solely in MDCK cells, and of their egg-adapted counterparts to preparations of cellular membranes, gangliosides, sialylglycoproteins, and sialyloligosaccharides. All egg-adapted variants differed from nonadapted strains by increased binding to the plasma membranes of chorio-allantoic (CAM) cells of CE and by the ability to bind to CAM gangliosides. In addition, there was no decrease in affinity for inhibitors within allantoic fluid. These findings indicate that growth of human influenza viruses in CE is restricted because of their inefficient binding to receptors on CAM cells and that gangliosides can play an important role in virus binding and/or penetration. The effects of the egg-adaptation substitutions on the receptor-binding properties of the viruses include (i) enhancement of virus binding to the terminal Sia(alpha2-3)Gal determinant (substitutions in HA positions 190, 225 of H1N1 strains and in position 186 of H3N2 strains); (ii) a decrease of steric interference with more distant parts of the Sia(alpha2-3Gal)-containing receptors (a loss of glycosylation sites in positions 163 of H1 HA and 187 of type B HA); and (iii) enhanced ionic interactions with the negatively charged molecules due to charged substitutions at the tip of the HA [187, 189, 190 (H1), and 145, 156 (H3)]. Concomitantly with enhanced binding to Sia(alpha2-3)Gal-terminated receptors, all egg-adapted variants decreased their affinity for equine macroglobulin, a glycoprotein bearing terminal 6'-sialyl(N-acetyllactosamine)-moieties. (+info)
DNA analyses support the hypothesis that infanticide is adaptive in langur monkeys.
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Although the killing of dependent infants by adult males is a widespread phenomenon among primates, its causes and consequences still remain hotly debated. According to the sexual selection hypothesis, infanticidal males will gain a reproductive advantage provided that only unrelated infants are killed and that the males increase their chances of siring the next infants. Alternatively, the social pathology hypothesis interprets infanticide as a result of crowded living conditions and, thus, as not providing any advantage. Based on DNA analyses of wild Hanuman langurs (Presbytis entellus) we present the first evidence that male attackers were not related to their infant victims. Furthermore, in all cases the presumed killers were the likely fathers of the subsequent infants. Our data, therefore, strongly support the sexual selection hypothesis interpreting infanticide as an evolved, adaptive male reproductive tactic. (+info)
Characterization of the major superoxide dismutase of Staphylococcus aureus and its role in starvation survival, stress resistance, and pathogenicity.
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A Staphylococcus aureus mutant (SPW1) which is unable to survive long-term starvation was shown to have a transposon insertion within a gene homologous to the sodA family of manganese-dependent superoxide dismutases (SOD). Whole-cell lysates of the parental 8325-4 strain demonstrated three zones of SOD activity by nondenaturing gel electrophoresis. The activities of two of these zones were dependent on manganese for activity and were absent in SPW1. The levels of SOD activity and sodA expression were growth-phase dependent, occurring most during postexponential phase. This response was also dependent on the level of aeration of the culture, with highest activity and expression occurring only under high aeration. Expression of sodA and, consequently, SOD activity could be induced by methyl viologen but only during the transition from exponential- to postexponential-phase growth. SPW1 was less able to survive amino acid limitation and acid stress but showed no alteration in pathogenicity in a mouse abscess model of infection compared to the parental strain 8325-4. (+info)