Better to Be in Bad Company than to Be Alone? Aedes Vectors Respond Differently to Breeding Site Quality in the Presence of Others

This study focuses on two competing species, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), both invasive mosquitoes of the New World. Context-specific competition between immature forms inside containers seems to be an important determinant of the coexistence or displacement of each species in different regions of the world. Here, competition experiments developed at low density (one, two or three larvae) and receiving four different resource food concentration, were designed to test whether Ae. albopictus and Ae. aegypti respond differently to competition, and whether competition can be attributed to a simple division of resources. Three phenotypic traits - larval development, adult survival under starvation and wing length - were used as indicators of performance. Larvae of neither species were limited by resource concentration when they were alone, unlike when they developed with competitors. The presence of conspecifics affected Ae. aegypti and Ae. albopictus, inducing slower development, reduced survival and wing length. The response to resource limitation was different when developing with heterospecifics: Ae. aegypti developing with one heterospecific showed faster development, producing smaller adults with shorter lives, while in the presence of two competitors, development increased and adults lived longer. Aedes albopictus demonstrated a better performance when developing with heterospecifics, with no loss in their development period and improved adult survival. Overall, our results suggest that response to competition can not simply be attributed to the division of resources, and that larvae of both species presented large phenotypic plasticity in their response to the presence or absence of heterospecifics and conspecifics.     

Biophysical properties of ergosterol-enriched lipid rafts in yeast and tools for their study: characterization of ergosterol/phosphatidylcholine membranes with three fluorescent membrane probes

In this work, binary mixtures of phospholipid/ergosterol (erg) were studied using three fluorescent membrane probes. The phospholipid was either saturated (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) or monounsaturated (1-palmitoyl-2-dioleoyl-sn-glycero-3-phosphocholine, POPC) phosphatidylcholine, to evaluate the fluorescence properties of the probes in gel, liquid ordered (l(o)) and liquid disordered (l(d)) phases. The probes have been used previously to study cholesterol-enriched domains, but their photophysical properties in erg-enriched membranes have not been characterized. N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (NBD-DPPE) presents modest blue-shifts upon erg addition, and the changes in the fluorescence lifetime are mainly due to differences in the efficiency of its fluorescence dynamic self-quenching. However, the steady-state fluorescence anisotropy of NBD-DPPE presents well-defined values in each lipid phase. N-(lissamine rhodamine B sulfonyl)-1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (Rhod-DOPE) presents a close to random distribution in erg-rich membranes. There are no appreciable spectral shifts and the steady-state fluorescence anisotropy presents complex behavior, as a result of different photophysical processes. The probe is mostly useful to label l(d) domains in yeast membranes. 4-(2-(6-(Dibutylamino)-2-naphthalenyl)ethenyl)-1-(3-sulfopropyl)-pyridinium (di-4-ANEPPS) is an electrochromic dye with excitation spectra largely insensitive to the presence of erg, but presenting a strong blue-shift of its emission with increasing concentrations of this sterol. Its partition coefficient is favorable to l(o) domains in POPC/erg mixtures. Although the fluorescence properties of di-4-ANEPPS are less sensitive to erg than to chol, in both cases the fluorescence lifetime responds monotonically to sterol mole fraction, becoming significantly longer in the presence of sterol as compared to pure POPC or DPPC bilayers. The probe displays a unique sensitivity to sterol-lipid interaction due to the influence of hydration and H-bonding patterns at the membrane/water interface on its fluorescence properties. This makes di-4-ANEPPS (and possibly similar probes) potentially useful in the study of erg-enriched domains in more complex lipid mixtures and in the membranes of living yeast cells.     

Biological hydroperoxides and singlet molecular oxygen generation

The decomposition of lipid hydroperoxides (LOOH) into peroxyl radicals is a potential source of singlet molecular oxygen ((1)O(2)) in biological systems. Recently, we have clearly demonstrated the generation of (1)O(2) in the reaction of lipid hydroperoxides with biologically important oxidants such as metal ions, peroxynitrite and hypochlorous acid. The approach used to unequivocally demonstrate the generation of (1)O(2) in these reactions was the use of an isotopic labeled hydroperoxide, the (18)O-labeled linoleic acid hydroperoxide, the detection of labeled compounds by HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) and the direct spectroscopic detection and characterization of (1)O(2) light emission. Using this approach we have observed the formation of (18)O-labeled (1)O(2) by chemical trapping of (1)O(2) with anthracene derivatives and detection of the corresponding labeled endoperoxide by HPLC-MS/MS. The generation of (1)O(2) was also demonstrated by direct spectral characterization of (1)O(2) monomol light emission in the near-infrared region (lambda = 1270 nm). In summary, our studies demonstrated that LOOH can originate (1)O(2). The experimental evidences indicate that (1)O(2) is generated at a yield close to 10% by the Russell mechanism, where a linear tetraoxide intermediate is formed in the combination of two peroxyl radicals. In addition to LOOH, other biological hydroperoxides, including hydroperoxides formed in proteins and nucleic acids, may also participate in reactions leading to the generation (1)O(2). This hypothesis is currently being investigated in our laboratory.     

Distinct groups of plasmids correlated with bacteriocin production in Staphylococcus aureus

The genetic basis of bacteriocin (Bac) production by six strains of Staphylococcus aureus was examined. Gene transfer experiments (in which the plasmids were tagged with the erythromycin resistance transposon Tn551) and plasmid-elimination experiments by growth at 43 degrees C associated bacteriocin production with a particular plasmid in each strain. The Bac plasmids could be separated into two distinct groups: the first comprised plasmids larger than 40 kb, which did not specify immunity to bacteriocins; the second comprised small plasmids (8.0-10.4 kb) which also specified immunity to bacteriocins. The sequence relations among the small plasmids (pRJ6, pRJ9, pRJ10 and pRJ11) were investigated by comparing restriction enzyme digest patterns and by hybridization. Plasmids pRJ10 and pRJ11 were indistinguishable and very closely related to plasmid pRJ9. Plasmid pRJ6, although different from the others, shared regions of sequence homology with them. No homology was found between plasmids pRJ6 or pRJ9 and the large Bac plasmids.     

Trametes versicolor: Potential for atrazine bioremediation in calcareous clay soil,under low water availability conditions

This study examined the feasibility of Trametes versicolor to actively degrade atrazine (0.5 μg g^?1) in non-sterile calcareous clay soil (Algarve, Portugal) microcosms for up to 24 weeks (20 °C), under low water availability (soil water potentials of ?0.7 and ?2.8 MPa). Soil respiration, laccase activity, and atrazine quantification by high-performance liquid chromatography (HPLC) were assessed. Respiration was significantly (p < 0.05) enhanced in soil containing the inoculant, particularly in the presence of atrazine, indicating that it remained metabolically active throughout the study. Furthermore, up to 98% and 85% (at ?0.7 and ?2.8 MPa, respectively) of atrazine was degraded in soil containing both the atrazine and the inoculant, compared to 96% and 50% in soil containing atrazine only. The contribution of T. versicolor to atrazine degradation was only significant (p < 0.005) under the driest soil treatment conditions. The strategies used for enhancing colonisation and biodegradation capabilities of the inoculant, as well as the selection of sawdust as carrier, were thus effective. However, there were no differences (p > 0.05) in quantified laccase activity in soil containing the inoculant and the control. Overall, this study demonstrated that T. versicolor was a strong candidate for atrazine bioremediation in soil with low moisture and organic matter contents, such as that found in semi-arid and Mediterranean-like ecosystems.