Continuous monitoring of phytoplankton dynamics in Lake Balaton (Hungary) using on-line delayed fluorescence excitation spectroscopy

1. This study introduces delayed fluorescence (DF) excitation spectroscopy as an on‐line tool for in situ monitoring of the composition and biomass of various colour classes of phytoplankton when they are photosynthetically active (cyanobacteria, chlorophytes, chromophytes and cryptophytes). The DF data are validated by comparison with those from conventional methods (weekly microscopic counts and the measurement of chlorophyll concentration). 2. The composition of phytoplankton as assessed by DF agreed reasonably well with the results from microscopic counts, particularly when differences in chlorophyll‐specific DF integrals of the various colour classes were taken into account. 3. Integrals of DF spectra were converted into concentration of chlorophyll a using empirical factors derived from field data. The value of the conversion factor was nearly twice as high when the relative abundance of cyanobacteria was low (<15%) than when it was high. The converted DF‐chl time series agreed well with chlorophyll measurements particularly when blooms were developing. As the DF method is inherently free of the interference caused by pigment degradation products, the discrepancy between the two data sets increased during the collapse of blooms and when sediment resuspension was intense. 4. Fourier spectrum analysis of the time series of DF‐chl indicated that samples must be taken, at a minimum, every 2–3 days to capture the dynamics of phytoplankton. As a consequence, the dynamics of various algal blooms, including their timing, duration and net growth rate, could be estimated with greater confidence than by using conventional methods alone. 5. On‐line DF spectroscopy is an advanced technique for monitoring daily the biomass and composition of the photosynthetically active phytoplankton in aquatic environments, including turbid shallow lakes. At present, the detection limit is around 1 mg DF‐chl a m^?3 in terms of total biomass but confidence in estimates of phytoplankton composition declines sharply below about 5 mg chl a m^?3. 6. On‐line DF spectroscopy represents a promising approach for monitoring phytoplankton. It will be useful in water management where it can act as an early‐warning system of declines in water quality. In basic ecological research it can supplement manual methods. While default calibration spectra may be acceptable for routine monitoring, we suggest a careful individual calibration of the DF spectrometer for basic research. The statistical methods developed here help to assess the adequacy of various calibration sets.     

Aquaporin 2 Mutations in Trypanosoma brucei gambiense Field Isolates Correlate with Decreased Susceptibility to Pentamidine and Melarsoprol

The predominant mechanism of drug resistance in African trypanosomes is decreased drug uptake due to loss-of-function mutations in the genes for the transporters that mediate drug import. The role of transporters as determinants of drug susceptibility is well documented from laboratory-selected Trypanosoma brucei mutants. But clinical isolates, especially of T. b. gambiense, are less amenable to experimental investigation since they do not readily grow in culture without prior adaptation. Here we analyze a selected panel of 16 T. brucei ssp. field isolates that (i) have been adapted to axenic in vitro cultivation and (ii) mostly stem from treatment-refractory cases. For each isolate, we quantify the sensitivity to melarsoprol, pentamidine, and diminazene, and sequence the genomic loci of the transporter genes TbAT1 and TbAQP2. The former encodes the well-characterized aminopurine permease P2 which transports several trypanocides including melarsoprol, pentamidine, and diminazene. We find that diminazene-resistant field isolates of T. b. brucei and T. b. rhodesiense carry the same set of point mutations in TbAT1 that was previously described from lab mutants. Aquaglyceroporin 2 has only recently been identified as a second transporter involved in melarsoprol/pentamidine cross-resistance. Here we describe two different kinds of TbAQP2 mutations found in T. b. gambiense field isolates: simple loss of TbAQP2, or loss of wild-type TbAQP2 allele combined with the formation of a novel type of TbAQP2/3 chimera. The identified mutant T. b. gambiense are 40- to 50-fold less sensitive to pentamidine and 3- to 5-times less sensitive to melarsoprol than the reference isolates. We thus demonstrate for the first time that rearrangements of the TbAQP2/TbAQP3 locus accompanied by TbAQP2 gene loss also occur in the field, and that the T. b. gambiense carrying such mutations correlate with a significantly reduced susceptibility to pentamidine and melarsoprol.     

Alterations in osteoclast morphology following osteoprotegerin administration in the magnesium-deficient mouse

In the present study, we used osteoprotegerin (OPG), which blocks osteoclastogenesis, to correct and thus explain the hypercalcemia that is seen during dietary Mg deficiency in the mouse. Control and Mg-deficient mice received injections for 12 days of either OPG or vehicle only. Serum Ca was similar in Mg-deficient mice treated with OPG and in control mice receiving OPG (9.2±0.3 mg/dl vs. 9.2±0.5). Both groups had significantly higher serum Ca than controls or Mg-deficient animals receiving vehicle alone. Surprisingly, Mg-depleted mice that received OPG in doses that inhibit osteoclastic bone resorption remained hypercalcemic. Because mature osteoclasts still present in the marrow might be hyperactive, we examined osteoclast morphology at the light microscopic and ultrastructural level. Light microscopic examination of trabecular bone showed few osteoclasts in OPG-treated mice. Ultrastructural examination revealed that osteoclasts in OPG-treated mice have decreased contact with the endosteal bone surface and absence of a ruffled border. Because the morphology of the existing pool of mature osteoclasts did not enhance resorption, another mechanism, such as increased intestinal absorption of Ca in Mg-deficient mice, likely contributes to the hypercalcemia observed during Mg deficiency.     

The physiology and ecological implications of efficient growth

The natural habitats of microbes are typically spatially structured with limited resources, so opportunities for unconstrained, balanced growth are rare. In these habitats, selection should favor microbes that are able to use resources most efficiently, that is, microbes that produce the most progeny per unit of resource consumed. On the basis of this assertion, we propose that selection for efficiency is a primary driver of the composition of microbial communities. In this article, we review how the quality and quantity of resources influence the efficiency of heterotrophic growth. A conceptual model proposing innate differences in growth efficiency between oligotrophic and copiotrophic microbes is also provided. We conclude that elucidation of the mechanisms underlying efficient growth will enhance our understanding of the selective pressures shaping microbes and will improve our capacity to manage microbial communities effectively.     

Virgin females compete for mates in the male lekking species Ceratitis capitata

Abstract. Aggressive behaviour occurring in intrasexual competition is an important trait for animal fitness. Although female intrasexual aggression is reported in several insect species, little is known about female competition and aggressive interactions in polygynous male lekking species. The interactions of female Mediterranean fruit flies, Ceratitis capitata (a male lekking species), with other females and mating pairs under laboratory conditions are investigated. Mature, unmated (virgin) females are aggressive against each other and against mating pairs, whereas immature females are not. Female aggression against other females decreases dramatically after mating; however, mated females maintain aggression against mating pairs. In addition, higher intrasexual aggression rates are observed for mature, virgin females than for virgin males of the same age. The results show that female aggressiveness is virginity related, suggesting female competition for mates. These findings have important implications for understanding the physiological aspects of a complex social behaviour such as aggression and should stimulate further research on female agonistic behaviour in male lekking mating systems.     

Peripartum Cardiomyopathy Presenting With Ventricular Tachycardia: A Rare Presentation

A 25-year-old previously asymptomatic pregnant woman at 36 weeks'' gestation was noticed to have repetitive monomorphic ventricular tachycardia. A dilated left ventricle with moderately reduced systolic function was found on echocardiographic examination. This is a very rare presentation of peripartum cardiomyopathy (PPCMP) presenting with repetitive monomorphic ventricular tachycardia.     

A Panel of Trypanosoma brucei Strains Tagged with Blue and Red-Shifted Luciferases for Bioluminescent Imaging in Murine Infection Models

Background

Genetic engineering with luciferase reporter genes allows monitoring Trypanosoma brucei (T.b.) infections in mice by in vivo bioluminescence imaging (BLI). Until recently, luminescent T.b. models were based on Renilla luciferase (RLuc) activity. Our study aimed at evaluating red-shifted luciferases for in vivo BLI in a set of diverse T.b. strains of all three subspecies, including some recently isolated from human patients.

Methodology/Principal findings

We transfected T.b. brucei, T.b. rhodesiense and T.b. gambiense strains with either RLuc, click beetle red (CBR) or Photinus pyralis RE9 (PpyRE9) luciferase and characterised their in vitro luciferase activity, growth profile and drug sensitivity, and their potential for in vivo BLI. Compared to RLuc, the red-shifted luciferases, CBR and PpyRE9, allow tracking of T.b. brucei AnTaR 1 trypanosomes with higher details on tissue distribution, and PpyRE9 allows detection of the parasites with a sensitivity of at least one order of magnitude higher than CBR luciferase. With CBR-tagged T.b. gambiense LiTaR1, T.b. rhodesiense RUMPHI and T.b. gambiense 348 BT in an acute, subacute and chronic infection model respectively, we observed differences in parasite tropism for murine tissues during in vivo BLI. Ex vivo BLI on the brain confirmed central nervous system infection by all luminescent strains of T.b. brucei AnTaR 1, T.b. rhodesiense RUMPHI and T.b. gambiense 348 BT.

Conclusions/Significance

We established a genetically and phenotypically diverse collection of bioluminescent T.b. brucei, T.b. gambiense and T.b. rhodesiense strains, including drug resistant strains. For in vivo BLI monitoring of murine infections, we recommend trypanosome strains transfected with red-shifted luciferase reporter genes, such as CBR and PpyRE9. Red-shifted luciferases can be detected with a higher sensitivity in vivo and at the same time they improve the spatial resolution of the parasites in the entire body due to the better kinetics of their substrate D-luciferin.