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Alexandrium tamarense is a harmful algal species that can produce saxitoxins, a suite of powerful neurotoxins that bioaccumulate up the food chain and can have severe economic and health impacts. With harmful algal blooms increasing temporally and spatially, it is important for us to understand the relationship between harmful algal blooms and nutrients, particularly nitrogen from anthropogenic sources. To this end, the stable nitrogen isotopic composition (δ¹⁵N) of medium nitrate, algal cells and toxin in both nitrogen-replete and nitrogen-limited batch cultures of A. tamarense were measured in order to assess the potential for using the δ¹⁵N of the toxin as a tracer of the nitrogen source used for growth. A. tamarense cells grown under nitrate-replete conditions were depleted by 1.5‰ relative to the growth medium, and saxitoxin was depleted by 1.5‰ relative to the whole cells. Under nitrate-limiting conditions, the isotopic difference between cells and saxitoxin changed as nitrate in the growth medium was depleted, indicating uncoupling of toxin synthesis and cell growth rates under changing external nutrient conditions. Determination of the absolute magnitude of the isotopic differences between the medium nitrate and either the cells or the saxitoxin was confounded by 1) using two different nitrate sources – one nitrate source was used to grow the inoculum and a different nitrate source was used for the experimental medium - with different ‰ values and 2) the presence of an unidentified, isotopically-light, nitrogen blank in the low-nitrate medium samples. I conclude that STX nitrogen isotope values have the potential to be used as nitrogen source indicators. However, overall fractionation between whole cells and STX is unknown due to the uncoupling between cell growth and STX synthesis observed during my nitrogen-limited experiment. Based on previous research on cell growth and toxin production dynamics under different nutrient regimes, it is also reasonable to assume that the observed results here may differ if a different nitrogen source was utilized by the cells for STX production. Further research could include isotope analysis of cultures grown on different nitrogen sources, such as ammonium and urea; isotopic analysis of additional compounds, such as amino acids; or use of additional stable isotopes, such as C or O. / text

Hemolytic uremic syndrome (HUS) induced by Shiga toxin-producing E. coli (STEC) is the most common causes of acute kidney injury in children. The therapy of the disease is symptomatic and the main factors leading to the development of severe course of a STEC-HUS are still unknown. In our study, we dealt with factors leading to development of a severe course of STEC-HUS in pediatric patients on both the host and pathogen side. Using retrospective analysis of the courses in children in the Czech Republic, we found that the most common cause of STEC-HUS was serotype O26 and HUS most often affected children under 3 years of age. 63,8 % required dialysis and mortality was 8.62 %. On the host side we focused on the relationship between the activation of the alternative complement pathway and the severity of the course of HUS. We found a significant difference in the level of the C3 part of complement in patients who required dialysis and patients for whom dialysis was not necessary. We also a cut-off value for the C3 part of complement and its reduction below 0.825 g / l was associated with the need for dialysis treatment and a higher incidence of extrarenal complications. Based not only on our results, it can be assumed that the therapeutic effect of complement could affect the severity of the disease....

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