Cyanobacterial Toxin Degrading Bacteria: Who Are They?

Cyanobacteria are ubiquitous in nature and are both beneficial and detrimental to humans. Benefits include being food supplements and producing bioactive compounds, like antimicrobial and anticancer substances, while their detrimental effects are evident by toxin production, causing major ecological problems at the ecosystem level. To date, there are several ways to degrade or transform these toxins by chemical methods, while the biodegradation of these compounds is understudied. In this paper, we present a meta-analysis of the currently available 16S rRNA and mlrA (microcystinase) genes diversity of isolates known to degrade cyanobacterial toxins. The available data revealed that these bacteria belong primarily to the Proteobacteria, with several strains from the sphingomonads, and one from each of the Methylobacillus and Paucibacter genera. Other strains belonged to the genera Arthrobacter, Bacillus, and Lactobacillus. By combining the ecological knowledge on the distribution, abundance, and ecophysiology of the bacteria that cooccur with toxic cyanobacterial blooms and newly developed molecular approaches, it is possible not only to discover more strains with cyanobacterial toxin degradation abilities, but also to reveal the genes associated with the degradation of these toxins

On the use of HDR 60Co source with the MammoSite® radiation therapy system

This work summarizes Monte Carlo results in order to evaluate the potential of using HDR Co60 sources in accelerated partial breast irradiation (APBI) with the MammoSite® applicator. Simulations have been performed using the MCNP5 Monte Carlo Code, in simple geometries comprised of two concentric spheres; the internal consisting of selected concentrations, C, of a radiographic contrast solution in water (Omnipaque 300™) to simulate the MammoSite balloon and the external consisting of water to simulate surrounding tissue. The magnitude of the perturbation of delivered dose due to the radiographic contrast medium used in the MammoSite® applicator is calculated. At the very close vicinity of the balloon surface, a dose build-up region is observed, which leads to a dose overestimation by the treatment planning system (TPS) which depends on Omnipaque™ 300 solution concentration (and is in order of 2.3%, 3.0%, and 4.5%, respectively, at 1 mm away from the balloon - water interface, for C=10%, 15%, and 20%). However, dose overestimation by the TPS is minimal for points lying at the prescription distance (d=1 cm) or beyond, for all simulated concentrations and radii of MammoSite® balloon. An analytical estimation of the integral dose outside the CTV in the simple geometries simulated shows that dose to the breast for MammoSite® applications is expected to be comparable using HDR Co60 and Ir192 sources, and higher than that for Yb169. The higher enegies of Co60 sources result to approximately twice radiation protection requirements as compared to Ir169 sources. However, they allow for more accurate dosimetry calculation with currently used treatment planning algorithms for Co60 sources, compared to Ir169. © 2008 American Association of Physicists in Medicine

A radiobiological investigation on dose and dose rate for permanent implant brachytherapy of breast using i 125 or P 103 d sources

Purpose: The present report addresses the question of what could be the appropriate dose and dose rate for 125I and 103Pd permanent seed implants for breast cancer as monotherapy for early stage breast cancer. This is addressed by employing a radiobiological methodology, which is based on the linear quadratic model, to identify a biologically effective dose (BED) to the prescription point of the brachytherapy implant, which would produce equivalent cell killing (or same cell survival) when compared to a specified external radiotherapy scheme. Methods: In the present analysis, the tumor and normal tissue BED ratios of brachytherapy and external radiotherapy are examined for different combinations of tumor proliferation constant (K), α/β ratios, initial dose rate (R0), and reference external radiotherapy scheme (50 or 60 Gy in 2 Gy per fraction). The results of the radiobiological analysis are compared against other reports and clinical protocols in order to examine possible opportunities of improvement. Results: The analysis indicates that physical doses of approximately 100-110 Gy delivered with an initial dose rate of around 0.05 Gyh-1 and 78-80 Gy delivered at 0.135 Gyh-1 for 125I and 103Pd permanent implants, respectively, are equivalent to 50 Gy external beam radiotherapy (EBRT) in 2 Gy per fraction. Similarly, for physical doses of approximately 115-127 Gy delivered with an initial dose rate of around 0.059 Gyh-1 and 92 Gy delivered at 0.157 Gyh-1 for 125I and 103Pd, respectively, are equivalent to 60 Gy EBRT in 2 Gy per fraction. It is shown that the initial dose rate required to produce isoeffective tumor response with 50 or 60 Gy EBRT in 2 Gy per fraction increases as the repopulation factor K increases, even though repopulation is also considered in EBRT. Also, the initial dose rate increases as the value of the α/β ratio decreases. The impact of the different α/β ratios on the ratio of the tumor BEDs is significantly large for both the 125I and 103Pd implants with the deviation between the α/β=10.0 Gy ratios and those using the 4.0 and 3.5 Gy values ranging between 18% and 22% in most of the cases. Conclusions: For the cases of 125I and 103Pd, the equivalent physical doses to 50 Gy EBRT in 2 Gy per fraction are associated with an overdosage of the involved normal tissue in the range of 4%-16% and an underdosage by 10%-15% for a BED for normal tissue, using an α/β value of 3.0 Gy (BEDNT,3 Gy) of 100 Gy. These values are lower by 10%-20% than the published value of 124 Gy for 125I and by about 13% when compared to the published isoeffective dose of 90 Gy for 103Pd. Similarly, the equivalent physical doses to 60 Gy EBRT in 2 Gy per fraction are associated with an overdosage of the involved normal tissue by 10%-20% and an underdosage by 4%-10% for BED NT,3 Gy of 110 Gy. © 2010 American Association of Physicists in Medicine