Competition and coexistence of sulfate-reducing bacteria, acetogens and methanogens in a lab-scale anaerobic bioreactor as affected by changing substrate to sulfate ratio

The microbial population structure and function of natural anaerobic communities maintained in lab-scale continuously stirred tank reactors at different lactate to sulfate ratios and in the absence of sulfate were analyzed using an integrated approach of molecular techniques and chemical analysis. The population structure, determined by denaturing gradient gel electrophoresis and by the use of oligonucleotide probes, was linked to the functional changes in the reactors. At the influent lactate to sulfate molar ratio of 0.35 mol mol−1, i.e., electron donor limitation, lactate oxidation was mainly carried out by incompletely oxidizing sulfate-reducing bacteria, which formed 80–85% of the total bacterial population. Desulfomicrobium- and Desulfovibrio-like species were the most abundant sulfate-reducing bacteria. Acetogens and methanogenic Archaea were mostly outcompeted, although less than 2% of an acetogenic population could still be observed at this limiting concentration of lactate. In the near absence of sulfate (i.e., at very high lactate/sulfate ratio), acetogens and methanogenic Archaea were the dominant microbial communities. Acetogenic bacteria represented by Dendrosporobacter quercicolus-like species formed more than 70% of the population, while methanogenic bacteria related to uncultured Archaea comprising about 10–15% of the microbial community. At an influent lactate to sulfate molar ratio of 2 mol mol−1, i.e., under sulfate-limiting conditions, a different metabolic route was followed by the mixed anaerobic community. Apparently, lactate was fermented to acetate and propionate, while the majority of sulfidogenesis and methanogenesis were dependent on these fermentation products. This was consistent with the presence of significant levels (40–45% of total bacteria) of D. quercicolus-like heteroacetogens and a corresponding increase of propionate-oxidizing Desulfobulbus-like sulfate-reducing bacteria (20% of the total bacteria). Methanogenic Archaea accounted for 10% of the total microbial community

Coherence-based contrast ultrasound diffusion imaging for prostate cancer detection

Prostate cancer is the most common form of cancer in men in western countries. The use of efficient focal therapies is currently hampered by limitations in early prostate cancer detection. With limited success, several quantitative ultrasound perfusion imaging methods have aimed at detection of microvascular changes associated to cancer growth. Alternatively, we recently introduced contrast ultrasound diffusion imaging, hypothesizing that these complex microvascular changes are better reflected by diffusion than by perfusion. In this paper we introduce the analysis of spatial similarity as an indirect estimation of diffusion. The passage of an intravenously injected contrast-agent bolus is recorded by transrectal ultrasound imaging, thereby measuring indicator dilution curves with a pixel resolution. The spatial similarity among these curves, within a kernel determined by the ultrasound scanner resolution, is estimated using coherence analysis. The coherence images generated from four patients were compared with histology data on a pixel basis. The results show a receiver operating characteristic curve area of 0.91, higher than that of any perfusion-related parameter. Although a method optimization and an extensive validation are required, these results confirm the promising value of contrast ultrasound diffusion imaging for prostate cancer detection