Model-aided targeted volatile fatty acid production from food waste using a defined co-culture microbial community.

The production of volatile fatty acids (VFA) is gaining momentum due to their central role in the emerging carboxylate platform. Particularly, the production of the longest VFA (from butyrate to caproate) is desired due to their increased economic value and easier downstream processing. While the use of undefined microbial cultures is usually preferred with organic waste streams, the use of defined microbial co-culture processes could tackle some of their drawbacks such as poor control over the process outcome, which often leads to low selectivity for the desired products. However, the extensive experimentation needed to design a co-culture system hinders the use of this technology. In this work, a workflow based on the combined use of mathematical models and wet experimentation is proposed to accelerate the design of novel bioprocesses. In particular, a co-culture consisting of Pediococcus pentosaceus and Megaphaera cerevisiae is used to target the production of high-value odd- and even­carbon VFA. An unstructured kinetic model was developed, calibrated and used to design experiments with the goal of increasing the selectivity for the desired VFA, which were experimentally validated. In the case of even­carbon VFA, the experimental validation showed an increase of 38 % in caproate yield and, in the case of enhanced odd­carbon VFA experiments, the yield of butyrate and caproate diminished by 62 % and 94 %, respectively, while propionate became one of the main end products and valerate yield value increased from 0.007 to 0.085 gvalearte per gconsumed sugar. The workflow followed in this work proved to be a sound tool for bioprocess design due to its capacity to explore and design new experiments in silico in a fast way and ability to quickly adapt to new scenarios.

Steering the conversion of protein residues to volatile fatty acids by adjusting pH.

This study investigates the influence of pH on protein conversion into volatile fatty acids by anaerobic mixed-culture fermentation, a topic that, in contrast to glucose fermentation, only had scarce and contradictory information available. Several experiments were performed with two model proteins (casein and gelatin) at three different pH values (5, 7 and 9) using chemostats and batch tests. Highest conversion was reached at neutral pH although complete acidification was never achieved. Longer chain carboxylates production was favoured at low pH, while acetic acid was the main product at pH 7 and 9. Amino acids preferential consumption also varied with pH and protein composition. In fact, protein conversion stoichiometry is mainly driven by energetic yields and amino acid molecular configuration. Overall, this study identifies pH adjustment as a way to steer volatile fatty acid production during mixed-culture fermentation of proteins.

Electron bifurcation mechanism and homoacetogenesis explain products yields in mixed culture anaerobic fermentations.

Anaerobic fermentation of organic wastes using microbial mixed cultures is a promising avenue to treat residues and obtain added-value products. However, the process has some important limitations that prevented so far any industrial application. One of the main issues is that we are not able to predict reliably the product spectrum (i.e. the stoichiometry of the process) because the complex microbial community behaviour is not completely understood. To address this issue, in this work we propose a new metabolic network of glucose fermentation by microbial mixed cultures that incorporates electron bifurcation and homoacetogenesis. Our methodology uses NADH balances to analyse published experimental data and evaluate the new stoichiometry proposed. Our results prove for the first time the inclusion of electron bifurcation in the metabolic network as a better description of the experimental results. Homoacetogenesis has been used to explain the discrepancies between observed and theoretically predicted yields of gaseous H2 and CO2 and it appears as the best solution among other options studied. Overall, this work supports the consideration of electron bifurcation as an important biochemical mechanism in microbial mixed cultures fermentations and underlines the importance of considering homoacetogenesis when analysing anaerobic fermentations.

[Collision tumor of the ampulla of Vater: carcinoid and adenocarcinoma]. / Tumor de colisión periampular.

We report the case of a periampullary collision tumor, in which a duodenal-wall carcinoid and an adenocarcinoma of the head of the pancreas coexisted. We describe the case of a 64-year-old man with a recent history of diarrhea, who was diagnosed with obstructive jaundice. A duodeno-pancreatectomy was performed, and the specimen showed two independent neoplasms in the histopathologic study. Solid cords and nests of neuroendocrine cells in the duodenal wall formed the carcinoid tumor, whereas the other neoplasm was made up of a well-differentiated adenocarcinoma of the pancreas. Both were confirmed by immunohistochemical analysis. According to the literature reviewed, this is the sixth reported case of this rare neoplastic association.

Henoch-Schönlein purpura as clinical presentation of a myelodysplastic syndrome.

Small-vessel vasculitis may be a paraneoplastic syndrome. It may be associated with haematologic malignancies and less frequently with solid tumors. We describe a patient with myelodysplastic syndrome presenting as Henoch-Schönlein Purpura. To our knowledge this association has not previously reported.

[Insular thyroid carcinoma]. / Carcinoma insular de tiroides.

A new case of insular carcinoma of the thyroid gland is presented. It was described by Carcangiu et al(1) in 1984 as a poorly differentiated carcinoma, less of one hundred cases were published after its description. We report a case of a patient who was referred for compressive symptoms caused by a mediastinal mass. It was found a tumor of left thyroid lobe strongly adherent to adjacent structures, which was informed as a poorly differentiated insular carcinoma. She underwent total thyroidectomy and posterior treatment with an ablative dose of 1311. She is currently free of disease after one year of follow-up. The diagnosis, treatment, differential diagnosis with another thyroid carcinomas and the rarety of this type of tumors are analyzed. The importance of a correct diagnosis is fundamental in order to carry out an aggressive treatment and a more exhaustive follow-up in these patients, taken account its behavior and its poor prognosis when compared with well-differentiated carcinomas.