Rodrigo Patiño

High-Yield Production of Dihydrogen from Xylose by Using a Synthetic Enzyme Cascade in a Cell-Free System**

Let enzymes work: H2 was produced from xylose and water in one reactor containing 13 enzymes (red). By using a novel polyphosphate xylulokinase (XK), xylose was converted into H2 and CO2 with approaching 100 % of the theoretical yield. The findings suggest that cell-free biosystems could produce H2 from biomass xylose at low cost. Xu5P = xylulose 5-phosphate, G6P = glucose 6-phosphate.

Use of plant growth regulators in micropropagation of Kappaphycus alvarezii (Doty) in airlift bioreactors

The effects of plant growth regulators on callus induction rate and regeneration of K. alvarezii explants was evaluated. K. alvarezii calluses were induced in vitro with kinetin (K), 6-benzylaminopurine (B), 1-naphtalene acetic acid (N) and spermine (S). After 30 days, K. alvarezii explants produced filamentous calluses and isolated crystalline filaments growing from the medullar region and from cortical cells at the cut edge. The plant growth regulators 1-naphtalene acetic acid (1 mg L−1) and 6-benzylaminopurine (1 mg L−1) and the 1-naphtalene acetic acid + kinetin + spermine (1, 1, 0.018 mg L−1 respectively) combination produced 85 to 129% more calluses, with significant differences versus the control (p<0.05). Spermine at 0.018 mg L−1 produced calluses in the apical, intercalary and basal regions of explants. Spermine also reduced callus induction time to 7 days, which is faster than previously reported induction times with other plant growth regulators. An airlift bioreactor was designed and characterized to micropropagate K. alvarezii calluses. The bioreactor had mixing times ranging from 4.6–10.3 s at T90 and T95, which is shorter than those for the Fernbach (5.2–13.4 s) and balloon flasks (6.3–17.3 s). Mixing time standard deviations were smaller for the bioreactor (1.1–4.6) than for the Fernbach (9.3–13.6) and balloon flasks (5.5–15.8), suggesting an adequate flow regime within the bioreactor. The results are useful for improving callus induction in K. alvarezii and propagating microplantlets in an airlift bioreactor, and provide baseline data for macroalgal bioreactor culture.

Harvesting microalgae cultures with superabsorbent polymers: Desulfurization of Chlamydomonas reinhardtii for hydrogen production

It is presented in this work a new methodology to harvest fresh water microalgae cultures by extracting the culture medium with superabsorbent polymers (SAPs). The microalgae Chlamydomonas reinhardtii were grown in the Sueoka culture medium, harvested with polyacrylic SAPs and re‐suspended in the culture medium tris‐acetate‐potassium without sulfur (TAP‐S) to generate hydrogen (H2) under anoxic conditions. The H2 production as an alternative fuel is relevant since this gas has high‐energy recovery without involving carbon. Before microalgae harvesting, a number of range diameters (1–7 mm) for SAPs spherical particles were tested, and the initial rate (V0) and the maximal capacity (Qmax) were determined for the Sueoka medium absorption. The SAP particles with the diameter range 2.0–2.5 mm performed the best and these were employed for the rest of the experiments. The Sueoka medium has a high salt content and the effect of the ionic strength was also studied for different medium concentrations (0–400%). The SAPs were reused in consecutive absorption/desorption cycles, maintaining their absorption capacity. Although the Sueoka medium reduces the SAPs absorption capacity to 40% compared with deionized water, the use of SAPs was very significant for the desulfurization process of C. reihardtii. The presence of C. reinhardtii at different concentrations does not affect the absorption capacity of the Sueoka culture medium by the SAPs. In order to reduce the time of the process, an increase of the SAPs concentration was tested, being 20 g of SAP per liter of medium, a condition to harvest the microalgae culture in 4 h. There were no evident cell ruptures during the harvesting process and the cells remained alive. Finally, the harvested biomass was re‐suspended in TAP‐S medium and kept under anaerobic conditions and illumination to produce H2 that was monitored by a PEM fuel cell. The use of SAPs for microalgae harvesting is a feasible non‐invasive procedure to obtain high concentrations of functional biomass at low cost; it offers an attractive alternative due to its versatility and simplicity. Biotechnol. Bioeng. 2013;110: 3227–3234.

A solar photobioreactor for the production of biohydrogen from microalgae

The green microalga Chlamydomonas reinhardtii is proposed to produce hydrogen in a low-cost system using the solar radiation in Yucatan, Mexico. A two-step process is necessary with a closed photobioreactor, in which the algae are firstly growth and then induced for hydrogen generation. Preliminary results are presented in this work with some planning for the future. Different culture broths, temperatures and light intensities were tested for biomass and hydrogen production in laboratory conditions. The first experiments in external conditions with solar radiation and without temperature control have been performed, showing the potential of this technique at larger scales. However, some additional work must be done in order to optimize the culture maintenance, particularly in relation with the temperature control, the light radiation and the carbon dioxide supply, with the idea of keeping an economic production.