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BackgroundLevan has been traditionally produced from microorganism. However, there is a continuous effort in looking for new strains that improve levan production yield and uses alternative sugar sources for growth. Despite having a wide range of data about levan yield, there are not papers which allow controlling molecular weight, and that plays an essential role for further applications.ResultsThe effect of the sucrose concentration on levan yield (and its molecular weight) from Bacillus atrophaeus and Acinetobacter nectaris (Gram positive and Gram negative respectively) was studied in this work. It was found that A. nectaris growth (from 3 to 1.5 g L−1 in 40 h) and its levan production (from 3 to 1.5 g L−1) decreases by increasing sucrose concentration (best results at a concentration of 120 g L−1) whereas B. atrophaeus growth (3.5 g L−1 in 30 h) and its levan production (also 3.5 g L−1) were not affected by modifying that parameter. Levan molecular weight from A. nectaris decreases by increasing sucrose concentration (from 8000 to 2000 kDa) whereas levan molecular weight from B. Atrophaeus remains always around 50 kDa. By performing a kinetic study, it was shown that A. nectaris growth follows a substrate-inhibition model, whereas Monod equation provided a good fit for B. atrophaeus growth. Finally, wastes from orange juice industry were used as a medium culture to cultivate those microorganism, obtaining good results with B. atrophaeus (growth 3 g L−1 in 30 h).ConclusionsLevan production kinetics was determined and compared between different bacteria types.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-017-0703-z) contains supplementary material, which is available to authorized users.

Some studies have described the use of phytohormones in microalgal culture for the production of biodiesel or selected fatty acids. However, no study has determined the amount of phytohormones that maximizes lipid yield. We determined the optimal concentration of auxins and gibberellins (which is between 40 and 60 μM) in two strains (Scenedemus abundans and Chlorella ellipsoidea) suitable for biodiesel production. More than 3-fold increment was reached with S. abundans and near 7-fold increment with C. ellipsoidea. Furthermore, this work suggests that the improved growth of the microalgae in the presence of the phytohormones was due to a reduction in the level of reactive oxygen species (ROS) in the cells. An economic analysis showed that, due to its low cost, auxin offers a positive cost-benefit balance and therefore could be used at large scale. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1203-1211, 2016.