Avaliação de parâmetros de crescimento das leveduras Kluyveromyces marxianus, Kluyveromyces lactis e Saccharomyces cerevisiae.

Abstract

The microorganisms most used in industries are yeasts. Kluyveromyces lactis is used in the production of proteins and the enzyme β-galactosidase by the pharmaceutical industry, in addition to the production of heterologous proteins of biotechnological importance. Kluyveromyces marxianus has metabolic diversity, thermotolerance, assimilates lactose as a source of energy and carbon and has the highest maximum growth rate (μmax) known among eukaryotic microorganisms. S. cerevisiae is widely used in fermented products, such as breads and alcoholic beverages, and can also be used in the bioremediation of heavy metals, such as zinc, mercury, lead, cadmium, nickel, arsenic, gold, chromium, uranium, and platinum. To produce yeast biomass on anindustrial scale, it is important to know some parameters such as the maximum growth rate and the saturation constant, as well as to determine the biomass production quickly. In this case, it is possible to correlate the biomass with the cell optical density. Thus, the objective of this work wasto compare the growth of K. marxianus, K. lactis and S. cerevisiae yeasts in YP medium with different glucose concentrations [2.5 g/L, 5.0 g/L, 10.0 g/L, and 20.0 g/L (w/v)], determining their maximum growth rates, the saturation constant and correlating biomass production with cellular optical densities. K. marxianus was incubated at 37 °C and K. lactis and S. cerevisiae at 30 °C in ashaker at 200 rpm. The cell optical density (OD) was determined in a spectrophotometer (600 nm).The optical density was measured after 2, 3, 4, 5 and 6 h of incubation. The maximum growth rates and saturation constants obtained for K. marxianus, K. lactis and S. cerevisiae were, respectively, 0.69 h-1 and 0.17 g/L, 0.45 h-1 and 0.385 g /L, 0.47 h-1 and 0.54 g/L. To calculate the correlation of biomass with cell optical densities, dilutions were prepared from a mother microbial suspension of each yeast species, obtaining dilutions 1:0, 1:1, 1:2, 1:4, 1:8 and 1:16. Considering these dilutions, respectively, the OD and biomass obtained for K. marxianus were 53.15 and 23.0 g/L, 27.68 and 12.0 g/L, 12.76 and 6.7 g/L, 7, 33 and 4.4 g/L, 4.04 and 2.9 g/L, 2.1 and 1.7 g/L. Likewise, for K. lactis the OD and biomass determined were 59.35 and 21 g/L, 28.80 and 11 g/L, 13.95 and 6.3 g/L, 8.16 and 3.4 g/L, 4.53 and 1.9 g/L, 2.25 and 1.2 g/L. And yet, for S. cerevisiae the OD andbiomass calculated were 39.3 and 16 g/L, 19.13 and 8.5 g/L, 9.04 and 4.7 g/L, 4.82 and 3, 4 g/L, 2.55 and 1.4 g/L, 1.39 and 1.2 g/L. It is concluded that, under the conditions evaluated, the yeast K. marxianus exhibited higher maximum growth velocity and biomass, with a lower saturation constant of glucose transporters when compared to K. lactis and S. cerevisiae.