A microfiltration bioreactor to achieve high cell density in Sulfolobus solfataricus fermentation

A novel technique is proposed to achieve higher cell yield in extremophile fermentation. Because the accumulation of toxic compounds is thought to be responsible for low biomass yields, a bioreactor has been designed based on a microfiltration hollow-fiber module located inside the traditional ferme ntation vessel. Using the cultivation of the thermoacidophilic archeon Sulf olobus solfataricus G theta as a model, a biomass of 35 gl(-1) dry weight w as obtained which proved greater than that of 2 gl(-1) obtained in batch fe rmentation. The bioreactor was characterized by running several fermentatio n experiments to check the high stability of the membrane module to sterili zation cycles, high temperatures, and acidic pHs, even for prolonged period s of time. It was shown that the exhaust medium is unable to sustain growth for the presence of toxic compounds, and ultrafiltration and ion-exchange techniques were used in all the attempts to regenerate it. The results demo nstrated the ability of the method to lower inhibitor concentrations and pr olong the growth phase, thus achieving high cell density. Furthermore, they indicated that the toxic compounds are ionic species of less than 1 kDa.