| Summary: | <p>Abstract</p> <p>Background</p> <p>The oxygen transfer rate (OTR) and dissolved oxygen tension (DOT) play an important role in determining alginate production and its composition; however, no systematic study has been reported about the independent influence of the OTR and DOT. In this paper, we report a study about alginate production and the evolution of the molecular mass of the polymer produced by a wild-type <it>A. vinelandii </it>strain ATCC 9046, in terms of the maximum oxygen transfer rate (OTR<sub>max</sub>) in cultures where the dissolved oxygen tension (DOT) was kept constant.</p> <p>Results</p> <p>The results revealed that in the two dissolved oxygen conditions evaluated, strictly controlled by gas blending at 0.5 and 5% DOT, an increase in the agitation rate (from 300 to 700 rpm) caused a significant increase in the OTR<sub>max </sub>(from 17 to 100 mmol L<sup>-1 </sup>h<sup>-1 </sup>for DOT of 5% and from 6 to 70 mmol L<sup>-1 </sup>h<sup>-1 </sup>for DOT of 0.5%). This increase in the OTR<sub>max </sub>improved alginate production, as well as the specific alginate production rate (SAPR), reaching a maximal alginate concentration of 3.1 g L<sup>-1 </sup>and a SAPR of 0.031 g <sub>alg </sub>g <sub>biom</sub><sup>-1 </sup>h<sup>-1 </sup>in the cultures at OTR<sub>max </sub>of 100 mmol L<sup>-1 </sup>h<sup>-1</sup>. In contrast, the mean molecular mass (MMM) of the alginate isolated from cultures developed under non-oxygen limited conditions increased by decreasing the OTR<sub>max</sub>, reaching a maximal of 550 kDa at an OTR<sub>max </sub>of 17 mmol L<sup>-1 </sup>h<sup>-1 </sup>. However, in the cultures developed under oxygen limitation (0.5% DOT), the MMM of the polymer was practically the same (around 200 kDa) at 300 and 700 rpm, and this remained constant throughout the cultivation.</p> <p>Conclusions</p> <p>Overall, our results showed that under oxygen-limited and non oxygen-limited conditions, alginate production and its molecular mass are linked to the OTR<sub>max</sub>, independently of the DOT of the culture.</p>
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