Oxygen transfer rate during the production of alginate by Azotobacter vinelandii under oxygen-limited and non oxygen-limited conditions

Abstract

BackgroundThe 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 A. vinelandii strain ATCC 9046, in terms of the maximum oxygen transfer rate (OTRmax) in cultures where the dissolved oxygen tension (DOT) was kept constant.ResultsThe 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 OTRmax (from 17 to 100 mmol L-1 h-1 for DOT of 5% and from 6 to 70 mmol L-1 h-1 for DOT of 0.5%). This increase in the OTRmax improved alginate production, as well as the specific alginate production rate (SAPR), reaching a maximal alginate concentration of 3.1 g L-1 and a SAPR of 0.031 g alg g biom-1 h-1 in the cultures at OTRmax of 100 mmol L-1 h-1. In contrast, the mean molecular mass (MMM) of the alginate isolated from cultures developed under non-oxygen limited conditions increased by decreasing the OTRmax, reaching a maximal of 550 kDa at an OTRmax of 17 mmol L-1 h-1 . 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.ConclusionsOverall, our results showed that under oxygen-limited and non oxygen-limited conditions, alginate production and its molecular mass are linked to the OTRmax, independently of the DOT of the culture.

Selection of Hyper Exopolysaccharide Producing and Cyst Forming Azotobacter Isolates for Better Survival under Stress Conditions

“…The result was in accordance with the Lozano et al, (2011). Thus, culture media samples were removed at intervals and quantitative extractions of EPS were made.…”

Alginate production and alg8 gene expression by Azotobacter vinelandii in continuous cultures

“…The production of alginates with specific molecular weights for biomaterials with specific applications can be achieved in a bacterial bioprocess. Studies have demonstrated that the culture conditions of agitation rate and oxygen transfer rate (OTR) affect alginate production in bioprocesses [7,15,19]. Peña et al [19] evaluated the effect of agitation rate and dissolved oxygen tension (DOT) and reported that the highest alginate production (5.0 g l -1 ) and molecular weight distribution were found at 3% DOT under a high agitation rate (700 rpm).…”

An investigation of agitation speed as a factor affecting the quantity and monomer distribution of alginate from Azotobacter vinelandii ATCC® 9046

“…In addition, one possible reason might be the variation in the maximum oxygen transfer rate (OTR max ). A very recent study [7] showed that alginate synthesis depends strongly on OTR max even when the DOT was maintained constant at 5% at two different agitation speeds of 300 and 700 rpm. This study reported that the highest alginate concentration, 3.1 g/l, and the maximum specific alginate production rate, 0.031g alg /g bio h, were obtained at OTR max of 100 mmol/l h, which was the highest value observed at 700 rpm.…”

“…However, it is critical to keep in mind that since the DOT was not controlled, a combined effect of mixing rate and DOT might be responsible for the results obtained by Parente et al [10] since the uncontrolled DOT might affect the molecular weight of alginates. Recently, it was found that the molecular weight of the alginate was greatly influenced by OTR max , rather than mixing rate [7]. In this study, two different mixing rates, 500 and 700 rpm, corresponding to similar OTR max (90 and 100 mmol/l h, respectively) were investigated.…”