The effect of agitation and aeration on the synthesis and molecular weight of gellan in batch cultures of sphingomonas paucimobilis

B. McNeil, L.M. Harvey, I. Giavasis

Research output: Contribution to journalArticle

41 Citations (Scopus)

Abstract

The effects of agitation and aeration upon synthesis and molecular weight of the biopolymer gellan were systematically investigated in batch fermenter cultures of the bacterium, Sphingomonas paucimobilis. High aeration rates and vigorous agitation enhanced growth of S. paucimobilis. Although gellan formation occurred mainly in parallel with cell growth, the increase in cells able to synthesise gellan did not always lead to high gellan production. For example, at very high agitation rates (1000 rpm) growth was stimulated at the expense of biopolymer synthesis. Maximal gellan concentration was obtained at 500 rpm agitation and either 1 or 2 vvm aeration (12.3 and 12.4 g/l gellan, respectively). An increase in aeration (from 1 to 2 vvm) enhanced gellan synthesis only at low agitation rates (250 rpm). However, high aeration or dissolved oxygen was not necessary for high gellan synthesis, in fact oxygen limitation always preceded the phase of maximum gellan production and probably enhanced polysaccharide biosynthesis. Some gellan was formed even after glucose exhaustion. This was attributed to the intracellular accumulation of polyhydroxyalkanoates, (such as polyxydroxybutyrate) which were found in S. paucimobilis cells indicating the existence of a carbon storage system, which may contribute to gellan biosynthesis under glucose-limiting conditions. The autolysis of the culture, which occurred at the late stages of the process, seemed to be triggered mainly by limitations in mass (nutrient) transfer, due to the highly viscous process fluid that gradually develops. Rheological measurements generally gave a very good near real time estimate of maximum biopolymer concentration offering the possibility of improved process control relative to time consuming gravimetric assay methods. While mechanical depolymerisation of gellan did not occur, high aeration rates (2 vvm) led to production of gellan of low molecular weight (at either 250 or 500 rpm). This effect of aeration rate upon gellan molecular weight is reported here for the first time, and is important for the properties and applications of gellan. Mechanisms which may have led to this are discussed, but control of molecular weight of the biopolymers is clearly an area needing further research.
Original languageEnglish
Pages (from-to)101-108
Number of pages7
JournalEnzyme and Microbial Technology
Volume38
Issue number1-2
DOIs
Publication statusPublished - 2006

Fingerprint

Sphingomonas
Batch Cell Culture Techniques
Biopolymers
Molecular Weight
Molecular weight
Biosynthesis
Glucose
Fermenters
Depolymerization
Cell growth
Dissolved oxygen
Polysaccharides
Nutrients
Process control
Assays
Bacteria
Carbon
Oxygen
Fluids
gellan gum

Keywords

  • gellan
  • biopolymer
  • agitation
  • aeration
  • rheology
  • molecular weight
  • pharmacology
  • biosciences

Cite this

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title = "The effect of agitation and aeration on the synthesis and molecular weight of gellan in batch cultures of sphingomonas paucimobilis",
abstract = "The effects of agitation and aeration upon synthesis and molecular weight of the biopolymer gellan were systematically investigated in batch fermenter cultures of the bacterium, Sphingomonas paucimobilis. High aeration rates and vigorous agitation enhanced growth of S. paucimobilis. Although gellan formation occurred mainly in parallel with cell growth, the increase in cells able to synthesise gellan did not always lead to high gellan production. For example, at very high agitation rates (1000 rpm) growth was stimulated at the expense of biopolymer synthesis. Maximal gellan concentration was obtained at 500 rpm agitation and either 1 or 2 vvm aeration (12.3 and 12.4 g/l gellan, respectively). An increase in aeration (from 1 to 2 vvm) enhanced gellan synthesis only at low agitation rates (250 rpm). However, high aeration or dissolved oxygen was not necessary for high gellan synthesis, in fact oxygen limitation always preceded the phase of maximum gellan production and probably enhanced polysaccharide biosynthesis. Some gellan was formed even after glucose exhaustion. This was attributed to the intracellular accumulation of polyhydroxyalkanoates, (such as polyxydroxybutyrate) which were found in S. paucimobilis cells indicating the existence of a carbon storage system, which may contribute to gellan biosynthesis under glucose-limiting conditions. The autolysis of the culture, which occurred at the late stages of the process, seemed to be triggered mainly by limitations in mass (nutrient) transfer, due to the highly viscous process fluid that gradually develops. Rheological measurements generally gave a very good near real time estimate of maximum biopolymer concentration offering the possibility of improved process control relative to time consuming gravimetric assay methods. While mechanical depolymerisation of gellan did not occur, high aeration rates (2 vvm) led to production of gellan of low molecular weight (at either 250 or 500 rpm). This effect of aeration rate upon gellan molecular weight is reported here for the first time, and is important for the properties and applications of gellan. Mechanisms which may have led to this are discussed, but control of molecular weight of the biopolymers is clearly an area needing further research.",
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The effect of agitation and aeration on the synthesis and molecular weight of gellan in batch cultures of sphingomonas paucimobilis. / McNeil, B.; Harvey, L.M.; Giavasis, I.

In: Enzyme and Microbial Technology, Vol. 38, No. 1-2, 2006, p. 101-108.

Research output: Contribution to journalArticle

TY - JOUR

T1 - The effect of agitation and aeration on the synthesis and molecular weight of gellan in batch cultures of sphingomonas paucimobilis

AU - McNeil, B.

AU - Harvey, L.M.

AU - Giavasis, I.

PY - 2006

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N2 - The effects of agitation and aeration upon synthesis and molecular weight of the biopolymer gellan were systematically investigated in batch fermenter cultures of the bacterium, Sphingomonas paucimobilis. High aeration rates and vigorous agitation enhanced growth of S. paucimobilis. Although gellan formation occurred mainly in parallel with cell growth, the increase in cells able to synthesise gellan did not always lead to high gellan production. For example, at very high agitation rates (1000 rpm) growth was stimulated at the expense of biopolymer synthesis. Maximal gellan concentration was obtained at 500 rpm agitation and either 1 or 2 vvm aeration (12.3 and 12.4 g/l gellan, respectively). An increase in aeration (from 1 to 2 vvm) enhanced gellan synthesis only at low agitation rates (250 rpm). However, high aeration or dissolved oxygen was not necessary for high gellan synthesis, in fact oxygen limitation always preceded the phase of maximum gellan production and probably enhanced polysaccharide biosynthesis. Some gellan was formed even after glucose exhaustion. This was attributed to the intracellular accumulation of polyhydroxyalkanoates, (such as polyxydroxybutyrate) which were found in S. paucimobilis cells indicating the existence of a carbon storage system, which may contribute to gellan biosynthesis under glucose-limiting conditions. The autolysis of the culture, which occurred at the late stages of the process, seemed to be triggered mainly by limitations in mass (nutrient) transfer, due to the highly viscous process fluid that gradually develops. Rheological measurements generally gave a very good near real time estimate of maximum biopolymer concentration offering the possibility of improved process control relative to time consuming gravimetric assay methods. While mechanical depolymerisation of gellan did not occur, high aeration rates (2 vvm) led to production of gellan of low molecular weight (at either 250 or 500 rpm). This effect of aeration rate upon gellan molecular weight is reported here for the first time, and is important for the properties and applications of gellan. Mechanisms which may have led to this are discussed, but control of molecular weight of the biopolymers is clearly an area needing further research.

AB - The effects of agitation and aeration upon synthesis and molecular weight of the biopolymer gellan were systematically investigated in batch fermenter cultures of the bacterium, Sphingomonas paucimobilis. High aeration rates and vigorous agitation enhanced growth of S. paucimobilis. Although gellan formation occurred mainly in parallel with cell growth, the increase in cells able to synthesise gellan did not always lead to high gellan production. For example, at very high agitation rates (1000 rpm) growth was stimulated at the expense of biopolymer synthesis. Maximal gellan concentration was obtained at 500 rpm agitation and either 1 or 2 vvm aeration (12.3 and 12.4 g/l gellan, respectively). An increase in aeration (from 1 to 2 vvm) enhanced gellan synthesis only at low agitation rates (250 rpm). However, high aeration or dissolved oxygen was not necessary for high gellan synthesis, in fact oxygen limitation always preceded the phase of maximum gellan production and probably enhanced polysaccharide biosynthesis. Some gellan was formed even after glucose exhaustion. This was attributed to the intracellular accumulation of polyhydroxyalkanoates, (such as polyxydroxybutyrate) which were found in S. paucimobilis cells indicating the existence of a carbon storage system, which may contribute to gellan biosynthesis under glucose-limiting conditions. The autolysis of the culture, which occurred at the late stages of the process, seemed to be triggered mainly by limitations in mass (nutrient) transfer, due to the highly viscous process fluid that gradually develops. Rheological measurements generally gave a very good near real time estimate of maximum biopolymer concentration offering the possibility of improved process control relative to time consuming gravimetric assay methods. While mechanical depolymerisation of gellan did not occur, high aeration rates (2 vvm) led to production of gellan of low molecular weight (at either 250 or 500 rpm). This effect of aeration rate upon gellan molecular weight is reported here for the first time, and is important for the properties and applications of gellan. Mechanisms which may have led to this are discussed, but control of molecular weight of the biopolymers is clearly an area needing further research.

KW - gellan

KW - biopolymer

KW - agitation

KW - aeration

KW - rheology

KW - molecular weight

KW - pharmacology

KW - biosciences

UR - http://dx.doi.org/10.1016/j.enzmictec.2005.05.003

U2 - 10.1016/j.enzmictec.2005.05.003

DO - 10.1016/j.enzmictec.2005.05.003

M3 - Article

VL - 38

SP - 101

EP - 108

JO - Enzyme and Microbial Technology

JF - Enzyme and Microbial Technology

SN - 0141-0229

IS - 1-2

ER -