in SRB numbers of up to 250-fold in amended sediments with a concomitant production
of sulphide (indicated by sediment blackening). As the ETS assay used also measures
mineralization by sulphate reduction (Olanczuk-Neyman and Vosjan, 1977) it would
apear that part of the increase in ETS activity in these sulphate-rich sediments,on
supplementation with xanthan, was due to a stimulation of SRB. Under anaerobic
conditions, the addition of deacetylated and depyruvylated xanthans to the sediments
caused a lower stimulation in degradation than with unmodified xanthan. It is thought
that naturally occurring xanthanase enzyme complexes attack the trisaccharide side
chains of the xanthan molecule to yield mannose, glucuronic acid, pyruvylated and
acetylated mannose (Cadmus et al. 1982). Under marine conditions these side chains
protect the β ( 1 → 4) glucose backbone from hydrolysis by cellulases (Rinaudo and
Milas, 1980). As SRB isolated from xanthan enrichments of these sediments cannot
utilize xanthan, glucuronic acid or mannose it is thought that SRB growth was occurring
on “xanthanase"liberated acetate, pyruvate and fermented mannose and glucuronic acid.
Hence, the decrease in stimulation with the modified xanthans may have been due to a
decrease in available substrates for SRB growth (i. e. acetate and pyruvate).
CONCLUSION
Xanthan has several advantages as a mobility control agent in enhanced oil recovery.
These include :
1) pseudoplasticity (i.e. : shear thinning properties)
2) thermal stability
3) salt compatibility
However, the date presented above indicate that despite the implicit benefits,the risks of
SRB proliferation which the addition of xanthan brings with it, militates against its use in
sulphate-rich injection waters.
CADMUS M.C., JACKSON L.K. BURTON K.A., PLATTNER R.D., et SLODKI M.E., 1982. Biodegradation of
xanthan gum by Bacillus sp. Applied and Environmental Microbiology 44, 5-11
DENTINI M., CRESCEZI V. et BLASI D., 1984. Conformational properties of xanthan derivatives in dilute
aqueous solution. International Journal of Biological Macromolecules 6, 93-98.
HARDY J.A., 1981. The enumeration, isolation and characterization of sulphate-reducing bacteria from North
Sea waters. Journal of applied Bacteriology 51, 505-516.
OLANCZUK-NEYMAN K.M. et VOSJAN J.H., 1977. Measuring respiratory electron-transport-system activity in
marine sediment. Netherlands Journal of Sea Research 11, 1-13
PAMATMAT M.M., GRAF G., G. BENGTSSON W. et NOVAK C.S., 1981. Heat production, ATP concentration and
electron transport activity of marine sediments. Marine Ecology-progress series 4, 135-143.
PFENNING N., WIDDEL F. et TRUPER H.G., 1981. The dissimiltory sulfate-reducing bacteria. In The Prokaryotes
a handbook on habitats, isolation and identification of bacteria vol 1 ed. Starr M.D., Stolp H., Truper H.G.,
Balows A., Schlegel H.G., pp. 926-940. New York Springer verlag.
POSTGATE J.R., 1979. The sulphate-reducing bacteria 1st. edn. pp. 25-28. Cambridge: Cambridge University
Press.
RINAUDO M. et MILAS P., 1980. Enzymic hydrolysis of the bacterial polysaccharide xanthan by cellulase.
International journal of Biological Macromolecules 2, 45-48.
614
of sulphide (indicated by sediment blackening). As the ETS assay used also measures
mineralization by sulphate reduction (Olanczuk-Neyman and Vosjan, 1977) it would
apear that part of the increase in ETS activity in these sulphate-rich sediments,on
supplementation with xanthan, was due to a stimulation of SRB. Under anaerobic
conditions, the addition of deacetylated and depyruvylated xanthans to the sediments
caused a lower stimulation in degradation than with unmodified xanthan. It is thought
that naturally occurring xanthanase enzyme complexes attack the trisaccharide side
chains of the xanthan molecule to yield mannose, glucuronic acid, pyruvylated and
acetylated mannose (Cadmus et al. 1982). Under marine conditions these side chains
protect the β ( 1 → 4) glucose backbone from hydrolysis by cellulases (Rinaudo and
Milas, 1980). As SRB isolated from xanthan enrichments of these sediments cannot
utilize xanthan, glucuronic acid or mannose it is thought that SRB growth was occurring
on “xanthanase"liberated acetate, pyruvate and fermented mannose and glucuronic acid.
Hence, the decrease in stimulation with the modified xanthans may have been due to a
decrease in available substrates for SRB growth (i. e. acetate and pyruvate).
CONCLUSION
Xanthan has several advantages as a mobility control agent in enhanced oil recovery.
These include :
1) pseudoplasticity (i.e. : shear thinning properties)
2) thermal stability
3) salt compatibility
However, the date presented above indicate that despite the implicit benefits,the risks of
SRB proliferation which the addition of xanthan brings with it, militates against its use in
sulphate-rich injection waters.
CADMUS M.C., JACKSON L.K. BURTON K.A., PLATTNER R.D., et SLODKI M.E., 1982. Biodegradation of
xanthan gum by Bacillus sp. Applied and Environmental Microbiology 44, 5-11
DENTINI M., CRESCEZI V. et BLASI D., 1984. Conformational properties of xanthan derivatives in dilute
aqueous solution. International Journal of Biological Macromolecules 6, 93-98.
HARDY J.A., 1981. The enumeration, isolation and characterization of sulphate-reducing bacteria from North
Sea waters. Journal of applied Bacteriology 51, 505-516.
OLANCZUK-NEYMAN K.M. et VOSJAN J.H., 1977. Measuring respiratory electron-transport-system activity in
marine sediment. Netherlands Journal of Sea Research 11, 1-13
PAMATMAT M.M., GRAF G., G. BENGTSSON W. et NOVAK C.S., 1981. Heat production, ATP concentration and
electron transport activity of marine sediments. Marine Ecology-progress series 4, 135-143.
PFENNING N., WIDDEL F. et TRUPER H.G., 1981. The dissimiltory sulfate-reducing bacteria. In The Prokaryotes
a handbook on habitats, isolation and identification of bacteria vol 1 ed. Starr M.D., Stolp H., Truper H.G.,
Balows A., Schlegel H.G., pp. 926-940. New York Springer verlag.
POSTGATE J.R., 1979. The sulphate-reducing bacteria 1st. edn. pp. 25-28. Cambridge: Cambridge University
Press.
RINAUDO M. et MILAS P., 1980. Enzymic hydrolysis of the bacterial polysaccharide xanthan by cellulase.
International journal of Biological Macromolecules 2, 45-48.
614