PRODUCTION OF DEXTRAN BY SOME LOCAL ISOLATES OF BACTERIA

Abstract

Dextran - a polymer of glucose- is widely used in a variety of industrial and pharmaceutical purposes. In Egypt, studies concerning dextran are limited and it is not produced on a large scale. In view of these facts, the present work was achieved to study dextran production by locally isolated strains. The study included isolation and selection of most efficient dextran producing bacteria from different foodstuffs, nutritional and environmental factors supporting their efficiencies to produce dextran. A part of the study concentrated on the use of some available raw materials and by-products as substrates for production on large scale as well as the production in the bioreactor as batch and continuous culture. In addition, the activity of cell-free supernatant of fermented liquor in producing dextran from molasses was studied.

Results could be summarized as follows:

1- A number of 63 dextran producing bacterial isolates were obtained from different foodstuffs using McCleskey's medium. Of these, 40 isolates were prelimenarily identified as Leuconostoc strains, while 23 were identified as Streptococcus strains.

2- In general, Leuconostoc isolates produced higher viscosities - as an index for dextran production-than Streptococcus isolates. Most efficient dextran producing bacteria were selected, namely, Lpcu49, Lsm60, Ltl4 (Leuconostoc strains), Spca 39 and St 26 (Steptococcus strains).

3- McCleskey, Tomczak and kurt media were compared as dextran production media by selected isolates. McCleskey' medium was superior in this respect and hence was selected as a production medium.