engleski

Impact of oxygen on D-lactic acid production by Lactobacillus coryniformis subsp. torquens

Lactic acid bacterium Lactobacillus coryniformis subsp. torquens is classified to unique phylogenetic group of genus Lactobacillus and, according to key characteristics of glucose fermentation, to facultatively heterofermentative-type group. The strain rank is based on very limited amount of genotypic, biochemical, and physiological data. However, this lactic acid bacterium attracted interest as a potential D-lactic acid producer to be employed in sustainable production of exclusively one isomeric form of lactic acid. Only few papers report on use of L. coryniformis subsp. torquens in production of lactic acid with D-configuration which can be largely utilized in poly(lactic acid) synthesis. Further improvement of the bioprocess includes utilization of renewable resources as carbon and nitrogen sources and scale-up procedure. Before application of the strain in a large scale bioprocess better understanding of carbohydrate metabolism and its regulation is required. Our lab-scale experiments indicated that basic rules of energy-generating metabolism in the bacterial cells, based mainly on conversion of glucose presumably via glycolysis and phosphogluconate pathway, are not absolutely valid. Configuration of produced lactic acid and fermentation under carbohydrate limitation to (un)desired end-products were characterized. Further investigation was related to the impact of oxygen on D-lactic acid production and biomass yield. Flexibility of the metabolism under chosen conditions was probed in batch cultures at relatively low temperature. Our results can provide novel clues for the optimization of growth conditions of L. coryniformis subsp. torquens as well as other lactic acid bacteria as industrially relevant microorganisms.

batch fermentation; carbohydrate metabolism and its regulation; D-lactic acid; impact of oxygen; Lactobacillus coryniformis subsp. torquens

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