0000000000681074
AUTHOR
P. Schmitt
A method for screening diacetyl and acetoin-producing bacteria on agar plates
A simple method for screening bacteria for diacetyl and acetoin production was developed. This method is based on the ability of diacetyl and acetoin to form a red insoluble complex with α-naphthol in the presence of creatine. Addition of carboxymethyl-cellulose containing calcium citrate in the medium allowed discrimination between citrate utilizing and non-utilizing bacteria.
Medium for Screening Leuconostoc oenos Strains Defective in Malolactic Fermentation
A new sensitive medium was developed to screen and isolate mutagenic Leuconostoc oenos strains defective in malolactic fermentation. The essential components of the medium included fructose (22 mM), l -malic acid (74.6 mM), bromocresol green (as pH indicator), and cellulose powder. The wild-type colonies turned blue, but defective malolactic colonies gave an acid reaction and remained yellow-green.
Comparison of α-acetolactate synthase and α-acetolactate decarboxylase in Lactococcus spp. and Leuconostoc spp.
Cell-free extracts of Leuconostoc and Lactococcus species were tested for their alpha-acetolactate synthase and alpha-acetolactate decarboxylase activities. In Leuconostoc mesenteroides subsp. cremoris, Leuconostoc mesenteroides subsp. mesenteroides and Leuconostoc lactis, the Km of alpha-acetolactate synthase for pyruvate was close to 10 mM whereas it was 30 mM in Lactococcus lactis subsp. lactis biovar. diacetylactis. The Km of alpha-acetolactate decarboxylase for alpha-acetolactic acid was very low (0.3 mM) in Leuconostoc species in comparison to Lactococcus lactis subsp. lactis biovar. diacetylactis (60 mM). In the latter bacterium, alpha-acetolactate decarboxylase showed a sigmoidal de…
Diacetyl and acetoin production from the co-metabolism of citrate and xylose by Leuconostoc mesenteroides subsp. mesenteroides.
The co-metabolism of citrate plus xylose by Leuconostoc mesenteroides subsp. mesenteroides results in a growth stimulation, an increase in D-lactate and acetate production and repression of ethanol production. This correlated well with the levels of key enzymes involved. A partial repression of alcohol dehydrogenase and a marked stimulation of acetate kinase were observed. High citrate bioconversion yields in diacetyl plus acetoin were obtained at pH 5.2 in batch (11.5%) or in chemostat (up to 17.4%) culture. In contrast, no diacetyl or acetoin was detected in citrate plus glucose fermentation.