Leuconostoc citreum, Leuconostoc cremoris
Leuconostoc lactis, Leuconostoc mesenteroides

Leuconostoc citreum
Bar: 1 m
Leuconostoc cremoris
Bar: 2 m
Leuconostoc lactis
Bar: 1 m
Leuconostoc mesenteroides
Bar: 1 m

The micrographs illustrating this page were obtained by scanning electron microscopy (SEM). Leuconostocs may be found in various environments. As indicated at the bottom of this site, the four strains of Leuconostoc spp. bacteria were provided from institutional collections.

The genus Leuconostoc belongs to the group of lactic acid bacteria. They are a group of related Gram-positive, non-sporulating bacteria that produce lactic acid as a result of carbohydrate fermentation.

Milk provides a good substrate (lactose = milk sugar) for microorganisms that further improve nutrition, texture and flavor characteristics of a wide variety of foods. Lactic acid bacteria are used in the production of fermented food products, such as yogurt (Streptococcus spp. and Lactobacillus spp. and other milk products (Lactococcus spp.), and sausages. However, fermented milk products also contain Leuconostoc spp. bacteria (e.g., L. cremoris, L. citrovorum (L. mesenteroides subsp. cremoris, and L. dextranicum) which impart characteristic flavour. They are used as part of bacterial starter cultures needed in the manufacture of dairy products. L. mesenteroides subsp. cremoris is used in cultured buttermilk and cultured sour cream. A variety of Leuconostoc strains is present in kefir.

Like the lactic acid bacteria, leuconostocs need complex media due to their multiple demands for amino acids, peptides, carbohydrates, vitamins and metallic ions. They represent about 12% of lactic acid bacteria isolated from various ecosystems, mostly from plant materials. Some may be isolated from the surfaces of a wide range of healthy vegetables and fruits, including grapes.

Sauerkraut fermentation relies on naturally occurring Leuconostoc spp. bacteria present on fresh cabbage leaves. Leuconostoc mesenteroides is the bacterium associated with the sauerkraut and pickle fermentations. It initiates the desirable lactic acid production in these products. Translated from German, "sauerkraut" means "sour cabbage". Lactic acid and the kitchen salt used produce an environment more favourable for Leuconostoc than other bacteria and, consequently, unwelcome coliform bacteria rapidly decline. Additional probiotic microrganisms are also involved in the production of sauerkraut. They multiply in large quantities in the juice. On sauerkraut particles the microorganisms may be found congregated at the leaf stomata as shown below.

Microbes in sauerkraut juice
Bar: 2 µm
Microbes at a leaf stoma
Bar: 5 µm

Information about pickled vegetables may be found in Microbiology for Teachers including olives , pickles, sauerkraut and kimchi

Viscous polysaccharides produced by L. mesenteroides are widely recognized as causing product losses and processing problems in the production of sucrose from sugar cane and sugar beets. However, polysaccharides produced by this bacterium are used in the manufacture of blood plasma extenders, heparin substitutes for anticoagulant therapy, cosmetics, and other products, such as Sephadex gels or beads. They are also used in dairy technology.

L. carnosum is an anaerobic bacterium found in spoiled, vacuum-packaged meat. It grows well in refrigerators at low temperatures of 1-5°C and rapidly dominates over other bacterial populations.
Bacteriocins produced by Leuconostoc species.

    For access to images of other microorganisms please visit the home page.

Bacterial cultures of Leuconostoc cremoris and L. lactis were provided by
Ms. Aileen Hawke (Guelph Food Research Centre)
and L. citreum and L. mesenteroides
were provided by Ms. Shuyan Liu (University of Guelph, Ontario, Canada).
The cells were cultured and examined by scanning electron microscopy by Milos Kalab.

Updated: March 12, 2013.

©SCIMAT 2013