Lactobacillus delbrueckii It is a Gram positive bacterium, shaped like an elongated rod and with rounded ends. It is catalase negative, homofermentative, and does not present a flagellum. It belongs to a group of species that bears its name as a type species. It is divided into six subspecies.
Some of these subspecies are considered probiotics and used in the food industry. Its main use is for the fermentation of dairy products and for the production of cheese and yogurt.
Lactobacillus delbrueckii it is Gram positive and catalase negative. It is homofermentative, producing D-lactic acid exclusively. All strains ferment glucose, fructose, mannose, and lactose.
The fermentation of sucrose and N-acetylglucosamine is more variable, depending on the subspecies and the strain. It can grow at temperatures above 45 ° C, but does not develop at 15 ° C or below.
According to the formal taxonomy, Lactobacillus delbrueckii belongs to the phylum Firmicutes, the class Bacilli, the order Lactobacillales, and the family Lactobacillaceae.
Additionally, it belongs to the functional group (without taxonomic validity) of Lactic Acid Bacteria (LAB). LABs have that name because they produce lactic acid during the fermentation of sugars..
The group Lactobacillus delbrueckii is currently composed of 27 species, being L. delbrueckii the type species, not only of the group, but also of the genus. This bacterium was named after Max Delbrück, a German biophysicist.
Lactobacillus delbrueckii comprises six subspecies: L. delbrueckii subsp delbrueckii, L. delbrueckii subsp lactis, L. delbrueckii subsp bulgaricus, L. delbrueckii subsp sunkii, L. delbrueckii subsp jakobsenii Y L. delbrueckii subsp indicus.
The six subspecies show a high degree of DNA-DNA relationship but can be differentiated on the basis of different phenotypic and genotypic traits..
All strains of this bacterium are shaped like an elongated rod. Its size ranges from 0.5 to 0.8 µm wide by 2.0 to 9.0 µm long. Its growth can be individually, in pairs or in short chains.
They do not present a scourge, so they are not mobile. The six subspecies differ in their ability to ferment different sugars. For example, L. delbrueckii subsp bulgaricus, L. delbrueckii subsp indicus Y L. delbrueckii subsp lactis, isolated for the first time from dairy products, they are all lactose-positive.
On the other hand, L. delbrueckii subsp delbrueckii Y L. delbrueckii subsp sunkii, that were isolated from non-dairy products are lactose-negative. This indicates a carbohydrate fermentation associated with the different niches that these subspecies occupy..
The subspecies of Lactobacillus delbrueekii they can be differentiated by phenotypic variations. For example, Lactobacillus delbrueekii subsp bulgarieus It ferments few carbohydrates, that is, glucose, lactose, fructose, mannose, and sometimes galactose. It is thermophilic, and has a growth temperature of up to 48 or 50 ° C. Presents a Guanine-Cytosine ratio of between 49 and 51%.
Lactobacillus delbrueekii subsp jakobsenii, For its part, it ferments several polysaccharides, including arabinose, erythritol, cellobiose, fructose, galactose, glucose, lactose, lactulose, lixose, maltose, mannitol, mannose, ribose, melibiose, sucrose, xylose, sorbitol, trehalose and raffinose. Growth occurs at 40 - 50 ° C, depending on the growing medium. Presents a Guanine-Cytosine ratio of 50.2%.
Only two of the subspecies of L. delbrueckii have commercial relevance, L. delbruckii subsp. bulgaricus Y L. delbrueckii subsp. lactis.
Lactobacillus delbruckii subsp. bulgaricus it was isolated for the first time from Bulgarian milk. This subspecies is used, in combination with Streptococcus thermophilus, for the commercial production of yogurt. It is also used in the production of Swiss and Italian cheeses..
The main role of S. thermophilus Y L. delbruckii subsp. bulgaricus in the manufacture of yogurt is to acidify the milk, producing a large amount of lactic acid from lactose.
Lactic acid, in addition to acidifying the milk, contributes to flavor the yogurt. The typical flavor of yogurt is due not only to lactic acid, but also to various carbonyl compounds, such as acetaldehyde, acetone, and diacetyl, produced by bacteria.
Lactobacillus delbruckii subsp. bulgaricus presents probiotic activity. Its intake in yogurt helps prevent diseases of the oral cavity.
Proposed mechanisms for the probiotic activity of this bacillus include: 1) antagonism with pathogens by competition for binding sites and / or inhibition of intracellular signaling pathways; 2) stimulation of the mucosal immune system and increased host defense against pathogenic bacteria and foreign antigens.
Some strains of this lactobacillus are capable of producing exopolysaccharides (EPS). Among the physiological effects of EPS are the improvement and regulation of the immune response and the reduction of cholesterol.
For his part, L. delbrueckii subsp. lactis it was initially isolated from a dairy source. The use of this subspecies is mainly for the commercial production of mozzarella cheese..
Recent studies have shown a high potential of a strain of Lactobacillus delbrueckii subsp. delbrueckii (AS13B) for use in aquaculture. This strain has been applied in the diet of seabass larvae (Dicentrarchus labrax, L.) in cultivation.
Its application improves the health of the fish and increases their survival, allowing to increase their production. The bacterium was supplied using Brachionus plicatilis me Artemia salina as carriers.
It has also been shown to stimulate the larval gut immune system and reduce the transcription of key pro-inflammatory genes. Its application in other crops and its profitability has yet to be evaluated.
Of the remaining subspecies of the species, L. delbrueckii subsp. indicus was first isolated in 2005 from a dairy product in India. Lactobacillus delbrueckii subsp. sunkii in 2012, from plant-based products; Lactobacillus delbrueckii subsp. jakobsenii, meanwhile, it was isolated from a fermented alcoholic beverage, in 2015.
The relatively recent finding of these latter subspecies may be one of the main reasons why they are not currently commercially relevant. Genome sequencing of each of them will likely help determine properties that could be of future commercial relevance..
It could also help explain their mechanisms of adaptation to complex environments. The latter could be used to improve qualities of known commercial species, especially in the areas of phage resistance, adaptation to environmental stress conditions. Or to enhance exopolysaccharide production and produce desired flavor compounds.
The different species of Lactobacillus they are generally considered non-pathogenic. However, Urinary Tract Infections (UTIs) caused by bacteria of this genus, including Lactobacillus delbrueckii, have been reported in recent years.
The main victims of these infections are elderly women. Because these species do not reduce nitrate to nitrite, the UTIs they cause usually go unnoticed on screening test strips. They have also been associated with bacteremia and pyelonephritis.