The starter bacterium (Lactobacillus delbrueckii)-Erakina

The bacterial species, Lactobacillus delbrueckii is part of the microbiota of human beings. This bacterial species has four important subspecies.

Genus Lactobacillus: An overview

Bacteria belonging to the genus Lactobacillus are present ubiquitously in both humans and animals. These bacteria comprise an important part of the microflora of the gastrointestinal and urogenital tracts. They play a primary role in the following areas-

  • Improving digestion.
  • Maintenance of gut health and pH.
  • They boost immunity. 
  • Protection of the reproductive tract from microbial infections.[Lactobacillus delbrueckii]

Almost all Lactobacilli possess probiotic abilities, meaning they provide certain health benefits to humans. These organisms are commensals and are known to form symbiotic relationships with their hosts. They are usually not parasitic and do not induce any detrimental effects in their hosts.

However, some studies have suggested that some species of Lactobacilli are opportunistic parasites that exhibit parasitic effects only when the hosts are vulnerable (Example: Lactobacillus psittaci).[Lactobacillus delbrueckii]

Physiology and morphology

The physiological and morphological characteristics of Lactobacilli are what makes them distinct from other bacterial species. Certain phenotypic characteristics are common to all Lactobacillus species. Identification of these characteristics enables the isolation of novel Lactobacillus species. Some important physiological and morphological features of all Lactobacillus species are as follows-

  • They are rod-shaped. 
  • They are catalase-negative; they do not employ the use of oxygen as a terminal electron acceptor during the process of respiration. 
  • These bacteria are Gram-positive; they have a thick peptidoglycan outer layer accompanied by the absence of an outer lipid membrane.
  • They are facultatively anaerobic. 
  • They produce lactic acid as the primary by-product of glucose fermentation. 
  • They occur singly or in pairs.
  • They are non-spore-forming.
Lactobacillus acidophilus Lactobacillus delbrueckii
SEM image of a species of Lactobacillus.[Lactobacillus delbrueckii]

Colony morphology

The colony characteristics of the colonies formed by Lactobacillus bacteria are unique to this genus. The growth of these colonies facilitates easy identification of the bacterial strains. The distinct colony characteristics of Lactobacillus bacteria are as follows-

  • Colonies are usually 2-5 mm in diameter. 
  • Colony colours range from white to brown.
  • Colonies are round in shape with irregular edges.
  • Colonies are umbonate; there is the presence of a protrusion along the edges of the colonies.
  • The profile is raised and convex in shape.
  • The texture is rough and colonies are usually opaque in appearance.
Gram-positive Lactobacillus species. Lactobacillus delbrueckii
Microscopic image of the colonies of a species of Lactobacillus.[Lactobacillus delbrueckii]

Lactobacillus delbrueckii: An introduction

The bacterial species Lactobacillus delbrueckii is an important part of the microflora of the human body. These bacteria are often used in the production of yoghurt as they exhibit optimal fermentation abilities required for the fermentation of milk into curd and yoghurt. Four important subspecies of this species of bacteria are as follows-

  • Subspecies bulgaricus 
  • Subspecies indicus 
  • Subspecies delbrueckii
  • Subspecies lactis

Physiology and morphology

The morphological and physiological features of this bacterial species are more or less similar to those of other bacterial species belonging to the same genus. The important characteristics of Lactobacillus delbrueckii are as follows-

  • They are Gram-positive.
  • They produce lactic acid as a product of carbohydrate fermentation. They are homofermentative bacteria.
  • They are rod-shaped bacteria that occur singly or in pairs.
  • They are catalase-negative. 
  • They are facultative anaerobes.

Optimal colony growth conditions

These bacterial subspecies grow optimally under the following growth conditions-

  • Temperature around 42 degrees celsius. 
  • Low pH range; they grow well under acidic conditions. 
  • These bacteria are allowed to grow on MRS agar before their use as inoculum or starter.

Industrial significance

The subspecies of Lactobacillus delbrueckii possess industrial significance due to the following reasons-

  • The subspecies lactis is primarily used in the manufacturing of cheese as it produces bacteriocins and is an important part of the fermentation process.
  • The subspecies bulgaricus form an association with Streptococcus thermophilus and are used as an important starter in the production and manufacture of yoghurt. These bacteria provide a unique taste to yoghurt through the production of compounds such as acetaldehyde.
  • Hence, these bacteria are industrially significant due to their use as a starter for the production of curd and other associated dairy products.[Lactobacillus delbrueckii]
Lactobacillus delbrueckii. subspecies bulgaricus. Lactobacillus delbrueckii
SEM image of a subspecies of Lactobacillus delbrueckii.


Lactobacillus delbrueckii is a rod-shaped bacterium that is commonly used as inoculum in the dairy industry for the production of cheese and curd. This bacterial species is further divided into four important subspecies. These bacteria are Gram-positive and produce lactic acid as the primary by-product of carbohydrate fermentation.

Internal links:

An Introduction to Bacterial Cell- Erakina

How to protect yourself from bacterias such as Escherichia coli, Salmonella, Clostridium

Lactobacillus timonensis – A Gut Bacteria

External links:

Read more about Lactobacillus delbrueckii bacteria

By:- Deepika Thilakan

Date;- 24/06/2022

Tags: animals, life science

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