Lactobacillus acetotolerans is a bacterial species that was first isolated from white wine vinegar.

The emerging importance of acid resistant bacteria

Acid-resistant bacterial strains have begun to become widely used in industrial production due to their acid-resistance. Acid resistant bacteria have certain distinct characteristics and properties, such as-

  • Development of protective mechanisms such as signal transduction. Bacterial signal transduction allows a bacterial cell to sense changes in the environment, which in turn directs the production of intracellular signals. This results in physiological and metabolic changes which help the organism to adapt to changes in the environment.
  • They possess the ability to make metabolic modifications.
  • They can repair damaged macromolecules.
  • They can maintain intracellular pH balance by regulating hydrogen ion entry.

It is important to note that these organisms produce acidophilic enzymes that are important in the food industry for fermentation purposes. These microbes are also biotechnologically significant as they can be used in genetic engineering to make other important microbes acid-resistant.

Beer brewing

The Lactobacillus genus: An overview

Bacteria belonging to the genus Lactobacillus are present ubiquitously in the human gut microbiota and are commonly known for their use as probiotics. Lactobacillus bacterial species are distinct from other bacterial species due to the production of lactic acid as a by-product during glucose fermentation. Lactobacilli are also industrially significant and play a major role as fermenters in the brewing and baking industries.

Significant physiological and morphological characteristics 

All Lactobacillus species share the following common characteristics. 

  • Rod-shaped in appearance
  • Production of lactic acid as a by-product of glucose fermentation.
  • Gram-positive in nature
  • Non-motile 
  • Non-spore-forming 
  • Facultative anaerobes; metabolism takes place even in the absence of oxygen.

 Lactobacillus acidophilus

Culture characteristics

Lactobacillus bacterial colonies exhibit the following characteristics-

  • Round in shape with uneven edges.
  • Elevated profile
  • Rough texture
  • Colours range from white to brown.
  • Convex shaped elevation.
  • Umbonate i.e., formation of a protrusion near the edges of the colony.
  • Bacteria are present in a single-celled manner or sometimes in pairs.
  • Colonies are usually opaque, with some being translucent.

Lactobacillus plantarum growing on MRS agar.

Lactobacillus acetotolerans: An introduction

Lactobacillus acetotolerans is a bacterial species that were isolated with thirteen other Lactobacillus species from fermented rice vinegar broth. The collected strains were grown on nutrient agar and a selective nutrient medium along with fermented rice vinegar broth. This bacterial species exhibits high resistance to acidic conditions and can survive even at an extremely low pH.

Morphology of the isolated bacteria

The isolated bacteria which were later identified to be Lactobacillus acetotolerans, exhibit the following morphological characteristics-

  • Non-motile
  • Non-spore-forming
  • Cell diameters rang between 0.4 and 0.5 micrometre.
  • Gram-positive in nature when viewed using the Gram stain.

Lactobacillus acetotolerans, a new species from fermented vinegar broth.

Cell culture morphology

The isolated bacterial colonies exhibited the following colony characteristics-

  • Circular in shape with irregular edges.
  • Undulate; wavy surface
  • Opaque 
  • Convex profile
  • Occurrence of bacteria singly or sometimes in pairs.
  • Yellowish-white in colour.

Nutrients required for cell growth

The following nutrients were added to the growth media in order to ensure the optimal growth of Lactobacillus acetotolerans colonies-

  • Riboflavin 
  • Pantothenic acid
  • Folic acid
  • Uracil 

The commercial uses of L. acetotolerans

  • Lactobacillus acetotolerans can survive and thrive in highly acidic conditions and hence produce industrially important enzymes.
  • They produce lactic acid which is important for digestion and maintenance of the balance of the gastrointestinal tract.
  • Due to the acidic nature of this bacterial species, it produces a desirable sour flavour when used in the brewing of beer.


Lactobacillus acetotolerans is a novel homofermentative bacterial species that is industrially significant. It not only provides health benefits by improving digestion and diversifying gut microflora, but it is also of commercial importance as it plays a major role in several industries. This bacterial species can also be employed in the future as a biotechnological tool for the purpose of DNA recombination due to its high resistance to acidic conditions.

Tags: Microbes

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