Difference Between Homofermentative and Heterofermentative Bacteria

The key difference between homofermentative and heterofermentative bacteria is that homofermentative bacteria are a type of lactic acid bacteria that produce only lactic acid as a primary by-product in glucose fermentation, while heterofermentative bacteria are a type of lactic acid bacteria that produce ethanol/acetic acid and CO₂ other than lactic acid as by-products in glucose fermentation.

Lactic acid bacteria (LAB) are common in the dairy industry. Lactic acid bacteria produce lactic acid as the principal by-product of sugar fermentation. They are gram-positive and rod or cocci shaped. These bacteria are more tolerant of low pH than other bacteria associated with the dairy industry. They are commonly used in starter cultures and dairy fermentations. Lactic acid bacteria cause milk to be sour. Moreover, these bacteria are classified as homofermentative and heterofermentative bacteria based on their by-product in sugar fermentation.

CONTENTS

1. Overview and Key Difference
2. What is Homofermentative Bacteria
3. What is Heterofermentative Bacteria
4. Similarities – Homofermentative and Heterofermentative
5. Homofermentative vs Heterofermentative Bacteria in Tabular Form
6. Summary – Homofermentative vs Heterofermentative Bacteria

What are Homofermentative Bacteria?

Homofermentative bacteria are a type of lactic acid bacteria that produce only lactic acid as a primary by-product in glucose fermentation. In biochemistry, homofermentative bacteria convert glucose molecules into two lactic acid molecules. They use this reaction to make two ATP molecules through substrate-level phosphorylation. Homofermentative bacteria include Lactococcus species, which is used in dairy starter cultures to rapidly-produce lactic acid in reduced pH conditions. In the dairy industry, Lactococcus species can be used in single-strain starter cultures or in mixed-strain cultures with other lactic acid bacteria such as Lactobacillus and Streptococcus.

Homofermentative Bacteria Produce

Lactococcus species are commonly used in the manufacture of fermented dairy products such as cheeses. Anyhow, the homofermentative state of Lactococcus can be adjusted by altering the environmental conditions such as pH, glucose concentration and nutrient limitation. Thermophilic strains of Lactobacillus helveticus are also used in cheese production. The homofermentative bacteria used in the yogurt industry includes strains of Lactobacillus delbruckii, Lactobacillus acidophilus and Streptococcus salivarius. Furthermore, Sterptococcus spp., Enterococcus, Pediococcus, and Aerococcus are other homofermentative bacteria used in the milk industry, but they are rarely used as starter cultures.

What are Heterofermentative Bacteria?

Heterofermentative bacteria are a type of lactic acid bacteria that produce ethanol/acetic acid and CO₂ in addition to lactic acid as by-products in glucose fermentation. In heterofermentative bacteria, other than the lactic acid as the principal end product, a significant amount of one or more metabolites (ethanol/acetic acid, CO₂) are also produced in the glucose fermentation. In biochemistry, heterofermentative bacteria produce one lactic acid and one ATP, together with CO₂ in glucose fermentation. But they also may produce several other end products such as ethanol, acetic acid, propionic acid, acetaldehyde, or diacetyl.

Testing for heterofermentative bacteria involves the detection of CO₂ gas. Though they are uncommon in the milk and dairy industry, they are rarely used as starter cultures in the dairy industry.  Sometimes, if they allow growth in significant numbers, heterofermentative bacteria can cause defects such as slits in hard cheeses and bloated packaging in other dairy products. Heterofermentative bacteria include Leuconostoc spp., Lactobacillus brevis, Lactobacillus fermentum, Lactobacillus reuteri, Lactobacillus plantarium, Lactobacillus casei, and Lactobacillus curvatus.

What are the Similarities Between Homofermentative and Heterofermentative Bacteria?

• Homofermentative and heterofermentative bacteria are types of lactic acid bacteria.
• Both are gram-positive and rod or cocci shaped.
• They produce lactic acid in glucose fermentation.
• They produce ATP in glucose fermentation.
• Both are used in the dairy industry.

What is the Difference Between Homofermentative and Heterofermentative Bacteria?

Homofermentative bacteria are a type of lactic acid bacteria that produce only lactic acid as a primary by-product in glucose fermentation. On the other hand, heterofermentative bacteria are a type of lactic acid bacteria that produce ethanol/acetic acid and CO₂ other than lactic acid as by-products in glucose fermentation. So, this is the key difference between homofermentative and heterofermentative bacteria. Moreover, homofermentative bacteria are usually used as starter cultures in the dairy industry. In contrast, heterofermentative bacteria are rarely used as starter cultures in the dairy industry.

The following infographic summarizes the difference between homofermentative and heterofermentative bacteria in tabular form.

Summary – Homofermentative vs Heterofermentative Bacteria

Lactic acid bacteria (LAB) are a heterogeneous group of bacteria that play a significant role in a variety of fermentation processes. They ferment carbohydrates in food and produce lactic acid as the main by-product. These bacteria are classified as homofermentative and heterofermentative bacteria based on their by-product in sugar fermentation.  Homofermentative bacteria are a type of lactic acid bacteria that produce only lactic acid as a primary by-product in glucose fermentation. On the other hand, heterofermentative bacteria are a type of lactic acid bacteria that produce ethanol/ acetic acid and CO₂ other than lactic acid as by-products in glucose fermentation. Thus, this is the key difference between homofermentative and heterofermentative bacteria.

Reference:

1. Müller, Thomas. “Comparison of Methods for Differentiation between Homofermentative and Heterofermentative Lactic Acid Bacteria.” ZentralblattFürMikrobiologie, Urban & Fischer, 16 Mar. 2012.
2. “Classification of Lactic Acid Cultures.” Food Science | University of Guelph.

Image Courtesy:

1. “Lactococcus lactis, scanning electron micrograph” By Kenneth Todar, PhD – Kenneth Todar, PhD, University of Wisconsin (CC BY 4.0) via Commons Wikimedia
2. “Figure-3-Scanning-electron-microscopy-analysis-of-EPS-producing-Leuconostoc-kimchii” By Ingrid Torres-Rodríguez, María Elena Rodríguez-Alegría, Alfonso Miranda-Molina, Martha Giles-Gómez, Rodrigo Conca Morales, Agustín López-Munguía, Francisco Bolívar, Adelfo Escalante – SpringerPlus doi:10.1186/2193-1801-3-583 (CC BY 4.0) via Commons Wikimedia