Lactic Acid Bacteria in Fermented Foods Uses Hybrid Metabolism, Scientists Find

University of California, Davis and Rice University researchers discovered a previously unknown energy metabolism in lactic acid bacteria, essential in creating fermented foods.

The species Lactiplantibacillus plantarum was found to have used a single pathway that "simultaneously blends features" of fermentation and respiration in the primarily fermentative microbe.

Co-corresponding author Maria Marco, a professor in the food science and technology department with the UC Davis College of Agricultural and Environmental Sciences says this blended metabolism allows lactic acid bacteria like L. plantarum "grow better and do a faster job acidifying its environment."

Phys.org presents this finding could "radically change" the scientific understanding of how bacteria thrive in their natural environments, and provide immediate biotechnology applications to produce healthier and tastier fermented foods and beverages.

Unique metabolic strategies increase the yield and efficiency of fermentation

The ways in which these microbes extract energy to maintain cellular functions come in two processes, respiration and fermentation.

"While respiration is often more energetically efficient, many bacteria rely on fermentation as their sole means of energy production," the authors wrote on the study published in the journal eLIFE.

According to the study, the ability to manipulate this metabolism could change the flavor and texture of fermented foods, benefit its habitat such as the digestive tract, and improve gut health.

It did have a "puzzling beginning", the team tells in the UCDAVIS official website.

Unlike fermentation, some microbes that mainly gain energy by respiration can use electron acceptors located outside the cell - a process called extracellular electron transfer. However, this ability has been tied to specific genes.

The found a newly identified set of extracellular electron transfer genes throughout lactic acid bacteria which rely on fermentative metabolism for energy conservation and growth.

"It was like finding the metabolic genes for a snake in a whale," said co-corresponding author Caroline Ajo-Franklin, a bioscientist with Rice University. "It didn't make a lot of sense, and we thought, 'We've got to figure this out.'"

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Shift and/or accelerate metabolism through extracellular electron transfer

While the common bacteria, L. plantarum, depends predominantly on fermentation, "they've got to do some workarounds" and that's when the new metabolism kicks in, Ajo-Franklin said.

According to Marco, "this blended metabolism allows L. plantarum to overcome major bottlenecks in growth by allowing the bacteria to send electrons outside of the cell." Subsequently, L. plantarum uses this metabolism to change its environment in food fermentation.

Once triggered, this single pathway of combined approaches may allow L. plantarum to adapt to different environments and grow faster, allowing it to compete against other species, and produce new biotechnologies and foods that are healthier, had less waste, or have different tastes and textures.

The implications of this trait at a metabolic and energetic level "have significance for the understanding of energy conservation strategies in primarily fermentative microorganisms and on lactic acid fermentations in food biotechnology," the co-authors including Eric Stevens, Peter Finnegan, James Nelson and Andre Knoessen of UC Davis, Sara Tejedor-Sanz of Rice University, and Samuel Light of the University of Chicago concluded.

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