Research discovery could lead to tastier fermented foods

Lactic acid bacteria are essential in creating fermented foods like yoghurt, cheese and sauerkraut. Certain strains are also used as probiotics to improve human gut health.

Researchers at the University of California, Davis and Rice University have now found a previously unknown energy metabolism in lactic acid bacteria species. The discovery radically changes the scientific understanding of how these bacteria may thrive in their natural environments and could lead to healthier, tastier fermented foods.

Researchers found the species Lactiplantibacillus plantarum uses a hybrid metabolism, which combines features of respiration with fermentation.

“Using this blended metabolism, lactic acid bacteria like L. plantarum grow better and do a faster job acidifying [their] environment,” said co-corresponding author Maria Marco, a professor in the food science and technology department with the UC Davis College of Agricultural and Environmental Sciences.

The findings, published in the journal eLIFE, could lead to new technologies that use lactic acid bacteria to produce healthier and tastier fermented foods and beverages in ways which also minimise food waste. Manipulating this metabolism could change the flavour and texture of fermented foods.

“We may also find that this blended metabolism has benefits in other habitats, such as the digestive tract,” Marco said. “The ability to manipulate it could improve gut health.”

The study began with a puzzle

Unlike fermentation, respiration requires an external molecule that can accept electrons, like oxygen in aerobic respiration. Some microorganisms that mainly gain energy by respiration can use electron acceptors located outside the cell. This ability, called extracellular electron transfer, has been tied to specific genes. A newly identified set of extracellular electron transfer genes which use fermentation metabolism for energy conservation and growth were found throughout lactic acid bacteria.

“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.’”

The common bacteria they studied, L. plantarum, depends predominantly on fermentation. “But when we put them under particular circumstances where we’re providing them with a carbon source that makes it harder to make lactate, the main end product made during fermentation, they’ve got to do some workarounds. 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.”

The research team showed how L. plantarum uses this metabolism to change its environment in a food fermentation. Triggering this pathway with electrodes also offers many possibilities for fine-tuning food fermentations to change how they taste.

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