Bacteria develop differently depending on whether they are isolated or cultured together with other species of bacteria. This can be important in producing dairy products or in cleaning of water. A researcher says that enabling bacteria to coexist before using them may have untapped industrial potential.
Bacteria play an important role in the dairy industry. Lactic acid bacteria are needed to make cheese, buttermilk, yogurt and many other products.
New research shows that the results differ depending on whether different species of dairy bacteria first encounter each other when they are added to the milk or whether they have coexisted beforehand.
In fact, the research shows that the properties of different species of lactic acid bacteria change if they coexist before turning milk into fermented dairy products. Coexistence alters their properties so that they become more efficient and perhaps also obtain completely new capabilities that may be useful in industry.
The research has been published in NPJ Biofilms and Microbiomes.
“Producing various dairy products requires that species of bacteria coexist and often also collaborate to create the final product. We thought we could increase the efficiency of the bacteria by enabling them to coexist in advance and thus adapt to each other before adding them to the milk. Our results show that introducing the bacteria to each other before use makes a big difference and can potentially save a lot of money by streamlining the production of dairy products and expanding the repertoire of possible products,” explains a researcher behind the study, Mette Burmølle, Associate Professor, Department of Biology, University of Copenhagen.
Dairies use bacterial isolates
Industrial dairy production is a very optimised process in which the dairies carefully screen for and select very specific bacterial species.
Making cheese requires certain species of bacteria, whereas buttermilk and yogurt each require other species.
However, making most dairy products requires mixing several species together with the milk so that they can perform their biological miracle.
This is called a starter culture: isolated species of bacteria that are added to the milk. This comprises carefully selected and isolated species of bacteria, and the aim is that they must all contribute to developing the final product, often by collaborating.
“When starter cultures are created, most often the bacteria do not encounter each other until they are added together in the milk. But we do not know whether they might outcompete each other or what else might happen and whether the results would differ if we mixed the bacteria beforehand and enabled them to coexist for some time. We envision that the dynamics of adaptation may influence the acidity of the product, the time elapsing before the product is finished and the amount of energy needed to produce the product,” says Mette Burmølle.
Glass beads prevent bacteria from outcompeting each other
To investigate the potential for mixing bacteria before using them in the dairy industry, Mette Burmølle and colleagues carried out various experiments.
They mixed two species of bacteria in 20 test tubes and cultured them together for 16 days. In six of 20 cases, one species of lactic acid bacteria outcompeted the other so that the final culture comprised just one of the species.
Mette Burmølle says that the same thing could happen in dairy production, which may be disadvantageous.
The researchers carried out another experiment with two species of lactic acid bacteria in which they added small glass beads to the test tubes on which the bacteria could grow and form biofilms.
These beads enable the bacteria to create small microenvironments as they grow, which can help to maintain diversity. In the presence of glass beads, none of the bacterial species were outcompeted.
“This experiment showed that the bacteria that have surfaces to grow on avoid outcompeting each other. When dairies use several species of bacteria, there are no glass beads, but clumps can form in which similar biofilms can be created. This can create good conditions for all species of bacteria to survive,” explains Mette Burmølle.
She speculates that the glass beads create separate ecological niches so that the bacteria do not encounter each other to the same extent, which makes them compete less.
Bacteria that learn to coexist grow more slowly but produce more
In the second part of the study, the researchers investigated whether various growth parameters differed depending on whether the bacterial species had grown in isolation or together over 16 days.
The researchers investigated how rapidly the bacteria grew, how much biomass they produced and whether they were better at making the culture medium acidic, which is required for buttermilk and other fermented products.
These results showed that co-cultured bacteria grow more slowly but yield more, producing more biomass with the same quantity of nutrients.
“A large dairy making thousands of litres of buttermilk can make big savings if they can add 10% fewer bacteria and obtain the same product when the bacteria coexist before being added to the milk,” says Mette Burmølle.
Mette Burmølle explains that the results indicate that two plus two may not always equal four but sometimes three or five: using bacteria industrially requires investigating how to optimise and mix bacteria to maximise yield.
Sometimes the bacteria may need to be added separately, and sometimes they perform better if they are mixed beforehand.
In addition, the bacteria may be able to make completely new products, depending on how they have been mixed.
“This is worth investigating and applies not only within the dairy industry but also in other situations using bacteria such as cleaning of water or oil decontamination. This is not just mixing the bacteria in general but mixing them to optimise the results,” concludes Mette Burmølle.