Ph.D. student Anette McLeod at Nofima Mat has been studying Lactobacillus sakei, a lactic acid bacteria that is important industrially and is primarily known for its ability to ferment and preserve meat.
Optimising through knowledge
In the work she has been doing for her doctorate, Anette McLeod has compared different strains of Lactobacillus sakei that have been isolated from meat, with the aim of understanding why this species thrives better on meat and fish that any other species of lactic acid bacteria.
“Her studies are an important part of Nofima Mat’s systematic research into understanding the primary metabolism of lactic acid bacteria - in other words how they utilise sugars to make acid. The bacteria’s growth and acid production inhibits pathogens and bacteria that cause decay and influences product qualities such as texture and aroma. Knowledge about the bacteria’s metabolic processes can be used in selecting specific strains that are the optimum for use as starter cultures, for example,” says McLeod’s supervisor, Senior Research Scientist Lars Axelsson of Nofima Mat.
Lactobacillus sakei is used today in the food industry as a starter culture for fermenting sausages and it has potential for use in safeguarding microbial safety by inhibiting bacterial growth on the surface of meat and fish products. Among the bacteria that it inhibits is the pathogen Listeria monocytogenes.
The type of sugar preferred by most lactic acid bacteria is glucose. The advantage of Lactobacillus sakei is that it also thrives on a combination of glucose and ribose, which are the two sugars most commonly found in meat, and it can also exploit other components from the meat. The bacteria can also tolerate the extreme conditions of meat processing and storage.
“I have studied the genetics of various strains of Lactobacillus sakei and made comparisons with the only sequenced strain. The genes that are important for adapting to a life in meat products are preserved in all the trains. I have also looked at the growth of different strains on glucose and ribose by analysing at protein level and by genetic expression, and by investigating properties for growth and acid production. From this basis, the active metabolic paths the bacteria use when they ferment the two types of sugar could be defined, and the bacteria appear to link the utilisation of ribose with the utilisation of nucleosides, something which is unique to L. sakei among Lactobacilli. The studies have also given us an insight into the global genetic regulatory mechanisms that the bacteria use for maximum exploitation of the various components in order to survive,” concludes the doctoral candidate, whose disputation is on 18 June.