New tool monitors strains throughout cheese-making process to maintain quality

A team of Norwegian researchers has developed a tool that can be= used to monitor the strains within a
culture with high resolution, in order to maintain cheese quality Industrial cheese production is
susceptible to viruses called “bacteriophage” or “phage” due to the industry’s use of “frozen batch inoculum,” which ensures that the cheese product will not vary by preventing bacterial evolution during
the cheese making process. “Monitoring could offer prompt detection of quality problems,” study author Helge Holo, PhD, professor of microbiology at Norwegian University of Life Sciences, said. To address this, researchers developed a monitoring tool that can identify strains most important to cheese quality. The specific tool that the researchers developed uses nextgeneration sequencing to identify a
gene called epsD – a protein that manufactures exopolysaccharide, a compound made largely of sugars,
that sits on the outer surfaces of cells and is linked preventing phage evolution. The tool can quantify the number of epsD sequences from a given strain, which can determine the number of bacteria of that strain that are present. “The loss of abundance, or disappearance of an epsD sequence indicates that something has gone wrong,” Holo said. “That could be a phage attack.” The study isolated more than 200 strains of bacteria from three commerical starter cultures, and from these, sequenced the genomes of 95 strains. Researchers found that epsD, the most variable gene, was present in 93 of the 95 strains. “The high degree of sequence variation of epsD represents evolutionary diversification,
indicating a history of selection pressure,” Holo wrote in the report. Much of that selection pressure
likely occurs when bacteriophage infects one or a few of the strains, Holo added. Bacteriophage are very specific, in that a certain bacteriophage will only infect a limited number of bacterial strains.