While Streptococcus mutans often gets blamed for tooth decay, Streptococcus sobrinus also accelerates tooth decay in some people, though little is known about it. But that may change as researchers in the Department of Bioengineering at the University of Illinois at Urbana-Champaign have successfully sequenced the complete genomes of three strains of S sobrinus.
S sobrinus is difficult to work with in the lab and isn’t present in all people, so researchers have focused on understanding the more stable and prevalent S mutans, which was sequenced in 2002, says assistant professor Paul Jensen, PhD, a researcher at the university’s Carl R. Woese Institute for Gemomic Biology.
“Although it is rare, S sobrinus produces acid more quickly and is associated with the poorest clinical outcomes, especially among children,” said Jensen. “If S sobrinus is present along with S mutans, you’re at risk for rampant tooth decay, which means there’s some level of communication or synergy between the two that we don’t understand yet.”
Now that the S sobrinus sequencing is complete, Jensen and his students are building computational models to better understand how the two bacteria interact and why S sobrinus can cause such potent tooth decay when combined with S mutans.
For example, the researchers already have confirmed that S sobrinus lacks complete pathways for quorum sensing, which is the ability bacteria that have to sense and react to nearby bacteria and ultimately proliferate.
According to Jensen, S mutans send out feelers in the form of a peptide to find out how many other S mutans cells are nearby. Once the S mutans cells reach a certain threshold, they attack and create an imbalance in the mouth between good and bad bacteria, which leads to rapid cavity formation.
“S sobrinus doesn’t have a complete system to do this,” said Jensen. “We’re really curious to explore this further and find out what is missing and why.”
A team of bioengineering undergraduates and students enrolled in the one-year Master of Engineering (MEng) program completed the entire S sobrinus genome sequencing instead of doctoral candidates, who typically conduct this type of research over several years.
“For the S sobriuns field, this is groundbreaking work because the field was plagued by a lack of information,” said Jensen. “In 2018, it is surprising that we had a whole species [of bacteria] that causes disease and no complete genome of it. Yet an ambitious tram of undergrads and MEng students completed the sequencing in a year.”
Mia Sales, who graduated with her bachelor’s degree this past May, completed the assemblies of two of the species of S sobrinus. Sales also built the computer that other team members used to complete the initial genome assemblies.
Fellow undergraduate Will Herbert worked on the annotation part of the project, finding genes in the strings of about 2 million adenine, cytosine, guanine, and thymine nucleotides that make up the S sobrinus genomes. Other contributors included MEng students Yuting Du, Amitha Sandur, and Naaman Stanley.
“This work exemplifies the students’ ability to synthesize their learning experience with a completely new insight, resulting in an original research publication,” said Dipanjan Pan, PhD, MS, director of the MEng program.
The researchers have uploaded the sequencing information to the GenBank public database so scientists worldwide will have access to the S sobrinus genetic information. The study, “Complete Genomic Sequences of Streptococcus sobrinus SL1 (ATCC 33478 = DSM 20742), NIDR 6715 (ATCC 27351 & 27352), and NCTC 10919 (ATCC 33402),” was published by Microbial Resource Announcements.