Citation: Minhas, Vikrant, Richard M. Harvey, Lauren J. McAllister, Torsten Seemann, Anna E. Syme, Sarah L.
Baines, James C. Paton, and Claudia Trappetti. 2019. Capacity to utilize raffinose dictates pneumococcal
disease phenotype. mBio 10(1):e02596-18.
Short Summary:
Streptococcus pneumoniae is a common inhabitant of the human nasopharynx but is also known to cause
serious, life-threatening disease in some individuals. This current study used a combination of genome
alignment, single nucleotide polymorphism (SNP) analysis, mutagenesis, qRT-PCR, and growth assays to
investigate differences among S. pneumoniae blood and ear isolates. SNP differences among the isolates
were identified in genes related to sucrose and raffinose metabolism. Blood, as compared to ear, isolates
consistently demonstrated raffinose utilization and better growth on media containing raffinose as the sole
carbon source. Mutagenesis and allergic exchange assays identified that a specific SNP in rafR, a raffinose
transcriptional regulator, was responsible for the difference in raffinose utilization and subsequent virulence in
mice models.
Questions:
Q.1) Do isolates grow better with glucose or raffinose as their sole carbon source? What evidence is there for
your answer, and why does this difference in growth exist?
Q.2) The authors identify 21 phosphotransferase systems (PTSs) and 8 ABC transport systems in S.
pneumoniae. What are the functions of PTSs and ABC transport systems? Why might S. pneumoniae have so
many different PTSs and ABC transporters?
Q.3) rafK encodes the ATP-binding protein component of the raffinose ABC transporter. What is the function of
a raffinose ABC transporter? What is the significance, or impact, of a mutation in the rafK gene sequence?
Q.4) Why did the authors use qRT-PCR to investigate the raffinose operon on S. pneumoniae serotype 14
ST15 and 3 ST180 strains? How did the genetic data compare to the results when grown on CDM with and
without raffinose?
Sample Solution