Methylation Warfare: Interaction of Pneumococcal Bacteriophages with Their Host.

Virus-host interactions are regulated by complex coevolutionary dynamics. In Streptococcus pneumoniae, phase-variable type I restriction-modification (R-M) systems are part of the core genome. We hypothesized that the ability of the R-M systems to switch between six target DNA specificities also has a key role in preventing the spread of bacteriophages. Using the streptococcal temperate bacteriophage SpSL1, we show that the variants of both the SpnIII and SpnIV R-M systems are able to restrict invading bacteriophage with an efficiency approximately proportional to the number of target sites in the bacteriophage genome. In addition to restriction of lytic replication, SpnIII also led to abortive infection in the majority of host cells. During lytic infection, transcriptional analysis found evidence of phage-host interaction through the strong upregulation of the nrdR nucleotide biosynthesis regulon. During lysogeny, the phage had less of an effect on host gene regulation. This research demonstrates a novel combined bacteriophage restriction and abortive infection mechanism, highlighting the importance that the phase-variable type I R-M systems have in the multifunctional defense against bacteriophage infection in the respiratory pathogen S. pneumoniaeIMPORTANCE With antimicrobial drug resistance becoming an increasing burden on human health, much attention has been focused on the potential use of bacteriophages and their enzymes as therapeutics. However, the investigations into the physiology of the complex interactions of bacteriophages with their hosts have attracted far less attention, in comparison. This work describes the molecular characterization of the infectious cycle of a bacteriophage in the important human pathogen Streptococcus pneumoniae and explores the intricate relationship between phase-variable host defense mechanisms and the virus. This is the first report showing how a phase-variable type I restriction-modification system is involved in bacteriophage restriction while it also provides an additional level of infection control through abortive infection.

Large scale genomic analysis shows no evidence for pathogen adaptation between the blood and cerebrospinal fluid niches during bacterial meningitis.

Recent studies have provided evidence for rapid pathogen genome diversification, some of which could potentially affect the course of disease. We have previously described such variation seen between isolates infecting the blood and cerebrospinal fluid (CSF) of a single patient during a case of bacterial meningitis. Here, we performed whole-genome sequencing of paired isolates from the blood and CSF of 869 meningitis patients to determine whether such variation frequently occurs between these two niches in cases of bacterial meningitis. Using a combination of reference-free variant calling approaches, we show that no genetic adaptation occurs in either invaded niche during bacterial meningitis for two major pathogen species, Streptococcus pneumoniae and Neisseria meningitidis. This study therefore shows that the bacteria capable of causing meningitis are already able to do this upon entering the blood, and no further sequence change is necessary to cross the blood-brain barrier. Our findings place the focus back on bacterial evolution between nasopharyngeal carriage and invasion, or diversity of the host, as likely mechanisms for determining invasiveness.

Effect of oxygen on glucose metabolism: utilization of lactate in Staphylococcus aureus as revealed by in vivo NMR studies.

The ability to successfully adapt to changing host conditions is crucial for full virulence of bacterial pathogens. Staphylococcus aureus has to cope with fluctuating oxygen concentrations during the course of infection. Hence, we studied the effect of oxygen on glucose metabolism in non-growing S. aureus COL-S cells by in vivo(13)C-NMR. Glucose catabolism was probed at different oxygen concentrations in suspensions of cells grown aerobically (direct effects on metabolism) or anaerobically (transcriptional adjustment to oxygen deprivation). In aerobically-grown cells, the rate of glucose consumption diminished progressively with decreasing oxygen concentrations. Additionally, oxygen deprivation resulted in biphasic glucose consumption, with the second phase presenting a higher rate. The fructose-1,6-bisphosphate pool peaked while glucose was still abundant, but the transient maximum varied with the oxygen concentration. As oxygen became limiting mannitol/mannitol-1-phosphate were detected as products of glucose catabolism. Under anoxic conditions, accumulation of mannitol-1-phosphate ceased with the switch to higher glucose consumption rates, which implies the activation of a more efficient means by which NAD(+) can be regenerated. The distribution of end-products deriving from glucose catabolism was dramatically affected by oxygen: acetate increased and lactate decreased with the oxygen concentration; ethanol was formed only anaerobically. Moreover, oxygen promoted the energetically favourable conversion of lactate into acetate, which was particularly noticeable under fully oxygenated conditions. Interestingly, under aerobiosis growing S. aureus cells also converted lactate to acetate, used simultaneously glucose and lactate as substrates for growth, and grew considerably well on lactate-medium. We propose that the efficient lactate catabolism may endow S. aureus with a metabolic advantage in its ecological niche.

The relationship of insulin resistance with SNP 276G>T at adiponectin gene and plasma long-chain polyunsaturated fatty acids in obese children.

This study examined the association of insulin resistance with single-nucleotide polymorphism (SNP) 276G>T at adiponectin gene and the plasma long-chain polyunsaturated fatty acids (LCPUFAs) profile in obese children. One hundred thirty-one normolipidaemic obese children aged 8-13 y (53 girls and 68 boys) entered the study. The prevalence of T allele carriers at SNP276 was 48.8%. Mean [SD] values of fasting insulin and homeostasis model assessment-insulin resistance (HOMA-IR) index in noncarriers versus carriers of T allele were 12.4 [6.4] versus 20.6 [6.3] muU/mL (p = 0.039) and 2.6 [1.4] versus 4.5 [1.7] (p = 0.032). Mean [SD] values of plasma C18:3n - 3, C20:5n - 3/C20:4n - 6, and n - 6/n - 3 LCPUFA in phospholipids in noncarriers versus carriers of T allele were 0.10 [0.04] versus 0.08 [0.03] % (p = 0.013), 0.04 [0.01] versus 0.03 [0.01] % (p = 0.045), and 4.4 [0.7] versus 4.9 [0.9] % (p = 0.005), respectively. Insulin resistance was independently associated with SNP 276G>T (p = 0.002) and n - 6/n - 3 LCPUFA (p = 0.042) in plasma phospholipids, and interaction was found between SNP 276G>T and n - 6/n - 3 LCPUFA (p = 0.046). These findings suggest that obese children carriers of the SNP 276G>T may be at increased risk of metabolic complications compared with noncarriers, possibly due in part to a different plasma phospholipids profile.