Abstract
Nicotinamide adenine dinucleotides (NAD(H)) play a vital role in various biological processes, including keeping the cellular redox balance. In this study, we investigate the regulatory responses of Streptococcus pneumoniae D39 to NADH and characterize the role of the Rex protein as a transcriptional repressor of the gapN, fba, pncB, adhB2, gap, and adhE genes. Transcriptomic analysis was used to observe the response of S. pneumoniae D39 to NADH. Our microarray studies revealed elevated expression of various genes/operons involved in transport and biosynthesis of niacin (gapN, fba, pncB, adhB2, gap, and adhE). Promoter lacZ-fusion assays and microarray studies with the rex mutant revealed the role of Rex as a transcriptional repressor of gapN, fba, pncB, adhB2, gap, and adhE involved in niacin uptake and biosynthesis, in the presence of NADH. We predict the operator site (5′-TTGTKAWAAWWTTCACAA-3′) of Rex in the regulatory regions of Rex-regulated genes that was subsequently validated by promoter mutational experiments.
Highlights
Streptococcus pneumoniae is an important human nasopharyngeal pathogen and causes several infections leading to over a million deaths around the globe each year (Ispahani et al, 2004; O’Brien et al, 2009)
Nicotinamide Adenine Dinucleotide (NAD) is required in several enzymatic processes where it acts as an electron carrier either by being oxidized (NAD+) or reduced (NADH) (Belenky et al, 2007)
Microarray comparison of S. pneumoniae was performed, where S. pneumoniae D39 wild-type was grown in chemically defined medium (CDM) having 0 mg/ml NADH and
Summary
Streptococcus pneumoniae is an important human nasopharyngeal pathogen and causes several infections leading to over a million deaths around the globe each year (Ispahani et al, 2004; O’Brien et al, 2009). Bacteria have to make use of the nutrients present in their surroundings, in addition to the virulence factors they possess, to successfully colonize and spread infections (Phillips et al, 1990; Titgemeyer and Hillen, 2002). The role of niacin in the regulatory mechanisms of NiaR and on global gene expression in S. pneumoniae has been revealed in our previous study (Afzal et al, 2017). Several genes, including nadC, niaX, fba, pnuC, rex, pncB, gapN, gap, adhB2, and adhE, were differentially expressed and role of NiaR as a transcriptional repressor of nadC, pnuC, and niaX was demonstrated in our study (Afzal et al, 2017)
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