Identification ofStreptococcus thermophilusCNRZ368 Genes Involved in Defense against Superoxide Stress

Abstract

To better understand the defense mechanism of Streptococcus thermophilus against superoxide stress, molecular analysis of 10 menadione-sensitive mutants, obtained by insertional mutagenesis, was undertaken. This analysis allowed the identification of 10 genes that, with respect to their putative functions, were classified into five categories: (i) those involved in cell wall metabolism, (ii) those involved in exopolysaccharide translocation, (iii) those involved in RNA modification, (iv) those involved in iron homeostasis, and (v) those whose functions are still unknown. The behavior of the 10 menadione-sensitive mutants exposed to heat shock was investigated. Data from these experiments allowed us to distinguish genes whose action might be specific to oxidative stress defense (tgt, ossF, and ossG) from those whose action may be generalized to other stressful conditions (mreD, rodA, pbp2b, cpsX, and iscU). Among the mutants, two harbored an independently inserted copy of pGh9:ISS1 in two loci close to each other. More precisely, these two loci are homologous to the sufD and iscU genes, which are involved in the biosynthesis of iron-sulfur clusters. This region, called the suf region, was further characterized in S. thermophilus CNRZ368 by sequencing and by construction of ⌬sufD and iscU 97 nonpolar mutants. The streptonigrin sensitivity levels of both mutants suggest that these two genes are involved in iron metabolism.

Cyclic di-GMP: the First 25 Years of a Universal Bacterial Second Messenger

“…Decreased resistance to ␤-lactam antibiotics upon decreased c-di-AMP levels was also observed in B. subtilis (445), where deletion of YbbP, one of three diadenylate cyclases, had the most pronounced effect. Screening studies of various Gram-positive bacteria provided further evidence for a more general role of c-di-AMP in resistance to various stresses, such as acid and oxidative stress (393,449,450). The next challenge is to identify c-di-AMP receptors, and there has also already been some progress.…”

Stress Physiology of Lactic Acid Bacteria

“…Inactivation of a gene encoding a DAC homolog in S. thermophilus, ossG, resulted in a methyl viologen-sensitive phenotype, suggesting the involvement of this gene in the oxidative stress response of this organism (144,145). On the other hand, inactivation of the Lc.…”

“…Iron is considered a key element in regulatory proteins sensing redox modifications in the presence of oxygen (274). This is illustrated by an S. thermophilus CNRZ368 mutant lacking the genes encoding an iron ABC transporter; the consequent imbalance in intracellular iron is the cause of an increase in superoxide anion radical sensitivity (145). In fact, control of iron homeostasis is considered to be coupled to ROS protection in streptococci (250).…”

cse , a Chimeric and Variable Gene, Encodes an Extracellular Protein Involved in Cellular Segregation in Streptococcus thermophilus

“…The increase of cell number per chain could be accompanied by obvious changes in cellular morphology. Thus, rodA, pbp2, and mreD mutants from Streptococcus thermophilus display not only long cell chains but also rod-shaped cells instead of ovoid wild-type cells (50,52,54). Also, an S. pneumoniae mutant depleted for expression of the essential pcsB gene forms long chains with irregularly shaped cells (33).…”

“…In-frame cse deletion mutants were constructed as previously described (52). Briefly, the two regions flanking the locus to be deleted were independently amplified by PCR, digested by appropriate restriction enzymes, and joined by ligation together and with pGh9.…”