Urease activity in Streptococcus salivarius at low pH

Sissons, C.H.; Hancock, E.M.

doi:10.1016/0003-9969(93)90187-q

Cited by 42 publications

(31 citation statements)

References 39 publications

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“…that are common among strains of a species can be regarded as support of bacteria to survive stresses common to their habitats due to 'stress proteins' [58][59][60][61].…”

Section: Adaptation By Oral Bacteria To Environmental Parametersmentioning

confidence: 99%

Dental Caries: A Microbiological Approach

Yadav¹,

Prakash²

2017

J Clin Infect Dis Pract

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“…that are common among strains of a species can be regarded as support of bacteria to survive stresses common to their habitats due to 'stress proteins' [58][59][60][61].…”

Section: Adaptation By Oral Bacteria To Environmental Parametersmentioning

confidence: 99%

Dental Caries: A Microbiological Approach

Yadav¹,

Prakash²

2017

J Clin Infect Dis Pract

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“…It is established that the cytoplasmic pH of streptococci is generally maintained at 0.5 to 1 pH unit higher than the extracellular environment (6) and that intracellular ureases are protected from inactivation by cell membrane barriers (11). Furthermore, in vitro analysis has shown that the purified urease enzyme retains about 50% of its activity at pH 4.0 (3).…”

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confidence: 99%

Dual Functions of Streptococcus salivarius Urease

2000

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A urease-deficient derivative of Streptococcus salivarius 57.I was constructed by allelic exchange at the ureC locus. The wild-type strain was protected against acid killing through hydrolysis of physiologically relevant concentrations of urea, whereas the mutant was not. Also, S. salivarius could use urea as a source of nitrogen for growth exclusively through a urease-dependent pathway.Bacterial ureases are multisubunit enzymes that require Ni 2ϩ for catalytic activity (9). Several bacterial urease gene clusters have been isolated, and high degrees of homology between species have been observed (5, 9). Most bacterial ureases consist of three subunits, ␣, ␤, and ␥, encoded by ureC, -B, and -A, respectively. Other genes are present in urease clusters, i.e., ureDEFG, which encode proteins that are required for incorporation of Ni 2ϩ into the metallocenter of the catalytic site (9). Additional gene products involved in urease biogenesis and urea metabolism include nickel and urea transporters (10,14).Urea is present in saliva and crevicular fluids at 3 to 10 mM in healthy individuals (7,8), and it is hydrolyzed by ureases to generate two molecules of ammonia and one molecule of CO 2 . Ammonia can neutralize acids generated from bacterial glycolysis, inhibiting the initiation and progression of tooth decay. Ureolysis also creates a less acidic environment, enhancing the survival of acid-sensitive species and promoting the stability of a healthy oral flora (1). Despite the abundance of urea and ureolytic activity in the oral cavity, and the impact of ureolysis on oral health and ecology, the benefits for oral microorganisms of possessing ureases are not established.In general, urease expression in enteric organisms is positively regulated and transcription is activated either in the absence of an assimilable nitrogen source or in the presence of urea (5, 9). Unlike in enteric bacteria, Streptococcus salivarius 57.I urease expression is derepressed at low pH and is further enhanced in the presence of excess carbohydrate (2). Based on this mode of regulation, ureolysis by S. salivarius may function primarily to protect the organisms against acid damage or the bacteria may use ureolysis to acquire nitrogen when carbohydrates are present in excess. To test these hypotheses, an otherwise isogenic, urease-deficient derivative of S. salivarius 57.I was constructed, and the behavior of this mutant and that of the wild-type strain under different growth conditions were compared.Construction of a urease-deficient S. salivarius strain. To construct a urease-deficient S. salivarius strain, a gene specifying erythromycin resistance (erm) was cloned within ureC, the gene encoding the ␣ subunit of urease, to generate plasmid pMC81 (Fig. 1A). Plasmid pMC81 contains an Escherichia coli replicon and thus can be used as a suicide vector in streptococcal hosts. Plasmid pMC81 was introduced into wild-type 57.I by electroporation as previously described (4), and erythromycin-resistant (Em r ) transformants were selected and subjected to S...

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“…In prokaryotes, ureolysis can provide a source of assimilable nitrogen (13), it can protect the organisms against lethal acidification (41), and in some bacteria, it can support ATP synthesis driven by the gradients established by ammonia generation (43). Accordingly, urease expression in bacteria is often regulated in response to environmental parameters such as nitrogen availability and pH (30).…”

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confidence: 99%

Analysis of Urease Expression in Actinomyces naeslundii WVU45

Morou-Bermúdez

Burne

2000

Infect Immun

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The hydrolysis of urea by ureases of oral bacteria in dental plaque can cause a considerable increase in plaque pH, which can inhibit the development of dental caries. There is also indirect evidence that urea metabolism may promote the formation of calculus and that ammonia release from urea could exacerbate periodontal diseases. Actinomyces naeslundii, an early colonizer of the oral cavity and a numerically significant plaque constituent, demonstrates comparatively low levels of urease activity on isolation, so this organism has not been considered a major contributor to total oral urease activity. In this study it was observed that urease activity and urease-specific mRNA levels in A. naeslundii WVU45 can increase up to 50-fold during growth under nitrogen-limiting conditions. Using primer extension analysis, a putative, proximal, nitrogen-regulated promoter of the A. naeslundii urease gene cluster was identified. The functionality and nitrogen responsiveness of this promoter were confirmed using reporter gene fusions and 5 deletion analysis. The data indicated that regulation of urease expression by nitrogen availability in A. naeslundii may require a positive transcriptional activator. Plaque bacteria may experience nitrogen limitation when carbohydrates are present in excess. Therefore, based on the results of this study and in contrast to previous beliefs, strains of A. naeslundii may have the potential to be significant contributors to total plaque ureolysis, particularly during periods when there is an increased risk for caries development.

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Urease activity in Streptococcus salivarius at low pH

Cited by 42 publications

References 39 publications

Dental Caries: A Microbiological Approach

Dental Caries: A Microbiological Approach

Dual Functions of Streptococcus salivarius Urease

Analysis of Urease Expression in Actinomyces naeslundii WVU45

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