| Veillonella species are commonly present in the human mouth and are strictly anaerobic Gram negative cocci.,The capability of its adherency to facing is very poor and It is difficult to binding hydroxyapatite ceramic of saliva.Nevertheless , Gram positive once adhere to facing,then Veillonella species followed.Metabolic cooperation among bacteria may be set up through this relationship and important to the increasment of dental plaque.it explains that Veillonella species could adhere to facing with the assistance of Gram positive and contribute to the establishment of dental plaque.However, The cariogenic ability of cariogenic bacteria is related not only with coherence, but also closely with acid resistance. Acid resistance is that bacteria can continue producing acid and performing its function under low pH value, which is regarded as an important determinant factor for survival of cariogenic bacteria in the biofilm on teeth.Some acid-resistant genes have been separated and cloned now. In this report we study the genes: fhs and dltC.dltC encoding D-alanyl carrier protein (Dcp) is a member of dlt operon , it participates in the biosynthesis of D-alanyl-lipoteichoic acid (LTA). Boyd inactivated the dltC gene of the dlt operon in S. mutans LT11 to create the mutant BH97LC. BH97LC was shown to be acid-sensitive, displaying a defective ATR and an increased permeability to protons compared to wild- type LT11. It was presumed that D-alanyl-LTA whose information needs Dcp act as cell membrane's natural barrier to H+. When dltC is inactivated, H+ enters cell interior to make pH of cell interior decreased, so the aciduricity depressed.The gene encodes formyl-tetrahydrofolate synthetase (Fhs) from both prokaryotic and eukaryotic sources. In many bacteria, Fhs catalyzes the formation of 10-formyl-tetrahydrofolate, which is used directly in purine biosynthesis and formylation of Met-tRNA and indirectly in the biosynthesis of methionine, serine, glycine, and thymine. For ATP is the substrate of H+-ATPase affection,we predicted that themutation induced the abnormal of acid resistance which because the purine synthesis abnormal cause ATP synthesis abnormal,which induced H+-ATPase remove H+ abnormal.Gene engineering opreates to DNA according to people contrivable blueprint at the molecular level. For the past few years , the investigations of dental microphytology already have some effect owing to it which provids new means for the reasch at the invasion ,pathopoiesis and immunity of pathogenic bacterium at the molecular level.In my experiment I get the standard veillonella dispar bacterium from vitro culture. and the genome was obtained by tradition method. we designed a pair of primers in the most reserved region of the sequences from GenBank database.we cloned the PCR product of veillonella dispar into the TA vector to detect whether veillonella dispar have the acid-resistant gene dltc, fhs and sequence them.In my stuty we could confirm that veillonella dispar have the acid-resistant gene dltc and fhs. we compared the product sequence with those from GeneBank database .compared by BLASTX, the highest identity of dltC was up to 83% and the highest identity of fhs was up to98%. the fhs sequence we obtained in this study was a partial fragment .we would made a further research about the open reading frame of the acid– resistant fhs gene of veillonella dispar in the future.Now the acid-resistant gene dltc, fhs have become a hot issue .we study the acid-resistant reason of veillonella dispar from the gene level ,make foundation for molecular structure of the dental caries pathopoiesis ,and it prepares to construct the vaccine for caries prevention.
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