Dissertation
Dissertation > Agricultural Sciences > Livestock, animal medicine,hunting,silkworm,bee > Animal Medicine ( Veterinary Medicine) > Basic Veterinary Science > Animal Microbiology ( Veterinary Microbiology, ) > Pathogenic bacteria > Cocci

Identification and Functional Characterization of Streptococcus Suis Serotype 2 Genes Up-regulated under Iron Starvation and in Porcine Lungs

Author LiZuo
Tutor ZhouRui
School Huazhong Agricultural University
Course Preventive Veterinary Medicine
Keywords Streptococcus suis serotype 2 Selective capture of transcribed sequences (SCOTS) Regulation of gene expression Porcine lung Iron restriction
CLC S852.611
Type Master's thesis
Year 2009
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Streptococcus suis serotype 2(SS2) is an important zoonotic pathogen causing septicaemia,meningitis,pneumonia and arthiritis in swine which lead to pig death and great economic loss in swine industry worldwide.It can also cause infections associated with meningitis,septic shock and death in certain people,especially those who have direct contact with pigs and pork.The process that pathogens cause diseases is manifested as a process of their survival,colonization,replication in the hosts as well as causing pathological lesions.Pathogens have to modulate their gene expression to respond to the changes in the environments both in vivo and in vitro.Thus,studies on the gene regulation of pathogens in vivo and in vitro are critical to discover their pathogenesis and useful for making strategies to prevent and treat the diseases they cause.In this study,selective capture of transcribed sequences(SCOTS) technique was used to investigate SS2 genes preferentially expressed in the lungs of infected pigs and under in vitro iron-restricted condition.A total of 145 genes were identified as up-regulated,some of which were subjected to functional analysis.1.Gene regulation of SS2 in the infected porcine lung tissuesIn the study,35-day-old healthy piglets were challenged with a virulent SS2 strain SC-19 intranasally.At the third day post of the infection,porcine lung tissues were isolated and used for RNA extraction.Through comparing the transcriptional profiles of SS2 in vivo and in vitro by SCOTS,82 SS2 genes were identified as up-regulated at infected porcine lung tissues which could be classified into five functional groups.34 genes were involved in metabolism,14 genes associated with bacterial cell wall,8 transporter genes,23 genes responsible for cell replication and 3 functionally unknown. The potential virulence genes,such as gidA,ssp,encode proteins that may be involved in translational/post-translational regulation.Genes ldh and pbp2A may be vital for SS2 survival in vivo through interfering host immune response.The hypothetical protein Hp1311 encoded by SSU051311 up-regulated in vivo was demonstrated to be a cell wall protein by western blot analysis.It had the ability to adhere to HEp-2 cells with its N-terimus confirmed by an indirect immuno-fluorescence assay.The newly identified SS2 virulence genes in this study provided a valuable starting point for determining their functions and roles in the bacterial pathogenesis.2.Gene regulation of SS2 in the iron-restricted cultureTo investigate SS2 genes induce-expressed under iron-restricted condition,SS2 was cultured in the medium restricted of iron.Using SCOTS technique,63 SS2 genes were identified as up-regulated under this condition:23 genes involved in metabolism,22 genes responsible for the replication and genetic information proceeding of the bacteria,8 genes relative to the construction of cell wall,5 ABC transporters,4 transcriptional regulators,and one uncharacterized gene conserved among Streptococcal species.To adapt to the stress,SS2 modulated its physiological activities that was validated by the up-regulation of RelA(a crucial enzyme in the stringent response),Area(a component of AD system catalyzing the conversion of arginine to ornithine) and CpdB(a cell surface protein being the substrate of sortase A).All of them were reported as virulence factors in S.suis or other bacteria.Besides,several homologous genes(fur,fhuGBDA operon) associated with iron uptake as reported in other bacteria were demonstrated to be up-regulated under iron-restricted condition in SS2 as well by quantitative RT-PCR. These identified genes are helpful for further investigation on iron-uptake mechanism of Gram-positive bacteria and its biological philosophy.

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