Abstract Acustom-mademicroarrayforPorphyromonas gingivalis wasconstructedtoinvestigatethe gene expression profilingduringitsin vitro growth. There was a strong positivecorrelationbetweentheresultsofbothmicroarrayandquantitativereal-timePCRanalyses(r=0.910,p<0.01).Manytranscriptschangeddramaticallyduringthelate-logtotheearlystationaryphase.Inastationaryphase,mostofthetranscriptsdecreased.However,transcripts related to the transposon function, oxidative stress, and energy metabolismwereincreasedorsustainedathighlevels.Morenotably,thetranscriptsrelatedtoproteinfoldingand protein stabilization, such asdnak, groEL, groES, and htpG, increasedsignificantlyafter10hinthestationaryphase,suggestingthatthesechaperoneproteinsmayplayanimportantroleinbacterialsurvival.Alltogether,ourcustomarrayisusefulfortranscriptionalresearchforP. gingivalis. Itprovidesthatthegeneexpressionsaregrowthphase-specificandarechangeddramaticallyinresponsetoenvironmentalchangeduringbacterialculture. Introduction Porphyromonas gingivalis, a Gram-negative bacterialpathogen, is closely associated with adult periodontaldisease.Thisbacteriumisknowntopossessmanyvirulencefactors, including fimbriae, proteases, hemagglutinins, andcapsularpolysaccharides(1).Microorganismsareoftenableto adapt to large changes in their environment. This isparticularlytruefororganismslivinginthemouth,wherethey are exposed to dramatic changes in oxygen tension,osmolarity,temperature,pH,andbacterialcelldensity(2).Moreover, several reports have demonstrated that theexpression of putative virulence factors in P. gingivalis isregulatedbyenvironmentalconditions,suchashemin,pH,andtemperature(3-5).Thus,adaptationtotheenvironmen-talchangesinthemouthmustinvolvedirectchangesinthesynthesisofvirulencefactors.Cultivatedbacteriaareusuallyusedinanin vitro study.However,itseemsthatresearchersmaynotconsiderthebacterial growth phase carefully, even if they use thebacteriaduringexponentialgrowth.Incomparisonwiththeeukaryote, it is well known that bacterial transcripts arebreakableandthecelldivisionisperformedinashorttime,indicatingthatthebacterialgeneexpressionsarechange-able duringits growth. Therefore, it is important andinterestingto know the profilingof interested geneexpressionsduringgrowth.Recent technological advances have made it possible tostudy global gene expressions in both prokaryotes andeukaryotes by usingDNA microarray. For example, theglobalpatternofgrowthphase-dependentgeneexpressionis analyzed in Helicobacter pylori duringgrowthin vitro,findingthatthelate-logphasemaybethemostvirulentandpathogenic phase of growth(6). The gene expressionpatternsofbiosynthetic,regulatory,andribosomalproteinsinStreptomyces coelicolor areanalyzedfromalterationsingeneexpressionduringthegrowth(7).Also,theinvestiga-tion under iron starvation conditions in H. pylori demon-strates that gene expressions between exponential andstationary phases are different responses for growth-IntJOral-MedSci11(3):141-150,2012