Legionella pneumophilaInfection Rewires theAcanthamoeba castellaniiTranscriptome, Highlighting a Class of Sirtuin Genes

Legionella pneumophilais an environmental bacterium that has evolved to survive predation by soil and water amoebae such asAcanthamoeba castellanii, and this has inadvertently led to the ability ofL. pneumophilato survive and replicate in human cells.L. pneumophilacauses Legionnaire's Disease, with human exposure occurring via the inhalation of water aerosols containing both amoebae and the bacteria. These aerosols originate from aquatic biofilms found in artifical water sources, such as air-conditioning cooling towers and humidifiers. In these man-made environments,A. castellaniisupportsL. pneumophilaintracellular replication, thereby promoting persistence and dissemination of the bacteria and providing protection from external stress. Despite this close evolutionary relationship, very little is known about howA. castellaniiresponds toL. pneumophilainfection. In this study, we examined the global transcriptional response ofA. castellaniitoL. pneumophilainfection. We comparedA. castellaniiinfected with wild typeL. pneumophilatoA. castellaniiinfected with an isogenic Delta dotAmutant strain, which is unable to replicate intracellularly. We showed thatA. castellaniiunderwent clear morphological and transcriptional rewiring over the course ofL. pneumophilainfection. Through improved annotation of theA. castellaniigenome, we determined that these transcriptional changes primarily involved biological processes utilizing small GTPases, including cellular transport, signaling, metabolism and replication. In addition, a number of sirtuin-encoding genes inA. castellaniiwere found to be conserved and upregulated duringL. pneumophilainfection. Silencing of sirtuin gene,sir6f(ACA1_153540) resulted in the inhibition ofA. castellaniicell proliferation during infection and reducedL. pneumophilareplication. Overall our findings identified several biological pathways in amoebae that may supportL. pneumophilareplication andA. castellaniiproliferation in environmental conditions.