Role of Hfq in an animal–microbe symbiosis under simulated microgravity conditions

Abstract

AbstractMicrogravity has a profound impact on the physiology of pathogenic microbes; however, its effects on mutualistic microbes are relatively unknown. To examine the effects of microgravity on those beneficial microbes that associate with animal tissues, we used the symbiosis between the bobtail squidEuprymna scolopesand a motile, luminescent bacterium,Vibrio fischerias a model system. Specifically, we examined the role of Hfq, an RNA-binding protein known to be an important global regulator under space flight conditions, in the squid–vibrio symbiosis under simulated microgravity. To mimic a reduced gravity environment, the symbiotic partners were co-incubated in high-aspect-ratio rotating wall vessel bioreactors and examined at various stages of development. Results indicated that under simulated microgravity,hfqexpression was down-regulated inV. fischeri. A mutant strain defective inhfqshowed no colonization phenotype, indicating that Hfq was not required to initiate the symbiosis with the host squid. However, thehfqmutant showed attenuated levels of apoptotic cell death, a key symbiosis phenotype, within the host light organ suggesting that Hfq does contribute to normal light organ morphogenesis. Results also indicated that simulated microgravity conditions accelerated the onset of cell death in wild-type cells but not in thehfqmutant strains. These data suggest that Hfq plays an important role in the mutualism betweenV. fischeriand its animal host and that its expression can be negatively impacted by simulated microgravity conditions.