Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2017

Investigating IEET syntrophy between electrogens (#314)

Brittney Phillips 1 , Lucie Semenec 1 , Ashley E Franks 1
  1. Physiology, Anatomy and Microbiology, La Trobe University, Melbourne, Victoria, Australia

Electrogenic microorganisms utilise insoluble electron acceptors or donors for anaerobic respiration and metabolism using extracellular electron transfer (EET) mechanisms1. These mechanisms can also be used for electron transfer between electrogens, known as interspecies EET (IET)2. IET mechanisms are contact-dependent, commonly employing cytochromes and pilin structures or contact-independent, whereby exogenous or endogenous redox molecules shuttle electrons between the bacteria2,3. To investigate the dynamic between these two modes of IET, syntrophic cocultures were established between G. metallireducens, known for utilizing pili during EET4 and P. aeruginosa, which produces endogenous phenazine redox shuttles to aid in EET3. These two microbes were placed in restrictive medium in which growth of the cocultures surpassed that of the pure cultures. To test whether the syntrophy was affected by the abundance of each microbe, cocultures containing different inoculum sizes of each microbe were established. Interestingly, the syntrophy between P. aeruginosa and G. metallireducens was found to be dependent upon the inoculation ratio of each microbe. The absolute abundance of each species in these cocultures of different inoculum ratios will be determined by quantitative PCR to determine whether proliferation of one limits or facilitates growth of the other. This will also be useful in determining how initial inoculation ratio changes over time within a syntrophic coculture. Successful growth of P. aeruginosa phenazine-deficient mutants in coculture with G. metallireducens revealed the syntrophy between these two microbes did not rely on phenazine redox shuttles. Furthermore, examination of the coculture biofilms via confocal microscopy revealed loosely associated flocs, suggesting the utilization of a contact-dependent IET mechanism. The expression of a G. sulfurreducens cytochrome homolog in G. metallireducens, previously implicated in accepting electrons from cathodes5, will also be monitored to determine whether it plays a role in accepting electrons extracellularly from P. aeruginosa.

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