An investigation of microbial diversity and microbiologically influenced corrosion in automotive fuel environments

Microbial contamination of fuels can cause issues such as biofouling, fuel degradation and microbiologically influenced corrosion (MIC). The focus of the research presented in this thesis was characterizing the microbial diversity of automotive fuels and automotive fuel environments in the United States via both molecular-based techniques as well as cultivation-based methods in order to gain insight into how this diversity is impacting fuels and fuel system infrastructure. A field survey of fuels including biodiesel, diesel, E10, E85, fuel-grade ethanol and gasoline was conducted; and 454 pyrosequencing of both 16S/18S rRNA genes as well as 16S/18S rRNA (transcribed into cDNA) was applied to identify both total and active microbial communities in these environments. Microbial communities in all fuel types were broadly similar, and prevalent phylotypes included Halomonas spp., Pseudomonas spp., Shewanella spp., Corynebacterium spp. and Acetobacter spp. Pyrosequencing libraries generated from cDNA and DNA indicated that the active and total communities of the sampled environments show significant overlap. The microbial communities of storage tanks containing fuel-grade ethanol and water were also characterized by molecular and cultivation-based techniques. Industry personnel have reported corrosion issues (suspected to be microbial corrosion) impacting storage tanks and other infrastructure exposed to fuel-grade ethanol and water, and acetic-acid-producing microbes were prevalent in samples collected from these environments. Acetobacter spp. and sulfate-reducing microbes were cultivated from samples collected from these storage tanks for laboratory corrosion testing. These corrosion tests (reported elsewhere) indicated that Acetobacter spp. increased pitting and cracking of carbon steels and that sulfate-reducing microbes increased general corrosion rates as well as increased pitting and cracking of carbon steels. Additionally, a Bacillus sp. that produces spores that catalyze Mn(II) oxidation was isolated from an E10 fuel sample. The potential impact that these sorts of microbes may have on corrosion in fuel system infrastructure is discussed. Increased knowledge of the the microbial diversity associated with fuel system infrastructure will improve monitoring and prevention strategies and guide future research of issues such as microbial corrosion in fuel systems.