Abstracts from invited speakers at LST-day 2017

How do bacterial populations actually evolve?

Jukka Corander, professor, University of Oslo and Helsinki Institute for Information Technology

DNA in bacteria is known to be a subject to multiple evolutionary forces, including mutations, homologous recombination and horizontal transfer of genes. Such changes may be beneficial, deleterious or selectively neutral. Several models have been proposed to explain the variation we see in the genomes of bacteria across natural populations, including ecotype and neutral models. In particular simple neutral models have been shown to have a surprisingly good fit to population surveys. However, in the light of most recent functional data we present conclusive evidence that both neutral and ecotype models provide poor explanations for the strong correlations discovered between accessory genome loci across multiple populations of Streptococcus pneumoniae, a major human pathogen. We introduce a mechanistic model of frequency-dependent selection operating via accessory genes which is able to accurately predict the changes to the composition of the populations following introduction of a vaccination campaign. Unrelated recent large-scale genome data from an E. coli population suggests that the frequency-dependent selection may be a common mechanism regulating the evolution of bacterial populations of many species.

Clostridium – Harnessing Friend Over Foe To Advance a Sustainable Future

Bryan P. Tracy, PhD, CEO White Dog Lab

Clostridium is a genus of obligate anaerobic, predominantly spore-forming, Gram-positive bacteria that is commonly feared due to a subset of “foes,” notably C. difficile, tetani, botulinum, and perfringens. In contrast, my research seeks to harness the industrial potential of the non-toxic, friendly majority that exhibits broad substrate utilization, diverse metabolite production, and robust growth. We are particularly focused on acetogenic Clostridium.

Our motivation stems from what we posit as the bioeconomy conundrum – dealing with oxygen in biomass feedstocks. The world’s transportation fuel and chemical production technologies largely produce chemically reduced products, and handle petroleum, a reduced feedstock. In comparison, sugar and biobased feedstocks are oxidized, rendering them deficient in the energy required to produce drop-in products, and posing mass yield challenges, as oxygen must be removed.  

Acetogenic Clostridium have the potential to perform what we refer to as Anaerobic, Non-Photosynthetic (ANP) mixotrophy – defined as the concurrent utilization of organic (e.g., glucose) and inorganic (e.g., CO2, CO and H2) substrates. As I will describe, our collaborators and White Dog Labs have developed genetic engineering tools, built diverse libraries of acetogens, and employed systems level approaches to apply ANP mixotrophy to this bioeconomy conundrum. As a result, we demonstrate new fermentation paradigms that unlock higher theoretical maximum yields, improve carbon life-cycles, and synergize biomass and fossil feedstocks to realize sustainable production processes for fuels, chemicals and nutrition products.