NOVEL BACTERIA ASSOCIATED WITH TWO MICROALGAE OPTIMIZED FOR CARBON DIOXIDE SEQUESTRATION FROM FLUE GAS

Abstract

The combustion of fossil fuels pollutes the atmosphere with carbon dioxide (CO2) and contributes to global warming. Microalgae are significant players in the capture and transformation of CO2 by way of their natural photosynthetic pathways. Moreover, the bacterial symbionts of microalgae can promote algal growth and resilience, thereby leading to additional carbon capture by microalgae. The significance of bacteria within microalgal systems is a significantly undervalued factor in microalgal research even though microalgae and bacteria are known to synergistically affect each other's growth and physiology. This dissertation focuses on the crucial and often unstudied contributions of bacteria in promoting microalgal growth. This work focuses on the role of bacteria in both small-scale (1 liter) and large-scale (500 liter, 6,800 liter) cultures of two microalgae, Tetradesmus obliquus strain HTB1 and Nannochloropsis oceanica strain IMET1 bubbled with simulated flue gas at 5% and 10% CO2. Bacterial community analysis by using 16S rRNA gene sequencing of themost productive algal cultures repeatedly revealed two dominant and novel bacteria with no taxonomic classification beyond the class level (Paceibacteria). Long read metagenomic sequencing yielded seven high quality metagenome assemble genomes (MAGs) of interest, including these two enigmatic unclassified bacteria. Two novel genera and species were taxonomically classified under the Seqcode (seqco.de/r:ywe1blo2): Phycocordibacter aenigmaticus gen. nov. sp. nov. and Minusculum obligatum gen. nov. sp. nov. The genus Phycocordibacter gen. nov. was proposed as the nomenclatural type of the family Phycocordibacteraceae fam. nov. and the order Phycocordibacterales ord. nov. In addition, functional analysis of plant growth promotion genes and metabolic reconstruction were conducted to elucidate how these bacterial symbionts promote microalgal growth and carbon fixation capacity. Epifluorescent microscopy and scanning electron microscopy (SEM) were conducted on both N. oceanica and T. obliquus cultures to understand the spatial relationship between each microalga and their respective bacterial symbionts. Digital PCR (dPCR) was conducted to quantify the ratio of microalgal cells to bacterial cells within cultures. To further improve CO2 capture strategies using microalgae, understanding the taxonomy and functional impact of bacterial symbionts is vital.