Detection of Horizontal Gene Transfer in the Choanoflagellate Salpingoeca rosetta

Horizontal gene transfer (HGT), the movement of heritable materials between distantly related organisms, is crucial in eukaryotic evolution. However, the scale of HGT in choanoflagellates, the closest unicellular relatives of metazoans, and its possible roles in the evolution of animal multicellularity remains unexplored. We identified 703 potential HGTs in the S. rosetta genome using sequence-based tests. The majority of which were orthologous to bacterial lineages, yet displayed genomic features consistent with the rest of the S. rosetta genome - evidence of ancient acquisition events. Putative functions include enzymes involved in amino acid and carbohydrate metabolism, cell signaling, the synthesis of extracellular matrix components, and the detection of bacterial compounds. Functions of candidate HGTs may have contributed to the ability of choanoflagellates to assimilate novel metabolites, thereby supporting adaptation, survival in diverse ecological niches, and response to external cues that are possibly critical in the evolution of multicellularity in choanoflagellates.