Microhomology-Mediated High-Throughput Gene Inactivation Strategy for the Hyperthermophilic Crenarchaeon Sulfolobus islandicus

Sulfolobus islandicus is rapidly emerging as a model system for studying the biology and evolution within the TACK lineage of the archaeal domain. As the tree of life grows, identifying the cellular functions of genes within this lineage will have significant impacts on our understanding of the evolution of the last archaeal eukaryote common ancestor (LEACA) and the differentiation of archaea from eukaryotes during the evolution of the modern-day cell. To increase our understanding of this key archaeal organism, we report a novel high-throughput method for targeted gene inactivation in S. islandicus through one-step microhomology-directed homologous recombination (HR). We validated the efficacy of this approach by systematically deleting 21 individual toxin-antitoxin gene pairs and its application to delete chromosomal regions as large as 50 kb. Sequence analysis of 96 ArgD(+) transformants showed that S. islandicus can effectively incorporate donor markers as short segments through HR in a continuous or discontinuous manner. We determined that the minimal size of homology allowing native argD marker replacement was as few as 10 bp, whereas argD marker replacement was frequently observed when increasing the size of homology to 30 to 50 bp. The microhomology-mediated gene inactivation system developed here will greatly facilitate isolation of S. islandicus gene deletion strains, making generation of a collection of genome-wide targeted mutants feasible and providing a tool to investigate homologous recombination in this organism. IMPORTANCE Current procedures for the construction of deletion mutants of S. islandicus are still tedious and time-consuming. We developed a novel procedure based on microhomology-mediated HR, allowing for rapid and efficient removal for genetic regions as large as 50 kb. Our work will greatly facilitate functional genomic studies in this promising model organism. Additionally, we developed a quantitative genetic assay to measure HR properties in S. islandicus, providing evidence that the ability to incorporate short, mismatched donor DNA into the genome through HR was probably a common trait for members of the Sulfolobus genus that are recombinogenic.