The targeted deletion of genes responsible for expression of the Mth60 fimbriae leads to loss of cell-cell connections in M. thermautotrophicus ΔH
This study was continued by the Environmental Biotechnology Group of the University of Tubingen in memoriam to Reinhard Wirth, who initiated the work on Mth60 fimbriae at the University of Regensburg. Growth in biofilms or biofilm-like structures is the prevailing lifestyle for most microbes in nature. The first step to initiate biofilms is the adherence of microbes to biotic and abiotic surfaces. Therefore, it is important to elucidate the initial step of biofilm formation, which is generally established through cell-surface structures (i.e., cell appendages), such as fimbriae or pili, that adhere to surfaces. The Mth60 fimbriae of Methanothermobacter thermautotrophicus {Delta}H are one of only few known archaeal cell appendages that do not assemble via the type-IV assembly mechanism. Here, we report the constitutive expression of Mth60 fimbriae-encoding genes from a shuttle-vector construct, as well as the deletion of the Mth60 fimbriae-encoding genes from the genomic DNA of M. thermautotrophicus {Delta}H. We expanded our system for genetic modification of M. thermautotrophicus {Delta}H by an allelic-exchange method. While overexpression of the respective genes resulted in an increase of the Mth60 fimbriae, deletion of the Mth60 fimbriae-encoding genes led to a loss of Mth60 fimbriae in planktonic cells of M. thermautotrophicus {Delta}H. This either increased or decreased number of Mth60 fimbriae correlated with a significant increase or decrease of biotic cell-cell connections in the respective M. thermautotrophicus {Delta}H strains compared to the wild-type strain. Originality-Significance StatementMethanothermobacter spp. have been studied for the biochemistry of hydrogenotrophic methanogenesis for many years. However, due to the lack of genetic tools, the detailed investigation of certain aspects, such as regulatory processes, was not possible. Here, we amend our genetic toolbox for M. thermautotrophicus {Delta}H with an allelic exchange method. We report the deletion of genes that encode for the Mth60 fimbriae. Our findings provide a first insight into the regulation of the expression of these genes and reveal a role of the Mth60 fimbriae in the formation of cell-cell connections of M. thermautotrophicus {Delta}H.