Tiirola, M. | bioRxiv Science

bioRxiv2020

Cooperation between CRISPR-Cas types enables adaptation in an RNA-targeting system

CRISPR-Cas immune systems adapt to new threats by acquiring spacers from invading nucleic acids such as phage genomes. However, some CRISPR-Cas loci lack genes necessary for spacer acquisition, despite apparent variation in spacer content between strains. It has been suggested that such loci may use acquisition machinery from co-occurring CRISPR-Cas systems. Here, using a lytic dsDNA phage, we observe spacer acquisition in the native host Flavobacterium columnare that carries an acquisition-deficient subtype VI-B locus and a complete subtype II-C locus. We characterize acquisition events in both loci and show that the RNA-targeting VI-B locus acquires spacers in trans using acquisition machinery from the DNA-targeting II-C locus. Our observations reinforce the concept of modularity in CRISPR-Cas systems and raise further questions regarding plasticity of adaptation modules.

microbiology↗

bioRxiv2019

Cryptogams signify key transition of bacteria and fungi in Arctic sand dune succession

O_LIPrimary succession models focus on aboveground vascular plants. However, the prevalence of mosses and lichens, i.e. cryptogams, suggests they play a role in soil successions. Here, we explore whether effects of cryptogams on belowground microbes can facilitate progressive shifts in sand dune succession. C_LIO_LIWe linked aboveground vegetation, belowground bacterial and fungal community, and soil chemistry in six successional stages in Arctic inland sand dunes: bare sand, grass, moss, lichen, ericoid heath and mountain birch forest. C_LIO_LICompared to the bare sand and grass stages, microbial biomass and the proportion of fungi increased in the moss stage, and later stage microbial groups appeared despite the absence of their host plants. The microbial communities of the lichen stage resembled the communities in the vascular plant stages. Bacterial community correlated better with soil chemistry than with vegetation, whereas the correlation of fungi with vegetation increased with vascular vegetation. C_LIO_LIDistinct bacterial and fungal patterns of biomass, richness, and plant-microbe interaction showed that the aboveground vegetation change structured the bacterial and fungal community differently. The nonalignment of aboveground vs. belowground changes suggests that cryptogams can drive succession towards vascular plant dominance through microbially mediated facilitation in eroded Arctic soil. C_LI

ecology↗