Meyer, M. M. | bioRxiv Science

bioRxiv2018

Changes in endosymbiont complexity drive host-level compensatory adaptations in cicadas

For insects that depend on one or more bacterial endosymbionts for survival, it is critical that these bacteria are faithfully transmitted between insect generations. Cicadas harbor two essential bacterial endosymbionts, Sulcia muelleri and Hodgkinia cicadicola. In some cicada species, Hodgkinia has fragmented into multiple distinct cellular and genomic lineages that can differ in abundance by more than two orders of magnitude. This complexity presents a potential problem for the host cicada, because low-abundance-but-essential Hodgkinia lineages risk being lost during the symbiont transmission bottleneck from mother to egg. Here we show that all cicada eggs seem to receive the full complement of Hodgkinia lineages, and that in cicadas with more complex Hodgkinia this outcome is achieved by increasing the number of Hodgkinia cells transmitted by up to six-fold. We further show that cicada species with varying Hodgkinia complexity do not visibly alter their transmission mechanism at the resolution of cell biological structures. Together these data suggest that a major cicada adaptation to changes in endosymbiont complexity is an increase in the number of Hodgkinia cells transmitted to each egg. We hypothesize that the requirement to increase the symbiont titer is one of the costs associated with Hodgkinia fragmentation.

evolutionary biology↗

bioRxiv2018

The Transcriptional landscape of Streptococcus pneumoniae reveals a complex operon architecture and abundant riboregulation critical for growth and virulence

Efficient and highly organized transcription initiation and termination is fundamental to an organisms ability to survive, proliferate, and quickly respond to its environment. Over the last decade, our simplistic outlook of bacterial transcriptional regulation and architecture has evolved to include stimulus-responsive regulation by untranslated RNA and the formation of alternate transcriptional units. In this study, we map the transcriptional landscape of the bacterial pathogen Streptococcus pneumoniae by applying a combination of high-throughput RNA-sequencing techniques. Our study reveals a complex transcriptome wherein environment-respondent alternate transcriptional units are observed within operons stemming from internal transcription start sites (TSS) and transcription terminators (TTS) suggesting that more fine-tuning of regulation occurs than previously thought. Additionally, we identify many putative cis-regulatory RNA elements and riboswitches within 5-untranslated regions (5-UTR) of genes. By integrating TSSs and TTSs with independently collected RNA-Seq datasets from a variety of conditions, we establish the response of these regulators to changes in growth conditions and validate several of them. Furthermore, to determine the importance of ribo-regulation by 5-UTR elements for in vivo virulence, we show that the pyrR regulatory element is essential for survival, successful colonization and infection in mice suggesting that such RNA elements are potential drug targets. Importantly, we show that our approach of combining high-throughput sequencing with in vivo experiments can reconstruct a global understanding of regulation, but also pave the way for discovery of compounds that target (ribo-) regulators to mitigate virulence and antibiotic resistance.

microbiology↗