7th joint conference "Joint Microbiology & Infection Conference 2024" of the DGHM and VAAM

Professor

Chair

PD Dr.

Prof. Dr.

Plasmid segregation in Haloferax volcanii is mediated by a hybrid partitioning system

Archaea & Extremophiles

Proper segregation of the genome, a fundamental process across all domains of life has not been extensively studied in Archaea. Archaea show a high degree of variability in the organisation and copy number of chromosomes and plasmids. The archaeon Haloferax volcanii is a polyploid organism containing two large and two small plasmids as part of its genome. It is generally accepted that genomic segregation is carried out randomly due to its polyploidy.However, we have identified multiple two-gene operons across its genome; one gene encoding a ParA like protein and the other encoding unknown proteins. One such operons in the large plasmid pHV3 contains the loci hpaB and hpaA (Haloarchaeal partitioning protein A/B). We show phylogenetic and functional similarities between the operon and the ParABS DNA segregation system from bacteria. The predicted structure and conserved domains in the sequence of HpaA suggest that it is a ParA-like protein having a bacterial origin, acquired via horizontal gene transfer. HpaB is a ParB analogue of archaeal origin capable of forming foci in the cytosol. HpaA is necessary for the proper spatial distribution of the HpaB foci. Single particle tracking shows that HpaB regulates the dynamics of HpaA. Comparative qPCR suggests HpaB is essential for maintaining the plasmid to chromosome ratio.We thus propose a bacterial-archaeal hybrid plasmid segregating system in H. volcanii comprising of a repurposed bacterial protein (HpaA) and a customized archaeal DNA adapter (HpaB); the HpaAB system. We further explore how it could be especially necessary for two-dimensional segregation of its genome as H. volcanii cells form flat disks in middle to late logarithmic phase of growth. Regular spatial distribution of all genome copies ensures proper genome segregation irrespective of the plane of division, which has been shown to not be influenced by the location of DNA in H. volcanii. We suggest that segregation of its genome depends on a two-dimensional distribution of all its copies rather than a directional movement across the plane of division.

Oral Presentation

Small protein mediates inhibition of ammonium transport in Methanosarcina mazei – an ancient mechanism?

Regulation & small proteins

Small ORF encoded proteins, with a length less than 70 amino acids have been overlooked for long in classical bioinformatics and biochemical approaches. In the past decade however, modern genomics and transcriptomic technologies have discovered small genes containing short open reading frames in many prokaryotic genomes. By differential RNA sequencing, 1340 small open reading frames have been identified in the model organism Methanosarcina mazei, of which 72 have been verified by Mass Spectrometry.While several bacterial small proteins have already been described, the number of identified and especially functionally characterized small proteins in archaea is still limited. We have discovered that the small protein 36 (sP36), which consists of only 61 aa, plays a critical role in regulating the nitrogen metabolism in M. mazei. The absence of sP36 significantly delays the growth of M. mazei when transitioning from nitrogen limitation to nitrogen sufficiency. Through in vivo experiments, we have observed that during nitrogen limitation, sP36 is dispersed throughout the cytoplasm; however, upon shifting the cells to nitrogen sufficiency, it relocates to the cytoplasmic membrane. Moreover, in vitro biochemical analysis clearly showed that sP36 interacts with high-affinity with the ammonium transporter AmtB1 (KD=0.26 µM) present in the cytoplasmic membrane during nitrogen limitation, as well as with the PII-like protein GlnK1 (KD=1.8 µM). We propose that in response to an ammonium up-shift, sP36 targets the ammonium transporter AmtB1 and inhibits its activity by mediating the interaction with GlnK1. This mechanism represents a fast and reversible archaeal way of AmtB regulation, in contrast to the well-studied regulation in bacteria, which depends on covalent modification of GlnK. We will in addition elaborate on the molecular sensing mechanism by sP36 and the observed correlation of sP36 presence and GlnD absence in archaea.

Abstract: In this talk, current insights will be presented into the genetic regulation of stress response in Sulfolobus acidocaldarius, a thermoacidophilic model crenarchaeon thriving in volcanic hot springs. The impact of heat shock on the transcriptomic and proteomic landscape is highlighted, revealing prominent roles of both transcriptional and post-transcriptional/post-translational regulation. These findings underscore the prevalence of alternative mechanisms beyond classical transcription factor regulation in Crenarchaeota. Notably, the presence of RNA thermometer-like elements is proposed as one such mechanism, as exemplified by their identification in a gene encoding a thermosome subunit. Furthermore, the significance of chromatin restructuring, particularly mediated by proteins from the Lrs14 family, is emphasized. These abundant small non-specific DNA-binding proteins are hypothesized to be involved in various stress responses beyond heat shock, as well as exerting a control over pleiotropic physiological switches, such as the transition between planktonic and biofilm growth.

Genetic regulation of stress response in the model archaeon Sulfolobus acidocaldarius

Invited Speaker

Invited Talk

Abstract: Viruses by far outnumber cells and there is an ongoing arms race for survival. Archaea are infected by unusual viruses that are structurally very diverse and include those with unique capsid shapes such as a bottle, and viruses with cosmopolitan morphologies, such as head-tailed viruses. As the archaeal cell envelope is fundamentally different from that of bacteria and archaea, archaeal viruses face different challenges when traversing the cell envelope on their way in and out of the cell. We use haloarchaea and their viruses to study viral infection mechanisms. In my talk I will focus on the tailed haloarchaeal virus HFTV1 and present data on the molecular mechanisms underlying infection. 

Symposium
Regulatory Pathways in Archaea

Appointment

Chair

Programme

SymposiumRegulatory Pathways in Archaea

Appointment

Chair

Programme

Symposium
Regulatory Pathways in Archaea