Graduate Students Mini Symposium II-2024
Graduate Students Mini-Symposium
- Date: Feb 12, 2024
- Time: 01:15 PM (Local Time Germany)
- Location: MPI for Terrestrial Microbiology
- Room: Lecture Hall / Hybrid
- Host: IMPRS
- Contact: imprs@mpi-marburg.mpg.de
01:15 PM Katherine Pintor (RG Diepold)
The role of type III secretion chaperones in
effector export
The
type III secretion system (T3SS) is used by many bacteria, including important
pathogens, to inject effector proteins into eukaryotic cells. Critical steps of
the secretion process such as the selection, recruitment, and export path of
the effector proteins are still poorly understood. Most effectors are bound to
specific T3SS chaperones that are often co-expressed in the cytosol, while some
cargo are secreted in a chaperone-independent manner. In order to elucidate how
chaperones enable or enhance effector export and translocation to the target
host cell, we measured and visualized the lifecycle of the chaperones SycH and
SycE in real time and at a single molecule level in Yersinia enterocolitica. Using
single particle tracking photoactivated localization microscopy (sptPALM) and fluorescence
correlation spectroscopy (FCS), we could show that SycH and SycE diffuse faster
in the absence of effectors, which
verifies the interaction of effectors and chaperones. Upon initiation of
secretion, SycH became more mobile, which could imply a transition from cargo
recognition to cargo handover mode during export. In contrast, SycE exhibited
slower mobility under secreting conditions, based on our FCS data. This suggests
that although both chaperone proteins share a similar biological function on the
secretion of substrates, they might adapt different regulatory mechanisms during
export. Moreover, we also explored how chaperones behave in the absence of the mobile
T3SS sorting platform (ΔSctQ) and the T3SS membrane rings (ΔSctD). While effector-bound chaperones diffuse slightly faster in the
absence of SctQ, mobility of the chaperones in the absence of effectors was not
significantly altered, implying that chaperones only bind to the sorting
platform transiently and in the presence of their respective effector proteins.
Moreover, deletion of SctD has no impact on the diffusion of chaperones, which
means the interaction of chaperones and effectors is independent of the
injectisome assembly. These findings
suggest that chaperones recognize and bind to effectors in the bacterial
cytosol, and hand over their cargo to mobile T3SS sorting platform components
for delivery into the T3SS upon activation of secretion.
01:45 PM Joana Kästle (RG Brune)
Reductive
genome evolution in Ca. Ancillulaceae
(Bifidobacteriales), a novel lineage
of endosymbionts in termite gut flagellates
Cellulolytic
gut flagellates of lower termites are essential for the symbiotic digestion of
lignocellulose. They are associated with diverse but host-specific consortia of
ecto- and endosymbiotic bacteria, whose functional roles in the multilayered
symbiotic system are largely unknown. Here, we investigated a termite-specific
clade of Bifidobacteriales (Actinobacteria) using 16S rRNA gene
libraries of capillary-picked flagellates, fluorescence in situ hybridization (FISH), and comparative genome analysis of
metagenome-assembled genomes (MAGs). We found that Ca. Ancillulaceae comprises two phylogenetically and functionally
distinct groups that experienced substantial genome reduction. Ca. Ancillula (average genome size 1.48
Mbp) are endosymbionts of Trichonympha spp.
and retained the capacity to synthesize amino acids, vitamins, and co-factors. Ca. Opitulatrix (average genome size 1.2
Mbp), a hitherto unknown lineage of putative flagellate symbionts, has lost
most biosynthetic capacities and depends on the uptake of numerous metabolites
from its flagellate hosts. Both groups retained an amino acid export system and
acquired novel gene functions in response to their intracellular lifestyle.
02:15 PM Juliana Effert (AG Bode)
Biosynthesis of
bacterial pyrrolizidine alkaloids and production of new derivatives
Pyrrolizidine alkaloids (PA) represent a class of widespread natural products from plants and bacteria, where they potentially have a biological role in host-bacteria interactions and virulence. PA compounds are recognized as privileged structural motifs in small molecule drug discovery and show a broad pharmaceutical activity. Therefore, it is of high interest to identify or generate novel PAs with beneficial bioactivities. Here, we identify a novel PA dimer, pyrrolizwilline, and unravel its biosynthesis pathway. Furthermore, we exploit the biosynthetic pathway of pyrrolizixenamide and successfully apply the NRPS engineering concepts developed in our lab, to broaden the structural diversity of PAs.