Graduate Students Mini Symposium I-2024

01:15 PM Leonard Ernst (ENG Rebelein)
Evolutionary reconstruction and biochemical characterization of ancestral nitrogenases & discovery of novel non-enzymatic methane formation pathways

01:45 PM Anne Bennion (AG Becker)
Tracking the cellular reprogramming of rhizobia during early plant host infection

Rhizobia enter into symbiosis with legumes where they fix nitrogen for their host in exchange for carbon substrates in specialized root organs called nodules. Rhizobia must invade their host, crossing several cell layers before reaching the developing nodules. In most cases, this is accomplished via a tunnel-like compartment called the infection thread (IT) that initiates in root hairs. While a major cellular and genetic reprogramming of rhizobia is known to occur inside nodules¹, very little is known about the bacterial reprogramming occurring during early stages of infection. We have generated molecular tools, which enable highly sensitive tracking of rhizobial (Sinorhizobium meliloti) promoter activities and protein accumulation patterns in ITs of model legume Medicago truncatula using fluorescent confocal microscopy. We are using these tools to address how rhizobia respond to the new plant-confined compartments, specifically in terms of cell proliferation. With cell cycle markers, we provide further evidence that proliferation of rhizobial cells is spatially and temporally dynamic in early infection compartments². We hypothesize that these dynamics are influenced by plant via specific modifications to the IT cell wall interface. Since bacterial cell proliferation has been proposed as a means for the progression toward the developing nodule, tracking these dynamics in early infection compartments could provide new insights into the factors impacting successful host invasion.

02:15 PM Ozan Ertekin (AG Sogaard-Andersen)

SgnC, a MshEN_N domain protein with a PATAN domain regulates Myxococcus xanthus motility

In M. xanthus the ubiquitous and highly versatile second messenger c-di-GMP regulates motility by unknown mechanism(s). The effect of c-di-GMP is implemented by binding to downstream effectors, including proteins with the recently identified MshEN_N domain. Interestingly, the M. xanthus genome encodes six MshEN_N domain proteins that also contain a PATAN domain, which is suggested to be important for the regulation of motility in M. xanthus. Here, we report that one of these proteins, SgnC, it is involved in regulation of the cellular reversal frequency, i.e. lack of SgnC causes hyper-reversals and SgnC overexpression causes hypo-reversals. SgnC binds c-di-GMP in vitro, but c-di-GMP binding does not appear to be important for SgnC function. Interestingly, an active SgnC-sfGFP fusion localizes to the leading cell pole of the rod-shaped cells. To understand the mechanism(s) of SgnC, we aim to identify interaction partners using proximity labelling. We will report on these findings.