M. Khademian – Virtual Seminar – May 8

ExplOrigins & Astrobiology Primer Community Review

Speaker: Maryam Khademian

Affiliation: University of Illinois, Department of Microbiology

Date: Friday, May 8, 2020 – 10:00am

Location: BlueJeans

Host: ExplOrigins Group

Title: Oxidative Stress in Anoxic Habitats

Abstract: Bacteroides thetaiotaomicron was examined to determine whether its obligate anaerobiosis is imposed by endogenous reactive oxygen species or by molecular oxygen itself. Previous analyses established that aerated B. thetaiotaomicron loses some enzyme activities due to a high rate of endogenous superoxide formation. However, the present study establishes that another key step in central metabolism is poisoned by molecular oxygen itself. Pyruvate dissimilation was shown to depend upon two enzymes, pyruvate:formate lyase (PFL) and pyruvate:ferredoxin oxidoreductase (PFOR), that lose activity upon aeration. PFL is a glycyl-radical enzyme whose vulnerability to oxygen is already understood. The rate of PFOR damage was unaffected by the level of superoxide or peroxide, showing that molecular oxygen itself is the culprit. The cell cannot repair PFOR, which amplifies the impact of damage. The rates of PFOR and fumarase inactivation are similar, suggesting that superoxide dismutase is calibrated so the oxygen- and superoxide-sensitive enzymes are equally sensitive to aeration. The physiological purpose of PFL and PFOR is to degrade pyruvate without disrupting the redox balance, and they do so using catalytic mechanisms that are intrinsically vulnerable to oxygen. In this way the anaerobic excellence and oxygen sensitivity of B. thetaiotaomicron are two sides of the same coin. 

Loren Williams speaks at ATL Science Tavern

Public Events

GT Biochemistry Professor Loren Williams will be presenting “Voyage from the Gates of the Hadean – Origins of Life Research at Georgia Tech” at the Atlanta Science Tavern on Saturday February 22, 2020 at 7pm at Manuel’s Tavern. Details and RSVP here and below.


– This event is a production of the Atlanta Science Tavern.
– It is free and open to the public.
– Seating is on a first-come basis.
– RSVPs are not required to attend nor do they reserve seats.
– Doors open at 6:00 pm for early arrival.
– Gather for dinner by 7:00.
– The evening’s presentation gets under way around 7:45.
– Parking at Manuel’s has changed; refer to the note below for details.

Loren Williams, Professor
School of Chemistry and Biochemistry
Georgia Institute of Technology

The origin of life (OOL) took place around 4 billion years ago, soon after the Earth cooled in the Hadean Eon. Water-based chemistry converted small building blocks to large polymeric molecules. Polymers have incredible properties, including ability to form assemblies. Polymers can assemble into compartments, fibers, enzymes and motors and can store and transduce information.

We have models, that are testable by experiment, to explain how increasing complexity of polymers led to simple microbial cells. For nearly 3 billion years microbes ruled the planet. Complex plants and animals are relatively recent branches on the tree of life.

The OOL can be studied from the bottom up (using chemical principles) or from the top down (mining information from biological systems). In this presentation I will discuss progress from long-running efforts at Georgia Tech that use both top-down and bottom-up approaches to unravel the OOL.

Consideration of OOL forces us to frame and confront the most profound and vexing questions in science and philosophy. The OOL tests our understanding of geological, chemical and biological principles and unsettles our sense of place in the universe.