Bejaysus I can read all right, and this is what I read:
"bacteria that converts nickel to methane..."
What the original scientific paper says is:
"The Siberian volcanoes could still be part of the story of the Permian Extinction Event, says Rothman. They were probably responsible for a sharp increase in nickel deposits that the authors found in ocean sediments from the time. In known methane-spewing microbes, the metal is a crucial component of enzymes involved in the reactions that produce the gas. The availability of nickel is in fact a limiting factor to these organisms' growth, so nickel from the volcanoes could have caused a runaway effect in Methanosarcina, says Rothman, and eventually death for other species."
Other papers suggest that increased temperatures diminished oxygen levels in the oceans and also increased metabolic rates of organisms leading to massive diebacks. Others suggest that whatever in the oceans was not killed by oxygen starvation were nobbled by green sulphur bacteria giving off hydrogen sulpide(0.1% in air will kill a human)
The explanation given for the Siberian Traps and associated vulcanicity is a mantle plume, which rose until it impacted against the bottom of the Earth's crust, producing volcanic eruptions through the Siberian Craton. It lasted less than 1 million years but left behind Earth's biggest "large igneous province," a pile of lava and other volcanic rocks about 720,000 cubic miles (3 million cubic kilometers) in volume.
The big unknown both then and today is the impact of feedback mechanisms.A few ideas below

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3357779/