Comment by adrian_b

In the second part of the article there is an explanation which for me is the most plausible, and which would not be applicable to Martian soil.

Even if they killed all living beings in the soil, after their death the enzymes that are the catalysts for metabolism would just become dispersed in the soil and they continue to catalyze reactions like those of the Krebs cycle.

After many years of storage the molecules of the enzymes will be degraded, i.e. they will break into fragments. That again does not mean much, because the catalytic action of the enzymes is typically caused by very small parts of the enzymes, which can remain intact even after fragmentation.

In general, the biggest part of an enzyme is just a scaffold that attaches the enzyme in precise places of a cell, usually on some intracellular membranes, so that a great number of enzymes can be assembled like a production line in a factory, to coordinate the metabolic reactions for maximum efficiency.

After death and enzyme fragmentation, even after many years, the catalytic fragments of the enzymes can still catalyze reactions like those of the Krebs cycle.

It is also possible that some of the observed chemical reactions are catalyzed by minerals present in the soil and not by remnants of the enzymes from the dead cells, but for now no evidence has been gathered about this.

Moreover, there are enzyme residues which are difficult to distinguish from abiotic minerals. Some of the enzymes involved here contain a catalytic part formed by a cluster of iron and sulfur atoms, which are attached to a protein molecule. That iron-sulfur cluster is pretty much identical with a very small fragment of an iron sulfide mineral.