ABSTRACT
The
ability of archaea to salvage cobinamide has been under question
because archaeal genomes lack orthologs to the bacterial nucleoside
triphosphate:5′-deoxycobinamide kinase enzyme (cobU in
Salmonella enterica). The latter activity is required for
cobinamide salvaging in bacteria. This paper reports evidence that
archaea salvage cobinamide from the environment by using a pathway
different from the one used by bacteria. These studies demanded the
functional characterization of two genes whose putative function had
been annotated based solely on their homology to the bacterial genes
encoding adenosylcobyric acid and adenosylcobinamide-phosphate
synthases (cbiP and cbiB, respectively) of S.
enterica. A cbiP mutant strain of the archaeon
Halobacterium sp. strain NRC-1 was auxotrophic for
adenosylcobyric acid, a known intermediate of the de novo cobamide
biosynthesis pathway, but efficiently salvaged cobinamide from the
environment, suggesting the existence of a salvaging pathway in this
archaeon. A cbiB mutant strain of Halobacterium was
auxotrophic for adenosylcobinamide-GDP, a known de novo intermediate,
and did not salvage cobinamide. The results of the nutritional analyses
of the cbiP and cbiB mutants suggested that the entry
point for cobinamide salvaging is adenosylcobyric acid. The data are
consistent with a salvaging pathway for cobinamide in which an
amidohydrolase enzyme cleaves off the aminopropanol moiety of
adenosylcobinamide to yield adenosylcobyric acid, which is converted by
the adenosylcobinamide-phosphate synthase enzyme to
adenosylcobinamide-phosphate, a known intermediate of the de novo
biosynthetic pathway. The existence of an adenosylcobinamide
amidohydrolase enzyme would explain the lack of an adenosylcobinamide
kinase in
archaea.
Isolation and functional characterization of 5-enolpyruvylshikimate 3-phosphate synthase gene from glyphosate-tolerant Pseudomonas nitroreducens strains FY43 and FY47
