l-Proline catabolism by the high G + C Gram-positive bacterium Paenarthrobacter aurescens strain TC1

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Abstract
Paenarthrobacter aurescens (formerly called Arthrobacter aurescens) strain TC1 is a high G + C Gram-positive aerobic bacterium that can degrade the herbicide atrazine. Analysis of its genome indicated strain TC1 has the potential to form a bifunctional PutA protein containing l-proline dehydrogenase and l-glutamate-γ-semialdehyde dehydrogenase (l-Δ1-pyrroline-5-carboxylate dehydrogenase) activities. P. aurescens strain TC1 grew well in minimal media with l-Proline as a supplemental nutrient, the nitrogen source, or the sole carbon and nitrogen source. Multicellular myceloids induced by NaCl or citrate also grew on l-proline. The specific activity of l-proline dehydrogenase in whole cells was higher whenever l-proline was added to the medium. Both l-proline dehydrogenase and l-glutamate-γ-semialdehyde dehydrogenase (l-Δ1-pyrroline-5-carboxylate dehydrogenase) activities were found primarily in a membrane fraction from exponential-phase cells. The two activities co-eluted from a Bio-Gel P-60 column after precipitation of proteins with ammonium sulfate and solubilization with 0.1% Tween 20. The PutA protein in the active fraction also oxidized 3,4-dehydro-dl-proline, but there was no activity with other l-proline analogues. When P. aurescens strain TC1 was grown in minimal media containing increasing concentrations of NaCl, there was a progressive decrease in the specific activity of l-proline dehydrogenase and a concomitant increase in the intracellular concentration of l-proline. These results indicate that P. aurescens strain TC1 can use l-proline as a nutrient in a regulated fashion. Because this bacterium also showed the ability to degrade most of the other common amino acids, it can serve as a useful model for the control of amino acid catabolism in the high G + C Actinobacteria.

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