FIG. 4.

¹³C-labeled NMR scans of putrescine and ornithine samples. (A) ¹³C-labeled NMR scans of 8.7 mM putrescine in MRS broth (putrescine was unlabeled, so natural ¹³C is shown, which results in higher background noise); (B) putrescine production by Lactobacillus sp. strain ATCC 33222 incubated at 37°C for 3 days in MRS with l-[U-¹³C₅]ornithine; (C) ¹³C-labeled NMR scans of a cell-free control incubated at 37°C for 3 days in MRS with l-[U-¹³C₅]ornithine; (D) assay for putrescine production by L. helveticus CNRZ 32 after incubation at 37°C for 3 days in MRS with l-[U-¹³C₅]ornithine. Peaks show resonating ¹³C atoms within a compound in parts per million after 1,000 (A) and 5,000 (B, C, and D) NMR scans at room temperature. Carbon reference chloroform-d was added by capillary insertion and is indicated by the peak at 77 ppm. Peaks from about 60 to 100 ppm in panel C are probably due to residual alcohol from cleaning.