Fig. 1

Graphic representation of putrescine/spermidine biosynthesis pathways and transport systems a) putrescine/spermidine biosynthesis, where the deleted genes in the present study are indicated by an asterisk; b) putrescine/spermidine main transport systems, where ‘p’ represents putrescine and ‘s’ represents spermidine c) graphic representation of putrescine/proton symporter and putrescine/ornithine antiporter, where ‘p’ represents putrescine and ‘o’ represents ornithine. The figure is revised from Shah (20) and BioCyc (https://biocyc.org); SAM: S-adenosylmethionine; Decarbox. SAM: Decarboxylated SAM