Biochemistry, Genetics and Molecular Biology (miscellaneous)

AbstractIncreasing evidence is proving the biological significance of the phytoplasma-secreted proteins. However, besides a few Sec-dependent secretory proteins, no other phytoplasma-secreted proteins have been reported yet. Candidatus Phytoplasma ziziphi is a phytoplasma that causes witches’-broom, a devastating jujube disease prevalent in east Asia. In this study, using the SecretomeP server coupled with an Escherichia coli-based alkaline phosphatase assay, we identified 25 non-classically secreted proteins (ncSecPs) from Ca. P. ziziphi, a novel type of secreted protein associated with phytoplasmas. Among them, six were characterized as hypersensitive cell death response (HR) suppressors that significantly attenuated both Bax- and INF1-triggered HR and H2O2 accumulation in Nicotiana benthamiana, indicating a so-far unknown role of the phytoplasma-secreted proteins. Further, we demonstrated that despite the diverse subcellular localizations in the N. benthamiana cells, the six HR-suppressing ncSecPs enhanced the gene expression of several known cell death inhibitors, including pathogenesis-related proteins (NbPR-1, NbPR-2, and NbPR-5) and Bax inhibitor-1 (NbBI-1 and NbBI-2). Together, our data indicated that Ca. P. ziziphi has evolved an arsenal of ncSecPs that jointly circumvent HR by activating the plant cell death inhibitors, thus providing new insight into understanding the pathogenesis of phytoplasmas.

Amycolatopsis coloradensis ATCC 53629 is the producer of the glycopeptide antibiotic avoparcin. While setting up the production of the avoparcin complex, in view of its use as analytical standard, we uncovered the production of a to-date not described ristosamynil-avoparcin. Ristosamynil-avoparcin is produced together with α- and β-avoparcin (overall indicated as the avoparcin complex). Selection of one high producer morphological variant within the A. coloradensis population, together with the use of a new fermentation medium, allowed to increase productivity of the avoparcin complex up to 9 g/L in flask fermentations. The selected high producer displayed a non-spore forming phenotype. All the selected phenotypes, as well as the original unselected population, displayed invariably the ability to produce a complex rich in ristosamynil-avoparcin. This suggested that the original strain deposited was not conforming to the description or that long term storage of the lyovials has selected mutants from the original population.