Metabolic regulation of phytoplasma malic enzyme and phosphotransacetylase supports the use of malate as energy source in these plant-pathogens

MARIANA SAIGO; ADRIÁN GOLIC; CLARISA E. ALVAREZ; CARLOS S. ANDREO; SASKIA HOGENHOUT; MARÍA ALEJANDRA MUSSI; MARÍA FABIANA DRINCOVICH

MICROBIOLOGY-UK

SOC GENERAL MICROBIOLOGY

Lugar: London; Año: 2014 vol. 160 p. 2794 - 2806

1350-0872

Phytoplasmas ("Candidatus Phytoplasma") are insect-vectored plant-pathogens. The genomes of these bacteria are small with limited metabolic capacities making them dependent on their plant and insect hosts for survival. In contrast to mycoplasmas and other relatives in the class Mollicutes, phytoplasmas encode genes for malate-transporters and malic enzyme (ME) for conversion of malate into pyruvate. It was hypothesized that malate is likely a major energy source for phytoplasmas as these bacteria are limited in the uptake and processing of carbohydrates. In this work, we investigated the metabolic capabilities of Aster Yellows Witches´ Broom (AYWB) phytoplasma Candidatus (Ca.) malic enzyme (AYWB-ME). We found that AYWB-ME has malate oxidative decarboxylation activity, being able to convert malate to pyruvate and CO2 with the reduction of either NAD or NADP and displaying distinctive kinetic mechanisms depending on the relative concentration of the substrates. AYWB-ME activity was strictly modulated by the ATP/ADP ratio, a feature which has not been found in other ME isoforms characterized so far. Moreover, we found that the Ca. Phytoplasma AYWB PduL-like enzyme (AYWB-PduL) harbours phosphotransacetylase activity, being able to convert acetyl-CoA to acetyl-P downstream of pyruvate. ATP also inhibited AYWB-PduL activity, like it did with AYWB-ME; furthermore, the product of the reaction catalyzed by AYWB-PduL, acetyl-P, stimulated AYWB-ME activity. Overall, our data indicate that AYWB-ME and AYWB-PduL activities are finely coordinated by common metabolic signals, like ATP/ADP ratios and acetyl-P, which supports their participation in energy (ATP) and reducing power (NAD(P)H) generation from malate in phytoplasmas.