Tracking and plant growth-promoting effect of Paraburkholderia tropica MTo-293 applied to Solanum lycopersicum.

Paraburkholderia tropica MTo-293 was applied as an experimental bio-input to Solanum lycopersicum (tomato) cv. Platense. Different plant growth systems and inoculation strategies were tested to evaluate P. tropica plant colonization at the seedling stage (growth chamber) using culture-dependent and -independent techniques. The effect of P. tropica on plant growth was evaluated in the growth chamber and greenhouse (productive stage) by biomass accumulation and fruit production, respectively. P. tropica was able to colonize the surface and inner root and stem of tomato seedlings regardless of the inoculation strategy-at sowing and/or before transplanting-showing the competitive nature of P. tropica in nonsterile substrate systems. A nested polymerase chain reaction was validated to track P. tropica in tomato plants even in the inner stem with endophytic P. tropica populations of less than 102 CFU g-1 of fresh weight. Efficient colonization of P. tropica correlated with a positive effect on tomato growth when applied at sowing and/or before transplanting: plant growth promotion was observed not only at the seedling stage but also at productive stages improving crop yield in two different seasons. To our knowledge, this report is the first to track and evaluate the plant growth-promoting effect of P. tropica MTo-293 in tomato plants grown in nonsterile substrate systems.

Glucose metabolism in batch and continuous cultures of Gluconacetobacter diazotrophicus PAL 3.

Periplasmic glucose oxidation (by way of a pyrrolo-quinoline-quinone [PQQ]-linked glucose dehydrogenase [GDH]) was observed in continuous cultures of Gluconacetobacter diazotrophicus regardless of the carbon source (glucose or gluconate) and the nitrogen source (N(2) or NH(3)). Its synthesis was stimulated by conditions of high energetic demand (i.e., N(2)-fixation) and/or C-limitation. Under C-excess conditions, PQQ-GDH synthesis increased with the glucose concentration in the culture medium. In batch cultures, PQQ-GDH was actively expressed in very early stages with higher activities under conditions of N(2)-fixation. Hexokinase activity was almost absent under any culture condition. Cytoplasmic nicotinamide adenine dinucleotide (NAD)-linked glucose dehydrogenase (GDH) was expressed in continuous cultures under all tested conditions, and its synthesis increased with the glucose concentration. In contrast, low activities of this enzyme were detected in batch cultures. Periplasmic oxidation, by way of PQQ-GDH, seems to be the principal pathway for metabolism of glucose in G. Diazotrophicus, and NAD-GDH is an alternative route under certain environmental conditions.