The decrease in the population of Gluconacetobacter diazotrophicus in sugarcane after nitrogen fertilization is related to plant physiology in split root experiments

Abstract

It has been established that a decrease in the population of Gluconacetobacter diazotrophicus associated with sugarcane occurs after nitrogen fertilization. This fact could be due to a direct influence of NH(4)NO(3) on bacterial cells or to changes in plant physiology after fertilizer addition, affecting bacterial establishment. In this work, we observed that survival of G. diazotrophicus was directly influenced when 44.8mM of NH(4)NO(3) (640mgN/plant) was used for in vitro experiments. Furthermore, micropropagated sugarcane plantlets were inoculated with G. diazotrophicus and used for split root experiments, in which both ends of the system were fertilized with a basal level of NH(4)NO(3) (0.35mM; 10mgN/plant). Twenty days post inoculation (dpi) one half of the plants were fertilized with a high dose of NH(4)NO(3) (6.3mM; 180 mgN/plant) on one end of the system. This nitrogen level was lower than that directly affecting G. diazotrophicus cells; however, it caused a decrease in the bacterial population in comparison with control plants fertilized with basal nitrogen levels. The decrease in the population of G. diazotrophicus was higher in pots fertilized with a basal nitrogen level when compared with the corresponding end supplied with high levels of NH4NO3 (100dpi; 80 days post fertilization) of the same plant system. These observations suggest that the high nitrogen level added to the plants induce systemic physiological changes that affect the establishment of G. diazotrophicus.

Compatible bacterial mixture, tolerant to desiccation, improves maize plant growth

“…The number of cells was determined in quintuplicate using the MSDP method with selective solid media ( S3 Table ). The seeds were washed with sterile water, rinsed with 70% ethanol for 10 min, immersed in 6.5% sodium hypochlorite, and agitated for 20 min; afterward, the seeds were washed eight times under sterile conditions [ 37 ]. One hundred thirty-five seeds of blue maize were soaked in each bacterial suspension ( A .…”

“…The weight of the vermiculite was obtained by drying samples without the roots as previously described [ 4 ]. Bacteria were inoculated onto selective media plates for the quantification of each experimental species, and incubation was carried out for 24 h at 30°C [ 37 ].…”

“…For each reference strain and strain isolated from the rhizosphere, the amplified gene encoding 16S rRNA was digested with 5 U of different restriction enzymes ( Alu I, Hha I, Hinf I, Rsa I, Mbo I and Msp I). The lengths of the restriction fragments generated for each tested strain were determined by electrophoresis in 2% agarose gels using a commercial molecular weight marker (100 bp DNA ladder), and the patterns of the isolated strains were compared with those of initially inoculated reference strains [ 4 , 37 , 40 ].…”

Desiccation-induced viable but nonculturable state in Pseudomonas putida KT2440, a survival strategy

“…Each suspension was aliquoted in microtubes of 1.5 mL capacity with 500 μL of bacterial suspension and covered with sterile cotton. Five samples from each treatment were used to determine the bacterial density (Colony Forming Units (CFU)/mL) contained in the suspensions before desiccation using the Massive Stamping Drop Plate (MSDP) method [34–36]. Desiccation was carried out at 30°C and 50% relative humidity (RH).…”

“…Every 3 days, the plants were irrigated to maintain substrate moisture. Rhizosphere samples were collected to evaluate colonization as previously described using five replicate plants from each treatment [20,36,38]. For this, the vermiculite adhered to the roots and considered as the rhizosphere was resuspended in water at a ratio of 1:10 (W/V).…”