Differential gene expression in Azospirillum brasilense Cd under saline stress

Abstract

Previous studies in our laboratory demonstrated that the attachment of Azospirillum brasilense Cd to maize and wheat roots was altered when the bacteria were grown under saline stress. The aim of this work was to analyze the interaction when either the plant or both components were exposed to saline conditions. We demonstrated that this stress altered the early stages of development, in this plant model, leading to an inadequate colonization. The effect of saline stress on the expression of A. brasilense N2 fixation gene promoters was also studied. While nifA expression was increased in stressed bacteria, nifH transcription was diminished, suggesting an alteration in the NifA activation process. The induction of the nif gene transcription by root exudates was investigated, and the results suggest that they could be modulating certain bacterial processes, such as nitrogen fixation. However, stressed bacteria did not respond to the exudate's action. This could be related to the modified membrane composition resulting from changes in proteins, glucans, and capsular, exo- and lipopolysaccharides. We conclude that saline stress alters the Azospirillum brasilense Cd - maize interaction, the normal colonization, and the nitrogen fixation process.Key words: Azospirillum brasilense, saline stress, Azospirillum-root interaction, exudates, nif genes.

Cultivation factors and population size control the uptake of nitrogen by the microalgae Chlorella vulgaris when interacting with the microalgae growth-promoting bacterium Azospirillum brasilense

“…Guckert and Cooksey [29] found that a higher pH of the medium substrate for microalgae interferes with the cell cycle and decreases microalgal population growth. is reported in higher plants for drought [30], salt [31][32][33], humic acid [34] and heavy metals [35]; however, it was never reported for microalgae. This may show an ameliorating effect of the bacteria on the microalgae.…”

“…Similar to the mitigation of the pH effect by co-immobilized bacteria, mitigation of environmental stress by Azospirillum spp. is reported in higher plants for drought [30], salt [31][32][33], humic acid [34] and heavy metals [35]; however, it was never reported for microalgae.…”

Identification of salt stress inducible genes that control cell envelope related functions in Azospirillum brasilense Sp7

“…Increase in salinity inhibited nitrogen Wxation at the level of nifH expression (Jofre et al 1998b) and nitrogenase activity (Tripathi et al 2002). The mechanism of osmoadaptation has been investigated in relatively greater detail in A. brasilense, wherein glycine betaine was shown to enhance growth and nitrogen Wxation under salt stress (Riou and Le Rudulier 1990).…”

“…This protein binds glycine betaine with high aYnity and facilitates its high intracellular accumulation (Riou et al 1991;Tripathi and Mishra 1998). Salinity stress also changed the composition of the cell envelope resulting in changes in proteins, periplasmic glucans, and capsular, exoand lipopolysaccharides (Jofre et al 1998b;Altabe et al 1994). However, the information about the genes involved in osmoadaptation in the genus Azospirillum is very limited.…”

Promoter-trap identification of wheat seed extract-induced genes in the plant-growth-promoting rhizobacterium Azospirillum brasilense Sp245

“…Two plants were studied per treatment. In the other experiments, a hydroponic system consisting of cottonplugged, 180615 mm Pankhurst glass tubes containing 8 ml nitrogen-free Marvin-Prevel-Charpentier-Lavigne (MPCL) medium (Jofré et al, 1998) and one seedling was used. The tubes were placed for 7 days in a growth chamber at 20 uC with 16 h light (150 mE m Qualitative analysis of fluorescence in bacterial colonies was done in a dark room using a transilluminator (UV Transilluminator 2000; Bio-Rad) fitted with 312 nm excitation bulbs.…”