The Azospirillum brasilense Core Chemotaxis Proteins CheA1 and CheA4 Link Chemotaxis Signaling with Nitrogen Metabolism

Abstract

Bacterial chemotaxis affords motile bacteria the ability to navigate the environment to locate niches for growth and survival. At the molecular level, chemotaxis depends on chemoreceptor signaling arrays that interact with cytoplasmic proteins to control the direction of movement. In Azospirillum brasilense, chemotaxis is mediated by two distinct chemotaxis pathways: Che1 and Che4. Both Che1 and Che4 are critical in the A. brasilense free-living and plant-associated lifestyles. Here, we use whole-cell proteomics and metabolomics to characterize the role of chemotaxis in A. brasilense physiology. We found that mutants lacking CheA1 or CheA4 or both are affected in nonchemotaxis functions, including major changes in transcription, signaling transport, and cell metabolism. We identify specific effects of CheA1 and CheA4 on nitrogen metabolism, including nitrate assimilation and nitrogen fixation, that may depend, at least, on the transcriptional control of rpoN, which encodes RpoN, a global regulator of metabolism, including nitrogen. Consistent with proteomics, the abundance of several nitrogenous compounds (purines, pyrimidines, and amino acids) changed in the metabolomes of the chemotaxis mutants relative to the parental strain. Further, we uncover novel, and yet uncharacterized, layers of transcriptional and posttranscriptional control of nitrogen metabolism regulators. Together, our data reveal roles for CheA1 and CheA4 in linking chemotaxis and nitrogen metabolism, likely through control of global regulatory networks. IMPORTANCE Bacterial chemotaxis is widespread in bacteria, increasing competitiveness in diverse environments and mediating associations with eukaryotic hosts ranging from commensal to beneficial and pathogenic. In most bacteria, chemotaxis signaling is tightly linked to energy metabolism, with this coupling occurring through the sensory input of several energy-sensing chemoreceptors. Here, we show that in A. brasilense the chemotaxis proteins have key roles in modulating nitrogen metabolism, including nitrate assimilation and nitrogen fixation, through novel and yet unknown regulations. These results are significant given that A. brasilense is a model bacterium for plant growth promotion and free-living nitrogen fixation and is used as a bio-inoculant for cereal crops. Chemotaxis signaling in A. brasilense thus links locomotor behaviors to nitrogen metabolism, allowing cells to continuously and reciprocally adjust metabolism and chemotaxis signaling as they navigate gradients.

Identification and widespread environmental distribution of a gene cassette implicated in anaerobic dichloromethane degradation

“…Separation was accomplished at a constant flow rate of 250 nl/min with a 90‐min gradient from 2% to 30% solvent B (0.1% formic acid/80% acetonitrile in water) followed by an increase to 40% solvent B within 10 min. Tandem mass spectrometry (MS/MS) data were collected using the Thermo Xcalibur software version 4.2.47 with similar parameters as reported before (Ganusova et al, 2021). Raw proteomics spectral data previously generated from Diel (Kleindienst et al, 2019) were re‐analyzed alongside newly generated Defo data using identical programs and parameters to avoid methodological biases.…”

Multiple CheY Proteins Control Surface-Associated Lifestyles of Azospirillum brasilense

“…A lower swimming speed for this strain would increase its residence time in proximity to surfaces, which could promote enhanced adhesion for this mutant relative to the other strains. Several lines of experimental evidence indicate that chemotaxis signaling regulates non-chemotaxis functions in A. brasilense, though the mechanism(s) are not known (Bible et al, 2008;Gullett et al, 2017;Ganusova et al, 2021). It is thus also possible that the cheY mutants have different cell surface properties which would modulate their ability to adhere to surfaces.…”

Genome-Wide Analyses of Proteome and Acetylome in Zymomonas mobilis Under N2-Fixing Condition

“…Since nitrogen fixation is a costly process that requires a supply of ATP and reducing power ( Yan et al, 2010 ; Varley et al, 2015 ; Suyal et al, 2017 ), it is reasonable that the proteins involved in energy production or oxidation–reduction were upregulated under nitrogen fixation. Flagellar motility and chemotaxis have been demonstrated to be involved in energy taxis, a behavior that bacteria seek optimal conditions for metabolic activity, under the condition of nitrogen fixation ( Xie et al, 2010 ; Ganusova et al, 2021 ). We hypothesize that the similar chemosensing and signaling machinery for nitrogen fixation exists in ZM4.…”