Studies Using Mutant Strains of Azospirillum brasilense Reveal That Atmospheric Nitrogen Fixation and Auxin Production Are Light Dependent Processes

Abstract

As the use of microbial inoculants in agriculture rises, it becomes important to understand how the environment may influence microbial ability to promote plant growth. This work examines whether there are light dependencies in the biological functions of Azospirillum brasilense, a commercialized prolific grass-root colonizer. Though classically defined as non-phototrophic, A. brasilense possesses photoreceptors that could perceive light conducted through its host’s roots. Here, we examined the light dependency of atmospheric biological nitrogen fixation (BNF) and auxin biosynthesis along with supporting processes including ATP biosynthesis, and iron and manganese uptake. Functional mutants of A. brasilense were studied in light and dark environments: HM053 (high BNF and auxin production), ipdC (capable of BNF, deficient in auxin production), and FP10 (capable of auxin production, deficient in BNF). HM053 exhibited the highest rate of nitrogenase activity with the greatest light dependency comparing iterations in light and dark environments. The ipdC mutant showed similar behavior with relatively lower nitrogenase activity observed, while FP10 did not show a light dependency. Auxin biosynthesis showed strong light dependencies in HM053 and FP10 strains, but not for ipdC. Ferrous iron is involved in BNF, and a light dependency was observed for microbial 59Fe2+ uptake in HM053 and ipdC, but not FP10. Surprisingly, a light dependency for 52Mn2+ uptake was only observed in ipdC. Finally, ATP biosynthesis was sensitive to light across all three mutants favoring blue light over red light compared to darkness with observed ATP levels in descending order for HM053 > ipdC > FP10.

The Hidden World within Plants 2.0

“…Although traditionally classified as non-phototrophic, Azospirillum brasilense possesses photoreceptors that allow it to perceive light, and previous studies have suggested its ability to respond to light stimuli [12]. The study by Housh et al [13] explores the light dependencies in the biological functions of A. brasilense, a bacterium commonly used as a microbial inoculant in agriculture. The study investigated the light dependency of atmospheric biological nitrogen fixation (BNF) and auxin biosynthesis, along with related processes such as ATP biosynthesis and iron and manganese uptake.…”

“…Legrifi et al [4] and Bustamante et al [11] provided valuable insights into biocontrol strategies against olive root rot and grapevine trunk diseases, showcasing the potential of specific bacterial strains as environmentally friendly alternatives to chemical fungicides. Housh et al [13] revealed unexpected lightdependent responses in Azospirillum brasilense, challenging conventional classifications and expanding our understanding of microbial behavior. Hernández et al [18] uncovered the hidden diversity of endophytic bacteria in Cuban rice seeds, proposing promising candidates for bio-stimulants aimed at boosting crop growth.…”