Housh, A.B.; Noel, R.; Powell, A.; Waller, S.; Wilder, S.L.; Sopko, S.; Benoit, M.; Powell, G.; Schueller, M.J.; Ferrieri, R.A. Studies Using Mutant Strains of Azospirillum brasilense Reveal That Atmospheric Nitrogen Fixation and Auxin Production Are Light Dependent Processes. Microorganisms2023, 11, 1727.
Housh, A.B.; Noel, R.; Powell, A.; Waller, S.; Wilder, S.L.; Sopko, S.; Benoit, M.; Powell, G.; Schueller, M.J.; Ferrieri, R.A. Studies Using Mutant Strains of Azospirillum brasilense Reveal That Atmospheric Nitrogen Fixation and Auxin Production Are Light Dependent Processes. Microorganisms 2023, 11, 1727.
Housh, A.B.; Noel, R.; Powell, A.; Waller, S.; Wilder, S.L.; Sopko, S.; Benoit, M.; Powell, G.; Schueller, M.J.; Ferrieri, R.A. Studies Using Mutant Strains of Azospirillum brasilense Reveal That Atmospheric Nitrogen Fixation and Auxin Production Are Light Dependent Processes. Microorganisms2023, 11, 1727.
Housh, A.B.; Noel, R.; Powell, A.; Waller, S.; Wilder, S.L.; Sopko, S.; Benoit, M.; Powell, G.; Schueller, M.J.; Ferrieri, R.A. Studies Using Mutant Strains of Azospirillum brasilense Reveal That Atmospheric Nitrogen Fixation and Auxin Production Are Light Dependent Processes. Microorganisms 2023, 11, 1727.
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. Evidence for light dependency of four microbial processes were examined and noted: biological nitrogen fixation (BNF), auxin biosynthesis, ATP biosynthesis, and iron and manganese uptake. Functional mutants of A. brasilense were leveraged and 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. Iron is involved in the BNF biological process, and 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.
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