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<p>Citrus Greening Disease (CGD), caused by <i>Candidatus</i> Liberibacter asiaticus (<i>C</i>Las), severely impairs citrus growth and productivity. Among five <i>Bacillus</i> isolates from acid lime leaves, <i>Bacillus subtilis</i> LBS5 exhibited superior plant growth-promoting traits, including a glucanolytic index of 5.85, siderophore production of 9.85 µmol/ml, IAA synthesis of 28.67&#xa0;µg/ml, and phosphate solubilization of 249.34&#xa0;µg/ml. LBS5 inhibited the surrogates, <i>Xanthomonas citri</i> and <i>Agrobacterium tumefaciens</i> with inhibition zones of 1.15&#xa0;cm and 1.06&#xa0;cm, respectively, and significantly reduced <i>C</i>Las titres from 6.33 ± 0.04 × 10⁸ to 9.15 ± 0.05 × 10³ copies within five days, comparable to tetracycline ((2.75 ± 0.91) × 10⁴). Gene expression analysis revealed marked upregulation of defense-related genes, <i>PAL</i> (5.87-17.05-fold) and <i>PR2</i> (3.87–16.05-fold), indicating activation of phenylpropanoid and glucanase-mediated defense pathways. Integrated metabolomic and pathway analyses, including PLS-DA, demonstrated coordinated upregulation of <i>PAL</i> (2.08 log₂FC) and <i>PR2</i> (2.65 log₂FC), accumulation of phenylpropanoid metabolites such as quinic acid (6.17 log₂FC), coumaric acid (2.62 log₂FC), and phenylalanine (1.36 log₂FC), and modulation of carbohydrate and antioxidant metabolism. FTIR and ¹H NMR analyses confirmed reduced lipid oxidation and lignin deposition, along with enhanced defense-related metabolites. Collectively, LBS5 effectively suppresses <i>C</i>Las, activates key defense pathways, and enhances metabolite-mediated resistance, highlighting its potential as a biocontrol and plant growth-promoting agent for sustainable management of CGD.</p>

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Targeted gene expression and associated metabolomic insights into Bacillus subtilis LBS5-mediated suppression of Candidatus liberibacter asiaticus in acid lime (Citrus aurantiifolia (christm.) swingle)

  • 期刊论文

  • 发表日期：

    2026年2月7日

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  • Ramesh Kumar Rajamahendran,
  • Manonmani Karunakaran,
  • Vellaikumar Sampathrajan,
  • Harish Sankarasubramanian,
  • Yesuraja Iruthayarajan,
  • Medari Sagarika,
  • Sariga Rajmohan,
  • Boopathi Natesan,
  • Anandham Rangasamy,
  • Johnson Iruthayasamy

摘要

Citrus Greening Disease (CGD), caused by Candidatus Liberibacter asiaticus (CLas), severely impairs citrus growth and productivity. Among five Bacillus isolates from acid lime leaves, Bacillus subtilis LBS5 exhibited superior plant growth-promoting traits, including a glucanolytic index of 5.85, siderophore production of 9.85 µmol/ml, IAA synthesis of 28.67 µg/ml, and phosphate solubilization of 249.34 µg/ml. LBS5 inhibited the surrogates, Xanthomonas citri and Agrobacterium tumefaciens with inhibition zones of 1.15 cm and 1.06 cm, respectively, and significantly reduced CLas titres from 6.33 ± 0.04 × 10⁸ to 9.15 ± 0.05 × 10³ copies within five days, comparable to tetracycline ((2.75 ± 0.91) × 10⁴). Gene expression analysis revealed marked upregulation of defense-related genes, PAL (5.87-17.05-fold) and PR2 (3.87–16.05-fold), indicating activation of phenylpropanoid and glucanase-mediated defense pathways. Integrated metabolomic and pathway analyses, including PLS-DA, demonstrated coordinated upregulation of PAL (2.08 log₂FC) and PR2 (2.65 log₂FC), accumulation of phenylpropanoid metabolites such as quinic acid (6.17 log₂FC), coumaric acid (2.62 log₂FC), and phenylalanine (1.36 log₂FC), and modulation of carbohydrate and antioxidant metabolism. FTIR and ¹H NMR analyses confirmed reduced lipid oxidation and lignin deposition, along with enhanced defense-related metabolites. Collectively, LBS5 effectively suppresses CLas, activates key defense pathways, and enhances metabolite-mediated resistance, highlighting its potential as a biocontrol and plant growth-promoting agent for sustainable management of CGD.