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<p>The escalating need for environmentally sustainable methodologies has spurred investigations into effective biocontrol organisms to mitigate the harm caused by arthropod pests and vectors. Entomopathogenic nematodes and their symbiotic bacteria may offer a solution; however, their limitations in harsh environments necessitate identifying species or isolates better adapted to high temperatures. This study presents the first detailed characterization of the thermotolerant capabilities of <i>Xenorhabdus stockiae</i> isolates recovered from a semi-arid region of Rajasthan, India. Two bacterial isolates, BSBT_X2 and BSBT_X4, were retrieved from the entomopathogenic nematode <i>Steinernema siamkayai</i>. Molecular analysis of 16&#xa0;S rRNA gene sequences confirmed that both isolates are X. stockiae, with 100% nucleotide identity to the type strain. Phylogenetic analysis robustly placed BSBT_X2 and BSBT_X4 within the <i>X. stockiae</i> clade, forming a sister group with <i>X. innexi</i> and <i>X. bharatensis</i>. Biochemical profiling revealed a consistent pattern: negative for O-Nitrophenyl-β-D-galactopyranoside (ONPG), urease, Voges–Proskauer, methyl red, and indole, but positive for esculin hydrolysis, trehalose, and glucose utilization. Phenotypically, these isolates displayed neutral red adsorption on MacConkey agar and produced brownish pigmented colonies on nutrient agar. This comprehensive evidence supports their classification as <i>X. stockiae</i>. Comparative growth analysis across various liquid media demonstrated that Tryptic Soy Broth (TSB) was optimal for in vitro cultivation. Crucially, thermal tolerance studies revealed the bacteria’s remarkable capacity for robust growth at 45&#xa0;°C and 50&#xa0;°C. This exceptional thermotolerance is a critical adaptation, directly reflecting the harsh, hot, arid-to-semiarid climatic conditions prevalent in Rajasthan from which they were isolated. This research provides vital physiological insights into a regional <i>X. stockiae</i> isolate, informing its potential for use in insect pest management strategies under extreme climatic conditions.</p>

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Isolation and characterization of the thermotolerant bacterial symbiont Xenorhabdus stockiae from Steinernema siamkayai, collected from the semi-arid region of Rajasthan, India

  • 期刊论文

  • 发表日期：

    2026年4月22日

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  • Parul Chauhan,
  • Istkhar Rao,
  • Sakshi Singh

摘要

The escalating need for environmentally sustainable methodologies has spurred investigations into effective biocontrol organisms to mitigate the harm caused by arthropod pests and vectors. Entomopathogenic nematodes and their symbiotic bacteria may offer a solution; however, their limitations in harsh environments necessitate identifying species or isolates better adapted to high temperatures. This study presents the first detailed characterization of the thermotolerant capabilities of Xenorhabdus stockiae isolates recovered from a semi-arid region of Rajasthan, India. Two bacterial isolates, BSBT_X2 and BSBT_X4, were retrieved from the entomopathogenic nematode Steinernema siamkayai. Molecular analysis of 16 S rRNA gene sequences confirmed that both isolates are X. stockiae, with 100% nucleotide identity to the type strain. Phylogenetic analysis robustly placed BSBT_X2 and BSBT_X4 within the X. stockiae clade, forming a sister group with X. innexi and X. bharatensis. Biochemical profiling revealed a consistent pattern: negative for O-Nitrophenyl-β-D-galactopyranoside (ONPG), urease, Voges–Proskauer, methyl red, and indole, but positive for esculin hydrolysis, trehalose, and glucose utilization. Phenotypically, these isolates displayed neutral red adsorption on MacConkey agar and produced brownish pigmented colonies on nutrient agar. This comprehensive evidence supports their classification as X. stockiae. Comparative growth analysis across various liquid media demonstrated that Tryptic Soy Broth (TSB) was optimal for in vitro cultivation. Crucially, thermal tolerance studies revealed the bacteria’s remarkable capacity for robust growth at 45 °C and 50 °C. This exceptional thermotolerance is a critical adaptation, directly reflecting the harsh, hot, arid-to-semiarid climatic conditions prevalent in Rajasthan from which they were isolated. This research provides vital physiological insights into a regional X. stockiae isolate, informing its potential for use in insect pest management strategies under extreme climatic conditions.