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<p>Phthalic acid (PA) is a key intermediate in the biodegradation of phthalate esters (PAEs), and its aerobic degradation pathways exhibit considerable diversity. In this study, a novel aerobic PA degradation bypass was discovered in <i>Klebsiella variicola</i> SY1. After blocking the classical 4,5-dioxygenase pathway, the strain retained the ability to utilize PA, and <i>gene 5193</i> encoding a UbiD family decarboxylase was significantly upregulated. Further knockout of <i>gene 5193</i> caused the loss of PA utilization ability. Metabolomic and LC-MS analysis revealed that this bypass is initiated by 4-monooxygenation of PA to 4-hydroxyphthalic acid, followed by decarboxylation to 4-hydroxybenzoic acid, which then enters protocatechuic acid or phenol metabolism. Heterologous expression of <i>gene 5193</i> did not confer the ability to convert PA or 4-hydroxyphthalic acid (4-HP), indicating that its product is not directly responsible for substrate conversion. Furthermore, by constructing a constitutive expression vector and introducing the esterase gene <i>pehA</i>, the recombinant strain achieved degradation rates exceeding 90% for dimethyl phthalate, diethyl phthalate, and dibutyl phthalate, effectively broadening the substrate spectrum. This finding enriches the understanding of the diversity of aerobic PA metabolism and provides both a strain resource and theoretical support for the bioremediation of phthalate ester pollution.</p>

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A novel phthalic acid degradation pathway in Klebsiella variicola SY1 and engineering the strain for degradation of multiple phthalate esters

  • 期刊论文

  • 发表日期：

    2026年7月6日

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  • Qiu Lequan,
  • Bao Mengyuan,
  • Yu Zhongqing,
  • Wang Longkuan,
  • Li Tongtong,
  • Wu Shijin

摘要

Phthalic acid (PA) is a key intermediate in the biodegradation of phthalate esters (PAEs), and its aerobic degradation pathways exhibit considerable diversity. In this study, a novel aerobic PA degradation bypass was discovered in Klebsiella variicola SY1. After blocking the classical 4,5-dioxygenase pathway, the strain retained the ability to utilize PA, and gene 5193 encoding a UbiD family decarboxylase was significantly upregulated. Further knockout of gene 5193 caused the loss of PA utilization ability. Metabolomic and LC-MS analysis revealed that this bypass is initiated by 4-monooxygenation of PA to 4-hydroxyphthalic acid, followed by decarboxylation to 4-hydroxybenzoic acid, which then enters protocatechuic acid or phenol metabolism. Heterologous expression of gene 5193 did not confer the ability to convert PA or 4-hydroxyphthalic acid (4-HP), indicating that its product is not directly responsible for substrate conversion. Furthermore, by constructing a constitutive expression vector and introducing the esterase gene pehA, the recombinant strain achieved degradation rates exceeding 90% for dimethyl phthalate, diethyl phthalate, and dibutyl phthalate, effectively broadening the substrate spectrum. This finding enriches the understanding of the diversity of aerobic PA metabolism and provides both a strain resource and theoretical support for the bioremediation of phthalate ester pollution.