Isolation and Genome Analysis of Serratia ureilytica T6, a Heavy Metal(loid)-Resistant and Plant Growth-Promoting...

Lead and zinc pollution is a prevalent issue in agricultural soils surrounding lead and zinc mines, posing a serious risk to crop growth and soil health. Heavy metal-resistant, plant growth-promoting bacteria (PGPB) capable of supporting plant development under high metal exposure have significant potential for mitigating these deleterious effects. Here we isolated and identified the Pb- and Zn-resistant and plant growth-promoting bacterial strain Serratia ureilytica T6 based on 16S rRNA and average nucleotide identity (ANI) analysis. Furthermore, 14 strains (T1-T14) from a rice paddy soil irrigated by Pb-Zn mine effluent were isolated and identified, and their phytopromoting characteristics were determined. Genome analysis of S. ureilytica T6 showed a genome size of 5,102,941 bp, with G + C content of 59.74%. A total of 4822 genes were annotated by RAST, among which 15 genes were putatively associated with Pb-Zn resistance. The genome of S. ureilytica T6 was found to possess multiple genes associated with probiotic properties by a comparative analysis of KEGG, GO, and COG databases. Several taxonomic identifications of S. ureilytica T6 revealed that strain T6 is Gram-negative, facultative anaerobic and motile. The pH growth range of S. ureilytica T6 was between 4.00 and 9.50; temperature growth range was 4-37 °C; NaCl tolerance was 0-9%. S. ureilytica T6 displayed a high tolerance to a variety of heavy metals, with minimum inhibitory concentrations of 1.5 and 9 mmol·L^-1 for Pb and Zn. S. ureilytica T6 can utilize a variety of carbon sources and nitrogen sources. T6 has the ability to produce indole-3-acetic acid (IAA), siderophore, and phosphorus and potassium solubilization, and it was initially judged that strain T6 has the potential for plant growth-promoting ability. Different plant growth-promoting effects of T6 inoculations were observed in improving rice biomass, plant height, etc. We observed that with increasing Pb and Zn stress, SOD activity first increased and then decreased, while POD and CAT activities gradually decreased. The addition of S. ureilytica T6 significantly enhanced the activities of SOD, POD, and CAT in rice seedlings under low to moderate Pb and Zn stress but had no significant effect under high concentrations (150 mg·L^-1) of Pb or Zn. In addition, S. ureilytica T6 has the potential to be used as a phytoremediation tool.