Chitinophaga silvatica sp. nov., isolated from forest soil, and reclassification of Chitinophaga extrema as a later heterotypic synonym of Chitinophaga solisilvae

Inoculation of multi-metal-resistant Bacillus sp. to a hyperaccumulator plant Sedum alfredii for facilitating phytoextraction of heavy metals from contaminated soil

Co-contamination of soil by multiple heavy metals is a significant global challenge. An effective strategy to address this issue involves using hyperaccumulators such as Sedum alfredii (S. alfredii). The efficiency of phytoremediation can be improved by supplementing with plant growth-promoting bacteria (PGPB). However, bacteria resources of PGPB resistant to multi-heavy metal contamination are still lacking. This study focused nine different strains of Bacillus and screened for resistance to heavy metals including cadmium (Cd), zinc (Zn), copper (Cu), and lead (Pb). A superior strain, Bacillus subtilis PY79 (B. subtilis), showed tolerance for all tested metals. Inoculation with B. subtilis in the rhizosphere of S. alfredii increased the accumulation of Cd, Zn, Cu, and Pb by 88.02%, 58.99%, 90.22%, and 54.97% in the plant shoots after 30 days respectively. B. subtilis application lowered the pH of the rhizosphere soil, thereby increasing the bioavailability of nutrients and heavy metals. Furthermore, B. subtilis helped S. alfredii recruit PGPB and heavy metal-resistant bacteria such as Edaphobacter, Niastella, and Chitinophaga, enhancing the growth and phytoremediation efficiency. Moreover, inoculation with B. subtilis not only upregulated genes of the ABC, HMA, ZIP, and MTP families involved in the translocation and detoxification of heavy metals but also increased the secretion of antioxidants within the cells. These findings indicate that B. subtilis enhances the tolerance, uptake, and translocation of heavy metals in S. alfredii, offering valuable insights for the phytoremediation of multi-metal-contaminated soils.

Chitinophaga nivalis sp. nov., isolated from forest soil in Pyeongchang, Republic of Korea

Rod-shaped Gram-stain-negative, aerobic bacterial strains, designated PC14 and PC15T, were isolated from a forest soil sample collected in Pyeongchang county, Gangwon-do, Republic of Korea. Strains PC14 and PC15T grew at 15-37 °C (optimum, 28-30 °C in tryptone soya agar and Mueller-Hinton agar), hydrolysed chitin and casein, and tolerated pH 8.5 and 2 % (w/v) NaCl. The strains were most closely related to members of the genus Chitinophaga, namely Chitinophaga arvensicola DSM 3695T (98.4 %), Chitinophaga longshanensis Z29T (98.3 %), Chitinophaga ginsengisegetis Gsoil 040T (97.8 %), Chitinophaga polysaccharea MRP-15T (97.8 %) and Chitinophaga niastensis JS16-4T (97.7 %). The type strain grew well on conventional commercial media in the laboratory, including tryptone soya agar, Mueller-Hinton agar, Reasoner's 2A agar, nutrient agar and Luria-Bertani agar. The major polar lipid profile comprised phosphatidylethanolamine, an unidentified aminolipid and unidentified polar lipids. The major respiratory quinone was menaquinone-7. The main fatty acids were iso-C15:0, C16:1 ω5c, C16:0 3-OH, iso-C15:0 3-OH and iso-C17:0 3-OH. The DNA G+C content of the isolated strain based on the whole genome sequence was 46.6 mol%. The average nucleotide identity and digital DNA-DNA hybridization values between strains PC14 and PC15T and the reference type strains ranged from 71.0 to 76.5 %, and from 20.3 to 20.7 %, respectively. Based on phenotypic, chemotypic and genotypic evidence, strain PC15T could be differentiated phylogenetically and phenotypically from the recognized species of the genus Chitinophaga. Therefore, strain PC15T is considered to represent a novel species, for which the name Chitinophaga nivalis sp. nov. is proposed. The type strain is PC15T (=KACC 22893T=JCM 35788T).