CRISPR systems are often encoded by many prokaryotes as adaptive defense against mobile genetic elements (MGEs), but several MGEs also recruit CRISPR components to perform additional biological functions. Type IV-A systems are identified in Klebsiella plasmids, yet the distribution, characterization, and role of these plasmids carrying CRISPR systems in the whole Klebsiella genus remain unclear. Here, we performed large-scale comparative analysis of these plasmids using publicly available plasmid genomes.

Wear and corrosion are the main failure mechanisms of bearings and it is important to prolong their working lifetimes by improving the bearing surface properties. Incorporation of rare-earth elements is one of the viable means in many technologies such as plating, chemical heat treatment, and thermal spraying. In this work, various kinds of rare earth ions including praseodymium, lanthanum and neodymium were implanted into W9Cr4V2Mo high-temperature bearing steel specimens using a metal vapor vacuum arc source. Pin-on-disk wear tests and microhardness and potentiodynamic polarization measurements were employed to evaluate the mechanical properties and chemical stability of the treated specimens. The chemical composition and surface morphology of the implanted layers were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Our results indicate that the tribological characteristics of the treated samples are affected significantly due to the smoother and harder surface, while the enhancement of the corrosion resistance in the 3.5 wt.% NaCl aqueous solution after ion implantation is not appreciable. The modified surface yields better wear resistance.

Klebsiella variicola (K. variicola) is an emerging human pathogen, which poses a threat to public health. The horizontal gene transfer (HGT) of plasmids is an important driver for the emergence of multiple antibiotic-resistant K. variicola. The clustered regularly interspersed short palindromic repeats coupled with the CRISPR-associated genes (CRISPR/Cas) constitute an adaptive immune system in bacteria, which provide acquired immunity against HGT. However, the information about CRISPR/Cas system in K. variicola is still limited. In this study, a total of 487 genomes from NCBI database were used to analyze the characterization of CRISPR/Cas systems. 105 of the 487 genomes harbored at least one confirmed CRISPR array. Three types of CRISPR/Cas system, including types I-E, I-E*, and Ⅳ-A systems, were identified among 105 strains. The distribution of type I system was strongly associated with MLST, whereas type IV system was randomly distributed. Approximately one-third of spacer origins were homologous with plasmids or phages, indicating the role of CRISPR/Cas systems in controlling HGT. Moreover, spacers in K. variicola tended to target mobile genetic elements (MGEs) from Klebsiella pneumoniae, which provides new evidence for their interaction during evolution. Collectively, our results provide valuable insights into the role of CRISPR/Cas systems in K. variicola.