Molecular analysis of the interactions between phages and the bacterial host Klebsiella pneumoniae

Abstract

Lytic phages are currently considered among the best options for treating infections caused by multi-drug resistant pathogens. Phages have some advantages over conventional antibiotics. For example, phages acquire modifications in accordance with their environment, and thus with the bacteria present, which has led to the co-evolution of both types of organism. Therefore, both phages and bacteria have acquired resistance mechanisms for protection. In this context, the aims of the present study were to analyze the proteins isolated from twenty-one novel lytic phages of Klebsiella pneumoniae in search of defence mechanisms against bacteria and also to determine the infective capacity of the phages. A proteomic study was also conducted to investigate the defence mechanisms of two clinical isolates of Klebsiella pneumoniae infected by phages. For this purpose, the twenty-one lytic phages were sequenced and de novo assembled using the Illumina-Miseq system and Spades V.3.15.2 respectively. Gene annotation was performed with Patric, Blast, Hhmer and Hhpred tools. The evolutionary relationships between phages were determined by RaxML. The host-range was determined in a collection of forty-seven clinical isolates of K. pneumoniae, revealing the variable infectivity capacity of the phages. Genome sequencing showed that all of the phages were lytic phages belonging to the family Caudovirales. The size and GC content of the phages ranged from 39,371 to 178,532 bp and from 41.72 % to 53.76 %, respectively. Phage sequence analysis revealed that the proteins were organized in functional modules within the genome. Although most of the proteins have unknown functions, multiple proteins were associated with defence mechanisms against bacteria, including the restriction-modification (RM) system, the toxin-antitoxin (TA) system, evasion of DNA degradation, blocking of host RM, the orphan CRISPR-Cas system and the anti-CRISPR system. Proteomic study of the phage-host interactions (i.e. between isolates K3574 and K3320, which have intact CRISPR-Cas systems, and phages vB_KpnS-VAC35 and vB_KpnM-VAC36, respectively) revealed the presence of several defence mechanisms against phage infection (prophage, plasmid, defence/virulence/resistance and oxidative stress proteins) in the bacteria, and of the Acr candidate (anti-CRISPR protein) in the phages. IMPORTANCEPhages, viral parasites of bacteria, have long protected the Earths biosphere against bacterial overgrowth and could now help in the fight against antimicrobial resistance. However, researchers, including microbiologists and infectious disease specialists, require more knowledge about the interactions between phages and their bacterial hosts and about the defence mechanisms in both viruses and bacteria. In this study, we analyzed the molecular mechanisms of viral and bacterial defence in phages infecting clinical isolates of Klebsiella pneumoniae. Viral defence mechanisms included RM system evasion, the Toxin-Antitoxin system, DNA degradation evasion, blocking of host RM and resistance to the abortive infection system (Abi), anti-CRISPR and CRISPR-Cas systems. Regarding bacterial defence mechanisms, proteomic analysis revealed overexpression of proteins involved in the prophage (FtsH protease modulator), plasmid (cupin phosphomannose isomerase protein), defence/virulence/resistance (porins, efflux pumps, LPS, pili elements, quorum network proteins, TA systems and methyltransferases), oxidative stress mechanisms and Acr candidates (anti-CRISPR protein). The findings reveal some important molecular mechanisms involved in the phage-host bacterial interactions; however, further study in this field is required to improve the efficacy of phage therapy.