Dynamics of Mycobacteriophage-Mycobacterial Host Interaction: Evidence for Secondary Mechanisms for Host Lethality

Abstract

bMycobacteriophages infect mycobacteria, resulting in their death. Therefore, the possibility of using them as therapeutic agents against the deadly mycobacterial disease tuberculosis (TB) is of great interest. To obtain better insight into the dynamics of mycobacterial inactivation by mycobacteriophages, this study was initiated using mycobacteriophage D29 and Mycobacterium smegmatis as the phage-host system. Here, we implemented a goal-oriented iterative cycle of experiments on one hand and mathematical modeling combined with Monte Carlo simulations on the other. This integrative approach lends valuable insight into the detailed kinetics of bacterium-phage interactions. We measured time-dependent changes in host viability during the growth of phage D29 in M. smegmatis at different multiplicities of infection (MOI). The predictions emerging out of theoretical analyses were further examined using biochemical and cell biological assays. In a phage-host interaction system where multiple rounds of infection are allowed to take place, cell counts drop more rapidly than expected if cell lysis is considered the only mechanism for cell death. The phenomenon could be explained by considering a secondary factor for cell death in addition to lysis. Further investigations reveal that phage infection leads to the increased production of superoxide radicals, which appears to be the secondary factor. Therefore, mycobacteriophage D29 can function as an effective antimycobacterial agent, the killing potential of which may be amplified through secondary mechanisms.

Antimycobacterial potential of Mycobacteriophage under disease-mimicking conditions

“…To determine the time it takes for OD of bacterial cultures to start reducing after phage addition, we took OD readings every 15-20 mins. We found that OD of the bacterial cultures starts to drop only after 120-150 mins (Supplementary Figure S4) which is consistent with the previously reported latency period of D29 (~60 min) (Samaddar et al, 2015; Bavda and Jain, 2020) and PDRPxv (~135 min) in M smegmatis (Sinha et al, 2020).…”

“…For phage therapy to be successful and efficient against mycobacterial infections, the phages need to retain their infectious activity in these extreme environments and infect non-replicative stationary phase bacteria. D29 is a well-known phage against M. tuberculosis known to produce superoxide radicals in oxygen-rich environments, which synergizes with phage mediated lysis to accelerate the killing of Mycobacterium (Samaddar et al, 2016). However, it is observed to be ineffective in hypoxic conditions (Swift et al, 2014).…”

Topologically Inspired Walks on Randomly Connected Landscapes With Correlated Fitness

“…A major aspect of network science is the intricate role of topology, as quantified by various metrics [39][40][41][42], which plays a prime part in the characterization, design and functioning of such systems. However, while networks have been used in a variety of biological problems [43][44][45][46][47][48], they have seen only limited application [4,5] in fitness landscapes and adaptive walks on them.…”

The Global Reciprocal Reprogramming between Mycobacteriophage SWU1 and Mycobacterium Reveals the Molecular Strategy of Subversion and Promotion of Phage Infection

“…Bacteriophages, the viruses of bacteria with an estimated size of 10 31 in the biosphere (Whitman et al, 1998 ), represent an enormous resource for biomedicine and biotechnology, as seen by the growing interest in their therapeutic and food safety applications (García et al, 2008 ; Monk et al, 2010 ). Insights into the evolutionary arms race between phage and bacterium have revealed many new molecular machineries such as the widespread bacterial defense system called CRISPR/Cas, which in turn has inspired revolutionary genome editing tools (Barrangou et al, 2007 ), and exciting novel approaches for antimicrobials discovery (Liu et al, 2004 ; Samaddar et al, 2016 ). Well-characterized bacteria hosts,including Escherichia coli, Salmonella typhimirium , and Bacillus subtilis , have made significant contribution to the understanding of factors essential for phage replication, assembly, and lysis (Young, 2013 ; Sun et al, 2014 ).…”