Amazing stuff!
"... Without defense mechanisms, Synechococcus would likely have become extinct because of the threats it faces from bacteriophages like Syn9. ... study describes an evolutionary scenario where protection arises from a reduced level of tRNA (transfer RNA), a molecule critical for gene translation.
“Studies on resistance often focus on genes providing active defense against infection,” ... “However, not all defenses stem from active mechanisms; some, like the one we discovered, arise from ‘passive resistance.’ Our findings show that normal tRNA level reduce bacterial resistance to the virus, while low levels increase such resistance. This is a passive mode of resistance where the loss of a certain intracellular function leads to resistance against viral infection.” ...
This phenomenon of passive resistance, the researchers suggest, is likely more widespread than previously thought and not limited to Synechococcus-Syn9 interactions."
"... that this mechanism does not prevent the phage from entering the bacterial cell but halts the formation of new viruses, allowing the bacteria to survive. ..."
From the abstract:
"Synechococcus is a significant primary producer in the oceans, coexisting with cyanophages, which are important agents of mortality. Bacterial resistance against phage infection is a topic of significant interest, yet little is known for ecologically relevant systems.
Here we use exogenous gene expression and gene disruption to investigate mechanisms underlying intracellular resistance of marine Synechococcus WH5701 to the Syn9 cyanophage. The restriction–modification and Gabija defence systems possessed by Synechococcus WH5701 did not contribute to resistance. Instead, resistance was primarily driven by insufficient levels of LeuTAA tRNA, preventing translation of key phage genes in a passive, intracellular mode of resistance.
Restoring cellular tRNA expression rendered the cyanobacterium sensitive to infection. We propose an evolutionary scenario whereby changes in cell codon usage, acquisition of tRNAs by the phage and loss of cell and phage tRNA expression resulted in an effective means of resistance, highlighting the dynamic interplay between bacteria and phages in shaping their co-evolutionary trajectories."
Protection Against Viruses – The Passive Version "Researchers at the Technion Faculty of Biology have discovered a unique mechanism that protects marine bacteria from viruses that attack them"
Adaptive loss of tRNA gene expression leads to phage resistance in a marine Synechococcus cyanobacterium (open access)
Fig. 1: The effect of known defence system genes on the sensitivity of Synechococcus WH5701 to the Syn9 phage.
Extended Data Fig. 3: Relevance of tRNA ValTAC for phage sensitivity.
The first author Sofia Zborovsky
The senior author Debbie Lindell
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