Final answer:
Bacteria defend against bacteriophage infections using restriction-modification systems, mutations that confer resistance, and antigenic variation. While they lack direct defense mechanisms against toxic proteins from the lytic cycle of phages, their other defenses help them survive phage attacks.
Step-by-step explanation:
In the context of bacteriophage lambda and the lytic and lysogenic cycles, bacteria do not have immune responses involving T/B cells as higher organisms do. Instead, their defense mechanisms are more rudimentary. Although the CRISPR systems in bacteria defend primarily against viral nucleic acids rather than proteins, bacteria can still combat phage infections through several means.
For instance, one defense mechanism is the restriction-modification system, where bacteria produce enzymes known as restriction endonucleases that cut viral DNA at specific sequences. Bacterial cells modify their own DNA to prevent it from being cut, thereby protecting against bacteriophage DNA but not proteins directly. Additionally, bacteria can indeed undergo mutations that result in a resistance to phages, including the production of proteins that can block phage assembly or attachment.
Another mechanism bacteria use is antigenic variation, which helps to evade recognition by altering their surface proteins. While not directly a defense against bacteriophages, bacteria such as Neisseria gonorrhoeae use antigenic variation to avoid immune defenses, demonstrating bacteria's capability to adapt surface proteins to avoid hostile interactions, which could theoretically be applied in defense against phages to some extent.
In conclusion, while bacteria do not have a direct defense against toxic proteins produced during the phage's lytic cycle, their other defense mechanisms against phage infection indirectly contribute to their survival against lytic phages.