What are the common methods for bacterial transformation?

Common bacterial transformation methods include: heat shock transformation where chemically competent cells (treated with CaCl2 or other salts) take up DNA after brief heat treatment (42C for 30-90 seconds); electroporation where electric pulses create transient membrane pores allowing DNA entry, achieving higher efficiency (~10^10 cfu/ug); and natural competence in some species that can naturally take up environmental DNA. Selection on antibiotic plates identifies transformed cells. Efficiency depends on cell competence, DNA purity and concentration, and technique. Electroporation is preferred for difficult-to-transform strains or when high efficiency is needed.