A mutation is made in dna polymerase such that it loses its

Question

A mutation is made in DNA polymerase such that it loses its 3'-5' editing ability (DnaQ activity). If you perform a viable plate count on these cells when they are fully grown, you get the following data:

Strain type VPC (CFU/ml) OD₆₀₀

Wild type 1.25 x 10⁹ 1.44

Mutant in dnaQ 1.25 x 10⁸ 1.43

Can you explain this phenomenon? It should take only a sentence or two to do so.