Recovery of low-copy plasmids is always reduced compared to high-copy plasmids. Ensuring the culture is grown with proper aeration and harvested before significant cell lysis occurs will increase the number of intact cells harboring the plasmid. Using more cells can compensate for some of the deficiency but stay within the supplied guidelines to ensure alkaline lysis is efficient and the column is not overloaded with cellular components. Please also review our guidelines for working with low-copy plasmids and our application note on removing genomic DNA when working with low-copy plasmids.