The copy number of plasmids in bacteria is influenced by a variety of factors that can be broadly categorized into those related to the plasmid itself, the host cell, and the external environment. Here are some key factors that govern plasmid copy numbers:

1. Plasmid Origin oflication (ori): The ori sequence is crucial for the initiation of plasmid replication. Different ori sequences can lead to high or low copy numbers. Plasmids like ColE1 have a high copy number, while others are designed to a low copy number. The interactions of various proteins with the sequence, like those in the ColE1 RNA I and RNA II system, are vital in regulating the copy number.

2. Size of the Plasmid: Larger plasmids are typically replicated frequently than smaller ones because they impose a more significant metabolic burden the host cell. The energy and resources required to duplicate large plasmids can affect the cell's growth and division.

3. Plasmid Partitioning Mechanisms: Certain plasmids carry genes that ensure equal plasmid segregation during cell division, affecting overall copy number stability.

. Plasmid-Coded Regulatory Elements: Repressors antirepressors, and other regulatory proteins encoded by the plasmid itself can influence its copy number by interacting with the ori or other control sequences.

5. Host Factors: The type of bacterial strain can affect plasmid replication. Some hosts may provide proteins that influence plasmid copy number, or they might have a higher metabolic capacity to support higher copy numbers.

6. Nutritional and Environmental Conditions: Nutritional status and environmental factors such as temperature, pH, and the presence of certain chemicals or antibiotics can affect plasmid replication enzymes and, consequently, plasmid copy number.

7. Interactions with Other Plasmids: The presence of other compatible or incompatible plasmids within the same host can result in copy number control through competition or cross-regulation.

As for the dependence on bacterial size, the notion of size here typically refers to the bacterial cell volume rather than physical dimensions. The copy number of a plasmid is not directly dependent on the size of the bacterial cell; however, the metabolic capacity and the biological constraints of the machinery could potentially influence how well a cell can accommodate and replicate multiple plasmid copies. Larger bacterial cells may have more resources and space to distribute multiple plasmid copies, but the relationship is not a direct one, given that plasmid replication is primarily a function of the aforementioned factors.