Module 4: Buoyancy

Description

The Buoyancy Module is key to both the degradation and the island formation systems. Buoyancy is required to position our bacteria in the water column, and also to enable them to buoy the plastic aggregates (Module 2).

This module requires driving the expression of a cluster of gas vesicle genes. Gas vesicles are formed within the cell, and are hollow spaces surrounding by a wall of hydrophobic protein. These gas vesicles are permeable to gases, which enter and inflate the vesicles to increase buoyancy. The gas vesicle system is driven by a constitutive Heat Shock Promoter BBa k338001 to ensure a constant drive for buoyancy.

While the promoter is constitutive, there is a gradient of activation which allows us to control the transcription of gas vesicle genes at different depths. The heat shock promoter in our system is activated in response to increases in ambient temperature. However we want to couple increases in temperature this to down regulation of Gas Vesicle formation, and so we will introduce a repressor between the Heat Shock Promoter and the Gas Vesicle cluster. Activation of Heat Shock Promoter, triggers expression of the repressor protein tetR, which binds and repressors the promoter p(TetR). p(TetR) is the promoter driving constitutive gas vesicle formation, and so activation of the repressor system down regulates gas vesicle formation.