The invention relates to the growth temperature of organisms, especially plants and microorganisms and the manipulation of the tolerable cultivation temperature. More specifically, the present invention relates to the expression of heterologous proteins in microorganisms, and especially to the heterologous expression of heat sensitive proteins in bacteria, either gram-negative or gram-positive. In a first aspect, the present invention provides a method for manipulation of cells and the resultant cells, wherein at least one gene from a psychrophilic micro organism coding for at least one chaperone or chaperonin is expressed. Such cells are selected among cultivated eukaryotic cells, i.e. animal and plant cells and entire plants, gram-negative and gram-positive bacteria, fungi and yeasts.