A biological system for diminishing cell growth or inducing selective killing of target cells, such as pathogenic bacterial or fungal cells, or cancer cells, comprising a vehicle with a first nucleic acid sequence or amino acid sequence encoding for a prokaryotic toxin of a prokaryotic toxin-antitoxin pair, and a second nucleic acid sequence or amino acid sequence encoding for the corresponding prokaryotic antitoxin of the prokaryotic toxin-antitoxin pair, characterized in that the toxin and/or the antitoxin is operably linked to a protein output modifier that comprises a nucleic acid sequence or amino acid sequence that modifies the relative rate of transcription, mRNA stability, mRNA translatability or protein stability of the toxin and/or antitoxin thereby changing the relative ratio in the concentration of the toxin and/or the antitoxin within the target cells and/or, where applicable, within non-target cells (i) by decreasing the antitoxin outputs in the target cells relative to their toxin outputs in said target cells, and/or (ii) by decreasing the toxin outputs in the non-target cells relative to their antitoxin outputs in said non-target cells, (iii) by increasing the antitoxin outputs in the non-target cells relative to their toxin outputs in said non-target cells, and/or (iv) by increasing the toxin outputs in the target cells relative to their antitoxin outputs in said target cells, wherein in the target cells the activity of the antitoxin is decreased relative to the activity of the toxin, wherein in the non-target cells the activity of the toxin is decreased relative to the activity of the antitoxin, and wherein the protein output modifier is selected from the group consisting of promoter/operator sequences, miRNA target sites, 3'-UTRs, ubiquitin ligase target domains, or a protein domain that is tagged for degradation by a proteosome. (i) by decreasing the antitoxin outputs in the target cells relative to their toxin outputs in said target cells, and/or (ii) by decreasing the toxin outputs in the non-target cells relative to their antitoxin outputs in said non-target cells, (iii) by increasing the antitoxin outputs in the non-target cells relative to their toxin outputs in said non-target cells, and/or (iv) by increasing the toxin outputs in the target cells relative to their antitoxin outputs in said target cells, wherein in the target cells the activity of the antitoxin is decreased relative to the activity of the toxin, wherein in the non-target cells the activity of the toxin is decreased relative to the activity of the antitoxin, and wherein the protein output modifier is selected from the group consisting of promoter/operator sequences, miRNA target sites, 3'-UTRs, ubiquitin ligase target domains, or a protein domain that is tagged for degradation by a proteosome. wherein in the target cells the activity of the antitoxin is decreased relative to the activity of the toxin, wherein in the non-target cells the activity of the toxin is decreased relative to the activity of the antitoxin, and wherein the protein output modifier is selected from the group consisting of promoter/operator sequences, miRNA target sites, 3'-UTRs, ubiquitin ligase target domains, or a protein domain that is tagged for degradation by a proteosome.