Abstract: Describe is a method for screening mutant prokaryotic cells to identify producers of a cytotoxic agent active against a target cell, the method comprising the steps of: (a) providing cells of a producer prokaryotic species; (b) generating a pool of mutant producer cells by transposon mutagenesis of the cells of step (a) with an activating transposon (TnA), wherein the TnA comprises an outward-facing promoter (TnAP) capable of increasing transcription of a gene at or near its insertion site in the DNA of said producer cells; (c) co-encapsulating individual members of the pool of step (b) with one or more target cells in microdroplets, the microdroplets comprising a volume of aqueous growth media suspended in an immiscible carrier liquid, thereby generating a library of microdroplets each comprising a single mutant producer cell and one or more target cell(s); (d) incubating the microdroplet library of step (c) under conditions suitable for co-culture of the single mutant producer cell and target cell(s) to pro

Abstract: Described is a process for producing a mutant bacterium which exhibits improved survival and/or growth under a selected growth condition, the process comprising the steps of: (a) generating a pool of mutant bacteria by transposon mutagenesis with an activating transposon (TnA), wherein the TnA comprises a promoter capable of increasing transcription of a gene at or near its insertion site; (b) growing bacteria from the mutant pool under the selected growth condition and under one or more reference conditions to produce two or more test cultures; and (c) comparing the distribution of TnA insertions between test cultures to identify a first class of genes which are disadvantageous for growth and/or survival under the selected growth condition and a second class of genes which are advantageous for growth and/or survival under the selected growth condition.