Most proteins comprise one or several domains. New domain architectures can be 
created by combining previously existing domains. The elementary events that 
create new domain architectures may be categorized into three classes, namely 
domain(s) insertion or deletion (indel), exchange and repetition. Using 
'DomainTeam', a tool dedicated to the search for microsyntenies of domains, we 
quantified the relative contribution of these events. This tool allowed us to 
collect homologous bacterial genes encoding proteins that have obviously evolved 
by modular assembly of domains. We show that indels are the most frequent 
elementary events and that they occur in most cases at either the N- or 
C-terminus of the proteins. As revealed by the genomic neighbourhood/context of 
the corresponding genes, we show that a substantial number of these terminal 
indels are the consequence of gene fusions/fissions. We provide evidence showing 
that the contribution of gene fusion/fission to the evolution of multi-domain 
bacterial proteins is lower-bounded by 27% and upper-bounded by 64%. We conclude 
that gene fusion/fission is a major contributor to the evolution of multi-domain 
bacterial proteins.