Herbaspirilum seropedicae is an endophytic diazotroph, which associates with important agricultural crops without causing disease. The Paraná State Genome Program (GENOPAR) has sequenced the genome of this bacterium. Sequence analysis indicated the presence of genes homologous to the Type Three Secretion System (TTSS) clustered in approximately 30 kb region. This region has a C+G content and a codon bias usage similar to that of the whole genome. In addition, tRNA genes or insertion sequences were not found in the flanking regions. The TTSS secretes bacterial protein effectors into the eukaryotic cells and it has been associated with the establishment of both pathogenic and symbiotic relation between bacteria and eukaryotic organisms. The region of the H. seropedicae genome coding for the putative TTSS contains 14 orfs similar to hrp/hrc genes, 2 pil-like genes and 15 hypothetic conserved genes. A possible regulator gene was also found: a hrpL-like gene, which codes for a putative s^E-type factor of the RNA polymerase. Furthermore, a hrpG-like gene, which codes for a possible transcriptional activator protein of the TTSS was found outside of the main cluster. The hrcV gene of H. seropedicae was knocked out by antibiotic resistance cassette insertion and the growth phenotype of mutant strain (ASD1) was analyzed. There was not an evident phenotype for when growing in liquid or solid medium, indicating that hrcV gene is not essential in those conditions.