1*Dong-A Univ, Busan 604-714, Republic of Korea*
Ralstonia solanacarum is a devastating plant pathogenic bacterium causing lethal wilt in members of solanceaous plants. In a stationary phase, R. solanacearum wild type produced brown pigment and much faster when supplemented with tyrosine, suggesting melanin-like pigment production. To identify genes responsible for melanin-like pigment production and its regulation in R. solanacearum, Tn5 transposon-inserted mutant library was screened in a liquid medium containing tyrosine. We selected 7 different kinds of low or non-producing mutant of the pigment in comparison to wild type strain. One of the mutants with hppd gene disruption indicated that R. solanacearum produces pyomelanin. In addition, mutations on several genes encoding regulatory proteins also abolished pigmentation, indicating that elaborate regulatory system controls melanin production in R. solanacearum. The expression level of each disrupted genes was monitored in wild type over time using RT-PCR. However, we could not observe any significant difference of gene expression at transcriptional level. To investigate the protein expression related to the tyrosine metabolic pathway under different mutational background, we conducted instrumental analysis to check the degree of tyrosine degradation or intermediate formation in melanin biosynthetic pathway. HPLC analysis under different regulatory mutation background provide an interesting insight for regulation of melanin-like pigment production.