Hierarchical involvement of various GGDEF domain proteins in rdar morphotype development of Salmonella enterica serovar Typhimurium

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Abstract
GGDEF and EAL domain proteins are involved in the turnover of the novel secondary messenger cyclic-di(3'-->5')-guanylic acid (c-di-GMP) in many bacteria. In this work the role of the 12 GGDEF domain proteins encoded by the Salmonella enterica serovar Typhimurium (S. Typhimurium) chromosome in rdar morphotype development was investigated. Previously, it was shown that the GGDEF domain protein AdrA activated the biosynthesis of cellulose by production of c-di-GMP. Enhancement of the c-di-GMP levels by overexpression of the GGDEF domain protein AdrA did lead to the activation of curli fimbriae biosynthesis through the elevated expression of CsgD and CsgA. Although knock-out of the chromosomal copy of adrA influenced CsgA expression, CsgD expression was not altered, although more than half of the total cellular c-di-GMP was produced by AdrA at 16 h of growth. On the other hand, chromosomally encoded GGDEF-EAL domain proteins STM2123 and STM3388 were required to additively activate CsgD expression on a transcriptional and post-transcriptional level. Enhanced c-di-GMP levels did overcome temperature regulation of rdar morphotype expression by activation of curli fimbriae as well as cellulose biosynthesis through CsgD expression. Thus in the regulatory cascade leading to rdar morphotype expression c-di-GMP activates several subsequent steps in the network.