We discovered previously that the small Escherichia coli proteins Hha (hemolysin expression modulating protein) and the adjacent, poorly-characterized YbaJ are important for biofilm formation; however, their roles been nebelous. Biofilms are intricate communities in which cell signaling often converts single cells into primitive tissues. Here we show that Hha decreases biofilm formation dramatically by repressing the transcription of rare codon tRNAs which serves to inhibit fimbriae production and by repressing to some extent transcription of fimbrial genes fimA and ihfA. In vivo binding studies show Hha binds to the rare condon tRNAs argU, ileX, ileY, and proL and to two prophage clusters D1P12 and CP4-57. Real-time PCR corroborated that Hha represses argU and proL, and Hha type I fimbriae repression is abolished by the addition of biofilm dipersal due to activation of prophage lytic genes rzpD, yfiZ, appY, and alpA and due to induction of CIpP/CIpX proteases which activate toxins by degrading antitoxins. YbaJ serves to mediate the toxicity of Hha. Hence, we have identified that a single prtein (Hha) can control biofilm formation by limiting fimbriae production as well by controlling cell death. The mechanism used by Hha is the control of translation via the availability of rare condo tRANs which reduces fimbriae production and activities prophage lytic genes. Therefore, Hha acts as a toxin in cojunction with co-transcribed YbaJ (TomB) that attenuates Hha toxicity.
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