Abstract
Many strains of Acinetobacter baumannii have been described as being able to form biofilm. Small non-coding RNAs (sRNAs) control gene expression in many regulatory circuits in bacteria. The aim of the present work was to provide a global description of the sRNAs produced both by planktonic and biofilm-associated (sessile) cells of A. baumannii ATCC 17978, and to compare the corresponding gene expression profiles to identify sRNAs molecules associated to biofilm formation and virulence. sRNA was extracted from both planktonic and sessile cells and reverse transcribed. cDNA was subjected to 454-pyrosequencing using the GS-FLX Titanium chemistry. The global analysis of the small RNA transcriptome revealed different sRNA expression patterns in planktonic and biofilm associated cells, with some of the transcripts only expressed or repressed in sessile bacteria. A total of 255 sRNAs were detected, with 185 of them differentially expressed in the different types of cells. A total of 9 sRNAs were expressed only in biofilm cells, while the expression of other 21 coding regions were repressed only in biofilm cells. Strikingly, the expression level of the sRNA 13573 was 120 times higher in biofilms than in planktonic cells, an observation that prompted us to further investigate the biological role of this non-coding transcript. Analyses of an isogenic mutant and over-expressing strains revealed that the sRNA 13573 gene is involved in biofilm formation and attachment to A549 human alveolar epithelial cells. The present work serves as a basis for future studies examining the complex regulatory network that regulate biofilm biogenesis and attachment to eukaryotic cells in A. baumannii ATCC 17978.
Highlights
Acinetobacter baumannii is a non-fermentative, oxidase negative and non-flagellated Gramnegative bacillus
Little is known about the involvement of small noncoding RNA transcripts in controlling biofilm formation. sRNA molecules serve a wide range of regulatory functions in bacteria and modulate almost every aspect of cell metabolism [25,26,27,28,29,30,31,32]
RNA regulators usually act at a level complementary to protein regulators, most often functioning at the post-transcriptional level as opposed to transcription factors that act before sRNAs or enzymes such as kinases or proteases that act after sRNAs
Summary
Acinetobacter baumannii is a non-fermentative, oxidase negative and non-flagellated Gramnegative bacillus. Since biofilm formation on abiotic surfaces contributes to the unique survival pattern of A. baumannii in hospital settings, several studies have focused on the description of the proteins and genes involved in the adoption of that lifestyle. Little is known about the involvement of small noncoding RNA transcripts (sRNAs) in controlling biofilm formation. Regulatory RNAs may control gene expression by a variety of mechanisms, including the modulation of transcription, translation, mRNA stability and DNA maintenance or silencing, most of the studied small RNA regulators act through base pairing with particular RNA targets, usually affecting the translation and stability of mRNAs. many sRNAs have been described as involved in the regulation of important bacterial survival responses [30]. Sharma et al [56] identified novel
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