Regulation of polyhydroxybutyrate accumulation in Sinorhizobium meliloti by the trans-encoded small RNA MmgR

ANTONIO LAGARES (H); GERMÁN CEIZEL BORELLA; UWE LINNE; ANKE BECKER; CLAUDIO VALVERDE

JOURNAL OF BACTERIOLOGY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2017 vol. 199 p. 1 - 17

0021-9193

Riboregulation has a major role in the fine-tuning ofmultiple bacterial processes. Among the RNA players, trans-encoded untranslated small RNAs (sRNAs) regulate complexmetabolic networks by tuning expression from multiple target genes in responseto numerous signals. In Sinorhizobium meliloti,over 400 sRNAs are expressed under different stimuli. The sRNA MmgR?standing for Makes more granules Regulator?has been of particularinterest to us since its sequence and structure are highly conserved among theα-proteobacteria, and its expression is regulated by the amount and quality ofthe bacterium?s available nitrogen source. In this work, we explored thebiological role of MmgR in S. meliloti2011 by characterizing the effect of a deletion of the internal conserved coreof mmgR (mmgRΔ33-51).This mutation resulted in higher amounts ofpolyhydroxybutyrate (PHB) distributed into more intracellular granules than arefound in the wild-type strain. This phenotype was expressed upon cessation ofbalanced growth owing to a nitrogen depletion in the presence of surplus carbon(i. e., at a carbon:nitrogen molarratio greater than 10). The normal PHB accumulation was complemented with awild-type mmgR copy, but not withunrelated sRNA genes. Furthermore, the expression of mmgR limited PHB accumulation in the wild-type, regardless of themagnitude of the C surplus. Quantitative proteomic profiling and qRT-PCRrevealed that the absence of MmgR results in a posttranscriptionaloverexpression of both PHB-phasin proteins (PhaP1, PhaP2). All together, ourresults indicate that the widely conserved α-proteobacterial MmgR sRNAfine-tunes the regulation of PHB storage in S.meliloti.