Dataset Information

Analysis of two polyhydroxyalkanoate synthases in Bradyrhizobium japonicum USDA 110.

ABSTRACT: Bradyrhizobium japonicum USDA 110 has five polyhydroxyalkanoate (PHA) synthases (PhaC) annotated in its genome: bll4360 (phaC1), bll6073 (phaC2), blr3732 (phaC3), blr2885 (phaC4), and bll4548 (phaC5). All these proteins possess the catalytic triad and conserved amino acid residues of polyester synthases and are distributed into four different PhaC classes. We obtained mutants in each of these paralogs and analyzed phaC gene expression and PHA production in liquid cultures. Despite the genetic redundancy, only phaC1 and phaC2 were expressed at significant rates, while PHA accumulation in stationary-phase cultures was impaired only in the ?phaC1 mutant. Meanwhile, the ?phaC2 mutant produced more PHA than the wild type under this condition, and surprisingly, the phaC3 transcript increased in the ?phaC2 background. A double mutant, the ?phaC2 ?phaC3 mutant, consistently accumulated less PHA than the ?phaC2 mutant. PHA accumulation in nodule bacteroids followed a pattern similar to that seen in liquid cultures, being prevented in the ?phaC1 mutant and increased in the ?phaC2 mutant in relation to the level in the wild type. Therefore, we used these mutants, together with a ?phaC1 ?phaC2 double mutant, to study the B. japonicum PHA requirements for survival, competition for nodulation, and plant growth promotion. All mutants, as well as the wild type, survived for 60 days in a carbon-free medium, regardless of their initial PHA contents. When competing for nodulation against the wild type in a 1:1 proportion, the ?phaC1 and ?phaC1 ?phaC2 mutants occupied only 13 to 15% of the nodules, while the ?phaC2 mutant occupied 81%, suggesting that the PHA polymer is required for successful competitiveness. However, the bacteroid content of PHA did not affect the shoot dry weight accumulation.

SUBMITTER: Quelas JI

PROVIDER: S-EPMC3697631 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature

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Analysis of two polyhydroxyalkanoate synthases in Bradyrhizobium japonicum USDA 110.

Quelas J Ignacio JI Mongiardini Elías J EJ Pérez-Giménez Julieta J Parisi Gustavo G Lodeiro Aníbal R AR

Journal of bacteriology 20130510 14

Bradyrhizobium japonicum USDA 110 has five polyhydroxyalkanoate (PHA) synthases (PhaC) annotated in its genome: bll4360 (phaC1), bll6073 (phaC2), blr3732 (phaC3), blr2885 (phaC4), and bll4548 (phaC5). All these proteins possess the catalytic triad and conserved amino acid residues of polyester synthases and are distributed into four different PhaC classes. We obtained mutants in each of these paralogs and analyzed phaC gene expression and PHA production in liquid cultures. Despite the genetic re ...[more]

PMID: 23667236

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Project description:Small open reading frames (sORFs) and genes for non-coding RNAs are poorly investigated components of most genomes. Our analysis of 1391 ORFs recently annotated in the soybean symbiont Bradyrhizobium japonicum USDA 110 revealed that 78% of them contain less than 80 codons. Twenty-one of these sORFs are conserved in or outside Alphaproteobacteria and most of them are similar to genes found in transposable elements, in line with their broad distribution. Stabilizing selection was demonstrated for sORFs with proteomic evidence and bll1319_ISGA which is conserved at the nucleotide level in 16 alphaproteobacterial species, 79 species from other taxa and 49 other Proteobacteria. Further we used Northern blot hybridization to validate ten small RNAs (BjsR1 to BjsR10) belonging to new RNA families. We found that BjsR1 and BjsR3 have homologs outside the genus Bradyrhizobium, and BjsR5, BjsR6, BjsR7, and BjsR10 have up to four imperfect copies in Bradyrhizobium genomes. BjsR8, BjsR9, and BjsR10 are present exclusively in nodules, while the other sRNAs are also expressed in liquid cultures. We also found that the level of BjsR4 decreases after exposure to tellurite and iron, and this down-regulation contributes to survival under high iron conditions. Analysis of additional small RNAs overlapping with 3'-UTRs revealed two new repetitive elements named Br-REP1 and Br-REP2. These REP elements may play roles in the genomic plasticity and gene regulation and could be useful for strain identification by PCR-fingerprinting. Furthermore, we studied two potential toxin genes in the symbiotic island and confirmed toxicity of the yhaV homolog bll1687 but not of the newly annotated higB homolog blr0229_ISGA in E. coli. Finally, we revealed transcription interference resulting in an antisense RNA complementary to blr1853, a gene induced in symbiosis. The presented results expand our knowledge on sORFs, non-coding RNAs and repetitive elements in B. japonicum and related bacteria.

Project description:B. japonicum cells were grown either in minimal medium (BVM) with L-arabinose as carbon and energy source or in complete medium (PSY) containing L-arabinose. Proteins extracted from three replicates of B. japonicum cells grown in complex and minimal medium with L-arabinose until mid-exponential phase were separated on a Tris-HCl polyacrylamide gel. After reduction and carbamidomethylation, the proteins were digested with trypsin (Promega, Madison, WI, USA), and the resulting peptides were separated by RP-HPLC and analyzed by a hybrid LTQ-Orbitrap XL mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) interfaced with a nanoelectrospray source. Mass spectra were further processed with an in-house processing pipeline. A total of 3,390 and 3,149 proteins were identified in complex and minimal medium respectively. We identified highly expressed products of candidate genes involved in the degradation of arabinose and suggest that glycolaldehyde is oxidized to glyoxylate and then reduced to glycerate through a glyoxylate carboligase and a tartronate semialdehyde reductase for assimilation and/or converted to oxalate and then oxidized to formate and CO2 through a formyl-CoA transferase (Frc) and an oxalyl-CoA decarboxylase (Oxc) for energy generation. Fragment ion mass spectra were extracted from Thermo RAW files using msconvert (ProteoWizard, version 3.0.3831), merged in one MGF file per gel and searched against a composite B. japonicum USDA 110 protein database (RefSeq NC_004463.1, July 22, 2013) containing 256 common contaminants (e.g. human keratin, trypsin) with the search engine MS-GF+ (MS-GFDB v7747) for a match to fully-tryptic and semi-tryptic peptides with up to two missed cleavage sites with a mass tolerance of 25ppm and with oxidation (M), deamidation (NQ), methylation (DE) as variable modifications and carbamidomethylation (C) as fixed modification. Using the decoy option of MS-GF+, we filtered the list of peptide spectrum matches (PSMs) to an estimated overall FDR of 0.2%, classified the PSMs with PeptideClassifier, and only further considered peptides (tryptic or semi-tryptic) that unambiguously imply one bacterial protein sequence. The FDR at the peptide level amounted to about 1.5%, that at the protein level to about 2.5% when requiring two peptides or three spectra for a protein identification.

Dataset Information

Analysis of two polyhydroxyalkanoate synthases in Bradyrhizobium japonicum USDA 110.

Publications

Analysis of two polyhydroxyalkanoate synthases in Bradyrhizobium japonicum USDA 110.

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