MucR is necessary for galactoglucan production in Sinorhizobium meliloti EFB1

Thermal adaptation of acetic acid bacteria for practical high-temperature vinegar fermentation

Thermotolerant microorganisms are useful for high-temperature fermentation. Several thermally adapted strains were previously obtained from Acetobacter pasteurianus in a nutrient-rich culture medium, while these adapted strains could not grow well at high temperature in the nutrient-poor practical culture medium, "rice moromi." In this study, A. pasteurianus K-1034 originally capable of performing acetic acid fermentation in rice moromi was thermally adapted by experimental evolution using a "pseudo" rice moromi culture. The adapted strains thus obtained were confirmed to grow well in such the nutrient-poor media in flask or jar-fermentor culture up to 40 or 39 °C; the mutation sites of the strains were also determined. The high-temperature fermentation ability was also shown to be comparable with a low-nutrient adapted strain previously obtained. Using the practical fermentation system, "Acetofermenter," acetic acid production was compared in the moromi culture; the results showed that the adapted strains efficiently perform practical vinegar production under high-temperature conditions.

Structural Insight of the Full-Length Ros Protein: A Prototype of the Prokaryotic Zinc-Finger Family

Ros/MucR is a widespread family of bacterial zinc-finger (ZF) containing proteins that integrate multiple functions such as virulence, symbiosis and/or cell cycle transcription. NMR solution structure of Ros DNA-binding domain (region 56–142, i.e. Ros87) has been solved by our group and shows that the prokaryotic ZF domain shows interesting structural and functional features that differentiate it from its eukaryotic counterpart as it folds in a significantly larger zinc-binding globular domain. We have recently proposed a novel functional model for this family of proteins suggesting that they may act as H-NS-‘like’ gene silencers. Indeed, the N-terminal region of this family of proteins appears to be responsible for the formation of functional oligomers. No structural characterization of the Ros N-terminal domain (region 1–55) is available to date, mainly because of serious solubility problems of the full-length protein. Here we report the first structural characterization of the N-terminal domain of the prokaryotic ZF family examining by means of MD and NMR the structural preferences of the full-length Ros protein from Agrobacterium tumefaciens.

The prokaryotic zinc-finger: structure, function and comparison with the eukaryotic counterpart

Classical zinc finger (ZF) domains were thought to be confined to the eukaryotic kingdom until the transcriptional regulator Ros protein was identified in Agrobacterium tumefaciens. The Ros Cys2 His2 ZF binds DNA in a peculiar mode and folds in a domain significantly larger than its eukaryotic counterpart consisting of 58 amino acids (the 9-66 region) arranged in a βββαα topology, and stabilized by a conserved, extensive, 15-residue hydrophobic core. The prokaryotic ZF domain, then, shows some intriguing new features that make it interestingly different from its eukaryotic counterpart. This review will focus on the prokaryotic ZFs, summarizing and discussing differences and analogies with the eukaryotic domains and providing important insights into their structure/function relationships.

Versatility of global transcriptional regulators in alpha-Proteobacteria: from essential cell cycle control to ancillary functions

Recent data indicate that cell cycle transcription in many alpha-Proteobacteria is executed by at least three conserved functional modules in which pairs of antagonistic regulators act jointly, rather than in isolation, to control transcription in S-, G2- or G1-phase. Inactivation of module components often results in pleiotropic defects, ranging from cell death and impaired cell division to fairly benign deficiencies in motility. Expression of module components can follow systemic (cell cycle) or external (nutritional/cell density) cues and may be implemented by auto-regulation, ancillary regulators or other (unknown) mechanisms. Here, we highlight the recent progress in understanding the molecular events and the genetic relationships of the module components in environmental, pathogenic and/or symbiotic alpha-proteobacterial genera. Additionally, we take advantage of the recent genome-wide transcriptional analyses performed in the model alpha-Proteobacterium Caulobacter crescentus to illustrate the complexity of the interactions of the global regulators at selected cell cycle-regulated promoters and we detail the consequences of (mis-)expression when the regulators are absent. This review thus provides the first detailed mechanistic framework for understanding orthologous operational principles acting on cell cycle-regulated promoters in other alpha-Proteobacteria.

The Rhizobium leguminosarum bv. trifolii RosR: transcriptional regulator involved in exopolysaccharide production

The acidic exopolysaccharide is required for the establishment of symbiosis between the nitrogen-fixing bacterium Rhizobium leguminosarum bv. trifolii and clover. Here, we describe RosR protein from R. leguminosarum bv. trifolii 24.2, a homolog of transcriptional regulators belonging to the family of Ros/MucR proteins. R. leguminosarum bv. trifolii RosR possesses a characteristic Cys2His2 type zinc-finger motif in its C-terminal domain. Recombinant (His)6RosR binds to an RosR-box sequence located up-stream of rosR. Deletion analysis of the rosR upstream region resulted in identification of two -35 to -10 promoter sequences, two conserved inverted palindromic pentamers that resemble the cAMP-CRP binding site of Escherichia coli, inverted repeats identified as a RosR binding site, and other regulatory sequence motifs. When assayed in E. coli, a transcriptional fusion of the cAMP-CRP binding site containing the rosR upstream region and lacZ gene was moderately responsive to glucose. The sensitivity of the rosR promoter to glucose was not observed in E. coli deltacyaA. A rosR frame-shift mutant of R. leguminosarum bv. trifolii formed dry, wrinkled colonies and induced nodules on clover, but did not fix nitrogen. In the rosR mutant, transcription of pssA-lacZ fusion was decreased, indicating positive regulation of the pssA gene by RosR. Multiple copies of rosR in R. leguminosarum bv. trifolii 24.2 increased exopolysaccharide production.

Determination of genetic differences between fluid and nonfluid variants of Clavibacter michiganensis subsp. sepedonicus using rep-PCR technique

Testing of 23 isolates of Clavibacter michiganensis subsp. sepedonicus for analysis by rep-PCR (using BOX, ERIC, REP primer sets) was used for the purpose of localization of genetic markers for fluid and/or nonfluid strains. None of the primer sets was successful in detecting genetic differences between the isolates and no polymorphism was generated.

MucR and mucS activate exp genes transcription and galactoglucan production in Sinorhizobium meliloti EFB1

When grown under standard conditions, Sinorhizobium meliloti EFB1 simultaneously produces two acidic exopolysaccharides, succinoglycan and galactoglucan, yielding very mucoid colonies. In this strain, MucR is essential for galactoglucan synthesis. A mutation in the mucS gene resulted in less mucoid colonies than in the wild-type EFB1. This mucS- strain was complemented to the wild-type phenotype by the cloned mucS gene, indicating that mucS is necessary for a wild-type level of galactoglucan production. Reverse transcription-polymerase chain reaction analysis of exp genes, which encode the pathway for galactoglucan production, in EFB1 and in the mutants affected in mucS, mucR, and both genes simultaneously, showed that MucS is a transcriptional activator of the exp genes but does not affect its own transcription. Furthermore, MucR is necessary for mucS transcriptional activation. As introduction of a cloned mucS gene in a mucR- strain yielded colonies less mucoid than the wild type, MucR could also activate exp genes transcription through other pathways. Deletion analysis of the expE promoter showed a region important for transcription and MucS activation. This region, containing a palindrome, is present in the putative expA, expC, expD, and expE promoters but not in the mucS promoter, suggesting that it is the target for MucS. A mucR-mucS- mutant, which does not produce galactoglucan, was impaired in competitive nodulation of alfalfa in soil microcosms, indicating another possible role for this exopolysaccharide in symbiosis.

PCR use of highly conserved DNA regions for identification of Sinorhizobium meliloti

A PCR identification method in which four primers that recognize homologous conserved regions in the Sinorhizobium meliloti genome are used was developed and tested. The regions used for identification were the nodbox 4 locus, which is located in one of the symbiotic megaplasmids, and the mucR gene, which is located in the chromosome. The new method was used to establish a collection of S. meliloti strains from polluted soils.