Operon of riboflavin biosynthesis in Bacillus subtilis. XVI. Localization of the ribC-group markers on the chromosome]

Regulatory markers of ribC group were located on the chromosome of Bacillus subtilis by means of genetic transformation. Markers of this group controlling the regulation of riboflavin biosynthesis were mapped between markers of resistance to acriflavin and streptomycin (strC group). The value of cotransfer index between acriflavin-resistance markers and ribC markers was found to be 26--32%. Acriflavin inhibits the riboflavin biosynthesis. The level of inhibition depends on the genotype of riboflavin-producing strains, while the inhibition of the cell growth does not depend on it.     

Supersynthesis of flavins in microorganisms and its molecular mechanism (review of the literature)

The present review discusses the significance of fundamental research into regulation of flavin biosynthesis for development of the knowledge about mechanisms of overproduction of these compounds and their manufacturing. The pathways of riboflavin, FMN and FAD biosyntheses and their regulation in some bacteria, yeasts and fungi are considered, as well as the recent advances in flavin biotechnology. The modern trends in microbial and enzymatic production of flavins are discussed.     

Operon of riboflavin biosynthesis in Bacillus subtilis. XV. A study of mutants related to the initial stages of biosynthesis. The origin of the ribityl chain of the riboflavin molecule]

The incorporation of 14C-labelled guanosine and xanthosine into riboflavin was studied. It is concluded that the ribose mojety of guanosine is converted to the ribityl side chain of riboflavin. Thus the immediate precursor of riboflavin biosynthesis is a guanosine compound. Two classes of the riboflavin-dependent mutants of Bacillus subtilis were studied. They are closely linked to the lysine markers and probably correspond to the initial steps of riboflavin biosynthesis pathway.     

核黄素参与水稻非生物胁迫响应的分析

为探究核黄素在水稻非生物胁迫响应中的作用,以粳稻Kitaake和籼稻T98B为试验材料,考察了核黄素对2种材料的盐、高温、渗透、碱和氧化胁迫响应的影响,重点测定了盐和高温胁迫下水稻体内核黄素合成基因的表达和相关生理指标。结果表明,(1)施加外源核黄素有效提高了2种水稻材料的盐和高温胁迫耐受性,降低了渗透胁迫耐受性,而其氧化和碱胁迫耐受性不受影响。(2)逆境胁迫均不同程度地促进了核黄素在2种水稻材料中的积累,尤其在盐和高温胁迫下促进效果最明显。(3)盐和高温胁迫均诱导了核黄素合成酶基因的表达,促进了核黄素的生物合成,改善了水稻的胁迫耐受性。研究表明,非生物逆境胁迫能促进核黄素在水稻体内的合成和积累,外源核黄素也能明显提高水稻对盐和高温胁迫的耐受性,但却降低了其对渗透胁迫的耐受性。     

Characterization of Actinobacillus pleuropneumoniae riboflavin biosynthesis genes.

In this paper, we report the identification, cloning, and complete nucleotide sequence of four genes from Actinobacillus pleuropneumoniae that are involved in riboflavin biosynthesis. The cloned genes can specify production of large amounts of riboflavin in Escherichia coli, can complement several defined genetic mutations in riboflavin biosynthesis in E. coli, and are homologous to riboflavin biosynthetic genes from E. coli, Haemophilus influenzae, and Bacillus subtilis. The genes have been designated A. pleuropneumoniae ribGBAH because of their similarity in both sequence and arrangement to the B. subtilis ribGBAH operon.     

Regulation of Riboflavin Biosynthesis in Bacillus subtilis Is Affected by the Activity of the Flavokinase/Flavin Adenine Dinucleotide Synthetase Encoded by ribC

This work shows that the ribC wild-type gene product has both flavokinase and flavin adenine dinucleotide synthetase (FAD-synthetase) activities. RibC plays an essential role in the flavin metabolism of Bacillus subtilis, as growth of a ribC deletion mutant strain was dependent on exogenous supply of FMN and the presence of a heterologous FAD-synthetase gene in its chromosome. Upon cultivation with growth-limiting amounts of FMN, this ribC deletion mutant strain overproduced riboflavin, while with elevated amounts of FMN in the culture medium, no riboflavin overproduction was observed. In a B. subtilis ribC820 mutant strain, the corresponding ribC820 gene product has reduced flavokinase/FAD-synthetase activity. In this strain, riboflavin overproduction was also repressed by exogenous FMN but not by riboflavin. Thus, flavin nucleotides, but not riboflavin, have an effector function for regulation of riboflavin biosynthesis in B. subtilis, and RibC seemingly is not directly involved in the riboflavin regulatory system. The mutation ribC820 leads to deregulation of riboflavin biosynthesis in B. subtilis, most likely by preventing the accumulation of the effector molecule FMN or FAD.     

Nitrogen assimilation enzymes in Bacillus subtilis mutants with hyperproduction of riboflavin

Three groups of the nitrogen assimilation cycle enzymes (glutamate synthases (GTS), glutamine synthases (GS), and glutamate dehydrogenases (GD)) were studied in Bacillus subtilis strains with hyperproduction of riboflavin (vitamin B2). It was found that in all strains tested activity of GS was virtually the same, activity of GD was absent, and activity of GTS was reduced. In strains 41 and 24, riboflavin producers, activity of GTS was 30-60% the enzyme activity in the original strain (wild-type RosR). The most pronounced decrease in the activity of GTS (0-12% relative to RosR) was observed in the strain AS5, which had the highest level of biosynthetic activity relative to the other strains. According to the results of determination of the sensitivity of induction of beta-xylosidase to glucose- and fructose-induced catabolic repression, none of the strains studied was characterized by disorders in the protein CcpA, a global regulator of the catabolic repression in gram-positive bacteria, which is required for reducing amination and resulting activation of biosynthesis of glutamic acid in cell. It was suggested that mutations responsible for partial or complete inhibition of GTS biosynthesis caused an increase in the intracellular pool of glutamine. The intracellular pool of glutamine is a nitrogen source for riboflavin in cell. It follows from the results of this work that there is a trend toward an increase in the rate of biosynthesis of vitamin B2 in mutants with inhibited GTS activity. However, the complexity of the processes of regulation of nitrogen assimilation enzymes makes it difficult to find a distinct correlation between GTS activity and riboflavin biosynthesis in these strains.