The 5'-GGATCC-3' cleavage specificity of BamHI is increased to 5'-CCGGATCCGG-3' by sequential double methylation with M.HpaII and M.BamHI

Genetic, Epigenetic and Phenotypic Diversity of Four Bacillus velezensis Strains Used for Plant Protection or as Probiotics

Bacillus velezensis strains are applied as ecologically safe biopesticides, plant growth promoting rhizobacteria (PGPR), and in veterinary probiotics. They are abundant in various environments including soil, plants, marine habitats, the intestinal micro-flora, etc. The mechanisms underlying this adaptive plasticity and bioactivity are not well understood, nor is it clear why several strains outperform other same species isolates by their bioactivities. The main objective of this work was to demonstrate versatility of bioactivities and lifestyle strategies of the selected B. velezensis strains suitable to serve as model organisms in future studies. Here, we performed a comparative study of newly sequenced genomes of four B. velezensis isolates with distinct phenotypes and isolation origin, which were assessed by RNA sequencing under the effect of root exudate stimuli and profiled by epigenetic modifications of chromosomal DNA. Among the selected strains, UCMB5044 is an oligotrophic PGPR strain adapted to nutrient poor desert soils. UCMB5113 and At1 are endophytes that colonize plants and require nutrient rich media. In contrast, the probiotic strain, UCMB5007, is a copiotroph, which shows no propensity to colonize plants. PacBio and Illumina sequencing approaches were used to generate complete genome assemblies, tracing epigenetic modifications, and determine gene expression profiles. All sequence data was deposited at NCBI. The strains, UCMB5113 and At1, show 99% sequence identity and similar phenotypes despite being isolated from geographically distant regions. UCMB5007 and UCMB5044 represent another group of organisms with almost identical genomes but dissimilar phenotypes and plant colonization propensity. The two plant associated strains, UCMB5044 and UCMB5113, share 398 genes putatively associated with root colonization, which are activated by exposure to maize root exudates. In contrast, UCMB5007 did not respond to root exudate stimuli. It was hypothesized that alterations in the global methylation pattern and some other epigenetic modifications enable adaptation of strains to different habitats and therefore may be of importance in terms of the biotechnological applicability of these bacteria. Contrary, the ability to grow on root exudates as a sole source of nutrients or a strong antagonism against phytopathogens showed by the strains in vitro cannot be considered as good predictors of PGPR activities.

An alternative approach to study the enzymatic specificities of the CfrBI restriction-modification system

Restriction–modification systems (RMS) are the main gene-engineering tools and a suitable model to study the molecular mechanisms of catalysis and DNA–protein interactions. Research into the catalytic properties of these enzymes, determination of hydrolysis and DNA-methylation sites remain topical. In our previous work we have cloned and sequenced the CfrBI restriction–modification system (strain Citrobacter freundii), which recognizes the nucleotide sequence 5′-CCWWGG-3′.

In this article we describe the cloning of the methyltransferase and restriction endonuclease genes (gene encoding CfrBI DNA methyltransferase (cfrBIM) and gene encoding CfrBI restriction endonuclease (cfrBIR)) separately to obtain strains overproducing the enzymes of this system. His₆-CfrBI, which had been purified to homogeneity, was used to establish the DNA-hydrolysis point in its recognition site. CfrBI was shown to cleave DNA after just the first 5′C within the recognition site and then to generate 4-nt 3′ cohesive ends (5′-C/CWWGG-3′).

To map the site of methylation by M.CfrBI, we exploited the fact that the CfrBI site partially overlaps with the recognition sites of the well-documented enzymes KpnI and ApaI. The M.CfrBI- induced hemimethylation of the internal C residue of the ApaI recognition sequence (GGGC^N4mCC) was observed to block cleavage by ApaI. In contrast, KpnI was able to digest its M.CfrBI-hemimethylated site (GGTA^N4mCC).

KpnI was used to restrict a fragment of DNA harbouring the CfrBI and KpnI sites, in which the CfrBI site was methylated in vitro by His₆-M.CfrBI using [³H]-SAM.

The subsequent separation of hydrolysis products by electrophoresis and the enumeration of incorporated [H3]-methyl groups in each of the fragments made it possible to determine that external cytosine undergoes modification in the recognition site.

The use of prokaryotic DNA methyltransferases as experimental and analytical tools in modern biology

Prokaryotic DNA methyltransferases (MTases) are used as experimental and research tools in molecular biology and molecular genetics due to their ability to recognize and transfer methyl groups to target bases in specific DNA sequences. As a practical tool, prokaryotic DNA MTases can be used in recombinant DNA technology for in vitro alteration and enhancing of cleavage specificity of restriction endonucleases. The ability of prokaryotic DNA MTases to methylate cytosine residues in specific sequences, which are also methylated in eukaryotic DNA, makes it possible to use them as analytical reagent for determination of the site-specific level of methylation in eukaryotic DNA. In vivo DNA methylation by prokaryotic DNA MTases is used in different techniques for probing chromatin structure and protein-DNA interactions. Additional prospects are opened by development of the methods of DNA methylation targeted to predetermined DNA sequences by fusion of DNA MTases to DNA binding proteins. This review will discuss the application of prokaryotic DNA MTases of Type II in the methods and approaches mentioned above.

DNA (cytosine-N4-)- and -(adenine-N6-)-methyltransferases have different kinetic mechanisms but the same reaction route. A comparison of M.BamHI and T4 Dam

We studied the kinetics of methyl group transfer by the BamHI DNA-(cytosine-N(4)-)-methyltransferase (MTase) from Bacillus amyloliquefaciens to a 20-mer oligodeoxynucleotide duplex containing the palindromic recognition site GGATCC. Under steady state conditions the BamHI MTase displayed a simple kinetic behavior toward the 20-mer duplex. There was no apparent substrate inhibition at concentrations much higher than the K(m) for either DNA (100-fold higher) or S-adenosyl-l-methionine (AdoMet) (20-fold higher); this indicates that dead-end complexes did not form in the course of the methylation reaction. The DNA methylation rate was analyzed as a function of both substrate and product concentrations. It was found to exhibit product inhibition patterns consistent with a steady state random bi-bi mechanism in which the dominant order of substrate binding and product release (methylated DNA, DNA(Me), and S-adenosyl-l-homocysteine, AdoHcy) was Ado-Met DNA DNA(Me) AdoHcy. The M.BamHI kinetic scheme was compared with that for the T4 Dam (adenine-N(6)-)-MTase. The two differed with respect to an effector action of substrates and in the rate-limiting step of the reaction (product inhibition patterns are the same for the both MTases). From this we conclude that the common chemical step in the methylation reaction, methyl transfer from AdoMet to a free exocyclic amino group, is not sufficient to dictate a common kinetic scheme even though both MTases follow the same reaction route.

Enzymatic cleavage of a bacterial chromosome at a transposon-inserted rare site

The sequential use of the methylase M.Xbal (5'.TCTAGm6A) and the methylation-dependent endonuclease Dpnl (5'-Gm6A decreases TC) results in cleavage at 5'.TCTAGA decreases TCTAGA. This recognition sequence was introduced into a transposon derived from the Mu bacteriophage and transposed into the genome of the bacterium Salmonella typhimurium. M.Xbal methylation was provided in vivo by a plasmid containing the M.Xbal gene and the S. typhimurium genome was cleaved to completion by Dpnl at one or more sites, depending on the number of transposon insertions. The resulting genomic fragments were resolved by pulsed-field electrophoresis. The potential use of single M.Xbal/Dpnl cleavage sites as reference positions to map rare restriction sites is discussed.

Specificity of restriction endonucleases and DNA modification methyltransferases a review (Edition 3)

The properties and sources of all known class-I, class-II and class-III restriction endonucleases (ENases) and DNA modification methyltransferases (MTases) are listed and newly subclassified according to their sequence specificity. In addition, the enzymes are distinguished in a novel manner according to sequence specificity, cleavage position and methylation sensitivity. Furthermore, new nomenclature rules are proposed for unambiguously defined enzyme names. In the various Tables, the enzymes are cross-indexed alphabetically according to their names (Table I), classified according to their recognition sequence homologies (Table II), and characterized within Table II by the cleavage and methylation positions, the number of recognition sites on the DNA of the bacteriophages lambda, phi X174, and M13mp7, the viruses Ad2 and SV40, the plasmids pBR322 and pBR328, and the microorganisms from which they originate. Other tabulated properties of the ENases include relaxed specificities (integrated within Table II), the structure of the generated fragment ends (Table III), interconversion of restriction sites (Table IV) and the sensitivity to different kinds of DNA methylation (Table V). Table VI shows the influence of class-II MTases on the activity of class-II ENases with at least partially overlapping recognition sequences. Table VII lists all class-II restriction endonucleases and MTases which are commercially available. The information given in Table V focuses on the influence of methylation of the recognition sequences on the activity of ENases. This information might be useful for the design of cloning experiments especially in Escherichia coli containing M.EcodamI and M.EcodcmI [H16, M21, U3] or for studying the level and distribution of site-specific methylation in cellular DNA, e.g., 5'- (M)CpG-3' in mammals, 5'-(M)CpNpG-3' in plants or 5'-GpA(M)pTpC-3' in enterobacteria [B29, E4, M30, V4, V13, W24]. In Table IV a cross index for the interconversion of two- and four-nt 5'-protruding ends into new recognition sequences is complied. This was obtained by the fill-in reaction with the Klenow (large) fragment of the E. coli DNA polymerase I (PolIk), or additional nuclease S1 treatment followed by ligation of the modified fragment termini [P3]. Interconversion of restriction sites generates novel cloning sites without the need of linkers. This should improve the flexibility of genetic engineering experiments [K56, P3].(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning type-II restriction and modification genes

We have cloned into Escherichia coli the genes for 38 type-II bacterial modification methyltransferases. The clones were isolated by selecting in vitro for protectively modified recombinants. Most of the clones modify their DNA fully but a substantial number modify only partially. In approximately one-half of the clones, the genes for the corresponding endonucleases are also present. Some of these clones restrict infecting phages and others do not. Clones carrying endonuclease genes but lacking methyltransferase genes have been found, in several instances, to be viable.