Regulation of secondary metabolism in streptomycetes

While the biological functions of most of the secondary metabolites made by streptomycetes are not known, it is inconceivable that they do not play an adaptive ecological role. The biosynthesis of secondary metabolites under laboratory conditions usually occurs in a growth phase or developmentally controlled manner, but is also influenced by a wide variety of environmental and physiological signals, presumably reflecting the range of conditions that trigger their production in nature. The expression of secondary metabolic gene clusters is controlled by many different families of regulatory proteins, some of which are found only in actinomycetes, and is elicited by both extracellular and intracellular signalling molecules. The application of a variety of genetic and molecular approaches is now beginning to reveal fascinating insights into the complex regulatory cascades that govern this process.

Isolation and identification of actinobacteria from surface-sterilized wheat roots

This is the first report of filamentous actinobacteria isolated from surface-sterilized root tissues of healthy wheat plants (Triticum aestivum L.). Wheat roots from a range of sites across South Australia were used as the source material for the isolation of the endophytic actinobacteria. Roots were surface-sterilized by using ethanol and sodium hypochlorite prior to the isolation of the actinobacteria. Forty-nine of these isolates were identified by using 16S ribosomal DNA (rDNA) sequencing and found to belong to a small group of actinobacterial genera including Streptomyces, Microbispora, Micromonospora, and Nocardiodes spp. Many of the Streptomyces spp. were found to be similar, on the basis of their 16S rDNA gene sequence, to Streptomyces spp. that had been isolated from potato scabs. In particular, several isolates exhibited high 16S rDNA gene sequence homology to Streptomyces caviscabies and S. setonii. None of these isolates, nor the S. caviscabies and S. setonii type strains, were found to carry the nec1 pathogenicity-associated gene or to produce the toxin thaxtomin, indicating that they were nonpathogenic. These isolates were recovered from healthy plants over a range of geographically and temporally isolated sampling events and constitute an important plant-microbe interaction.

Primary metabolism and its control in streptomycetes: a most unusual group of bacteria

Streptomycetes are Gram-positive bacteria with a unique capacity for the production of a multitude of varied and complex secondary metabolites. They also have a complex life cycle including differentiation into at least three distinct cell types. Whilst much attention has been paid to the pathways and regulation of secondary metabolism, less has been paid to the pathways and the regulation of primary metabolism, which supplies the precursors. With the imminent completion of the total genome sequence of Streptomyces coelicolor A3(2), we need to understand the pathways of primary metabolism if we are to understand the role of newly discovered genes. This review is written as a contribution to supplying these wants. Streptomycetes inhabit soil, which, because of the high numbers of microbial competitors, is an oligotrophic environment. Soil nutrient levels reflect the fact that plant-derived material is the main nutrient input; i.e. it is carbon-rich and nitrogen- and phosphate-poor. Control of streptomycete primary metabolism reflects the nutrient availability. The variety and multiplicity of carbohydrate catabolic pathways reflects the variety and multiplicity of carbohydrates in the soil. This multiplicity of pathways has led to investment by streptomycetes in pathway-specific and global regulatory networks such as glucose repression. The mechanism of glucose repression is clearly different from that in other bacteria. Streptomycetes feed by secreting complexes of extracellular enzymes that break down plant cell walls to release nutrients. The induction of these enzyme complexes is often coordinated by inducers that bear no structural relation to the substrate or product of any particular enzyme in the complex; e.g. a product of xylan breakdown may induce cellulase production. Control of amino acid catabolism reflects the relative absence of nitrogen catabolites in soil. The cognate amino acid induces about half of the catabolic pathways and half are constitutive. There are reduced instances of global carbon and nitrogen catabolite control of amino acid catabolism, which again presumably reflects the relative rarity of the catabolites. There are few examples of feedback repression of amino acid biosynthesis. Again this is taken as a reflection of the oligotrophic nature of the streptomycete ecological niche. As amino acids are not present in the environment, streptomycetes have rarely invested in feedback repression. Exceptions to this generalization are the arginine and branched-chain amino acid pathways and some parts of the aromatic amino acid pathways which have regulatory systems similar to Escherichia coli and Bacillus subtilis and other copiotrophic bacteria.

Culturable marine actinomycete diversity from tropical Pacific Ocean sediments

Actinomycetes were cultivated using a variety of media and selective isolation techniques from 275 marine samples collected around the island of Guam. In total, 6425 actinomycete colonies were observed and 983 (15%) of these, representing the range of morphological diversity observed from each sample, were obtained in pure culture. The majority of the strains isolated (58%) required seawater for growth indicating a high degree of marine adaptation. The dominant actinomycete recovered (568 strains) belonged to the seawater-requiring marine taxon 'Salinospora', a new genus within the family Micromonosporaceae. A formal description of this taxon has been accepted for publication (Maldonado et al., 2005) and includes a revision of the generic epithet to Salinispora gen. nov. Members of two major new clades related to Streptomyces spp., tentatively called MAR2 and MAR3, were cultivated and appear to represent new genera within the Streptomycetaceae. In total, five new marine phylotypes, including two within the Thermomonosporaceae that appear to represent new taxa, were obtained in culture. These results support the existence of taxonomically diverse populations of phylogenetically distinct actinomycetes residing in the marine environment. These bacteria can be readily cultured using low nutrient media and represent an unexplored resource for pharmaceutical drug discovery.

Two minimal Tat translocases in Bacillus

Activity of the Tat machinery for protein transport across the inner membrane of Escherichia coli and the chloroplast thylakoidal membrane requires the presence of three membrane proteins: TatA, TatB and TatC. Here, we show that the Tat machinery of the Gram-positive bacterium Bacillus subtilis is very different because it contains at least two minimal Tat translocases, each composed of one specific TatA and one specific TatC component. A third, TatB-like component is apparently not required. This implies that TatA proteins of B. subtilis perform the functions of both TatA and TatB of E. coli and thylakoids. Notably, the two B. subtilis translocases named TatAdCd and TatAyCy both function as individual, substrate-specific translocases for the twin-arginine preproteins PhoD and YwbN, respectively. Importantly, these minimal TatAC translocases of B. subtilis are representative for the Tat machinery of the vast majority of Gram-positive bacteria, Streptomycetes being the only known exception with TatABC translocases.

Streptacidiphilus gen. nov., acidophilic actinomycetes with wall chemotype I and emendation of the family Streptomycetaceae (Waksman and Henrici (1943)AL) emend. Rainey et al. 1997

The taxonomic position of acidophilic actinomycetes selectively isolated from acidic soils and litter was examined using a polyphasic approach. The distinct 16S rDNA phyletic branch formed by representative strains was equated with related monophyletic clades that corresponded to the genera Kitasatospora and Streptomyces. The acidophilic isolates also exhibited a distinctive pH profile, a unique 16S rDNA signature, and contained major amounts of LL-diaminopimelic acid, galactose and rhamnose in whole-organism hydrolysates. It is proposed that these acidophilic actinomycetes be assigned to a new genus, Streptacidiphilus gen. nov., on the basis of genotypic and phenotypic differences. Three species were defined on the basis of DNA:DNA pairing and phenotypic data, namely, Streptacidiphilus albus sp. nov., the type species, Streptacidiphilus neutrinimicus sp. nov. and Streptacidiphilus carbonis sp. nov. Members of the genera Kitasatospora, Streptacidiphilus and Streptomyces share a number of key characteristics and form a stable monophyletic branch in the 16S rDNA tree. It is, therefore, proposed that the description of the family Streptomycetaceae be emended to account for properties shown by Kitasatospora and Streptacidiphilus species.

Secretion of active-form Streptoverticillium mobaraense transglutaminase by Corynebacterium glutamicum: processing of the pro-transglutaminase by a cosecreted subtilisin-Like protease from Streptomyces albogriseolus

The transglutaminase secreted by Streptoverticillium mobaraense is a useful enzyme in the food industry. A fragment of transglutaminase was secreted by Corynebacterium glutamicum when it was coupled on a plasmid to the promoter and signal peptide of a cell surface protein from C. glutamicum. We analyzed the signal peptide and the pro-domain of the transglutaminase gene and found that the signal peptide consists of 31 amino acid residues and the pro-domain consists of 45 residues. When the pro-domain of the transglutaminase was used, the pro-transglutaminase was secreted efficiently by C. glutamicum but had no enzymatic activity. However, when the plasmid carrying the S. mobaraense transglutaminase also encoded SAM-P45, a subtilisin-like serine protease derived from Streptomyces albogriseolus, the peptide bond to the C side of 41-Ser of the pro-transglutaminase was hydrolyzed, and the pro-transglutaminase was converted to an active form. Our findings suggest that C. glutamicum has potential as a host for industrial-scale protein production.

Staurosporine and rebeccamycin aglycones are assembled by the oxidative action of StaP, StaC, and RebC on chromopyrrolic acid

In the biosynthesis of the antitumor indolocarbazoles rebeccamycin and staurosporine by streptomycetes, assembly of the aglycones involves a complex set of oxidative condensations. Overall formation of aglycones K252c and arcyriaflavin A from their biosynthetic precursor chromopyrrolic acid involves four- and eight-electron oxidations, respectively. This process is catalyzed by the remarkable enzyme StaP, with StaC and RebC acting to direct the level of oxidation in the newly formed five-membered ring. An aryl-aryl coupling reaction is integral to this transformation as well as oxidative decarboxylation of the dicarboxypyrrole moiety of chromopyrrolic acid. Herein we describe the heterologous expression of staP, staC, and rebC in Escherichia coli and the activity of the corresponding enzymes in constructing the two distinct six-ring scaffolds. StaP is a cytochrome P450 enzyme, requiring dioxygen, ferredoxin, flavodoxin NADP(+)-reductase, and NAD(P)H for activity. StaP on its own converts chromopyrrolic acid into three aglycone products, K252c, arcyriaflavin A, and 7-hydroxy-K252c; in the presence of StaC, K252c is the predominant product, while the presence of RebC directs formation of arcyriaflavin A. (18)O-Labeling studies indicate that the oxygen(s) of the pyrrolinone and maleimide functionalities of the aglycones formed are all derived from dioxygen. This work allowed for the in vitro reconstitution of the full biosynthetic pathway from l-tryptophan to the staurosporine and rebeccamycin aglycones, K252c and 1,11-dichloroarcyriaflavin A.

Grouping of streptomycetes using 16S-ITS RFLP fingerprinting

A total of 463 Streptomyces and Kitasatospora type strains were screened using 16S-ITS RFLP fingerprinting (combined restriction digest using enzymes BstUI and HaeIII). In total, 59 clusters could be delineated, each comprising multiple strains with nearly identical patterns. Good correlation was found in general with phylogeny, as revealed by 16S rDNA sequencing. Most strains assigned to a particular 16S-ITS RFLP cluster were classified into the corresponding 16S sequencing cluster whether a 16S similarity cut-off value of 97 or 98% was used. We conclude that the taxonomic resolution of 16S-ITS RFLP fingerprinting is higher than that of 16S rDNA sequencing; this may provide a tool for reducing the number of laborious DNA-DNA hybridizations necessary for discovering potentially new species within Streptomyces.

A new shuttle cosmid vector, pKC505, for streptomycetes: its use in the cloning of three different spiramycin-resistance genes from a Streptomyces ambofaciens library

A new shuttle cosmid vector, pKC505, was constructed for the cloning of Streptomyces DNA. This vector, which can be conjugally transferred between different streptomycetes, was used to construct a genomic library from a spiramycin-producing S. ambofaciens strain. By transformation of the spiramycin-sensitive S. griseofuscus with the library, three phenotypically different spiramycin-resistance genes were isolated. S. ambofaciens DNA in these clones was colinear with the chromosome, and the cloned DNA was stable in E. coli, S. griseofuscus and S. fradiae. These cosmids could be isolated easily from S. griseofuscus, an improvement over the previous shuttle cosmid vector, pKC462a [Stanzak et al., Bio/Technology 4 (1986) 229-232], which was somewhat difficult to isolate from S. lividans.

Production and secretion of proteins by streptomycetes

Streptomycetes produce a large number of extracellular enzymes as part of their saprophytic mode of life. Their ability to synthesize enzymes as products of their primary metabolism could lead to the production of many proteins of industrial importance. The development of high-yielding expression systems for both homologous and heterologous gene products is of considerable interest. In this article, we review the current knowledge on the various factors that affect the production and secretion of proteins by streptomycetes and try to evaluate the suitability of these bacteria for the large-scale production of proteins of industrial importance.

Taxonomic re-evaluation of whorl-forming Streptomyces (formerly Streptoverticillium) species by using phenotypes, DNA-DNA hybridization and sequences of gyrB, and proposal of Streptomyces luteireticuli (ex Katoh and Arai 1957) corrig., sp. nov., nom. rev

The taxonomic status of 64 strains of whorl-forming Streptomyces (formerly Streptoverticillium) species was re-evaluated and strains were reclassified on the basis of their phenotypes, DNA-DNA hybridization data and partial sequences of gyrB, the structural gene of the B subunit of DNA gyrase. These strains, which consisted of 46 species and eight subspecies with validly published names and 13 species whose names have not been validly published [including 10 strains examined by the International Streptomyces Project (ISP)], were divided into two groups, namely typical and atypical whorl-forming Streptomyces species, based on their phenotypes and gyrB gene sequences. The typical whorl-forming species (59 strains) were divided into six major clusters of three or more species, seven minor clusters of two species and five single-member clusters, based on the threshold value of 97 % gyrB sequence similarity. Major clusters were typified by Streptomyces abikoensis, Streptomyces cinnamoneus, Streptomyces distallicus, Streptomyces griseocarneus, Streptomyces hiroshimensis and Streptomyces netropsis. Phenotypically, members of each cluster resembled each other closely except for the S. distallicus cluster, which was divided phenotypically into the S. distallicus and Streptomyces stramineus subclusters, and the S. netropsis cluster, which was divided into the S. netropsis and Streptomyces eurocidicus subclusters. Strains in each minor cluster closely resembled each other phenotypically. DNA-DNA relatedness between the representative species and others in each major cluster and/or subcluster, and between strains in the minor clusters, was >70 %, indicating that the major clusters and/or subclusters and the minor clusters each comprise a single species. It was concluded that 59 strains of typical whorl-forming Streptomyces species consisted of the following 18 species, including subjective synonym(s): S. abikoensis, Streptomyces ardus, Streptomyces blastmyceticus, S. cinnamoneus, S. eurocidicus, S. griseocarneus, S. hiroshimensis, Streptomyces lilacinus, 'Streptomyces luteoreticuli', Streptomyces luteosporeus, Streptomyces mashuensis, Streptomyces mobaraensis, Streptomyces morookaense, S. netropsis, Streptomyces orinoci, S. stramineus, Streptomyces thioluteus and Streptomyces viridiflavus.

'Candidatus Streptomyces philanthi', an endosymbiotic streptomycete in the antennae of Philanthus digger wasps

Symbiotic interactions with bacteria are essential for the survival and reproduction of many insects. The European beewolf (Philanthus triangulum, Hymenoptera, Crabronidae) engages in a highly specific association with bacteria of the genus Streptomyces that appears to protect beewolf offspring against infection by pathogens. Using transmission and scanning electron microscopy, the bacteria were located in the antennal glands of female wasps, where they form dense cell clusters. Using genetic methods, closely related streptomycetes were found in the antennae of 27 Philanthus species (including two subspecies of P. triangulum from distant localities). In contrast, no endosymbionts could be detected in the antennae of other genera within the subfamily Philanthinae (Aphilanthops, Clypeadon and Cerceris). On the basis of morphological, genetic and ecological data, 'Candidatus Streptomyces philanthi' is proposed. 16S rRNA gene sequence data are provided for 28 ecotypes of 'Candidatus Streptomyces philanthi' that reside in different host species and subspecies of the genus Philanthus. Primers for the selective amplification of 'Candidatus Streptomyces philanthi' and an oligonucleotide probe for specific detection by fluorescence in situ hybridization (FISH) are described.

Conserved cis-Acting Elements Upstream of Genes Composing the Chitinolytic System of Streptomycetes Are DasR-Responsive Elements

For soil-dwelling bacteria that usually live in a carbon-rich and nitrogen-poor environment, the ability to utilize chitin - the second most abundant polysaccharide on earth - is a decisive evolving advantage as it is a source for both elements. Streptomycetes are high-GC Gram-positive soil bacteria that are equipped with a broad arsenal of chitinase-degrading genes. These genes are induced when the streptomycetes sense the presence of chitooligosaccharides. Their expression is repressed as soon as more readily assimilated carbon sources become available. This includes for example glucose or N-acetylglucosamine, the monomer subunit of chitin. Historically, the first cis-acting elements involved in carbon regulation in streptomycetes were found more than a decade ago upstream of chitinase genes, but the transcriptional regulator had so far remained undiscovered. In this work, we show that these cis-acting elements consist of inverted repeats with multiple occurrences and are bound by the HutC/GntR type regulator DasR. We have therefore designated these sites as DasR-responsive elements (dre). DasR, which is also the repressor of the genes for the N-acetylglucosamine-specific phosphotransferase transport system, should therefore play a critical role in sensing the balance between the monomeric and polymeric forms of N-acetylglucosamine.

High level expression of Streptomyces mobaraensis transglutaminase in Corynebacterium glutamicum using a chimeric pro-region from Streptomyces cinnamoneus transglutaminase

We previously observed secretion of native-type Streptomyces mobaraensis transglutaminase (MTGase) in Corynebacterium glutamicum by co-expressing the subtilisin-like protease SAM-P45 from S. albogriseolus which processes the pro-region. In the present study, we have used a chimeric pro-region consisting of S. mobaraensis and Streptomyces cinnamoneus transglutaminases for the production of MTGase in C. glutamicum. As a result, secretion of MTGase using the chimeric pro-region is increased compared to that using the native pro-region.

Overproduction of microbial transglutaminase in Escherichia coli, in vitro refolding, and characterization of the refolded form

(MTG) The Streptoverticillium transglutaminase gene, synthesized previously for yeast expression, was modified and resynthesized for overexpression in E. coli. A high-level expression plasmid, pUCTRPMTG-02(+), was constructed. Furthermore, to eliminate the N-terminal methionine, pUCTRPMTGD2 was constructed. Cultivation of E. coli transformed with pUCTRPMTG02(+) or pUCTRPMTGD2 yielded a large amount of MTG (200-300 mg/liter) as insoluble inclusion bodies. The N-terminal amino acid residue of the expressed protein was methionine or serine (the second amino acid residue of the mature MTG sequence), respectively. Transformed E. coli cells were disrupted, and collected pellets of inclusion bodies were solubilized with 8 M urea. Rapid dilution treatment of solubilized MTG restored the enzymatic activity. Refolded MTG, purified by ion-exchange chromatography, which had an N-terminal methionine or serine residue, showed activity equivalent to that of native MTG. These results indicated that recombinant MTG could be produced efficiently in E. coli.

Prepeptide sequence of cinnamycin (Ro 09-0198): the first structural gene of a duramycin-type lantibiotic

The tetracyclic polypeptide antibiotic cinnamycin (Ro 90-0198) belongs to the duramycin-type lantibiotics and contains the unusual amino acids threo-3-methyl-lanthionine, meso-lanthionine, lysinoalanine and 3-hydroxyaspartic acid. Its structural gene, referred to as cinA, has been identified on isolated chromosomal DNA of the Ro 09-0198-producing strain Streptoverticillium griseoverticillatum via a 39-residue oligonucleotide probe derived from fragment 7-19 of the hypothetical prolantibiotic sequence CRQSCSFGPFTFVCDGNTK. This propeptide part was then found within an open reading frame of 77 amino acids. In contrast to the nisin-type prelantibiotics, this first duramycin-type prelantibiotic has an unusually long leader sequence of 58 amino acids. it also differs in the processing site and the direction of the formation of the threo-3-methyl-lanthionine bridges is from N-terminal cysteine to C-terminal dehydrated threonine residues, whereas the meso-lanthionine and lysinoalanine bridges are formed by addition reactions from C-terminal cysteine or lysine to N-terminal dehyrated serine residues.

Purification, characterisation, and gene cloning of transglutaminase from Streptoverticillium cinnamoneum CBS 683.68

The transglutaminase (TGase; EC 2.3.2.13) from Streptoverticillium cinnamoneum CBS 683.68 has been purified, characterised and its gene cloned. The purified enzyme had a relative molecular mass of 37,660 determined by mass spectrometry and contained a single Cys residue that was essential for the catalytic activity. Contrary to eukaryotic TGases, this enzyme was calcium-independent. The fact that TGase was capable to incorporate a wide variety of aliphatic and aromatic non-polar compounds suggested that the amine fixation site could be an hydrophobic pocket. S cinnamoneum CBS 683.68 TGase was synthesised as a protein precursor of 411 amino acid residues corresponding to a signal peptide of 81 amino acid residues and a mature TGase of 330 amino acid residues. Amino acid sequence analysis revealed that the S cinnamoneum CBS 683.68 TGase had little sequence homology with eukaryotic TGases, but shared high identity with the sequence of Streptoverticillium strain S-8112. In accordance with kinetics data, hydropathy analysis showed that the active site of the enzyme was in an hydrophobic environment as for eukaryotic TGases.

Purification, characterization, and sequence determination of phospholipase D secreted by Streptoverticillium cinnamoneum

Phospholipase D (PLD), secreted into the culture medium of an actinomycete, Streptoverticillium cinnamoneum, has been purified to homogeneity and characterized. The Stv. cinnamoneum PLD efficiently catalyzes both the hydrolysis and transphosphatidylation of various phospholipids, including phosphatidylethanolamine (PE), phosphatidylcholine (PC), and phosphatidylserine (PS). However, the substrate specificity differs between the two reactions; PE serves as the most preferred substrate for the hydrolysis, but PC and PS are better substrates than PE for the transphosphatidylation. In addition, the transphosphatidylation but not the hydrolysis of PE and PC is markedly activated on the addition of metal ions, especially Al3+. Nucleotide and amino acid sequence determination of the Stv. cinnamoneum PLD revealed the presence of common structural motifs identified in all PLD sequences from various species.

Phylogenetic analysis of the genera Streptomyces and Kitasatospora based on partial RNA polymerase beta-subunit gene (rpoB) sequences

The RNA polymerase beta-subunit genes (rpoB) of 67 Streptomyces strains, representing 57 species, five Kitasatospora strains and Micromonospora echinospora KCTC 9549 were partially sequenced using a pair of rpoB PCR primers. Among the streptomycetes, 99.7-100 % similarity within the same species and 90.2-99.3 % similarity at the interspecific level were observed by analysis of the determined rpoB sequences. The topology of the phylogenetic tree based on rpoB sequences was similar to that of 16S rDNA. The five Kitasatospora strains formed a stable monophyletic clade and a sister group to the clade comprising all Streptomyces species. Although there were several discrepancies in the details, considerable agreement was found between the results of rpoB analysis and those of numerical phenetic classification. This study demonstrates that analysis of rpoB can be used as an alternative genetic method in parallel to conventional taxonomic methods, including numerical phenetic and 16S rDNA analyses, for the phylogenetic analyses of the genera Streptomyces and Kitasatospora.

Chemical synthesis of the gene for microbial transglutaminase from Streptoverticillium and its expression in Escherichia coli

The gene coding for microbial transglutaminase (TGase) from Streptoverticillium, which consists of 331 amino acids, was chemically synthesized. The codons have been substituted for those mainly favored in yeast. Our strategy involved the construction of the TGase gene in five sections (54 oligomers) that contained unique restriction enzyme sites at both ends, which could readily be ligated to form the full-length product. The chemically synthesized gene was inserted downstream from the ompA signal peptide of the E. coli expression vector, pIN-III-ompA, which carries lpp and lac promotors. The resultant plasmid directed the expression of TGase, with the activity being secreted mainly into the periplasmic space of E. coli. The induced gene product was identical with native TGase in size and in immunological properties, though the enzyme activity was low.

The bacterial paromomycin resistance gene, aphH, as a dominant selectable marker in Volvox carteri

The aminoglycoside antibiotic paromomycin that is highly toxic to the green alga Volvox carteri is efficiently inactivated by aminoglycoside 3'-phosphotransferase from Streptomyces rimosus. Therefore, we made constructs in which the bacterial aphH gene encoding this enzyme was combined with Volvox cis-regulatory elements in an attempt to develop a new dominant selectable marker--paromomycin resistance (PmR)--for use in Volvox nuclear transformation. The construct that provided the most efficient transformation was one in which aphH was placed between a chimeric promoter that was generated by fusing the Volvox hsp70 and rbcS3 promoters and the 3' UTR of the Volvox rbcS3 gene. When this plasmid was used in combination with a high-impact biolistic device, the frequency of stable PmR transformants ranged about 15 per 106 target cells. Due to rapid and sharp selection, PmR transformants were readily isolated after six days, which is half the time required for previously used markers. Co-transformation of an unselected marker ranged about 30%. The chimeric aphH gene was stably integrated into the Volvox genome, frequently as tandem multiple copies, and was expressed at a level that made selection of PmR transformants simple and unambiguous. This makes the engineered bacterial aphH gene an efficient dominant selection marker for the transformation and co-transformation of a broad range of V. carteri strains without the recurring need for using auxotrophic recipient strains.

Genetic and phenotypic traits of streptomycetes used to characterize antibiotic activities of field-collected microbes

Although antibiotic production may contribute significantly to microbial fitness, there is limited information on the ecology of antibiotic-producing microbial populations in soil. Indeed, quantitative information on the variation in frequency and intensity of specific antibiotic inhibitory and resistance abilities within soil microbial communities is lacking. Among the streptomycetes, antibiotic production is highly variable and resistance to antibiotics is highly specific to individual microbial strains. The objective of this work was to genetically and phenotypically characterize a reference collection of streptomycetes for use in distinguishing inhibition and resistance phenotypes of field-collected microbes. Specifically, we examined inhibition and resistance abilities of all isolates in all possible pairwise combinations, genetic relatedness using BOX-PCR and 16S rDNA sequence analyses, nutrient utilization profiles, and antibiotic induction among all possible three-way combinations of isolates. Each streptomycete isolate possessed a unique set of phenotypic and genetic characteristics. However, there was little correspondence between phenotypic and genetic traits. This collection of reference isolates provides the potential for distinguishing 1024 inhibition and resistance phenotypes in field-collected microbes. Relationships between the genetic and phenotypic characteristics examined may provide preliminary insight into the distinct strategies that microbes use in optimizing their fitness in natural environments.Key words: antibiotic inhibition, resistance, nutrient utilization, BOX-PCR, 16S rDNA.

Versatile Oxidase and Dehydrogenase Activities of Bacterial Pyranose 2-Oxidase Facilitate Redox Cycling with Manganese Peroxidase In Vitro

Pyranose 2-oxidase (POx) has long been accredited a physiological role in lignin degradation, but evidence to provide insights into the biochemical mechanisms and interactions is insufficient. There are ample data in the literature on the oxidase and dehydrogenase activities of POx, yet the biological relevance of this duality could not be established conclusively. Here we present a comprehensive biochemical and phylogenetic characterization of a novel pyranose 2-oxidase from the actinomycetous bacterium Kitasatospora aureofaciens (KaPOx) as well as a possible biomolecular synergism of this enzyme with peroxidases using phenolic model substrates in vitro A phylogenetic analysis of both fungal and bacterial putative POx-encoding sequences revealed their close evolutionary relationship and supports a late horizontal gene transfer of ancestral POx sequences. We successfully expressed and characterized a novel bacterial POx gene from K. aureofaciens, one of the putative POx genes closely related to well-known fungal POx genes. Its biochemical characteristics comply with most of the classical hallmarks of known fungal pyranose 2-oxidases, i.e., reactivity with a range of different monosaccharides as electron donors as well as activity with oxygen, various quinones, and complexed metal ions as electron acceptors. Thus, KaPOx shows the pronounced duality of oxidase and dehydrogenase similar to that of fungal POx. We further performed efficient redox cycling of aromatic lignin model compounds between KaPOx and manganese peroxidase (MnP). In addition, we found a Mn(III) reduction activity in KaPOx, which, in combination with its ability to provide H2O2, implies this and potentially other POx as complementary enzymatic tools for oxidative lignin degradation by specialized peroxidases.IMPORTANCE Establishment of a mechanistic synergism between pyranose oxidase and (manganese) peroxidases represents a vital step in the course of elucidating microbial lignin degradation. Here, the comprehensive characterization of a bacterial pyranose 2-oxidase from Kitasatospora aureofaciens is of particular interest for several reasons. First, the phylogenetic analysis of putative pyranose oxidase genes reveals a widespread occurrence of highly similar enzymes in bacteria. Still, there is only a single report on a bacterial pyranose oxidase, stressing the need of closing this gap in the scientific literature. In addition, the relatively small K. aureofaciens proteome supposedly supplies a limited set of enzymatic functions to realize lignocellulosic biomass degradation. Both enzyme and organism therefore present a viable model to study the mechanisms of bacterial lignin decomposition, elucidate physiologically relevant interactions with specialized peroxidases, and potentially realize biotechnological applications.

Discovery of a Short-Chain ε-Poly-l-lysine and Its Highly Efficient Production via Synthetase Swap Strategy

ε-Poly-l-lysine (ε-PL) is a natural antimicrobial cationic peptide, which is generally recognized as safe for use as a food preservative. To date, the production capacity of strains that produce low-molecular weight ε-PL remains very low and thus unsuitable for industrial production. Here, we report a new low-molecular weight ε-PL-producing Kitasatospora aureofaciens strain. The ε-PL synthase gene of this strain was cloned into a high ε-PL-producing Streptomyces albulus strain. The resulting recombinant strain efficiently produced ε-PL with a molecular weight of 1.3-2.3 kDa and yielded of 23.6 g/L following fed-batch fermentation in a 5 L bioreactor. In addition, circular dichroism spectra showed that this ε-PL takes on a conformation similar to an antiparallel pleated-sheet. Moreover, it demonstrated better antimicrobial activity against yeast compared to the 3.2-4.5 kDa ε-PL. This study provides a highly efficient strategy for production of the low-molecular weight ε-PL, which helps to expand its potential applications.