Corallococcus senghenyddensis sp. nov., a myxobacterium with potent antimicrobial activity

AIM

Corallococcus species are diverse in the natural environment with 10 new Corallococcus species having been characterized in just the last 5 years. As well as being an abundant myxobacterial genus, they produce several secondary metabolites, including Corallopyronin, Corramycin, Coralmycin, and Corallorazine. We isolated a novel strain Corallococcus spp RDP092CA from soil in South Wales, UK, using Candida albicans as prey bait and characterized its predatory activities against pathogenic bacteria and yeast.

METHODS AND RESULTS

The size of the RDP092CA genome was 8.5 Mb with a G + C content of 71.4%. Phylogenetically, RDP092CA is closely related to Corallococcus interemptor, C. coralloides, and C. exiguus. However, genome average nucleotide identity and digital DNA-DNA hybridization values are lower than 95% and 70% when compared to those type strains, implying that it belongs to a novel species. The RDP092CA genome harbours seven types of biosynthetic gene clusters (BGCs) and 152 predicted antimicrobial peptides. In predation assays, RDP092CA showed good predatory activity against Escherichia coli, Pseudomonas aeruginosa, Citrobacter freundii, and Staphylococcus aureus but not against Enterococcus faecalis. It also showed good antibiofilm activity against all five bacteria in biofilm assays. Antifungal activity against eight Candida spp. was variable, with particularly good activity against Meyerozyma guillermondii DSM 6381. Antimicrobial peptide RDP092CA_120 exhibited potent antibiofilm activity with >50% inhibition and >60% dispersion of biofilms at concentrations down to 1 μg/ml.

CONCLUSIONS

We propose that strain RDP092CA represents a novel species with promising antimicrobial activities, Corallococcus senghenyddensis sp. nov. (=NBRC 116490T =CCOS 2109T), based on morphological, biochemical, and genomic features.

Expanding the Myxochelin Natural Product Family by Nicotinic Acid Containing Congeners

Myxobacteria represent a viable source of chemically diverse and biologically active secondary metabolites. The myxochelins are a well-studied family of catecholate-type siderophores produced by various myxobacterial strains. Here, we report the discovery, isolation, and structure elucidation of three new myxochelins N1-N3 from the terrestrial myxobacterium Corallococcus sp. MCy9049, featuring an unusual nicotinic acid moiety. Precursor-directed biosynthesis (PDB) experiments and total synthesis were performed in order to confirm structures, improve access to pure compounds for bioactivity testing, and to devise a biosynthesis proposal. The combined evaluation of metabolome and genome data covering myxobacteria supports the notion that the new myxochelin congeners reported here are in fact frequent side products of the known myxochelin A biosynthetic pathway in myxobacteria.

Culture-dependent and -independent methods revealed an abundant myxobacterial community shaped by other bacteria and pH in Dinghushan acidic soils

Myxobacteria are one of the most promising secondary metabolites producers. However, they are difficult to isolate and cultivate. To obtain more myxobacteria and know the effects of environmental factors on myxobacterial community, we characterized myxobacterial communities in Dinghushan acidic forest soils of pH 3.6-4.5 with culture-dependent and -independent techniques, and analyzed environmental factors shaping myxobacterial communities. A total of 21 myxobacteria were isolated using standard cultivation methods, including eleven isolates of Corallococcus, nine isolates of Myxococcus and one isolate of Archangium, and contained three potential novel species. In addition, a total of 67 unknown myxobacterial operational taxonomic units (OTUs) were obtained using high-throughput sequencing method. The abundance of Myxococcales account for 0.9-2.2% of bacterial communities, and Sorangium is the most abundant genus (60.1%) in Myxococcales. Correlation analysis demonstrated that bacterial diversity and soil pH are the key factors shaping myxobacterial community. These results revealed an abundant myxobacterial community which is shaped by other bacteria and pH in Dinghushan acidic forest soils.

Geobacter, Anaeromyxobacter and Anaerolineae populations are enriched on anodes of root exudate-driven microbial fuel cells in rice field soil

Plant-based sediment microbial fuel cells (PMFCs) couple the oxidation of root exudates in living rice plants to current production. We analysed the composition of the microbial community on anodes from PMFC with natural rice field soil as substratum for rice by analysing 16S rRNA as an indicator of microbial activity and diversity. Terminal restriction fragment length polymorphism (TRFLP) analysis indicated that the active bacterial community on anodes from PMFCs differed strongly compared with controls. Moreover, clones related to Deltaproteobacteria and Chloroflexi were highly abundant (49% and 21%, respectively) on PMFCs anodes. Geobacter (19%), Anaeromyxobacter (15%) and Anaerolineae (17%) populations were predominant on anodes with natural rice field soil and differed strongly from those previously detected with potting soil. In open circuit (OC) control PMFCs, not allowing electron transfer, Deltaproteobacteria (33%), Betaproteobacteria (20%), Chloroflexi (12%), Alphaproteobacteria (10%) and Firmicutes (10%) were detected. The presence of an electron accepting anode also had a strong influence on methanogenic archaea. Hydrogenotrophic methanogens were more active on PMFC (21%) than on OC controls (10%), whereas acetoclastic Methanosaetaceae were more active on OC controls (31%) compared with PMFCs (9%). In conclusion, electron accepting anodes and rice root exudates selected for distinct potential anode-reducing microbial populations in rice soil inoculated PMFC.

[Isolation, identification and biological activity of myxobacteria from soils]

OBJECTIVE

Purpose of this work was to screen myxobacteria from soils and study their biological activities towards pathogenic bacteria, tumor cells and insects.

METHODS

Through inactivated E. coli and filter paper inducing methods, we isolated and purified myxobacteria from soil samples. Then we identified these purified strains based on morphological observation, physiological and biochemical characteristics, and the 16S rDNA sequences homologous analysis. By plate diffusion experiments, oral toxicity tests and tetrazolium assays, we investigated the biological activities of the myxobacterial culture supernatant.

RESULTS

We isolated 35 myxobacterial strains and classified them as 4 genera: Myxococcus (9), Corallococcus (9), Nannocystis (11) and Sorangium (6). Eight purified myxobacteria were identified and named. Cytotoxicity tests show that strain C. macrospores S22 had potent and broad-spectrum cytotoxic effect on tumor cell lines including B16, 4T1, HeLa and HCT-116, so did the strains M. fulvus S51, C. exiguus S22 and M. Xanthus S55. Additionally, C. macrospores S22 also shows inhibitory activity to pathogenic bacteria Bacillus subtillis and Candida albicans.

CONCLUSION

Myxobacteria are widely distributed in natural soils. C. macrosporus has potent toxicity against cancer cells and pathogenic bacteria; and C. exiguus with antitumor activity. The myxobacterial strains are promising resources for discovery and development of new active natural products and drugs.

[Isolation and identification of Myxobacteria strain STXZ54 with antitumor activities]

OBJECTIVE

We isolated Myxobacteria strains from soil samples collected from Guangzhou, identified the strain and studied the antitumor activity.

METHODS

We isolated Myxobacteria strains from soil samples through inactivated E. coli inducing method, identified the strain according to morphological observation, physiological and biochemical characteristics, and the homologous analysis of 16S rRNA sequences of nucleotides. The antitumor spectrum and the corresponding IC50 of the active component separated from the culture was analyzed. Confocal laser scanning microscope was used to examine the growth inhibitory effect of the active component on B16 cells.

RESULTS

We isolated a Myxobacteria strain and identified as Myxococcus macrosporus STXZ54. The active component termed SGF5 showed cytostatic activity against B16, Hela, 4T1, Hep-3B with IC50 values of 10 microg/mL, and HCT-116 cell with IC50 values of 70 microg/mL. Subcellular structure of B16 cells were abnormal observed by confocal laser scanning microscope. Combining the apoptosis and necrosis assay result it is likely that SGF5 can induce apoptosis of B16 cells.

CONCLUSION

The active component separated from the culture of Myxococcus macrosporus STXZ54 has a significant antitumor activity tested by cytotoxicity assay, which was worth exploiting as potential antitumor drugs.

Myxobacterial community is a predominant and highly diverse bacterial group in soil niches

Although many molecular ecological surveys have been conducted, there is little concerning the details of specific bacterial groups, resulting in an incomplete understanding of the microorganismal composition and community structures in the environment. Myxobacteria are micropredators that are metabolically active in the soil microbial food web and have typically been considered minority components of soil bacterial communities. In this study, we surveyed the percentage of myxobacteria in a single soil sample via pyrosequencing on combined universal libraries of the V3-V4 and V6-V8 hypervariable regions of the 16S rRNA gene. Surprisingly, myxobacteria accounted for 4.10% of the bacterial community and 7.5% of the total operational taxonomic units at the 3% similarity level in the soil, containing almost all of the cultivated myxobacterial families or genera. To testify the appearance of myxobacteria in soil niches, we retrieved myxobacteria-related 16S rRNA gene sequences of 103 high-throughput sequencing data sets obtained from public databases. The results indicated that myxobacteria-related sequences were among the predominant groups in these data sets accounting for 0.4-4.5% of bacterial communities. The abundance of myxobacterial communities were correlated with site temperature, carbon-to-nitrogen ratio and pH values. Based on these results, we discussed the survival strategies of myxobacterial community in soil.

Isolation and identification of myxobacteria from saline-alkaline soils in Xinjiang, China

Fifty-eight terrestrial and salt-tolerant myxobacteria were isolated from the saline-alkaline soils collected from Xinjiang, China. Based on the morphologies and the 16S rRNA gene sequences, these isolates were assigned into 6 genera, Myxococcus, Cystobacter, Corallococcus, Sorangium, Nannocystis and Polyangium. All the strains grew better with 1% NaCl than without NaCl. Some Myxococcus strains were able to grow at 2% NaCl concentration, suggesting that these strains may be particular type of terrestrial myxobacteria.

[Isolation and identification of cultivable myxobacteria in the rhizosphere soils of medicinal plants]

OBJECTIVE

We isolated myxobacteria and explored their diversity from the rhizosphere soils of some medicinal plants.

METHODS

We used the helper bacteria baiting technique to isolate myxobacteria from the rhizosphere soils collected in South China Botanical Garden and Nanling National Forest Park. The myxobacteria were identified by morphological characteristics and 16S rDNA gene sequences analysis.

RESULTS

A total of 50 strains were isolated from 22 soil samples, which were identified into 7 genera, Myxococcus (18), Corallococcus (11), Cystobacter (7), Archangium (8), Stigmatella (1), Chondromyces (4) and Pyxidicoccus (1). The dominant genera were Myxococcus and Corallococcus.

CONCLUSION

Environmental factors were associated with the diversity of myxobactria. Myxobacteria better adapt in high organic matter content and neutral pH environments. The strains of Myxococcus and Corallococcus had a good adaptability for different pH. Meanwhile, the dependence of the strains of Myxococcus and Cystobacter on organic carbon content was not too obvious, and they can also be found in the poor soils. Our findings provided an important scientific base for the development and utilization of myxobacteria resources.

[Influence of different prey strains on isolation myxobacteria in saline-alkaline soils of Xinjiang]

OBJECTIVE

We isolated myxobacteria in saline-alkaline soils of Xinjiang using a prey-predator strategy where the prey bacteria can induce the predator myxobacteria to form visible fruiting body, and evaluated intrinsic relationships between prey and predator myxobacteria.

METHODS

Sixteen bacteria with inductive effects of fruiting body formation were obtained, and then used as preys to isolate the myxobacteria.

RESULTS

A total of 55 myxobacteria strains were isolated from 25 soil samples, which were identified to the genera of Myxococcus, Corallococcus, Pyxidicoccus, Cystobacter, and Nannocystis. Besides, 6 unpurified isolates were believed to be myxobacteria. All the 16 prey bacteria had preferable inductive effects on Myxococcus spp., whereas Pyxidicoccus spp. and Cystobacter spp. were only induced by Gram-positive strains.

CONCLUSION

The prey-predator strategy provided a new and more effective way to isolate myxobacteria.

A comparison between ice and salt storages on bacteriological quality of Asian seabass (Lates calcarifer)

The study compares the bacteriological quality on Asian seabass (Lates calcarifer) between ice and salt storage methods. The main objectives of the study were to identify different bacteria constituents and quantitative bacterial load in Asian seabass when preserved with ice and sea salt. For the purpose of this study, Asian seabass was stored in two different conditions of ice-chilled and salted for 2 days. All fish samples were analyzed by performing bacteriological analysis and the isolated bacteria were identified by using API identification system. In case of the quantity of bacteria in the flesh, Chilling and salting had no significant difference to the quantity of bacteria on fish flesh. As for the skin, salt-preserved fish showed higher quantity of bacteria than ice-preserved fish. Acinetobacter baumannii and Pseudomonas fluorescens had been identified from skin sample of ice-chilled fish. Besides P. fluorescens and A. baumannii other isolates identified include Vibrio and Myxobacteria. All bacteria were cocci-shaped except a few bacilli. In term of bacteria number and morphological characteristics, ice-chilled preserved fish was better than salt preserved fish. Overall, less number of bacteria was observed in both ice-chilled and sea salt preserved fish. The result of this study indicated that the quick preservation is a very important factor to control bacterial load in the preserved fish.

[Isolation and identification of myxobacteria in the saline-alkaline soils of Akesu in Xinjiang]

OBJECTIVE

To isolate myxobacteria and investigate their diversity in saline-alkaline soils from Akesu in Xinjiang.

METHODS

Conventional culture-dependent methods, e. g. baiting technique, water agar, soil extract agar and mineral agar, were used to isolate myxobacteria from 25 soil samples collected from Akesu areas of Xinjiang. Combining with physicochemical properties (acidity/alkalinity, salt concentration, vegetation and geographical locations) of the soil samples, myxobacterial diversity was studied.

RESULTS

In total 58 strains were isolated, and identified as belonging to 6 different genera, i.e. Myxococcus, Cystobacter, Corallococcus, Sorangium, Nannocystis and Polyangium of Myxococcales. The most frequent genus isolated was Myxococcus which may better adapt in harsh environments. Different myxobacterial diversity was detected in different habitat.

CONCLUSION

Myxobacteria diversity was low in saline-alkaline soils of Akesu in Xinjiang.

Isolation of Sorangium cellulosum carrying epothilone gene clusters

Epothilone and its analogs are a potent new class of anticancer compounds produced by myxobacteria. Thus, in an effort to identify new myxobacterial strains producing epothilone and its analogs, cellulose-degrading myxobacteria were isolated from Korean soils, and 13 strains carrying epothilone biosynthetic gene homologs were screened using a polymerase chain reaction. A migration assay revealed that Sorangium cellulosum KYC3013, 3016, 3017, and 3018 all produced microtubule-stabilizing compounds, and an LCMS/ MS analysis showed that S. cellulosum KYC3013 synthesized epothilone A.

Identification of acetate-assimilating microorganisms under methanogenic conditions in anoxic rice field soil by comparative stable isotope probing of RNA

Acetate is the most abundant intermediate of organic matter degradation in anoxic rice field soil and is converted to CH(4) and/or CO(2). Aceticlastic methanogens are the primary microorganisms dissimilating acetate in the absence of sulfate and reducible ferric iron. In contrast, very little is known about bacteria capable of assimilating acetate under methanogenic conditions. Here, we identified active acetate-assimilating microorganisms by using a combined approach of frequent label application at a low concentration and comparative RNA-stable isotope probing with (13)C-labeled and unlabeled acetate. Rice field soil was incubated anaerobically at 25 degrees C for 12 days, during which (13)C-labeled acetate was added at a concentration of 500 muM every 3 days. (13)C-labeled CH(4) and CO(2) were produced from the beginning of the incubation and accounted for about 60% of the supplied acetate (13)C. RNA was extracted from the cells in each sample taken and separated by isopycnic centrifugation according to molecular weight. Bacterial and archaeal populations in each density fraction were screened by reverse transcription-PCR-mediated terminal restriction fragment polymorphism analysis. No differences in the bacterial populations were observed throughout the density fractions of the unlabeled treatment. However, in the heavy fractions of the (13)C treatment, terminal restriction fragments (T-RFs) of 161 bp and 129 bp in length predominated. These T-RFs were identified by cloning and sequencing of 16S rRNA as from a Geobacter sp. and an Anaeromyxobacter sp., respectively. Apparently these bacteria, which are known as dissimilatory iron reducers, were able to assimilate acetate under methanogenic conditions, i.e., when CO(2) was the predominant electron acceptor. We hypothesize that ferric iron minerals with low bioavailability might have served as electron acceptors for Geobacter spp. and Anaeromyxobacter spp. under these conditions.

The geographic distribution of the putative agent of epizootic bovine abortion in the tick vector, Ornithodoros coriaceus

Epizootic bovine abortion (EBA), also known as "foothill abortion", is a vector borne disease of beef cattle that graze in the mountainous regions of California, southern Oregon and western Nevada transmitted by the argasid tick Ornithodoros coriaceus. Recently, the putative agent of EBA was identified as a novel Deltaproteobacter in the order Myxococcales. In this study, a TaqMan real-time PCR (TM-PCR) protocol specific to the putative EBA agent was developed. The new real-time TM-PCR assay functioned sensitively and specifically to detect pathogen DNA in field-collected O. coriaceus ticks. The assay had an analytical sensitivity of a single plasmid copy and, when evaluated with a collection of tick-borne pathogens, yielded a positive PCR-result only for the agent of EBA. Use of the TM-PCR represents an effective tool for rapid and highly sensitive assessment of environmental risk and spatial and statistical analysis to highlight areas where there may be increased risk for EBA in susceptible cattle.

An outbreak of myxobacterial disease in coho salmon (Oncorhynchus kisutch) reared in a Maine estuary

An epizootic of a myxobacterial infection in coho salmon (Oncorhynchus kisutch) was responsible for the death of 50,000 fish, 30% of the population. Cartiage in the nose, mouth and lower jaw was eroded, and yellow sheets of bacterial growth were observed in the mouth, pharynx and pneumatic duct. The severity of the disease increased with increasing water temperature. Pathogenicity trials were inconclusive; only two of 18 experimentally infected fish succumbed to the disease. However, the lesions, and the absence of other known pathogens suggests the myxobacterium was responsible.

Rubellimicrobium thermophilum gen. nov., sp. nov., a red-pigmented, moderately thermophilic bacterium isolated from coloured slime deposits in paper machines

Six red-pigmented strains of the Alphaproteobacteria with optimal growth between 45 and 54 °C were previously isolated from coloured biofilms in two fine-paper machines and one pulp dryer. The strains were found to be resistant to 15 p.p.m. 2,2-dibromo-3-nitrilopropionamide, a common industrial biocide. 16S RNA gene sequence similarity of the isolates was 99.7–100 %. Ribotyping using the restriction enzymes PvuII and EcoRI showed that four of the isolates (C-lvk-R2A-1, C-lvk-R2A-2T, C-R2A-52d and C-R2A-5d) belong to a single species. 16S rRNA gene-based phylogenetic analysis revealed that, together with Rhodobacter blasticus ATCC 33485T, the isolates form a deep line of descent (94.7–94.9 % sequence similarity) within the family Rhodobacteraceae loosely affiliated with the Rhodobacter/Paracoccus clade. The isolates were strictly aerobic and oxidase-positive (catalase was weakly positive) and utilized a wide range of substrates including pentoses, hexoses, oligosaccharides and sugar alcohols. The predominant constituents in their cellular fatty acid profiles were C19 : 0 cyclo ω8c (39–44 %), C18 : 0 (21–24 %) and C16 : 0 (21–23 %). Fatty acids present in smaller amounts included C18 : 1 ω7c, C10 : 0 3-OH, C18 : 1 ω7c 11-methyl, C20 : 2 ω6,9c and C17 : 0 cyclo, amongst others. Polar lipids included diphosphatidylglycerol, phosphatidylcholine and an unidentified aminolipid, but not phosphatidylethanolamine. Carotenoid pigments were synthesized but bacteriochlorophyll a was not. The polyamine patterns consisted of the major compounds putrescine, spermidine and sym-homospermidine. The major respiratory lipoquinone was ubiquinone Q-10. The DNA G+C content was 69.4–70.2 mol%. On the basis of the phylogenetic and phenotypic evidence, the biofilm isolates were classified in a new genus, Rubellimicrobium gen. nov.; four of the isolates are assigned to the type species, Rubellimicrobium thermophilum gen. nov., sp. nov. Strain C-lvk-R2A-2T (=CCUG 51817T=DSM 16684T=HAMBI 2421T) is the type strain of Rubellimicrobium thermophilum.

Exploring the diversity of myxobacteria in a soil niche by myxobacteria-specific primers and probes

The diversity of myxobacteria in a soil niche was explored using culture-dependent and -independent methods. Conventional cultivation for bacteriolytic myxobacteria produced six types of myxobacteria, which were identified as two Myxococcus spp., two Corallococcus spp., a Cystobacter sp. and a Nannocysts sp. Hybridization analysis of the soil bacterial 16S rRNA gene library with myxobacteria-specific probes revealed that myxobacteria accounted for less than 1% in the bacterial community. A Cystobacterineae 16S rRNA genes-rich library was further established from the soil DNA by polymerase chain reaction amplification with a Cystobacterineae-specific primer combined with a universal bacterial primer. Screening of the special library using Cystobacterineae- and Sorangineae-specific probes produced approximately 45% and 3% positive signals respectively. Sixty-four positive clones were randomly selected for sequencing. Except three repeats, the sequences were diverse ranging from 0.3% to 21.3%, and homologous with the known myxobacteria at 77.6-99.8%, including 57 in Cystobacterineae, one close to Nannocystis and three much more distant from the known myxobacteria. The sequences in the Cystobacterineae can further be divided into at least 12 groups, of which most were unreported. The results suggest that myxobacteria in nature are much more diverse than were ever known, even in one soil niche.

Sugar composition and FT-IR analysis of exopolysaccharides produced by microbial isolates from paper mill slime deposits

Thirty exopolysaccharides (EPS) produced by bacteria isolated from biofilms or slimelayers from different paper and board mills in Finland, France and Spain were subjected to size exclusion chromatography and sugar compositional analysis. High performance size exclusion chromatography (HPSEC) analysis revealed that some samples were composed of several molecular weight populations. These samples were fractionated by size exclusion chromatography and pooled accordingly. Principal components analysis (PCA) of the sugar compositions of the different pools indicated the presence of glucans and mannans caused by insufficient removal of the carbon or nitrogen source (yeast extract) from the bacteria growth medium leading to an overestimation of the glucose and mannose level in the sample, respectively. From the point of view of slime problems the EPS populations are the most important for multivariate analysis. Four groups of EPSs have been recognized by PCA analysis: a group of EPSs produced by Enterobacter and related genera similar to the regularly reported colanic acid; a group of Methylobacterium EPSs having high galactose and pyruvate levels and two groups that showed less dense clusters produced by Bacillus and related genera, showing high mannose and/or glucose levels and Klebsiella EPSs that showed galactose with rhamnose as major characteristic sugar moieties. Fourier transform infrared spectroscopy (FT-IR) of the same samples followed by discriminant partial least squares regression (DPLS) and linear discriminant analysis (LDA) showed that, when used with a well-defined training set, FT-IR could be used clustering instead of time-consuming sugar composition analysis. The Enterobacter and Methylobacetrium EPS groups could be recognized clearly. However the fact that this could hardly be done for the other two groups in the dataset indicates the importance of a larger and well-defined training or calibration set. The potential to use FT-IR, as a tool for pattern recognition and clustering with respect to EPS structures produced by micro organisms isolated from a paper mill environment is discussed.

Characteristics and living patterns of marine myxobacterial isolates

The growth, morphology, and life cycle of two marine myxobacterial isolates, halotolerant Myxococcus fulvus strain HW-1 and halophilic Haliangium ochraceum strain SMP-2, were studied as models to determine the living patterns of myxobacteria in the ocean. The growth, morphology, and development of halotolerant strain HW-1 shifted in response to salinity. The optimal seawater concentration for growth of HW-1 was 0 to 80% (salinity, 0.1 to 2.9%), and the strain grew poorly in media with a salinity of more than 4%. The cells became shorter as the seawater concentration increased. The fruiting body structure was complete only on agar prepared with low concentrations of seawater or salts (less than 60% seawater; salinity, 2.1%), and rudimentary structures or even simple cell mounds appeared as the seawater concentration increased. In contrast, the halophilic strain SMP-2 was unable to grow without NaCl. The cell length and the morphology of the fruiting body-like structure did not change in response to salts. In seawater liquid medium, the cells of both strains were confirmed to be able to form myxospores directly from vegetative cells, but they could not do so in medium containing a low seawater concentration (10% or less). HW-1 cells from medium containing a high concentration of seawater grew independent of cell density, while cells from medium containing a low concentration of seawater (10% or less) showed density-dependent growth. SMP-2 cells showed density-dependent growth under all salinity conditions. The results suggest that the halotolerant myxobacteria are the result of degenerative adaptation of soil myxobacteria to the marine environment, while the halophilic myxobacteria form a different evolutionary group that is indigenous to the ocean.

Gene sequence heterogeneity of Corallococcus coralloides strains isolated from geographically diverse locations

Thirty-three strains classified as Corallococcus coralloides isolated from mostly soil samples in 14 countries of four continents, were subjected to phylogenetic analyses. Based on 16S rDNA analyses the strains form a highly related cluster, sharing above 98.7% sequence similarity. Four groups were recognized within this cluster, only one of which, containing two strains from St. Lucia, Lower Antilles, was exclusively defined by strains from the same sample. The other groups contained members from different countries, even continents. The largest group embraced the type strains of C. coralloides DSM 2259(T) and Corallococcus exiguus 14696(T) which were almost indistinguishable in their 16S rRNA gene sequence. Corallococcus macrosporus DSM 14697(T) grouped outside the C. coralloides cluster, showing a higher relationship to a member of Myxococcus. The topology of the tree generated on the basis of the partial gyrase B (gyrB) gene sequence supports the rRNA gene tree, though some differences in the order of branching were observed. As judged by the binary similarity values the higher resolution power of gyrB sequences was confirmed. From a taxonomic standpoint, the size of myxospores is not a valuable taxonomic criterion, as small- and medium-sized myxospores are members of the same group. If the species status of C. coralloides and C. exiguus is verified by other methods (e.g. DNA-DNA hybridisation, RiboTyping), the genus Corallococcus may embrace a broad range of yet-to-be described novel species. The presence of strains within the same sample displaying higher relatedness to strains from other locations points towards an intensive dispersal of myxospores across continents.

Myxobacteria isolated in Israel as potential source of new anti-infectives

AIMS

To evaluate the patterns of the production of antimicrobial compounds by Israeli myxobacteria newly isolated from soil samples and barks by a battery of isolation and purification methods.

METHODS AND RESULTS

A total of 100 myxobacteria belonging to five of the 12 described genera, were isolated from 48 soil and 45 tree bark samples collected in different areas inside the State of Israel. Four isolation methods based on the peculiar metabolic and cell cycle aspects of myxobacteria, were combined with purification procedures and optimization of cultivation conditions. Ninety-seven strains were fermented and screened for antimicrobial activities. Production of antimicrobial activities was detected in 62 isolates. More than 50% of the collection (54 strains) was able to inhibit Escherichia coli growth.

CONCLUSIONS

The results of this study support the idea that myxobacterial strains can be isolated from particular habitats and then cultivated and screened for their capacity to produce secondary metabolites endowed with antibacterial and antifungal activities. Myxovirescin, a typical poliketide myxobacterial antibiotic, has been identified in one Israeli isolate. Althiomycin, a thiazolyl peptide, which inhibits prokaryotic protein synthesis, usually produced by actinomycetes, was detected in three strains selected in this study.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results confirm that myxobacteria are prolific producers of a variety of bioactive secondary metabolites including antibacterial and antifungal compounds, being their high frequency of anti-Gram-negative activities particularly appealing for the current anti-infective research. So far their screening has often been hampered because their isolation is time-consuming and are quite difficult to handle and cultivate. In this paper we demonstrate that a proper combination of isolation, purification and cultivation methods allow their pharmaceutical exploitation.

Moderately thermophilic Myxobacteria: novel potential for the production of natural products isolation and characterization

Novel moderately thermophilic Myxobacteria from both known suborders (Cystobacterineae and Sorangineae) were isolated from soil samples of semiarid and warm climates. The addition of the anthelmintic and amoebizidal agent levamisole was a new and crucial improvement for the fast isolation of overall 37 strains, which grew very fast at temperatures of 42-44 degrees C. When the 16S rDNAs were compared with GenBank data of common Myxobacteria, identities were 98-99%, thus not reflecting the physiological differences. Similar to the Myxobacteria described so far, the new isolates are multiresistant against a variety of antibiotics and are producers of typical myxobacterial secondary metabolites. Analysis of our previous strain collection isolated from soil samples taken worldwide revealed a more or less uniform distribution of strains which synthesize specific metabolites. Therefore these moderately thermophilic Myxobacteria, which grow 2-3 times faster, have the potential to replace the slow-growing isolates and provide a means for fast and cost-saving production of myxobacterial metabolites in the future.

Myxobacterial Biodiversity in an Established Oak-Hickory Forest and a Savanna Restoration Site

The purpose of this study was to establish the myxobacterial biodiversity of an established oak-hickory forest and a savanna restoration site that has been cut and subsequently burned on four occasions between 1993 and 1998 in an attempt to restore the land to the native savanna ecosystem. Soil and bark samples were processed through standard methods specifically for myxobacteria and numbers and types of species were recorded for both locations. Species were identified through morphology of fruiting bodies, SDS-PAGE of whole cell protein profiles, and 16S rRNA gene sequences. Statistical analyses were employed and suggested that significantly greater numbers and types of myxobacteria are present on the bark of the trees in the established oak-hickory forest than the bark of trees in the savanna restoration site, while little difference in numbers and types of species were observed between the soil samples of the two locations.

Improved methods of isolation and purification of myxobacteria and development of fruiting body formation of two strains

By using baiting techniques and different purification methods, a high number of myxobacterial strains have been isolated as pure cultures from soil of different regions of China. Because myxobacterial cells do not disperse easily in liquid media, a medium containing an enzymatic hydrolysate of casein (CEH) medium have been used for purification and purity tests combined in a single step. The key method, in which isolates are reintroduced to sterile rabbit dung to induce fruiting bodies formation, facilitates purification of myxobacteria. Sterile rabbit dung pellets are used to mimic the natural growth substance of these organisms which has the advantage that characteristic fruiting bodies emerge, which is a key characteristics in the taxonomy of myxobacteria. In this study, the optimum program of isolation and purification of some myxobacteria strains has been established which will facilitate screening programs. Moreover, the development of fruiting body formation of strain BD20 (Chondromyces) and strain BD54 (Cystobacter) have been recorded in this study.

[The quantity and structure of the root-associated microbial complexes of two greenhouse rose cultivars]

The study of the root-associated microbial complexes of affected and healthy rose plants of two cultivars (Grand gala and Royal velvet) grown in a greenhouse showed that the biomass of eukaryotic microorganisms in the rhizoplane and rhizosphere of healthy rose plants and in the surrounding soil was considerably lower than in the same loci of affected plants. In contrast, the biomass of root-associated prokaryotic microorganisms was higher in the case of healthy than in the case of affected rose plants. The root-associated bacterial complexes of both affected and healthy rose plants were dominated by the genera Arthrobacter, Rhodococcus, and Myxobacterium and did not contain phytopathogenic bacteria. The root-associated fungal complex of healthy roses was dominated by fungi of the genus Trichoderma, whereas that of the affected rose plants was dominated by the species Aureobasidium microstictum. The affected cane cuttings and cankers occurring on affected canes were found to contain Coniothyrium fuckelii (the causal fungus of rose stem canker) and sclerotia of Botrytis cinerea (the causal fungus of gray rot). The micromycete complex of healthy rose plants was not so diverse as was the micromycete complex of affected rose plants.

Enhygromyxa salina gen. nov., sp. nov., a slightly halophilic myxobacterium isolated from the coastal areas of Japan

Six isolates of novel marine myxobacteria, designated strains SHK-1T, SMK-1-1, SMK-1-3, SMK-10, SKK-2, and SMP-6, were obtained from various coastal samples (mud, sands and algae) collected around Japan. All of the isolates had Gram-negative rod-shaped cells, motile by gliding and grew aerobically. They showed bacteriolytic action, fruiting body formation, and NaCl requirement for growth with an optimum concentration of 1.0-2.0% (w/v). In addition, divalent cationic components of seawater, such as Mg2+ or Ca2+, were also needed for growth. The major respiratory quinone was MK-7. The G+C content of genomic DNA ranged from 65.6 to 67.4 mol% (by HPLC). The isolates shared almost identical 16S rDNA sequences, and clustered with a recently described marine myxobacterium, Plesiocystis pacifica, as their closest relative on a phylogenetic tree (95.9-96.0% similarity). Physiological and chemotaxonomic differences between the new strains and strains of the genus Plesiocystis justify the proposal of a new genus. Therefore, we propose to classify the six isolates into a new taxon of marine myxobacteria with the name, Enhygromyxa salina gen. nov., sp. nov. The type strain is SHK-1(T) (JCM 11769(T) = DSM 15217(T) = AJ 110011(T)).

Plesiocystis pacifica gen. nov., sp. nov., a marine myxobacterium that contains dihydrogenated menaquinone, isolated from the Pacific coasts of Japan

Two strains of a novel myxobacterium (designated SIR-1T and SHI-1) were isolated from Japanese coasts located in the Pacific subtropical zone. Cells of both strains were Gram-negative, rod-shaped and motile by gliding. The strains were chemoheterotrophic and strictly aerobic. They had the common characteristics associated with myxobacteria, such as bacteriolytic action and fruiting-body formation. The characteristic feature of the strains was a NaCl growth requirement with an optimum concentration of 2.0-3.0 % (w/v), comparable to that of sea water. In addition, other cationic components of sea water, such as Mg2+, Ca2+ and K+, were needed for growth. The major respiratory quinone was MK-8(H2). The cellular fatty acid profile was characterized by the predominance of iso-C15:0. Characteristic fatty acids anteiso-C16:0 and anteiso-C17:0, and a long-chain polyunsaturated fatty acid (C20:4), were also detected. The G + C content of the genomic DNA of strains SIR-1T and SHI-1 was between 69.3 and 70.0 mol% (as determined by HPLC). Strains SIR-1T and SHI-1 shared almost identical 16S rDNA sequences, and clustered with the genus Nannocystis as their closest relative upon phylogenetic analysis. However, the phylogenetic distance between the novel strains and the genus Nannocystis was large enough to warrant their different generic allocation. This finding was supported by significant phenotypic differences between the novel strains and Nannocystis. Thus, strains SIR-1T and SHI-1 represent a novel genus and species, for which the names Plesiocystis and Plesiocystis pacifica, respectively, are proposed. The type strain of the species is SIR-1T (=JCM 11591T =DSM 14875T =AJ 13960T).

Haliangium ochraceum gen. nov., sp. nov. and Haliangium tepidum sp. nov.: novel moderately halophilic myxobacteria isolated from coastal saline environments

Phenotypic and phylogenetic studies were performed on two myxobacterial strains, SMP-2 and SMP-10, isolated from coastal regions. The two strains are morphologically similar, in that both produce yellow fruiting bodies, comprising several sessile sporangioles in dense packs. They are differentiated from known terrestrial myxobacteria on the basis of salt requirements (2-3% NaCl) and the presence of anteiso-branched fatty acids. Comparative 16S rRNA gene sequencing studies revealed that SMP-2 and SMP-10 are genetically related, and constitute a new cluster within the myxobacteria group, together with the Polyangium vitellinum Pl vt1 strain as the closest neighbor. The sequence similarity between the two strains is 95.6%. Based on phenotypic and phylogenetic evidence, it is proposed that these two strains be assigned to a new genus, Haliangium gen. nov., with SMP-2 designated as Haliangium ochraceum sp. nov. (= JCM 11303(T) = DSM 14365(T)), and SMP-10 as Haliangium tepidum sp. nov. (= JCM 11304(T)= DSM 14436(T)).

[Isolation and identification of myxobacteria]

This paper reported that the authors isolated large numbers of myxobacteria from more than 100 samples collected in many places of China. More than 400 pure strains were obtained. These strains belonged to 10 genera of Myxococcales. The most frequent genera isolated were Myxococcus, Sorangium, Corallococcus, and Cystobacter. Melittangium was seldom isolated. No Chondromyces and Haploangium were found.

Biology and global distribution of myxobacteria in soils

This review presents an overview of the present status of the biology of the myxobacteria, including the molecular biology of the systems that control and regulate myxobacterial gliding movement and morphogenesis. The present status of myxobacterial taxonomy and phylogeny is described. The evolutionary biology of the myxobacteria is emphasized with respect to their social behavior and the molecular basis of their signal chains. Most important within the metabolic physiology are the biologically active secondary metabolites of myxobacteria and their molecular mechanisms of action. The global distribution of myxobacteria in soils is described on the basis of data given in the literature as well as of comprehensive analyses of 1398 soil samples from 64 countries of all continents. The results are analyzed with respect to the spectrum and number of species depending on ecological and habitat-specific factors. The myxobacterial floras of different climate zones are compared. Included are myxobacterial species adapted to extreme biotopes. The efficiency of different methods used presently for isolation of myxobacteria is compared.

[Taxonomy of denitrifying bacteria in soddy podzolic soil]

The taxonomic composition of denitrifying bacteria in soddy podzolic soil was studied by the succession analysis method. This method revealed a significant variation in the taxonomic composition of denitrifying microorganisms in the course of succession. In contrast to succession analysis, the single microbiological analysis of soil samples reflected only the late stage of succession and thus led to an underestimation of the major members of succession. Myxobacteria were found to be the most active denitrifiers at the early stages of succession, whereas bacilli dominated at its late stages. The bacilli were represented by three facultatively anaerobic species, Bacillus cereus, Bac. circulans, and Bac. polymyxa.

Isolation of myxobacteria from the marine environment

In an attempt to isolate indigenous marine myxobacteria from coastal samples, we obtained two swarm forming bacteria. Both isolates formed cell aggregates which, at least in one isolate, developed to fruiting body-like structures consisting of a mass of myxospore-like cells. The optimum NaCl concentrations for their growth were between 2 and 3%, comparable to the NaCl concentration of seawater. This growth characteristic strongly suggests that the two isolates are specific marine bacteria. The 16S rDNA sequence studies indicated that the two isolates were related to the genus Nannocystis. Based on the phylogenetic distances between branches, we concluded that the isolates should be assigned to two new myxobacterial genera.

[Bacteria of the Flexibacter/Sporocytophaga group and violet-pigmented bacteria as indicators for hygienically doubtful drinking water]

Bacteria of the Flexibacter/Sporocytophaga group indicate, that drinking water is deficiently protected by the soil covering or may be infiltrated by surface waters. In South Bavaria those germs could be demonstrated in 1225 of 3743 samples from central water supplies and in 951 of 1714 samples from decentralized water supplies. F/Sp-bacteria could be isolated to a much greater extend from samples which were likewise polluted with Escherichia coli, coliforms and colony counts in excess. Over the year, bacteria of the F/Sp group are constantly distributed in contrast to E.coli or coliforms and will therefore constitute an useful indicator germ for hygienic hazardous drinking water supplies. In agreement with that violet-colored bacteria could also be isolated to a greater extend from polluted drinking water samples.

dsg, a gene required for cell-cell interaction early in Myxococcus development

dsg mutants of Myxococcus xanthus are conditionally defective in fruiting body development, including sporulation. Unable to develop on their own, these mutants can assemble fruiting bodies with spores if they are mixed with wild-type cells. To elucidate the developmental defect in dsg mutants by close comparison with wild type, such mutants have been backcrossed by transduction, using a closely linked insertion of transposon Tn5 for selection. Backcrossed dsg mutants form aggregates that are larger, less compact, and less symmetrical than dsg+ fruiting bodies. Also, the starvation-induced sporulation in dsg aggregates is delayed and reduced. However, dsg mutants can be induced by glycerol or dimethyl sulfoxide to sporulate at levels approaching those of wild type. dsg mutants may thus have a primary defect early in development which diminishes their capacity to aggregate and which indirectly decreases the number of fruiting body spores. The linked insertion of Tn5 also facilitated cloning the dsg gene. The cloned dsg+ allele was shown to be dominant to both the dsg-429 and dsg-439 alleles, and both mutant alleles were shown to belong to the same genetic complementation group. Subcloning of restriction fragments, deletions, and insertions of transposon Tn5 agree in locating the dsg gene to an 850-base-pair segment of the cloned region.

[Aquatic myxobacteria as indicators in the evaluation of drinking water quality (author's transl))]

Aquatic myxobacteria were shown to be good indicators of surface contamination of drinking water, or water filtered by an inadequate soil profile, both in experiments with sterilized or biologically active soil profiles, resp., and in actual comparison data obtained in practical drinking water analyses. In experimental investigations with artificial profiles, aquatic myxobacteria were retained to a considerably greater degree than E. coli or P. fluorescens due to stronger forces of adhesion. In a number of bacteriological drinking water analyses, this property was confirmed insofar as aquatic myxobacteria could regularly be demonstrated when inspecting hygienically deficient wells or springs. The confirmed presence of E. coli, on the other hand, showed a considerably lesser correlation with the results of on the spot evaluations of hygienic conditions. It must be urgently advised to include the search for aquatic myxobacteria in bacteriological drinking water analyses, since, contrary to the demonstration of E. coli, not only the actual but, in addition, the potential hazard of contamination of drinking water with bacteria present in superficial soil strata is indicated.

[Occurrence and distribution of fruiting body-forming myxobacteria in Siebengebirge. Comparative studies with special reference to characteristic biotypes]

In the region of the "Siebengebirge" near Bonn, six characteristic biotopes were studied with respect to the occurrence of fruiting body forming myxobacteria. 23 different species, belonging to the 8 known genera, were found. The number of species in the respective biotopes varied between 6 and 17, the average numbers of species per sampling area were between 2.1 and 10.0. 15 species were found on dung pellets of wild living herbivorous mammals. Deciduous forest soils contained 13 species in spring, 17 species in autumn. Rock coverings contained 14, creek slopes 16, bark of living trees 9, and rotting wood 16 fruiting myxobacterial species. Myxococcus fulvus, Myxococcus coralloides and Archangium gephyra occurred in all biotops studied. The rare species were Melittangium boletus, Polyangium vitellinum, Stigmatella aurantiaca, and Chondramyces apiculatus. The composition of the myxobacterial flora depends on ecological factors (kind of dung pellets, rock, bark and pH). The ecological influences upon the distribution are discussed.

The isolation and characterization of gliding motility mutants of Myxococcus xanthus

Nonmotile and motility-altered mutants of Myxococcus xanthus have been obtained by the use of chemical mutagens, ultraviolet irradiation, and a procedure for selective spontaneous mutants. As judged by their behaviour on a variety of growth media, in both plate and slide culture, the mutants were divided into four groups. One group contains mutants which are truly nonmotile. Myxococcus xanthus NM, previously described as a nonmotile mutant, may be similar to type 3 mutants (described in text).