Effects of chaotropic salts on global proteome stability in halophilic archaea: Implications for life signatures on Mars

Halophilic archaea thriving in hypersaline environments, such as salt lakes, offer models for putative life in extraterrestrial brines such as those found on Mars. However, little is known about the effect of the chaotropic salts that could be found in such brines, such as MgCl₂, CaCl₂ and (per)chlorate salts, on complex biological samples like cell lysates which could be expected to be more representative of biomarkers left behind putative extraterrestrial life forms. We used intrinsic fluorescence to study the salt dependence of proteomes extracted from five halophilic strains: Haloarcula marismortui, Halobacterium salinarum, Haloferax mediterranei, Halorubrum sodomense and Haloferax volcanii. These strains were isolated from Earth environments with different salt compositions. Among the five strains that were analysed, H. mediterranei stood out as a results of its high dependency on NaCl for its proteome stabilization. Interestingly, the results showed contrasting denaturation responses of the proteomes to chaotropic salts. In particular, the proteomes of strains that are most dependent or tolerant on MgCl₂ for growth exhibited higher tolerance towards chaotropic salts that are abundant in terrestrial and Martian brines. These experiments bridge together global protein properties and environmental adaptation and help guide the search for protein-like biomarkers in extraterrestrial briny environments.     

Alleviating salt stress in tomato seedlings using Arthrobacter and Bacillus megaterium isolated from the rhizosphere of wild plants grown on saline–alkaline lands

Salt-induced soil degradation is common in farmlands and limits the growth and development of numerous crop plants in the world. In this study, we isolated salt-tolerant bacteria from the rhizosphere of Tamarix chinensis, Suaeda salsa and Zoysia sinica, which are common wild plants grown on a saline–alkaline land, to test these bacteria's efficiency in alleviating salt stress in tomato plants. We screened out seven strains (TF1–7) that are efficient in reducing salt stress in tomato seedlings. The sequence data of 16S rRNA genes showed that these strains belong to Arthrobacter and Bacillus megaterium. All strains could hydrolyze casein and solubilize phosphate, and showed at least one plant growth promotion (PGP)-related gene, indicating their potential in promoting plant growth. The Arthrobacter strains TF1 and TF7 and the Bacillus megaterium strain TF2 and TF3 could produce indole acetic acid under salt stress, further demonstrating their PGP potential. Tomato seed germination, seedling length, vigor index, and plant fresh and dry weight were enhanced by inoculation of Arthrobacter and B. megaterium strains under salt stress. Our results demonstrated that salt-tolerant bacteria isolated from the rhizosphere of wild plants grown on saline–alkaline lands could be used for alleviating salt stress in crop plants.     

DNA base compositions of halophilic and nonhalophilicBacillus firmus strains of marine origin

The mineral salt requirements of 27 strains ofBacillus firmus were determined. Twenty-six of these strains were of marine origin and one terrestrial strain was used as a reference. Three strains demonstrated strictly halophilic behavior, i.e., they showed no growth in media prepared without sodium chloride. Seven strains were nonhalophilic. The growth of 17 strains was stimulated by the addition of sodium chloride, but the cells were able to grow without it. These results were compared with the DNA base compositions of the strains. In contrast to literature data, relationships between the DNA base ratios and the halophilic or nonhalophilic behavior of the cells could not be detected. But strains with guanine plus cytosine values above 41 mol% did grow well at 44°C, and those strains showing poor growth at this temperature had lower guanine plus cytosine percentages.     

Identification and characterization of CMTM4, a novel gene with inhibitory effects on HeLa cell growth through Inducing G2/M phase accumulation

Human CMTM is a novel gene family consisting of CKLF and CMTM1-8. CMTM4 is the most conserved gene and has three RNA splicing forms designated as CMTM4-v1, -v2 and -v3, but in many types of tissue and cell lines, only CMTM4-v1 and -v2 could be detected. CMTM4-v2 is the full length cDNA product, which has been highly conserved during evolution. CMTM4-v1 and -v2 are broadly expressed in normal types of tissue. They are distributed on the cell membrane and across the cytoplasm in a speckled pattern. Overexpression of CMTM4-v1 and -v2 can inhibit HeLa cell growth via G2/M phase accumulation without inducing apoptosis. Therefore, CMTM4 might be an important gene involved in cell growth and cell cycle regulation.     

Effect of salinity on growth of four strains of Rhizobium and their infectivity and effectiveness on two species of Acacia

Two Rhizobium strains (WU1001 and WU1008) were isolated from nodules of Acacia redolens growing in saline areas of south-west Australia, and two strains selected from the University of Western Australia's culture collection (WU429 isolated from A. saligna and WU433 from A. cyclops). The growth of each in buffered, yeast extract mannitol broth culture was largely unaffected by salt up to 300 mM NaCl. A slight increase in lag time occurred at concentrations of 120 mM NaCl and above, but cell number at the static phase was not affected. Each of the four Rhizobium strains tested accumulated Na⁺ but showed decreasing levels of sugar with increasing salt in the external medium. Amino acid levels also increased, in some cases by more than tenfold. However, the relative proportion of each remained fairly constant in the bacteria, irrespective of salt treatment. Only trace quantities of proline were detected and there was no increase in this amino acid with salt. Acidic amino acids (glutamate and aspartate) remained as a constant proportion.Rhizobium strains WU429, WU1001 and WU1008 produced effective nodules on both A. cyclops and A. redolens grown in sand with up to 80 mM NaCl (added in nutrient solutions free of nitrogen). Strain WU433 was highly infective on both Acacia species tested at low salt concentrations (2–40 mM NaCl), but infection was sensitive to salt levels at 120 mM NaCl and above. Nodules formed with strain WU433 were, however, ineffective on both A. redolens and on A. cyclops and showed nil or negligible rates of acetylene reduction at all salt concentrations. Strains WU429, WU1001 and WU1008 in combination with a highly salt-tolerant provenance of A. redolens formed symbioses which did not vary significantly in nodule number and mass, specific nodule activity or total N content irrespective of salt level up to 160 mM NaCl. On a more salt sensitive provenance of A. redolens and on A. cyclops the infectivity and effectivity of the Rhizobium strains tested usually decreased as the external salt concentration increased. These data are interpreted to indicate that tolerance of the legume host was the most important factor determining the success of compatible Rhizobium strains in forming effective symbioses under conditions of high soil salinity.     

3株罗伊氏乳杆菌生物学特性的分析比较

【目的】对3株罗伊氏乳杆菌的生物学特性进行分析比较,为后期生产应用提供一定的参考。【方法】对实验室保藏的3株罗伊氏乳杆菌的生长曲线、pH曲线、耐受人工胃液能力、耐受猪胆盐能力、黏附能力、抑菌能力和对抗生素的耐药性等特性进行了分析比较。【结果】3株菌生长趋势大致相同;3株菌对人工胃液均具有良好的耐受性,且可以有效地抑制大肠杆菌和金黄色葡萄球菌的生长;菌株L0和L2对高胆盐的环境耐受性较差,菌株L1则对高胆盐环境具有极强的耐受性;菌株L1和L2具有很强的黏附能力;3株菌对20种抗生素表现出不同的耐受性。【结论】菌株L1的生物学特性明显优于其他两株菌株,有利于后期的生产应用。     

The colicin A pore-forming domain fused to mitochondrial intermembrane space sorting signals can be functionally inserted into the Escherichia coli plasma membrane by a mechanism that bypasses the Tol proteins

Colicin A is a pore-forming bacteriocin that depends upon the Tol proteins in order to be transported from its receptor at the outer membrane surface to its target, the inner membrane. The presequence of yeast mitochondria cytochrome c₁ (pc1) as well as the first 167 amino acids of cytochrome b₂ (pb2) were fused to the pore-forming domain of colicin A (pfColA). Both hybrid proteins (pc1-pfColA and pb2-pfColA) were cytotoxic for Escherichia coli strains devoid of colicin A immunity protein whereas the pore-forming domain without presequence had no lethal effect. The entire precursors and their processed forms were found entirely associated with the bacterial inner membrane and their cytotoxicities were related to their pore-forming activities. The proteins were also shown to kill the tol bacterial strains, which are unable to transport colicins. In addition, we showed that both the cytochrome C₁ presequence fused to the dihydrofolate reductase (pc1-DHFR) and the cytochrome c, presequence moiety of pc1-pfColA were translocated across inverted membrane vesicles. Our results indicated that: (i) pc1-pfColA produced in the cell cytoplasm was able to assemble in the inner membrane by a mechanism independent of the tol genes; (ii) the inserted pore-forming domain had a channel activity; and (ii) this channel activity was inhibited within the membrane by the immunity protein.     

Chemical composition of the peptidoglycan-free cell walls of methanogenic bacteria

Cell walls were prepared from freeze-dried samples of 7 strains of Methanobacterium by mechanical disintegration of the cells followed by incubation with trypsin. Electron microscopy revealed the presence of sacculi exhibiting the shape of the original cells, on which no surface structure could be detected. Ultrathin sections of the isolated sacculi showed a homogenously electron dense layer of about 10–15 nm in width. The ash content varied between 8 and 18% of dry weight. The sacculi of all the strains contained Lys: Ala: Glu: GlcNAc or GalNAc in a molar ratio of about 1:1.2:2:1. In one strain (M. ruminantium M 1) alanine is replaced by threonine, however. Neutral sugars and-in some strains-additional amounts of the amino sugars were present in variable amounts, and could be removed by formamide extraction or HF treatment without destroying the sacculi. No muramic acid or d-amino acids typical of peptidoglycan were found. Therefore, the sacculi of the methanobacteria consist of a different polymer containing a set of three l-amino acids and one N-acetylated amino sugar. From cells of Methanospirillum hungatii no sacculi, but tube-like sheaths could be isolated, which tend to fracture perpendicularly to the long axis of the sheath along the fibrills seen on the surface. The sheaths consist of protein containing 18 amino acids and small amounts of neutral sugars. They are resistent to the proteinases tested and are not disintegrated by boiling in 2% sodium dodecylsulfate for 30 min.The three Gram-negative strains Black Sea isolate JR-1, Cariaco isolate JR-1 and Methanobacterium mobile do not contain a rigid sacculus, but merely a SDS-sensitive surface layer composed of regularly arranged protein subunits. This evidence indicates that, within the methanogens, different cell wall polymers characteristic of particular groups of organisms may have evolved during evolution, and supports the hypothesis that the evolution of the methanogens was separated from that of the peptidoglycan-containing procaryotic organisms at a very early stage.Non Standard Abbreviations SDS sodium dodecylsulfate - EDTA ethylenediaminetetra acetic acid - DNP dinitrophenyl Dedicated to Prof. Dr. Adolf Butenandt on the occasion of his 75th birthday     

Influence of Incubation Atmosphere on Growth and Amino Acid Requirements of Streptococcus mutans

The growth response of Streptococcus mutans representing antigenic type a or d in a chemically defined medium was influenced by the oxygen concentration of the growth atmosphere. Under controlled aerobic (1.5% O(2)) conditions these cultures attained a greater density than when the atmosphere contained 0.006% O(2) or less. The growth of S. mutans strains representing antigenic types b or c in the defined medium was independent of the oxygen concentration of the growth environment. Under the conditions used in this study, none of the strains tested could utilize ammonium ion as a sole source of nitrogen for growth. The requirement for certain amino acids and inhibition by other amino acids varied with antigenic type and relative oxygen concentration of the growth environment. Under conditions where the atmospheric oxygen was reduced to 0.0006% O(2) or less, the amino acid requirements of the cultures became either more numerous or more stringent. S. mutans strains of type c generally required the least number of amino acids, whereas cultures of type d had more numerous requirements. Nearly every culture tested under the anaerobic atmosphere was inhibited by one of the branched-chain amino acids, leucine, valine, or isoleucine. Methionine and lysine were also found to be inhibitory, particularly toward the type c strains.     

Strain-specific salt tolerance and chemotaxis ofAzospirillum brasilense and their associative N-fixation with finger millet in saline calcareous soil

Three salt-tolerantAzospirillum brasilense strains were isolated from the roots of finger millet grown in saline calcareous soil and characterized. The effect of various salts on growth and N₂ase activity of these strains was tested and strain STR1 was found more tolerant at higher concentrations of Cl^-, SO₄ ² and HCO₃ ^-. Bicarbonate was found to be the most toxic. The content and concentrations of root exudates of finger millet genotypes were different and chemotaxis to sugars, amino acids, organic acids and root exudates was strain specific. Under salt stress, significant interactions between strains and genotypes of finger millet resulted in different responses of N₂ase activity, endo- and exorhizospheric population, dry weight of root, shoot and grain yield.     

Aspects of physiology of Histoplasma capsulatum (A review)

Yeast and mycelial forms of several strains of Histoplasma capsulatum have been analysed with respect to their ability to grow on a defined medium with or without the amino acid supplement. It appeared that whereas mycelial cells of all strains tested were prototrophic, the yeast cells of most strains stringently required L-cysteine for growth. This was due to the absence from these cells of an active form of an enzyme, sulfite reductase, normally needed for cysteine biosynthesis. We have found that the yeast cells of two strains (Downs and G 184 B) can grow without cysteine supplement if L-serine is added to the medium. These cells have an active sulfite reductase but the enzyme disappears when cysteine is added. Thus, the regulation of sulfite reductase is different in mycelium and yeast — the enzyme is constitutive or repressible, respectively.Examination of RNA synthetic components of H. capsulatum revealed that the major proportion of RNA polymerase of the yeast form is sensitive to inhibition by -amanitin. The sensitivity to the toxin disappears completely upon conversion to mycelial phase. The yeast cells possess an unusual enzyme capable of synthesizing oligonucleotides without the aid of a DNA template. The enzyme stimulates DNA synthesis in the reaction catalyzed by DNA polymerase from H. capsulatum or Escherichia coli. The above data are discussed in terms of regulatory mechanisms involved in the process of morphological conversion. It is proposed that efforts be directed toward the identification and isolation of specific gene products so that qualitative and quantitative analysis of the conversion could be carried out.presented, in part, at the 1st International Histoplasmosis Conference, held on April 10–12, 1978 in Atlanta, Georgia, U.S.A.     

Morphometry and growth of three <Emphasis Type="Italic">Synechococcus</Emphasis>-like picoplanktic cyanobacteria at different culture conditions

Three phycocyanin-rich strains of Synechococcus-like picoplanktic cyanobacteria, isolated from the plankton of Czech oligotrophic to eutrophic freshwater reservoirs, were investigated in crossed gradients of light and temperature and in combination with two different culture media (BG-11 and WC). The strains exhibited similar growth and reproduction patterns and displayed overlapping ranges of cell size (1.5 × 0.8 μm) under standardized laboratory conditions (18 μmol m⁻² s⁻¹; 20°C). However, strains behavior differed in the crossed gradients. All strains preferred BG-11 medium, where also remarkable size changes could be observed. Length, width, cell abundance and growth rate of two strains were positively correlated with temperature and nutrients, whereas the impact of light intensity was insignificant. Maximum cell elongation (involution cells up to 19 μm) occurred in two strains only in BG-11 medium at highest temperature (28°C) and highest irradiance (53 μmol m⁻² s⁻¹). Cell dimensions in WC medium were constant under most conditions given. The third strain was influenced by all three factors, from which light and nutrients played pivotal role. The length of the lag-phase for all strains appeared to be temperature dependent (negative correlation). Despite the fact that the cell volume in all strains increased more than five times under the lowest light and low temperature (6 μmol m⁻² s⁻¹, <15°C) in both media, the length/width ratio remained unchanged. The strains differed in the degree of cell enlargement and cell division symmetry as well as in optimum temperature and light dependence. Based on this experimental work two strains could be identified as Synechococcus sp. and one as Cyanobium sp., which can be used as a support for the following genetical analyses.     

Development of a chemically defined medium for growth ofNeisseria gonorrhoeae

A chemically defined medium satisfactory for growth of a number of laboratory strains and recent isolates ofNeisseria gonorrhoeae has been devised. It contains inorganic salts, dextrose, guanine, cytosine, B-vitamin supplement, and the following amino acids:l-arginine,l-aspartic acid,l-cystine,l-isoleucine,l-leucine,l-proline,l-threonine, andl-valine.Nine of the eleven strains grew satisfactorily in this medium without being provided supplemental CO₂ during incubation, and a tenth strain grew in the medium supplemented with glutamine. No single B-vitamin or purine or pyrimidine base was essential for growth of any of the strains, but some combinations of them were stimulatory. Riboflavin, however, was inhibitory. The strains showed variations in requirements for amino acids. The amino acids which were either essential or stimulatory for one or more of the strains were included in the medium. Those to which the strains responded differently were used at concentrations intermediate between those optimal for growth of one strain and inhibitory for another. Conventional agar was inhibitory, but a purified agar, having a gel strength twice that of conventional agar, was satisfactory. An aqueous solution of 0.1% cysteine and 0.86% NaCl was satisfactory for preparation of inocula.This investigation was supported by a Public Health Service Predoctoral Fellowship (F-FI-GM-24-755-01A1) from the National Institute of General Medical Sciences of the United States Public Health Service to the senior author.     

Construction and Analyses of Mutant <Emphasis Type="Italic">ftsH</Emphasis> Alleles of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> Involving the ATPase- and Zn-Binding Domains

The ftsH gene, present in all eubacterial species, is anchored in the cytoplasmic membrane and contains an ATP- and a Zn-binding domain that are both part of a metalloprotease activity. The Bacillus subtilis ftsH is not essential, but null mutants exhibit a pleiotropic phenotype including filamentous growth; hypersensitivity towards heat and salt stress and a failure to sporulate. To find out whether one or the other functional domain is involved in these different phenotypes, point mutations were introduced into the coding region for both domains leading to a replacement of conserved amino acid residues. The mutant alleles were fused to a xylose-inducible promoter and integrated ectopically into two different strains, one expressing the wild-type ftsH allele and the other carrying a ftsH knockout. While none of the strains exhibited a growth defect in rich medium at 37°C, those strains expressing only the mutant alleles did not resume growth after heat or salt stress challenge. Furthermore, none of the mutant alleles promoted sporulation. While only those purified mutant FtsH proteins with an intact Walker A box exhibited ATPase activity, all of them failed to degrade -casein.     

Allelic diversification at the C (OsC1) locus of wild and cultivated rice: nucleotide changes associated with phenotypes

Divergent phenotypes are often detected in domesticated plants despite the existence of invariant phenotypes in their wild forms. One such example in rice is the occurrence of varying degrees of apiculus coloration due to anthocyanin pigmentation, which was previously reported to be caused by a series of alleles at the C locus. The present study reveals, on the basis of comparison of its maps, that the C gene appears to be the rice homolog (OsC1) of maize C1, which belongs to the group of R2R3-Myb factors. Two different types of deletions causing a frameshift were detected in the third exon, and both of the deleted nucleotides corresponded to the positions of putative base-contacting residues, suggesting that the Indica and Japonica types carry loss-of-function mutations with independent origins. In addition, replacement substitutions were frequently detected in OsC1 of strains carrying the previously defined C alleles. Molecular population analysis revealed that 17 haplotypes were found in 39 wild and cultivated rices, and the haplotypes of most cultivated forms could be classified into one of three distinct groups, with few shared haplotypes among taxa, including Indica and Japonica types. The genealogy of the OsC1 gene suggests that allelic diversification causing phenotypic change might have resulted from mutations in the coding region rather than from recombination between preexisting alleles. The McDonald and Kreitman test revealed that the changes in amino acids might be associated with selective forces acting on the lineage of group A whose haplotypes were carried by most Asian cultivated forms. The results regarding a significant implication for genetic diversity in landraces of rice are also discussed.     

The Interactive Effects of Temperature and Osmotic Potential on the Growth of Aquatic Isolates of Fusarium culmorum

The mycelial growth of 10 Fusarium culmorum strains isolated from water of the Andarax riverbed in the provinces of Granada and Almeria in southeastern Spain was tested on potato-dextrose-agar adjusted to different osmotic potentials with either KCl or NaCl (?1.50 to ?144.54 bars) at 10°C intervals ranging from 15° to 35°C. Fungal growth was determined by measuring colony diameter after 4 d of incubation. Mycelial growth was maximal at 25°C. The quantity and capacity of mycelial growth of F. culmorum were similar at 15 and 25°C, with maximal growth occurring at ?13.79 bars water potential and a lack of growth at 35°C. The effect of water potential was independent of salt composition. The general growth pattern of Fusarium culmorum growth declined at potentials below ?13.79 bars. Fungal growth at 25°C was always greater than growth at 15°C, at all of the water potentials tested. Significant differences were observed in the response of mycelia to water potential and temperature as main and interactive effects. The number of isolates that showed growth was increasingly inhibited as the water potential dropped, but some growth was still observable at ?99.56 bars. These findings could indicate that F. culmorum strains isolated from water have a physiological mechanism that permits survival in environments with low water potential. Propagules of Fusarium culmorum are transported long distances by river water, which could explain the severity of diseases caused by F. culmorum on cereal plants irrigated with river water and its interaction under hydric stress or moderate soil salinity. The observed differences in growth magnitude and capacity could indicate that the biological factors governing potential and actual growth are affected by osmotic potential in different ways.     

High Throughput Phenotypic Analysis of Mycobacterium tuberculosis and Mycobacterium bovis Strains' Metabolism Using Biolog Phenotype Microarrays

Tuberculosis is a major human and animal disease of major importance worldwide. Genetically, the closely related strains within the Mycobacterium tuberculosis complex which cause disease are well-characterized but there is an urgent need better to understand their phenotypes. To search rapidly for metabolic differences, a working method using Biolog Phenotype MicroArray analysis was developed. Of 380 substrates surveyed, 71 permitted tetrazolium dye reduction, the readout over 7 days in the method. By looking for ≥5-fold differences in dye reduction, 12 substrates differentiated M. tuberculosis H37Rv and Mycobacterium bovis AF2122/97. H37Rv and a Beijing strain of M. tuberculosis could also be distinguished in this way, as could field strains of M. bovis; even pairs of strains within one spoligotype could be distinguished by 2 to 3 substrates. Cluster analysis gave three clear groups: H37Rv, Beijing, and all the M. bovis strains. The substrates used agreed well with prior knowledge, though an unexpected finding that AF2122/97 gave greater dye reduction than H37Rv with hexoses was investigated further, in culture flasks, revealing that hexoses and Tween 80 were synergistic for growth and used simultaneously rather than in a diauxic fashion. Potential new substrates for growth media were revealed, too, most promisingly N-acetyl glucosamine. Osmotic and pH arrays divided the mycobacteria into two groups with different salt tolerance, though in contrast to the substrate arrays the groups did not entirely correlate with taxonomic differences. More interestingly, these arrays suggested differences between the amines used by the M. tuberculosis complex and enteric bacteria in acid tolerance, with some hydrophobic amino acids being highly effective. In contrast, γ-aminobutyrate, used in the enteric bacteria, had no effect in the mycobacteria. This study proved principle that Phenotype MicroArrays can be used with slow-growing pathogenic mycobacteria and already has generated interesting data worthy of further investigation.     

Improved Salinity Tolerance of <Emphasis Type="Italic">Arachis</Emphasis><Emphasis Type="Italic">hypogaea</Emphasis> (L.) by the Interaction of Halotolerant Plant-Growth-Promoting Rhizobacteria

Salinity adversely affects plant growth and development. Halotolerant plant-growth-promoting rhizobacteria (PGPR) alleviate salt stress and help plants to maintain better growth. In the present study, six PGPR strains were analyzed for their involvement in salt-stress tolerance in Arachis hypogaea. Different growth parameters, electrolyte leakage, water content, biochemical properties, and ion content were analyzed in the PGPR-inoculated plants under 100 mM NaCl. Three bacterial strains, namely, Brachybacterium saurashtrense (JG-06), Brevibacterium casei (JG-08), and Haererohalobacter (JG-11), showed the best growth of A. hypogaea seedlings under salt stress. Plant length, shoot length, root length, shoot dry weight, root dry weight, and total biomass were significantly higher in inoculated plants compared to uninoculated plants. The PGPR-inoculated plants were quite healthy and hydrated, whereas the uninoculated plant leaves were desiccated in the presence of 100 mM NaCl. The percentage water content (PWC) in the shoots and roots was also significantly higher in inoculated plants compared to uninoculated plants. Proline content and soluble sugars were significantly low, whereas amino acids were higher than in uninoculated plants. The MDA content was higher in uninoculated plants than in inoculated plants at 100 mM NaCl. The inoculated plants also had a higher K⁺/Na⁺ ratio and higher Ca²⁺, phosphorus, and nitrogen content. The auxin concentration was higher in both shoot and root explants in the inoculated plants. Therefore, it could be predicted that all these parameters cumulatively improve plant growth under saline conditions in the presence of PGPR. This study shows that PGPR play an important role in inducing salinity tolerance in plants and can be used to grow salt-sensitive crops in saline areas.     

Morphological and biochemical characterization of the exocellular investments of polysaccharide-producing Nostoc strains from the Pasteur Culture Collection

A total of 40 Nostoc strains, belonging to the Pasteur Culture Collection and originally isolated from different habitats, were photoautotrophically grown in liquid cultures and tested for the presence of exocellular polysaccharidic investments surrounding the trichomes. However, 25 of them showed a significant presence of these structures, coupled with the release of polysaccharidic material (RPS) into the medium. A rather large number of different morphological forms was observed in the cultures during growth, but at the time of harvesting the predominant morphological form was, in most cases, the vegetative trichome. With regard to the exocellular mucilaginous investments, three main types of morphologies were observed: (i) capsules surrounded by an external pellicle, (ii) capsules with sharp outlines but without an external pellicle, (iii) slimy investments that either loosely surrounded the trichomes without following their shape or were organized in large globular lumps. Among the twenty-five strains that released polysaccharides into the culture medium, three showed mean daily productivities ranging from 30 to 50 mg (RPS) l⁻¹ d⁻¹, values comparable with those of the most productive cyanobacterial strains so far described. The morphological characteristics of the polysaccharidic investments produced by the Nostoc strains seem not to be related to their original habitats. Furthermore, the differences in RPS productivities observed among the strains seem not to be related to the shape of the mucilaginous exocellular investments. Chemical analysis of purified samples of the polysaccharides demonstrated that all the polymers possess an acidic nature, due to the presence of uronic acids, and that they are characterized by the presence of a peptidic moiety and of amino sugars. This revised version was published online in July 2006 with corrections to the Cover Date.