镉对满江红（Azolla imbricata）-鱼腥藻（Anabaena azollae）共生体氮代谢的影响

在实验室条件下,研究了不同浓度(0、0.01、0.05、0.1、0.5mg/L)的Cd对满江红-鱼腥藻共生体异型胞频率,固氮酶、谷氨酰氨合成酶活性以及铵态氮、游离氨基酸、可溶性蛋白、总氮含量的影响.结果表明,在整个实验期间,0.01mg/L Cd处理对上述指标均没产生显著影响,说明满江红-鱼腥藻共生体对Cd具有较强的耐性.当培养液中Cd浓度≥0.05mg/L时,随溶液中Cd浓度的增加和处理时间的推移,异型胞频率、固氮酶活性、谷氨酰氨合成酶活性、可溶性蛋白含量和总氮含量逐渐下降,而铵态氮含量在处理初期显著降低,随后迅速增加,游离氨基酸含量则逐渐增加.研究结果表明高浓度的Cd处理导致满江红-鱼腥藻共生体氮代谢的紊乱,最终造成氮素积累量的下降.     

黄进华 Electron Microscopic Observation of Symbiotic Relationship Between Azolla and Anabaena During the Megaspore Germination and the Sporeling Development of Azolla

The process of establishing symbiotic relationship of Anabaena azollae with its host during the megaspore germination and sporeling development was examined using electron microscope. The observations revealed that most of the Anabaena spores were primarily adhered to the hair cells arisen from the sporeling subsequently introduced into the cavity of the 1st true leaf by the hair ceils. Following the sporeling development, the Anabaena spores were migrated to the newly developing cavities and the branch apex in the same way. The pattern of germination of the Anabaena spore is similar to that of free-living cyanobacteria. Germinating Anabaena spores were only found at shoot apex region and the cavities of the sporeling, 92% of them being onto or near the hair cells which exhibit the ultrastructural characteristics of the transfer cell. The results suggested that Anabaena spore might get the chemical signal stimulating germination or the substance supporting cell multiplication from the host. Some of vegetative cells derived from the Anabaena spore were differentiated in to nitrogen-fixing heterocysts within the cavity. This means that the new generation of the symbiosis between Anabaena and Azolla has begun.     

Isolation of sulfate‐reducing bacteria from deep sediment layers of the pacific ocean

Bacterial populations exist at great depths in marine sediments, but little is known about the type and characteristics of organisms in this unique bacterial environment. Cascadia Margin sediments from the Pacific Ocean have deep bacterial activity and bacterial populations, which are stimulated around a gas hydrate zone (215–225 m below sea floor [mbsf]). Bacterial sulfate reduction is the dominant anaerobic process within these sediments, and the depth distribution of sulfate‐reducing activity corresponds with distributions of viable sulfate‐reducing bacteria (SRB). Anaerobically stored sediments from this site were used to isolate sulfate‐reducing bacteria using a temperature‐gradient system, elevated pressure and temperatures, different media, and a range of growth substrates. A variety of enrichments on lactate were obtained from 0.5 and 222 mbsf, with surprisingly more rapid growth from the deeper sediments. The temperature range of enrichments producing strong growth from 222 mbsf was markedly wider than those from the near surface sediment (15–45°C and 9–19°C, respectively). This presumably reflects a temperature increase in deeper sediments. Only a few of these enrichments were successfully isolated due to very slow or no growth on subculture, despite the use of a wide range of different media and growth conditions. Psychrophilic and mesophilic sulfate‐reducing isolates were obtained from 0.5 m depth. As the minimum growth temperature of the mesophile (probably a Desulfotomaculum sp.) was above the in situ temperature of 3°C, it must have been present in the sediment as spores. A larger number of isolates (23) was obtained from 222 mbsf, and these barophilic SRB were closely related (based on 16S rRNA gene analysis), but not identical to, Desulfovibrio profundus, recently isolated from deep sediments from the Japan Sea. Bacteria related to D. profundus may be widespread in deep marine sediments.     

Copper and antimony extraction from tetrahedrite‐containing dolomite heterotrophic bacteria

Three hundred and thirty‐five strains of heterotrophic bacteria, isolated from various metal‐containing ores, were tested in submerged culture for their capacity to leach copper and antimony from tetrahedrite‐containing dolomitic ore (particle size <0.1 mm; Schwaz, Austria). Experiments showed that after 8 days of incubation, it was possible to differentiate between active and inactive strains. Maximum extraction values for copper (1.0%) and antimony (1.6%) were achieved with Pseudomonas spp. after 8 days. Final pH values were 6.8 in sterile controls and slightly alkaline (up to pH 8.3) in inoculated flasks. Starch and glutamine (C/N ratio of 50:1) proved to be the best carbon and nitrogen sources for growth. Variation of the C/N source resulted in only a very slight increase in the rates of extraction for copper and antimony. Not even 24 h preliminary incubation of a culture before the ore was added improved metal extraction.     

Polyamine-induced changes in symbiotic parameters of the Galega orientalis–Rhizobium galegae nitrogen-fixing system

Plants of goat's rue (Galega orientalis) inoculated with Rhizobium galegae strain HAMBI 540 were grown in the presence of putrescine (Put), spermidine (Spd) or spermine (Spm), and several symbiotic characteristics were investigated to delineate the influence of polyamines (PA) on this nitrogen-fixing system. All three PA exerted a concentration-dependent effect on the nodule parameters tested. The increment of nodulation ability and nodule biomass accumulation was extreme (from 2.4- to 4.0-fold) when plants were subjected to 10 and 50 M of various PA. However, at 100 M a negative effect was observed. The acetylene-reduction activity of nodulated roots was increased also in response to treatment with the lower PA concentrations. The level of nitrogenase activity supported by succinate was significantly higher in bacteroids isolated from PA-treated nodules than in bacteroids from control nodules. The symbiotic parameters were also dependent on the type of PA used; the most effective being the diamine Put, while Spm showed a smaller physiological effect with respect to the others. Polyamines altered the ultrastructure of Galega nodule infected cells. After treatment with these substances, pronounced changes in the relative volume of the main components of infected cells and their compartments were observed. The significance of the structural observations and morphometric analyses, their relationship to differences in nitrogen fixation and possible modes of action are discussed.     

Isolation and identification of entomopathogenic nematodes and their symbiotic bacteria from Hérault and Gard (Southern France)

Isolation and identification of native nematode-bacterial associations in the field are necessary for successful control of endemic pests in a particular location. No study has yet been undertaken to recover and identify EPN in metropolitan France. In the present paper, we provide results of a survey of EPN and their symbiotic bacteria conducted in Hérault and Gard regions in Southern France. Molecular characterization of isolated nematodes depicted three different Steinernema species and one Heterorhabditis species, H. bacteriophora. Steinernema species recovered were identified as: S. feltiae and S. affine and an undescribed species. Xenorhabdus symbionts were identified as X. bovienii for both S. feltiae and S. affine. Phylogenetic analysis placed the new undescribed Steinernema sp. as closely related to S. arenarium but divergent enough to postulate that it belongs to a new species within the “glaseri-group”. The Xenorhabdus symbiont from this Steinernema sp. was identified as X. kozodoii. All Heterorhabditis isolates recovered were diagnosed as H. bacteriophora and their bacterial symbionts were identified as Photorhabdus luminescens. Molecular characterization of these nematodes enabled the distinction of two different H. bacteriophora strains. Bacterial symbiontic strains of these two H. bacteriophora strains were identified as P. luminescens ssp. kayaii and P. luminescens ssp. laumondii.     

Evolution of the mammary gland from the innate immune system?

The mammary gland is a skin gland unique to the class Mammalia. Despite a growing molecular and histological understanding of the development and physiology of the mammary gland, its functional and morphological origins have remained speculative. Numerous theories on the origin of the mammary gland and lactation exist. The purpose of the mammary gland is to provide the newborn with copious amounts of milk, a unique body fluid that has a dual role of nutrition and immunological protection. Interestingly, antimicrobial enzymes, such as xanthine oxidoreductase or lysozyme, are directly involved in the evolution of the nutritional aspect of milk. We outline that xanthine oxidoreductase evolved a dual role in the mammary gland and hence provide new evidence supporting the hypothesis that the nutritional function of the milk evolved subsequent to its protective function. Therefore, we postulate that the mammary gland evolved from the innate immune system. In addition, we suggest that lactation partly evolved as an inflammatory response to tissue damage and infection, and discuss the observation that the two signaling pathways, NF-kB and Jak/Stat, play central roles in inflammation as well as in lactation.     

Can marine bacteria be recruited from freshwater sources and the air?

There is now clear evidence that microorganisms present biogeographic patterns, yet the processes that create and maintain them are still not well understood. In particular, the contribution of dispersal and its exact impact on local community composition is still unclear. For example, dispersing cells may not thrive in recipient environments, but may still remain part of the local species pool. Here, we experimentally tested if marine bacteria can be retrieved from freshwater communities (pelagic and sediment) and the atmosphere by exposing bacteria from three lakes, that differ in their proximity to the Norwegian Sea, to marine conditions. We found that the percentage of freshwater taxa decreased with increasing salinities, whereas marine taxa increased along the same gradient. Our results further showed that this increase was stronger for lake and sediment compared with air communities. Further, significant increases in the average niche breadth of taxa were found for all sources, and in particular lake water and sediment communities, at higher salinities. Our results therefore suggests that marine taxa can readily grow from freshwater sources, but that the response was likely driven by the growth of habitat generalists that are typically found in marine systems. Finally, there was a greater proportion of marine taxa found in communities originating from the lake closest to the Norwegian Sea. In summary, this study shows that the interplay between bacterial dispersal limitation and dispersal from internal and external sources may have an important role for community recovery in response to environmental change.     

A new α-galactosidase from symbiotic Flavobacterium sp. TN17 reveals four residues essential for α-galactosidase activity of gastrointestinal bacteria

The α-galactosidase gene, galA17, was cloned from Flavobacterium sp. TN17, a symbiotic bacterium isolated from the gut of Batocera horsfieldi larvae. The 2,205-bp full-length gene encodes a 734-residue polypeptide (GalA17) containing a putative 28-residue signal peptide and a catalytic domain belonging to glycosyl hydrolase family 36 (GH 36). The deduced amino acid sequence of galA17 was most similar to a putative α-galactosidase from Pedobacter sp. BAL39 (EDM38577; 66.6% identity) and a characterized α-galactosidase from Carnobacterium piscicola BA (AAL27305; 30.1%). Phylogenetic analysis revealed that GalA17 was similar to GH 36 α-galactosidases from symbiotic bacteria sharing two putative catalytic motifs, KWD and SDXXDXXXR, in which D480, S548, D549, and R556 were essential for α-galactosidase activity based on site-directed mutagenesis. Purified recombinant GalA17 showed apparent optimal activity at pH 5.5 and 45°C; exhibited strong resistance to digestion by trypsin, α-chymotrypsin, collagenase, and proteinase K; and efficiently hydrolyzed several synthetic and natural substrates (p-nitrophenyl-α-d-galactopyranoside, stachyose, melibiose, raffinose, soybean meal, locust bean gum, and guar gum).     

Microbial oxidation of arsenite and occurrence of arsenite‐oxidizing bacteria in acid mine water from a sulfur‐pyrite mine

The acid mine waters (pH 2.0–2.4) discharged from the Matsuo sul‐fur‐pyrite mine contained high concentrations of dissolved inorganic arsenic (2–13 ppm). Arsenic in the superficial acid mine waters was predominantly in the (V) state (arsenate); however, the element in the water from a deep mine drift was almost in the (III) state (arsenite). Microbial arsenite oxidation occurred in the acid mine waters and along the stream of the river, which was contaminated with a large volume of the mine drift water. Arsenite (500 ppm As)‐resistant bacteria (0–27 colonies/ml) were detected in the water samples and 208 slant cultures were obtained. Arsenite‐oxidizing activities of all the cultures were determined and six strains with strong arsenite‐oxidizing activity were isolated. These bacteria were acidophilic (optimum growth pH, 3—4), gram‐negative, aerobic, and rod‐shaped. They could not oxidize ferrous iron and elemental sulfur as a sole energy source and not derive the energy for chemoautotrophic growth from arsenite oxidation.     

The role of sulfate‐reducing bacteria in the deposition of sedimentary uranium ores

The formation of many important sediment‐hosted uranium ore deposits is thought to have resulted from the reduction of relatively soluble uranyl ion—U(VI)—to insoluble uranium (IV) oxides and silicates by aqueous sulfide species. This study focused on the influence that the sulfate‐reducing bacteria Desulfovibrio desulfuricans (ATCC 7757) has on this process. Preliminary studies showed that bacterial growth was not inhibited by concentrations of uranyl ion up to 100 mg U per liter. More detailed studies showed that sulfate‐reducing bacteria have an influence on uranyl ion removal beyond the simple production of the aqueous sulfide reductant. Comparative studies of bacterial cultures containing high densities of the sulfate reducers with bacterial cell‐free but otherwise identical media showed that the bacteria themselves enhance uranium removal from solution. At pH 8.0, no reaction was observed in H₂S‐bearing cell‐free media, whereas at the same H₂S concentration, the uranyl ion decreased markedly in the presence of the bacteria. At pH 7.0, some uranium removal occurred in the absence of bacteria, but it was much more rapid in their presence. We postulate that these effects are due to the ability of bacterial cell walls to adsorb uranium. Adsorption to surfaces is known from independent studies to enhance uranium reduction, and evidently this two‐step adsorption‐reduction mechanism is occurring in our experiments. We conclude that sulfate‐reducing and other bacteria may play a significant role in the geochemical cycling of uranium.     

Volatile compounds associated to the loss of astringency in persimmon fruit revealed by untargeted GC–MS analysis

High resolution volatile profiling (67 compounds identified) of fruits from 12 persimmon cultivars was established and used to characterize the different astringency types of persimmon fruit before and after deastringency treatment. Analysis of the volatile profile of fruit enables us to differentiate between cultivars that at the moment of harvest produced non-astringent fruit (Pollination Constant Non Astringent—PCNA-type) from astringent ones (non-PCNA-type). Fruit failing to accumulate astringent compounds naturally (PCNA fruit) showed high levels of 3(2H)-benzofuranone, while this compound was not detected in any astringent type fruit (non-PCNA). In addition to this, PCNA cultivars also showed at harvest higher accumulation of benzeneacetaldehyde and lipid-derived aldehydes (hexanal, heptanal, octanal and decanal) than non-PCNA fruit. The application of postharvest deastringency treatment to all non-PCNA cultivars resulted on an important insolubilization of tannins. In general the CO₂-treatment enhanced the levels of acetaldehyde, however those cultivars showing high levels of dihydrobenzofuran at harvest did not present an increment of acetaldehyde. In contrast, all non-PCNA cultivars exhibited an important accumulation of lipid-derived aldehydes due to CO₂-treatment. Therefore, we propose that lipid-derived aldehydes (mainly decanal, octanal and heptanal) may be playing a role in the astringency loss. Our results suggest that 3(2H)-benzofuranone, benzeneacetaldehyde and lipid-derived aldehydes could be used as markers for both natural and artificial loss of astringency.     

Species diversity of magnetotactic bacteria from the Ol’khovka River, Russia

A fraction of magnetotactic bacteria was isolated by magnetic separation from the water and silt samples collected from the Ol’khovka River (Kislovodsk, Russia). A 16S rRNA clone library was obtained from the total DNA of the fraction by PCR amplification and molecular cloning. Phylogenetic analysis of 67 16S rRNA gene sequences of randomly selected clones demonstrated that two phylotypes of magnetotactic bacteria were present in the library: the first phylotype consisted of 42 sequences and the second one included only one sequence. The remaining 24 sequences belonged to non-magnetotactic bacteria. According to the results of phylogenetic analysis, both phylotypes were magnetotactic cocci; the predominant sequences were almost identical to the 16S rRNA sequence of the freshwater coccus TB24 (X81185.1) identified earlier among the magnetotactic bacteria isolated from Lake Chiemsee (Bavaria). The phylotype represented by a single sequence formed a separate branch in the dendrogram, with 97% similarity between its sequence and that of TB24. The discovered phylotypes formed with the sequences of uncultured freshwater magnetotactic cocci a separate branch within the class Alphaproteobacteria and presumably belonged to a separate family within the recently described order Magnetococcales. Despite the fact that phylogenetic analysis of the 16S rRNA clone library did not reveal any phylotypes of magnetotactic spirilla, after the secondary enrichment of the fraction of magnetotactic bacteria using the “race track” technique, a new strain of magnetotactic spirilla, Magnetospirillum SO-1, was isolated. The closest relative of strain SO-1 was the previously described magnetotactic spirillum Magnetospirillum magneticum AMB-1.     

Kinetics of the AHL regulatory system in a model biofilm system: how many bacteria constitute a "quorum"?

Acylated homoserine lactones (AHLs) regulate a wide variety of phenotypes in Gram-negative bacteria. Most research suggests that AHL-mediated phenotypes are not expressed in populations until late logarithmic phase or stationary phase. Here, we model how the concentration of AHLs inside bacterial cells and in a biofilm changes over time as a function of population growth rate, diffusion of AHLs and the rate of autoinduction. Our theoretical results show that the concentration of AHLs inside a single bacterium (and by implication induction of a phenotype) has a non-trivial behaviour over time, and often exhibits a rapid increase early in population growth. This rapid increase is followed by a plateau, followed by another rise in the concentration of AHLs, to a second plateau. High concentrations of AHLs inside the bacterial cell early in population growth are positively affected by slow diffusion rates out of the cell and the biofilm, slow bacterial growth rates and fast autoinduction. In contrast, fast growth rates, slow autoinduction rates and high diffusion rates result in a high concentration plateau in stationary phase. More generally, the density-dependent nature of AHL regulation can be viewed as a trade-off between factors that dilute intracellular concentrations of AHLs (diffusion out of the cell, cell division), and those that increase concentrations (a slowing or restriction of diffusion or growth, or autoinduction). These results suggest that expression of AHL-mediated phenotypes can occur at relatively low cell densities and low external/environmental AHL concentrations.     

A Nereites ichnofacies from the Ordovician‐Silurian Welsh Basin

The sediments of the Ordovician‐Silurian succession of west Wales are interpreted as turbiditic sands with associated pelagic and hemi‐pelagic mudstones. The strata contain a trace fossil assemblage consisting of fifteen ichnogenera, namely: Chondrites, Circulichnis, Cochlichnus, Cosmorhaphe, Desmograpton, Gordia, Helminthoida, Helminthopsis, Neonereites, Nereites, Paleodictyon, Palaeophycus, Planolites, Protopaleodictyon and Spirophycus. The ichnofaunal assemblage is typical of the Nereites ichnofacies. Twenty three ichno‐species are described, two of which (Helminthoida granulata, Palaeophycus serratus) are new. Turbiditic sands contain the most abundant and diverse ichnoassemblages, a reflection of favorable environmental conditions for habitation by benthic organisms. Both the turbiditic mudstones and anoxic hemipelagites contain just two ichno‐species, namely Chondrites ichnosp. and Planolites montanus both of which are common, albeit less so in the latter facies. The effects of preservation potential, medium and preservation mechanisms are also important controls on distribution.     

A preliminary study of anaerobic thiosulfate‐oxidizing bacteria as denitrifiers in the Arabian Sea

Bacteria which oxidize thiosulfate and reduce nitrate (TONRB) and bacteria which oxidize thiosulfate and denitrify (TODB) sampled at 5‐, 100‐, 200‐ and 300‐m depths were enumerated in agar shake cultures by colony counting and by applying MPN technique, respectively. Lithotrophic denitrification was generally high at the surface but did not vary much with the distance from shore as indicated by the number of TODB. The number of TONRB shows that nitrate‐reduction was much higher at near‐shore stations. The low TODBITONRB ratios at intermediate depths and at 100 m show in particular that the relative abundance of these organisms could be one of the possible reasons for higher nitrite concentrations sometimes reported at these depths. Thiosulfate‐oxidizing and simultaneous nitrate‐reducing abilities of the isolates indicated that the strains isolated from near shore and surface waters were more active nitrate reducers than their counterparts in offshore or deeper waters. The growth yield values of these organisms ranged from 1.1 to 17.9 mg protein mmol^‐1 thiosulfate and from 11.7 to 36.3 mg protein mmol^‐1 sulfide and suggest that they could contribute to chemosynthetic production.     

Did the molecules of adaptive immunity evolve from the innate immune system?

The antigen receptors on cells of innate immune systems recognizebroadly expressed markers on non-host cells while the receptorson lymphocytes of the adaptive immune system display a higherlevel of specificity. Adaptive immunity, with its exquisitespecificity and immunological memory, has only been found inthe jawed vertebrates, which also display innate immunity. Jawlessfishes and invertebrates only have innate immunity. In the adaptiveimmune response, T and B-lymphocytes detect foreign agents orantigens using T cell receptors (TCR) or immunoglobulins (Ig),respectively. While Ig can bind free intact antigens, TCR onlybinds processed antigenic fragments that are presented on moleculesencoded in the major histocompatibility complex (MHC). MHC moleculesdisplay variation through allelic polymorphism. A diverse repertoireof Ig and TCR molecules is generated by gene rearrangement andjunctional diversity, processes carried out by the recombinaseactivating gene (RAG) products and terminal deoxynucleotidyltransferase (TdT). Thus, the molecules that define adaptiveimmunity are TCR, Ig, MHC molecules, RAG products and TdT. Nodirect predecessors of these molecules have been found in thejawless fishes or invertebrates. In contrast, the complementcascade can be activated by either adaptive or innate immunesystems and contains examples of molecules that gradually evolvedfrom non-immune functions to being part of the innate and thenadaptive immune system. In this paper we examine the moleculesof the adaptive immune system and speculate on the existenceof direct predecessors that were part of innate immunity.