Number Of Microbial Cells Research Articles

Prokaryotic ultramicroforms in a Sphagnum peat bog of upper Volga catchment

The waters of small lakes located in swampy catchment areas of upper Volga contain considerable amounts of ultrasmall microbial cells that pass through 0.22-μm-pore-size filters. As shown in our previous study [1], most of these cells represent the bacterial genera Herbaspirillum, Herminiimonas, Curvibacter, and Burkholderia of the class Betaproteobacteria, as well as euryarchaea of the uncharacterized clade LDS. The aim of the present study was to investigate the possible effect of the waters draining swampy areas on the composition of the filterable microbial fraction in lakes fed by swampy catchments. To address this question molecular identification was performed of prokaryotic ultramicroforms in the peat of the ombrotrophic Sphagnum bog Obukhovskoe, located, like the lakes studied previously [1], in the Mologa-Sheksna catchment area. The number of filterable microorganisms in 1 g wet peat was 3.8 × 106 cells, or 0.5% of total microbial cell number in the peat. From the DNA of the filterable cell fraction, 100 clones of bacterial and 77 clones of archaeal 16S rRNA genes were obtained. The bacterial clone library contained 16S rRNA gene sequences representing the classes Beta- and Gammaproteobacteria (the genera Janthinobacterium and Pseudomonas, respectively) and the phylum Bacteroidetes (the genera Chryseobacterium and Epilithonimonas) and differed significantly from the clone library of bacterial ultramicroforms of lake water. By contrast, the pools of filterable archaea in bogs and lakes were essentially similar. They were represented by the euryarchaeal clade LDS and methanogens of the orders Methanobacteriales and Methanosarcinales. Additionally, the pool of filterable archaea of the bog included methanogens of the order Methanomicrobiales and representatives of the uncharacterized euryarchaeal clade RC-V (Rice Cluster V) and of the phylum Thaumarchaeota.

Assessing sub‐seafloor microbial activity by combined stable isotope probing with deuterated water and 13C‐bicarbonate

Sub-seafloor sediments are populated by large numbers of microbial cells but not much is known about their metabolic activities, growth rates and carbon assimilation pathways. Here we introduce a new method enabling the sensitive detection of microbial lipid production and the distinction of auto- and heterotrophic carbon assimilation. Application of this approach to anoxic sediments from a Swedish fjord allowed to compare the activity of different functional groups, the growth and turnover times of the bacterial and archaeal communities. The assay involves dual stable isotope probing (SIP) with deuterated water (D(2) O) and (13) C(DIC) (dissolved inorganic carbon). Culture experiments confirmed that the D content in newly synthesized lipids is in equilibrium with the D content in labelled water, independent of whether the culture grew hetero- or autotrophically. The ratio of (13) C(DIC) to D(2) O incorporation enables distinction between these two carbon pathways in studies of microbial cultures and in environmental communities. Furthermore, D(2) O-SIP is sufficiently sensitive to detect the formation of few hundred cells per day in a gram of sediment. In anoxic sediments from a Swedish fjord, we found that > 99% of newly formed lipids were attributed to predominantly heterotrophic bacteria. The production rate of bacterial lipids was highest in the top 5 cm and decreased 60-fold below this depth while the production rate of archaeal lipids was rather low throughout the top meter of seabed. The contrasting patterns in the rates of archaeal and bacterial lipid formation indicate that the factors controlling the presence of these two lipid groups must differ fundamentally.

Real-Time Field Monitoring To Optimize Microbe Control

Technology Update Microbial growth in oil and gas systems can cause numerous problems that result in production downtime, lost revenue, and safety concerns. Unfortunately, microbial populations are ubiquitous in many oil and gas production zones and minimizing their impact is challenging. The most common effects of microbial growth are corrosion, hydrogen sulfide (H2S) production, and biofouling. The ability to minimize the negative impact of microbes is confounded by the current field monitoring technology, which is unable to detect many of the organisms. These monitoring technologies are culture-based, meaning that organisms must be grown in culture to be detected and quantified. It is well documented in many systems that less than 1% of the total organisms present are culturable. In addition, the culture-based methods commonly take days or weeks to produce a result. Thus, operators must wait a considerable time before taking control measures, and the impact of microbial populations can increase during the long period of undetection. New Development in Monitoring Method Two essential parameters for any new field monitoring technology are the ability to obtain a result in real time and the ability to detect all organisms, not just the ones that can be grown in culture. The industry has evaluated several of these technologies over the years, including a first-generation adenosine triphosphate (ATP) assay in which the level of ATP is used to measure the number of actively growing microbes in a sample. ATP is the molecule used by cells to drive any process that requires energy. This includes metabolism, protein translation, DNA repair, and cell division. Although there are differences in the absolute quantity of ATP in different species or organisms, it is assumed that actively growing bacterial cells hold relatively similar amounts of ATP, and a calculation has been determined to quantify microbial cell numbers based on a measurement of ATP. The major challenge of using this technology in oilfield systems is that the enzymatic assay used to quantify ATP is very sensitive to the quality of the fluids tested. This means that many oilfield fluids such as oil, emulsions, produced water with significant solids, high-salinity fluids, and fluids contaminated with certain chemicals would not yield meaningful results. As an example, the first-generation ATP test was not generally accepted by oilfield operators and has been little used. However, a second-generation ATP test that addresses the concerns has been developed recently. Specifically, additional steps were developed to enable accurate testing of fluids that contain oil, high salinity, residual chemicals, and solids. This technology also meets the other necessary criteria—real-time results and detection of all microbes, not only those that grow in culture.

Characterization of Metabolically Active Bacterial Populations in Subseafloor Nankai Trough Sediments above, within, and below the Sulfate-Methane Transition Zone.

A remarkable number of microbial cells have been enumerated within subseafloor sediments, suggesting a biological impact on geochemical processes in the subseafloor habitat. However, the metabolically active fraction of these populations is largely uncharacterized. In this study, an RNA-based molecular approach was used to determine the diversity and community structure of metabolically active bacterial populations in the upper sedimentary formation of the Nankai Trough seismogenic zone. Samples used in this study were collected from the slope apron sediment overlying the accretionary prism at Site C0004 during the Integrated Ocean Drilling Program Expedition 316. The sediments represented microbial habitats above, within, and below the sulfate–methane transition zone (SMTZ), which was observed approximately 20 m below the seafloor (mbsf). Small subunit ribosomal RNA were extracted, quantified, amplified, and sequenced using high-throughput 454 pyrosequencing, indicating the occurrence of metabolically active bacterial populations to a depth of 57 mbsf. Transcript abundance and bacterial diversity decreased with increasing depth. The two communities below the SMTZ were similar at the phylum level, however only a 24% overlap was observed at the genus level. Active bacterial community composition was not confined to geochemically predicted redox stratification despite the deepest sample being more than 50 m below the oxic/anoxic interface. Genus-level classification suggested that the metabolically active subseafloor bacterial populations had similarities to previously cultured organisms. This allowed predictions of physiological potential, expanding understanding of the subseafloor microbial ecosystem. Unique community structures suggest very diverse active populations compared to previous DNA-based diversity estimates, providing more support for enhancing community characterizations using more advanced sequencing techniques.

Carbon and nitrogen assimilation in deep subseafloor microbial cells

Remarkable numbers of microbial cells have been observed in global shallow to deep subseafloor sediments. Accumulating evidence indicates that deep and ancient sediments harbor living microbial life, where the flux of nutrients and energy are extremely low. However, their physiology and energy requirements remain largely unknown. We used stable isotope tracer incubation and nanometer-scale secondary ion MS to investigate the dynamics of carbon and nitrogen assimilation activities in individual microbial cells from 219-m-deep lower Pleistocene (460,000 y old) sediments from the northwestern Pacific off the Shimokita Peninsula of Japan. Sediment samples were incubated in vitro with (13)C- and/or (15)N-labeled glucose, pyruvate, acetate, bicarbonate, methane, ammonium, and amino acids. Significant incorporation of (13)C and/or (15)N and growth occurred in response to glucose, pyruvate, and amino acids (∼76% of total cells), whereas acetate and bicarbonate were incorporated without fostering growth. Among those substrates, a maximum substrate assimilation rate was observed at 67 × 10(-18) mol/cell per d with bicarbonate. Neither carbon assimilation nor growth was evident in response to methane. The atomic ratios between nitrogen incorporated from ammonium and the total cellular nitrogen consistently exceeded the ratios of carbon, suggesting that subseafloor microbes preferentially require nitrogen assimilation for the recovery in vitro. Our results showed that the most deeply buried subseafloor sedimentary microbes maintain potentials for metabolic activities and that growth is generally limited by energy but not by the availability of C and N compounds.

Abstract LB-281: Enteric bacterial protein AvrA enhances tumorigenesis through activating intestinal STAT/beta-catenin signaling pathways

Abstract Enteric bacteria play an important role in the pathogenesis of colon cancer. More than 1000 species of bacteria coexist in the human colon. The number of microbial cells is about 10 times larger than the number of eukaryotic cells in the human body. Due to the complexity of the gut flora, identification of the specific microbial agents contributing to colon cancer remains challenging. How bacterial products directly contribute to colorectal cancer is still unknown. Many researchers have taken advantage of the colitis induced by Salmonella Typhimurium to study the early phase of inflammation and infection. A few reports have been on chronic infection in vivo. Bacteria can modulate the host by secreting bacterial effector proteins to the host cells. AvrA is a pathogenic gene of Salmonella and E.coli, whose encoded protein is inserted into intestinal mucosa. AvrA influences eukaryotic cell pathways utilizing ubiquitin and acetylation. We hypothesize that the bacterial effector AvrA activates the STAT/beta-catenin pathway to promote colonic tumorigenesis. In the current study, we investigated a chronic bacterial infected cancer model with Salmonella Typhimurium colonization in the mouse intestine for 49 weeks. Mice were colonized with AvrA-sufficient or deficient bacterial strains, then stimulated with a carcinogen azoxymethane (10mg/kg body weight, intraperitoneal injection) and 1% dextran sodium sulfate (induced colitis) in vivo. We found that mice infected with AvrA-expressed bacteria had significantly high incidence of tumor in colon. We found that AvrA expression decreased the phosphorylated-beta-catenin and inhibits the ubiquitination of beta-catenin in mouse colonic epithelial cells in vivo. Additionally, bacterial AvrA expression enhanced the acetylated beta-catenin, which regulates the beta-catenin transcription activity and stabilizes beta-catenin. Moreover, we found the infected colon had higher STAT 1 and 3 expressions. Inflammatory cytokines such as IL-6 and INF-gamma in serum were increased. The STAT pathway was activated by infection and promoted epithelial cancer. STAT and its acute STAT activation promoted inflammation in the infected colon. Overall, AvrA activation of the STAT/beta-catenin pathway promoted colonic tumorigenesis. Our findings provide important insights into how a bacterial effector protein contributes to the development of colon cancer. We believe that determining the responses and underlying mechanisms by which bacteria modulate the STAT/beta-catenin pathway will identify novel approaches to target the specific signal pathway that contributes to tumorigenesis. Our findings can also be applied to the risk assessment and prevention of colon carcinogenesis. This work was supported by NIH DK075386 and ACS RSG-09–075–01-MBC to Jun Sun. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-281. doi:10.1158/1538-7445.AM2011-LB-281

Enteric Bacteria and Cancer Stem Cells

Intestinal bacteria can contribute to cell proliferation and cancer development, particularly in chronic infectious diseases in which bacteria and/or bacterial components might interfere with cell function. The number of microbial cells within the gut lumen is estimated to be 100 trillion, which is about 10-times larger than the number of eukaryotic cells in the human body. Because of the complexity of the gut flora, identifying the specific microbial agents related to human diseases remains challenging. Recent studies have demonstrated that the stemness of colon cancer cells is, in part, orchestrated by the microenvironment and is defined by high Wnt activity. In this review article, we will discuss recent progress with respect to intestinal stem cells, cancer stem cells, and the molecular mechanisms of enteric bacteria in the activation of the Wnt pathway. We will also discuss the roles of other pathways, including JAK-STAT, JNK, and Notch, in regulating stem cell niches during bacterial infections using Drosophila models. Insights gained from understanding how host-bacterial interaction during inflammation and cancer may serve as a paradigm for understanding the nature of self-renewal signals.

Monitoring of the microbial community composition in deep subsurface saline aquifers during CO2 storage in Ketzin, Germany

Abstract This study characterized the composition and activity of the autochthonous microbial community in formation fluids of a saline CO 2 storage aquifer during CO 2 injection and during an N 2 lift. The clean-up of the wells prior CO 2 injection by N 2 lift decreased the total microbial cell numbers, and the number of sulphate reducing bacteria (SRB) was reduced by at least two orders of magnitude. Fluorescence in situ Hybridisation (FISH) and molecular fingerprinting demonstrated that the microbial community was strongly influenced by the CO 2 injection. Before CO 2 arrival, up to 106 cells ml-1 were detected by DAPI-staining at a depth of 647 m below the surface. The microbial community was dominated by fermentative halophilic bacteria and sulphate reducing bacteria. Both the FISH and fingerprinting analyses revealed quantitative and qualitative changes after CO 2 arrival. An enhanced activity and quantity of the microbial population after five months of CO 2 storage indicated that the community was able to adapt to the extreme conditions of the deep biosphere and to the extreme changes of these anthropogenically modified conditions.

Evaluation of river model biofilm for assessing pesticide effects: a case study with atrazine

The dose response of the biological parameters of the model river biofilm, consisting of two diatom strains and three bacterial strains on the glass surface, was examined with atrazine. Good correlations (r2=0.90–0.93) between the atrazine log concentration and the relative increase rates of microbial cell numbers and the amount of chlorophyll a in the model biofilm formation were shown, and similar EC50 values for the biological parameters including esterase activity were tentatively obtained as an endpoint. The results suggested that this model biofilm could be used for testing the potential effects of pesticides on natural river biofilms at a community level with high reproducibility.

PRODUKSI MASAL INOKULUM AZOTOBACTER, AZOSPIRILLUM DAN BAKTERI PELARUT FOSFAT DENGAN MENGGUNAKAN MEDIA ALTERNATIF

<p>Azotobacter, Azospirillum and phosphate solubilizing bacteria are the most common microbial inoculants used as biofertilizer. To have good quality of biofertilizer, the high number of inoculant cells and suitable carriers as well as the method of carrier sterilization are among the most important factors determined the quality of biofertilizer. Related to the number of inoculant cells in carriers, the growing medium used to cultivate the microbial cells play very important role. For mass production of microbial cells, the medium should be able to support fast growth of microbial cells. The price of medium should be reasonably cheap and the materials used in medium should be available easily. The purpose of this study was to obtain a cheap growing medium that can support high number of microbial inoculant cells and the components of the medium should be easyly obtain and the price is not expensive. The study was conducted at the Department of Soil Science and Land Resources, Faculty of Agriculture, Bogor Agricultural University (IPB). The results showed that the medium IPB RI-1 was able to support the growth of 1010 cfu ml-1 Azotobacter, 108 cfu ml-1 Azospirillum and 109 cfu ml-1 Phosphate Solubilizing Bacteria. The number of bacterial cells in Nutrient Broth medium was only 108 cfu ml-1. This means that the IPB RI-1 medium was able to produce 100-fold population of Azotobacter compared to the growth of this bacterium in Nutrient Broth and Phosphate Solubilizing Bacteria was 10-fold higher than population in Nutrient Broth medium. The costs of the IPB RI-1 and IPB RI-2 were much cheaper compared to the cost of Nutrient Broth medium. The cost of medium IPB RI-1 only 3% (IDR 945) and IPB RI-2 about 2% (IDR 690) of the cost of Nutrient Broth medium (IDR 27,752) per liter medium in the year of 2010.<br />Keywords : Alternative media, Azotobacter, Azospirillum, Nutrient Broth, Phosphate Solubilizing Bacteria</p>

Repression of potential nitrification activities by matgrass sward species

Soil nitrification is a key process in regulating the relative availability of the various inorganic N forms to plants. In the current study, we investigated the effect of different plant species on numbers of ammonia-oxidizing microbial cells by measuring the potential nitrification activity (PAA). Soil from matgrass sward and from calcareous grassland was collected in the field and four characteristic plant species of each vegetation type were cultivated from seed. These plant species grew for 4 months in the two soil types. After those 4 months, PAA were significantly higher in calcareous soil compared to the matgrass sward soil and the presence of matgrass sward species had significantly decreased PAA in this soil. In soils from matgrass stands, PAA were much lower, and no effect of the different plant species could be detected. Plant biomass of the calcareous grassland species was overall positively correlated with PAA, whereas for matgrass plant species a negative trend was found. We conclude that matgrass sward plant species had a clear repressing effect on the potential ammonia-oxidizing activity in calcareous grassland soil within this 4-month growth experiment. The observed repression of PAA is in accordance with earlier field observations of PAA in the different vegetation zones, where repressed PAA and significant higher ammonium to nitrate ratios were observed in the matgrass sward vegetation compared to the other vegetation zones. Major findings of this study indicate that plant species can influence the nitrification potential of their habitats, i.e. certain species can repress nitrification potential and others can increase nitrification potential of their habitats.

Species and strain composition of microbial associations oxidizing different types of gold-bearing concentrates

Quantitative abundance of microbial species within an association was found to depend on the energy substrate and the oxidation temperature of sulfide minerals. The number of microbial cells varied depending on the position of reactor in the chain, i.e., the stage of the energy substrate oxidation. Microbial associations oxidized the energy substrate more efficiently than any of their individual components. The increase in pulp density up to the solid : liquid ratio of 1 : 2.5 had an unfavorable effect on microorganisms comprising microbial associations.

Microbial colonization of Ca-sulfate crusts in the hyperarid core of the Atacama Desert: implications for the search for life on Mars

The scarcity of liquid water in the hyperarid core of the Atacama Desert makes this region one of the most challenging environments for life on Earth. The low numbers of microbial cells in the soils suggest that within the Atacama Desert lies the dry limit for life on our planet. Here, we show that the Ca-sulfate crusts of this hyperarid core are the habitats of lithobiontic micro-organisms. This microporous, translucent substrate is colonized by epilithic lichens, as well as endolithic free-living algae, fungal hyphae, cyanobacteria and non photosynthetic bacteria. We also report a novel type of endolithic community, "hypoendoliths", colonizing the undermost layer of the crusts. The colonization of gypsum crusts within the hyperarid core appears to be controlled by the moisture regime. Our data shows that the threshold for colonization is crossed within the dry core, with abundant colonization in gypsum crusts at one study site, while crusts at a drier site are virtually devoid of life. We show that the cumulative time in 1 year of relative humidity (RH) above 60% is the best parameter to explain the difference in colonization between both sites. This is supported by controlled humidity experiments, where we show that colonies of endolithic cyanobacteria in the Ca-sulfate crust undergo imbibition process at RH >60%. Assuming that life once arose on Mars, it is conceivable that Martian micro-organisms sought refuge in similar isolated evaporite microenvironments during their last struggle for life as their planet turned arid.

Effect of electrokinetic remediation on indigenous microbial activity and community within diesel contaminated soil

Electrokinetic remediation has been successfully used to remove organic contaminants and heavy metals within soil. The electrokinetic process changes basic soil properties, but little is known about the impact of this remediation technology on indigenous soil microbial activities. This study reports on the effects of electrokinetic remediation on indigenous microbial activity and community within diesel contaminated soil. The main removal mechanism of diesel was electroosmosis and most of the bacteria were transported by electroosmosis. After 25 days of electrokinetic remediation (0.63 mA cm − 2 ), soil pH developed from pH 3.5 near the anode to pH 10.8 near the cathode. The soil pH change by electrokinetics reduced microbial cell number and microbial diversity. Especially the number of culturable bacteria decreased significantly and only Bacillus and strains in Bacillales were found as culturable bacteria. The use of EDTA as an electrolyte seemed to have detrimental effects on the soil microbial activity, particularly in the soil near the cathode. On the other hand, the soil dehydrogenase activity was enhanced close to the anode and the analysis of microbial community structure showed the increase of several microbial populations after electrokinetics. It is thought that the main causes of changes in microbial activities were soil pH and direct electric current. The results described here suggest that the application of electrokinetics can be a promising soil remediation technology if soil parameters, electric current, and electrolyte are suitably controlled based on the understanding of interaction between electrokinetics, contaminants, and indigenous microbial community.

Construction of River Model Biofilm for Assessing Pesticide Effects

Due to the high importance of biofilms on river ecosystems, assessment of pesticides' adverse effects is necessary but is impaired by high variability and poor reproducibility of both natural biofilms and those developed in the laboratory. We constructed a model biofilm to evaluate the effects of pesticides, consisting in cultured microbial strains, Pedobacter sp. 7-11, Aquaspirillum sp. T-5, Stenotrophomonas sp. 3-7, Achnanthes minutissima N71, Nitzschia palea N489, and/or Cyclotella meneghiniana N803. Microbial cell numbers, esterase activity, chlorophyll-a content, and the community structure of the model biofilm were examined and found to be useful as biological factors for evaluating the pesticide effects. The model biofilm was formed through the cooperative interaction of bacteria and diatoms, and a preliminary experiment using the herbicide atrazine, which inhibits diatom growth, indicated that the adverse effect on diatoms inhibited indirectly the bacterial growth and activity and, thus, the formation of the model biofilm. Toxicological tests using model biofilms could be useful for evaluating the pesticide effects and complementary to studies on actual river biofilms.

The Interaction of Large Bowel Microflora with the Colonic Mucus Barrier

The colonic mucus barrier is the first line of defence that the underlying mucosa has against the wide range of potentially damaging agents of microbial, endogenous, and dietary origin that occur within the colonic lumen. The functional component of mucus is the secreted, polymeric glycoprotein mucin. The mucus barrier can either act as an energy source or a support medium for growth to the intestinal microflora. The mucus barrier appears to effectively partition the vast number of microbial cells from the underlying epithelium. The normal functionality and biochemistry of this mucus barrier appears to be lost in diseases of the colorectal mucosa. Germ-free animal studies have highlighted the necessity of the presence of the colonic microflora to drive the maturation of the colonic mucosa and normal mucus production. A number of by-products of the microflora have been suggested to be key luminal drivers of colonic mucus secretion.

English

Accidental leakages during hydrocarbon fuels transportation and other activities are inevitable, making these hydrocarbons the most common global environmental pollutants. Current understanding in diesel degradation involves the study of Gram-negative microorganisms. Seven Gram-positive and one Gram-negative diesel degrading bacteria isolated from contaminated soil were used in this study. The overnight bacterial cultures were standardized and transferred into Bushnell-Haas medium supplemented with glucose and incubated at 30°C at 160 rpm for 48 h. The level of diesel degradation was determined using gravimetric analysis. Cell numbers were calculated using total heterotrophic plate count. All isolates were capable of degrading 70 - 80% of n-paraffin whilst isolates D2, D9, D10 and DJLB possessed better abilities of diesel degradation at 65.4 - 83.12% under the standard conditions. Diesel degradation rates and microbial cell number, increased with an increase in glucose composition. The addition of glucose to the liquid medium had a positive effect, with an increase in growth of the isolates thus leading to significantly (p < 0.05) higher percentages of diesel degradation and greater emulsification activity. The ability of Gram-positive bacteria to degrade diesel increased in a comparable trend as its biosurfactant production increased. The E24 index was highest at 87.6% for isolate D9. Isolates D2, D9 and D10, were identified as Paenibacillus sp. whilst isolate DJLB was found to belong to Stenotrophomonas sp. This study clearly demonstrates that Gram-positive biosurfactant producing bacteria are effective in diesel degradation.

EVALUATION OF MTT METHOD FOR QUANTIFICATION OF MICROBIAL CELL VIABILITY IN MICROPLATES

In the study of microbiology,the activity and the number of microbial cells are often determined to reflect the growth of microbial cells. The conventional methods usually include plate culture method,the cell number of automatic analyzer,turbidity,dry cell weight and biological fluorescence method,and so on. Among these conventional methods,the plate culture method is cumbersome,time-consuming and poor reproducibility,and most importantly,it can not truly reflect the growth of bacteria,furthermore,it is not suitable for bigger quantities experiment. For the other conventional methods,they even could not distinguish between live and dead cells,and the number and activity of cells are vulnerable to the medium and metabolites. In recent years,MTT colorimetric method is used to evaluate the microbial cell activity,which is more simple,rapid,sensitive and stable compared with the conventional methods. The principle is that the living cells can reduce MTT to a blue-violet matter by mitochondrial dehydrogenase in cells,the matter has the optical absorption value from 560 nm to 610 nm,and most reports indicate that blue-violet matter have the best optical absorption value at 570 nm. MTT colorimetric method was always used to detect the activity of immune cells and other animal cells,but it was rarely reported in the detection of the activity of the microbial cells. In this paper,MTT colorimetric method for quantification of microbial cell viability or cell growth in microplates was discussed. Escherichia coli was employed to determine the conditions of assay,which included the feasibility,reaction periods,microbial cell number,the concentration of MTT and so on. It was found that MTT had a high correlation between the values of OD570 and the microbial cell number,which was from 4.9×107 cells/mL to 4.9×108 cells/mL. The correlation was the best when bacteria was treated with MTT 0.5 mg/mL of 20μL for 20 min,and the correlation and regression equation was y = 0.1769x + 0.03,R2 = 0.9983; when bacteria was treated with MTT 5 mg/mL of 20μL for 30 min,the correlation and regression equation was y = 0.4032x + 0.0143 R2 = 0.998. MTT colorimetric method is economic,simple,fast,stable,high sensitive,and the results can show the number of live micro-organisms or cells activity clearly. Previous studies also showed that MTT colorimetric method was superior to other color,such as the TTC,INT,XTT,blade,etc. among evaluation methods of cell viability.

Functional differences between Arctic seawater and sedimentary microbial communities: contrasts in microbial hydrolysis of complex substrates

The activities and structural specificities of extracellular enzymes that initiate microbial remineralization of high-molecular-weight (MW) organic matter were investigated in surface waters and sediments of an Arctic fjord of Svalbard. Hydrolysis rates of a suite of fluorescently labeled macromolecular substrates, including seven commercially available polysaccharides and three high-carbohydrate-content plankton extracts ranged from rapid to not detectable, and differed markedly between seawater and sediments. Order (fastest to slowest) of hydrolysis in surface water was laminarin, Spirulina extract, xylan>chondroitin, alginic acid, Wakame extract>arabinogalactan, fucoidan>Isochrysis extract>>>pullulan, while in sediments the order was pullulan, laminarin, alginic acid, Wakame extract>chondroitin, xylan>arabinogalactan, Isochrysis extract>Spirulina extract>fucoidan. These differences cannot be explained by simple scaling factors such as differences in microbial cell numbers between seawater and sediments. Other investigations have shown that microbial community composition of Svalbard sediments and of polar bacterioplankton samples differ markedly. These results demonstrate that sedimentary and seawater microbial communities also differ fundamentally in their abilities to access specific high-MW substrates. Substrate bioavailability depends on the capabilities of a microbial community, as well as the chemical and structural features of the substrate itself.

Response of benthic microbial communities to chitin enrichment: an in situ study in the deep Arctic Ocean

In situ enrichment experiments were carried out in the Arctic deep sea (Fram Strait region) to observe the response of benthic microbial communities to chitin supply. Chambers of a benthic lander were filled in July 2004 with deep-sea sediments enriched with 1.3–7.0 g m−2 of chitin and the effects of chitin enrichment were assessed on the microbial hydrolytic activity potential, cell number and community structure after periods of 1 week and 1 year of in situ deployment. The input of chitin had no effect on microbial abundance and chitobiase activity after 7 days of incubation, whereas community structure in enriched sediments, determined by terminal restriction fragment length polymorphism analysis of 16S rRNA genes, was different from the controls. After 1 year, microbial numbers and activity significantly increased in sediments enriched with high chitin concentrations and bacterial community structure was different from that of the other treatments. The present study suggests that microbial community structure in Arctic deep-sea sediments can react quickly to sudden large chitin inputs into the sediments and that this appears to precondition subsequent enhanced growth and enzymatic activity changes.