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1.
Abstract
Zonations of photosynthesis and photopigments in artificial cyanobacterial mats were studied with (i) oxygen and pH microsensors,
(ii) fiber-optic microprobes for field radiance, scalar irradiance, and PSII fluorescence, and (iii) a light microscope equipped
with a spectrometer for spectral absorbance and fluorescence measurements. Our analysis revealed the presence of several distinct
1–2 mm thick cyanobacterial layers mixed with patches of anoxygenic photosynthetic bacteria. Strong attenuation of visible
light confined the euphotic zone to the uppermost 3 mm of the mat, where oxygen levels of 3–4 times air saturation and a pH
peak of up to pH 8.8 were observed under saturating irradiance (413 μmol photon m−2 s−1). Oxygen penetration was 5 mm in light and decreased to 1 mm in darkness. Volumetric oxygen consumption in the photic and
aphotic zones of illuminated mat was 5.5 and 2.9 times higher, respectively, than oxygen consumption in dark incubated mats.
Scalar irradiance reached 100–150% of incident irradiance in the upper 0.5 mm of the mat due to intense scattering in the
matrix of cells, exopolymers, and carbonate precipitates. In deeper mat layers scalar irradiance decreased nearly exponentially,
and highest attenuation coefficients of 6–7 mm−1 were found in cyanobacterial layers, where photosynthesis and photopigment fluorescence also peaked. Visible light was attenuated
>100 times more strongly than near infrared light. Microscope spectrometry on thin sections of mats allowed detailed spectral
absorbance and fluorescence measurements at defined positions relative to the mat surface. Besides strong spectral signals
of cyanobacterial photopigments (Chl a and phycobiliproteins), the presence of both green and purple photosynthetic bacteria was evident from spectral signals of
Bchl a and Bchl c. Microprofiles of photopigment absorbance correlated well with microdistributions of phototrophs determined in an accompanying
study.
Received: 20 December 1999; Accepted: 10 June 2000; Online Publication: 28 August 2000 相似文献
2.
J. N. Harney E. E. Grossman B. M. Richmond C. H. Fletcher III 《Coral reefs (Online)》2000,19(2):141-154
The origin, age, and dynamics of carbonate sediments in Kailua Bay on Oahu, Hawaii, are described. The shoreface (from shoreline
to 4 km offshore) consists of a broad (5 km2) fringing coral reef ecosystem bisected by a sinuous, shore-normal, sand-filled paleostream channel 200–300 m wide. The median
grain diameter of surface sands is finest on the beach face (<0.3 mm) and increases offshore along the channel axis. Kailua
sands are >90% biogenic carbonate, dominated by skeletal fragments of coralline algae (e.g. Porolithon, up to 50%) followed by the calcareous green alga Halimeda (up to 32%), coral fragments (1–24%), mollusc fragments (6–21%), and benthic foraminifera (1–10%). Sand composition and age
across the shoreface are correlated to carbonate production. Corals and coralline algae, principal builders of the reef framework,
are younger and more abundant in sands along the channel axis and in offshore reefal areas, while Halimeda, molluscs, and foraminifera are younger and more dominant in nearshore waters shoreward of the main region of framework building.
Shoreface sediments are relatively old. Of 20 calibrated radiocarbon dates on skeletal constituents of sand, only three are
younger than 500 years b.p.; six are 500–1000 years b.p.; six are 1000–2000 years b.p.; and five are 2000–5000 years b.p. Dated fine sands are older than medium to coarse sands and hence may constitute a reservoir of fossil carbonate that is
distributed over the entire shoreface. Dominance of fossiliferous sand indicates long storage times for carbonate grains,
which tend to decrease in size with age, such that the entire period of relative sea-level inundation (∼5000 years) is represented
in the sediment. Despite an apparently healthy modern coral ecosystem, the surficial sand pool of Kailua Bay is dominated
by sand reflecting an antecedent system, possibly one that existed under a +1–2 m sea-level high stand during the mid- to
late Holocene.
Accepted: 20 December 1999 相似文献
3.
Confocal Laser Scanning Microscopy Image Analysis for Cyanobacterial Biomass Determined at Microscale Level in Different Microbial Mats 总被引:1,自引:0,他引:1
We recently published a new method based on determining cyanobacterial biomass by confocal laser scanning microscopy image
analysis (CLSM-IA) (Solé et al., Ultramicrosc 107:669–673, 2007). CLSM-IA allows biomass calculation for microorganisms of
a small size, since the limit of the technique’s resolution is that generated by a voxel, the smallest unit of a three-dimensional
digital image, equivalent to 1.183 × 10−3 mgC/cm3 of sediment. This method is especially suitable for the quantitative analysis of a large number of CLSM images generated
from benthic sediments in which complex populations of cyanobacteria are abundant, such as microbial mats. In order to validate
the new CLSM approach, mats with varying structural characteristics were studied. We have grouped them into three types: Microcoleus mats (laminated), sandy mats (nonlaminated and composed of well-sorted quartz sands), and oil-polluted mats. In this work,
we applied CLSM-IA in natural [the Ebro delta and Sant Jordi colony (Spain), Salins-de-Giraud and Etang de Berre (France),
and Orkney Islands (Scotland)] and artificial [mesocosms (Israel)] microbial mats. A total of 4,103 confocal images were obtained
in order to determine total and individual cyanobacteria biomass profiles, at microscale level. The data presented in this
paper show the efficacy of the method, as it can be applied to highly diverse mat samples. 相似文献
4.
Various types of sub-aerially exposed microbial mats, including emergent mats, beach sand, beach rock and Kopara mats, are
widespread on the 78 km (25 km2) of rim surrounding the Tikehau atoll lagoon. These mats form laminated accretions or diffuse microbial communities growing
under high insolation and temperatures, and are therefore subject to desiccation. Both heterocystous and non-heterocystous
cyanobacteria occur in these mats. Using acetylene reduction techniques, nitrogenase activity was observed at all sites over
a period of 5 years and was 3–17 times higher during daylight than at night in all communities except for beach rock. 15N2 measurements indicated a molar ratio of acetylene reduction to N2 fixed of 1.6 for all exposed communities. Estimated N2 fixation ranged from 1.44 to 8.0 mg N m−2 day−1 in these exposed communities (mean of 4.66 mg N m−2 day−1) with beachrock showing the highest rates. For the whole reef rim, daily N2 fixation amounted to 98.42 kg N day−1 which represents 28% of the rate of fixation in the entire lagoon (area 400 km2). 相似文献
5.
Summary Snails and nematodes, the potential cyanobacterial grazers, differ in their choice for cyanobacterial diet. Snails prefer
non-mucilaginous forms while nematodes prefer mucilaginous forms. Such differences in feeding choice between the cyanobacteria
suggests that it may not be possible to select strains of diazotrophic cyanobacteria that are resistant to all grazers. The
potential consumption of cyanobacteria at an average field density of 20,000 snails ha−1 was estimated to be about 50 kg (fresh weight) ha−1 day−1. Dorylamus sp. was most dominant nematode associated with cyanobacterial consumption. Phytoextracts of neem (Azadirachta indica), bel (Aegle marmelos) and tobacco (Nicotiana tabacum) were effective in controlling these cyanobacterial grazers. The minimum concentration of neem, bel and tobacco phytoextract
in water for 100 % mortality of snails were 0.1, 2.0 and 0.05%, respectively. However, trepellent level was only 0.01% for
neem and tobacco phytoextract. Complete mortality of nematode (Dorylamus spp.) required a higher concentration level (2%) even in the most effective tobacco phytoextract. Lower levels of phytoextract
(0.1%) were found to stimulate growth and nitrogen fixation of cyanobacteria. Application of these plant biomasses resulted
in significant increase in cyanobacterial acetylene-reducing activity (ARA) and rice yield and a significant decrease in snail
and nematode population. Augmentation of cyanobacterial acetylene-reducing activity was two to three times higher in comparison
to the control in both the years of experimentation. Rice yield also increased between 3.8 and 58.5% over the control, depending
on the quantity and nature of plant biomass. Tobacco waste was significantly superior in comparison to neem and bel biomass
as carrier of cyanobacterial culture. 相似文献
6.
Effects of the inoculation of cyanobacteria on the microstructure and the structural stability of a tropical soil 总被引:3,自引:0,他引:3
Oumarou Malam Issa Christian Défarge Yves Le Bissonnais Béatrice Marin Odile Duval Ary Bruand Luigi Paolo D’Acqui Sofie Nordenberg Marcus Annerman 《Plant and Soil》2007,290(1-2):209-219
Cyanobacteria are widespread photosynthetic microorganisms among which some are able to fix atmospheric nitrogen. We investigated
the impact of indigenous cyanobacteria strains (Nostoc) inoculation on physical characteristics of poorly aggregated soils from Guquka (Eastern Cape, South Africa). The soil aggregates
(3–5 mm) were arranged into a layer of 10–20 mm thick, and sprayed with cyanobacteria solution. Subsequently the inoculated
and un-inoculated samples were incubated (30°C, 80% humidity, continuous illumination at 100 μmol m−2 s−1). Their micromorphological characteristics and aggregate stability were investigated, after 1, 2, 3, 4 and 6 weeks of incubation,
by using high resolution Cryo-SEM and aggregate breakdown tests.
Micromorphological investigations revealed that the surface of un-inoculated samples remained uncovered, while the inoculated
samples were partially covered by cyanobacteria material after one week of incubation. A dense superficial network of cyanobacterial
filaments and extracellular polymer secretions (EPS) covered their surface after 4 and 6 weeks of incubation. Organo-mineral
aggregates comprising cyanobacterial filaments and EPS were observed after 6 weeks of incubation. The results of aggregate
breakdown tests showed no significant difference between un-inoculated samples after 1, 2, 3, 4 or 6 weeks, while they revealed
improvement of aggregate stability for inoculated samples. The improvement of aggregate stability appeared in a short while
following inoculation and increased gradually with time and cyanobacteria growth. The increase in aggregate stability is likely
related to the changes induced in micromorphological characteristics by cyanobacterial filaments and EPS. It reflects the
effect of coating, enmeshment, binding and gluing of aggregates and isolated mineral particles by cyanobacteria material.
Our study presents new data demonstrating the improvement of soil physical quality in a few weeks after cyanobacteria inoculation.
The interaction of the inocula and other biotic components is worthy of study before field application of cyanobacteria. 相似文献
7.
The roles of weather variability and sunspots in the occurrence of cyanobacteria blooms, were investigated using cyanobacteria
cell data collected from the Fred Haigh Dam, Queensland, Australia. Time series generalized linear model and classification
and regression tree (CART) model were used in the analysis. Data on notified cell numbers of cyanobacteria and weather variables
over the periods 2001 and 2005 were provided by the Australian Department of Natural Resources and Water, and Australian Bureau
of Meteorology, respectively. The results indicate that monthly minimum temperature (relative risk [RR]: 1.13, 95% confidence
interval [CI]: 1.02–1.25) and rainfall (RR: 1.11; 95% CI: 1.03–1.20) had a positive association, but relative humidity (RR:
0.94; 95% CI: 0.91–0.98) and wind speed (RR: 0.90; 95% CI: 0.82–0.98) were negatively associated with the cyanobacterial numbers,
after adjustment for seasonality and auto-correlation. The CART model showed that the cyanobacteria numbers were best described
by an interaction between minimum temperature, relative humidity, and sunspot numbers. When minimum temperature exceeded 18°C
and relative humidity was under 66%, the number of cyanobacterial cells rose by 2.15-fold. We conclude that weather variability
and sunspot activity may affect cyanobacteria blooms in dams. 相似文献
8.
Somatic embryogenesis and in vitro rosmarinic acid accumulation in Salvia officinalis and S. fruticosa leaf callus cultures 总被引:1,自引:0,他引:1
The effect of explant age, plant growth regulators and culture conditions on somatic embryogenesis and rosmarinic acid production
from leaf explants of Salvia officinalis and S. fruticosa plants collected in Greece was investigated. Embryogenic callus with numerous spherical somatic embryos could be induced
on explants derived from both species and cultured for 3 weeks on a Murashige and Skoog (MS) medium supplemented with 1.8–18
μm 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin (Kin) or 10.5–21 μm 1-naphthalenacetic acid and 6-benzyladenine. Only explants from young plants (with six to eight leaves) responded to the
culture treatments and, in general, low light intensities (50 μmol m–2 s–1) favoured callus formation and induction of somatic embryos. Somatic embryos were further developed on the same medium. Heart-
and torpedo-shaped embryos (1–2 mm long) were subcultured on a growth-regulator-free MS medium for maturation. Maximum rosmarinic
acid accumulation in S. officinalis and S. fruticosa callus cultured on 4.5 μm 2,4-D and 4.5 μm Kin was 25.9 and 29.0 g/l, respectively.
Received: 17 January 1997 / Revision received: 26 May 1997 / Accepted: 30 June 1997 相似文献
9.
10.
Loic Charpy Katarzyna A. Palinska Beatriz Casareto Marie José Langlade Yoshimi Suzuki Raeid M. M. Abed Stjepko Golubic 《Microbial ecology》2010,59(1):174-186
Dinitrogen-fixing organisms in cyanobacterial mats were studied in two shallow coral reef ecosystems: La Reunion Island, southwestern
Indian Ocean, Sesoko (Okinawa) Island, and northwestern Pacific Ocean. Rapidly expanding benthic miniblooms, frequently dominated
by a single cyanobacterial taxon, were identified by microscopy and molecular tools. In addition, nitrogenase activity by
these blooms was measured in situ. Dinitrogen fixation and its contribution to mat primary production were calculated using
15N2 and 13C methods. Dinitrogen-fixing cyanobacteria from mats in La Reunion and Sesoko showed few differences in taxonomic composition.
Anabaena sp. among heterocystous and Hydrocoleum majus and Symploca hydnoides among nonheterocystous cyanobacteria occurred in microbial mats of both sites. Oscillatoria bonnemaisonii and Leptolyngbya spp. occurred only in La Reunion, whereas Hydrocoleum coccineum dominated in Sesoko. Other mats dominated by Hydrocoleum lyngbyaceum, Phormidium laysanense, and Trichocoleus tenerrimus occurred at lower frequencies. The 24-h nitrogenase activity, as measured by acetylene reduction, varied between 11 and 324 nmoles
C2H2 reduced μg−1 Chl a. The highest values were achieved by heterocystous Anabaena sp. performed mostly during the day. Highest values for nonheterocystous cyanobacteria were achieved by H. coccineum mostly during the night. Daily nitrogen fixation varied from nine (Leptolyngbya) to 238 nmoles N2 μg−1 Chl day−1 (H. coccineum). Primary production rates ranged from 1,321 (S. hydnoides) to 9,933 nmoles C μg−1 Chl day−1 (H. coccineum). Dinitrogen fixation satisfied between 5% and 21% of the nitrogen required for primary production. 相似文献
11.
Excitation–emission fluorescence matrices of phytoplankton communities were simulated from laboratory-grown algae and cyanobacteria
cultures, to define the optical configurations of theoretical fluorometers that either minimize or maximize the representation
of these phytoplankton groups in community variable fluorescence measurements. Excitation sources that match the photosystem
II (PSII) action spectrum of cyanobacteria do not necessarily lead to equal representation of cyanobacteria in community fluorescence.
In communities with an equal share of algae and cyanobacteria, inducible PSII fluorescence in algae can be retrieved from
community fluorescence under blue excitation (450–470 nm) with high accuracy (R
2 = 1.00). The highest correlation between community and cyanobacterial variable fluorescence is obtained under orange-red
excitation in the 590–650 nm range (R
2 = 0.54). Gaussian band decomposition reveals that in the presence of cyanobacteria, the emission detection slit must be narrow
(up to 10 nm) and centred on PSII chlorophyll-a emission (~683 nm) to avoid severe dampening of the signal by weakly variable phycobilisomal fluorescence and non-variable
photosystem I fluorescence. When these optimizations of the optical configuration of the fluorometer are followed, both cyanobacterial
and algal cultures in nutrient replete exponential growth exhibit values of the maximum quantum yield of charge separation
in PSII in the range of 0.65–0.7. 相似文献
12.
Józef Kaźmierczak Stephan Kempe Barbara Kremer Purificación López-García David Moreira Rosaluz Tavera 《Facies》2011,57(4):543-570
The structure, mineralogy, and accretion processes of the modern and subfossil cyanobacterial microbialites from the alkaline
crater lake Alchichica (Puebla, Mexico) were studied, along the lake’s bathymetry and hydrochemistry. The recent lowering
of the lake level had exposed microbialitic carbonate mounds and crusts, which emerged up to 2 m above the water surface,
while accreting cyanobacterial microbialites were present down to a depth of ~15 m. Morphological and molecular analysis found
that the living cyanobacterial mats were composed of diverse filamentous and coccoid cyanobacteria (Nostocales, Chroococcales,
Oscillatoriales, and Pleurocapsales). The emerged subfossil microbialites comprised two generations: “white” (domes and crusts
composed mainly of hydromagnesite with an admixture of huntite and calcite, 238U/230Th age of ~2.8 ka BP), and “brown” (chimneys, columns and laminated crusts composed of aragonite with an admixture of Mg-calcite,
238U/230Th age of ~1.1 ka BP). The significant age, structural, mineralogical, and isotopic differences suggest that the two generations
were formed in different environmental conditions: the “white” during a dry period, and the “brown” in wet climate associated
with high water level and intense inflow of ground water, which lowered the Mg/Ca ratio resulting in formation of aragonite
instead of hydromagnesite. The hydromagnesite, replacing the primary aragonite precipitated in the living cyanobacterial biofilm,
frequently undergoes silicification, which obliterates both the primary structure of the carbonate and the enclosed remains
of cyanobacterial microbiota. This process helps to explain the abundant formation of dolomites and cherts in an allegedly
highly alkaline Early Precambrian ocean. Thus, Lake Alchichica represents a modern alkaline environment where biosedimentary
structures resembling Precambrian deposits are generated. 相似文献
13.
A survey of 11 sites covering three large (>10 km long, 6 sites) playa lakes and four pans (<1 km2, 5 sites) of the Yarra Yarra salt lake system in the Northern Agricultural Region of Western Australia commenced in 2001.
These salt lakes are shallow and ephemeral, with inundation being more regular following winter rainfall, but summer inundation
also occurred in 2001. Salinity was generally higher in playas (156–368 g l−1) than pans (30–284 g l−1), but salinity responded noticeably to heavy rainfall events, especially in pans. pH values in the playa lakes (6.68–7.82)
were less variable than in the pans (6.81–8.08). The range of dissolved oxygen concentrations was greater in pans (3.7–14.4
mg l−1) than in playas (3.9–8.2 mg l−1). Cationic concentrations generally followed the pattern of sea water cation dominance. Benthic microbial communities comprised
either cohesive to loosely mucilaginous mats, or thin films of diatoms. Five genera of diatom and two species of filamentous
cyanobacteria were recorded.
Guest Editor: John M. Melack
Saline Waters and their Biota 相似文献
14.
Plant regeneration via somatic embryogenesis, and transient gene expression in sweet potato protoplasts 总被引:1,自引:0,他引:1
A method for regenerating plants from petiole protoplasts of the in vitro-raised sweet potato cultivar Jewel is described.
Protoplast yields of 3.0–5.0×106 were obtained following 4–6 h digestion of 1- to 2-cm petioles (1 g fresh weight) with 1% Cellulase-R10, 2% Macerozyme-R10,
and 0.3% Pectolyase Y-23 in a washing solution with 9% mannitol. A plating density of 105 protoplasts/ml was optimal for subsequent division. An initial division frequency of 12–15% was obtained in liquid or agarose-solidified
KP8 culture medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) (0.9 μm), and zeatin (2.3 μm). Colonies consisting of 100–200 cells were formed after 4 weeks in the dark at 24±2°C. The frequency of colony formation
was improved by the gradual addition of fresh liquid KP8 medium of lower osmoticum. Protocalli (1–2 mm in diameter) were formed
after an additional 4–6 weeks under continuous illumination and regular dilution with fresh culture medium. Morphogenic callus
formed globular and heart-shaped embryos that developed into cotyledon stage embryos, following transfer of calli onto medium
containing 2,4-D (11.3 μm) and benzylaminopurine (2.2 μm). Subsequently, embryo conversion to plantlets was obtained on basal medium with 2% sucrose and 3.5 μm gibberellic acid. Regenerated plantlets were successfully transplanted in soil. Mature plants appeared phenotypically normal.
The same petiole protoplast populations showed transient expression of the gusA gene introduced using electroporation.
Received: 10 October 1997 / Revision received: 10 February 1998 / Accepted: 2 March 1998 相似文献
15.
《Harmful algae》2012
Recent surveys of periphyton in Lake Tikitapu revealed widespread benthic mats dominated by cyanobacteria. All mats tested positive for the cyanobacterial toxin nodularin-R. The New Zealand native freshwater crayfish or kōura (Paranephrops planifrons) are benthic-dwelling, opportunistic omnivores that are common in Lake Tikitapu. Benthic mats constitute a potential food source for this species. In this study an in-lake feeding experiment with isotopically labeled 13C benthic mats confirmed they were consumed by kōura. Consumption was variable amongst individuals, suggesting the benthic mats are an optional rather than primary food source. Nine kōura were also tested using liquid chromatography–mass spectrometry to determine if nodularin-R bioaccumulated in the hepatopancreas and tail tissue. The hepatopancreas of all kōura were positive for nodularin-R (9.7–225.3 μg kg−1 ww) and nodularin-R was detected in low concentrations in the tail tissue of two individuals (0.5–0.7 μg kg−1 ww). The detection of nodularin-R in kōura is the first in a freshwater organism in a freshwater system, and the first to show the accumulation of nodularin-R from freshwater benthic cyanobacterial mats. Benthic mats may need to be considered as a potential source of cyanotoxins in future freshwater food-web studies. 相似文献
16.
Effects of limiting nutrients and N:P ratios on the phytoplankton growth in a shallow hypertrophic reservoir 总被引:4,自引:0,他引:4
Ho-Sub Kim Soon-Jin Hwang Jae-Ki Shin Kwang-Guk An Chun Gyeong Yoon 《Hydrobiologia》2007,581(1):255-267
The purpose of this study was to evaluate the effects of limiting nutrients and the N:P ratios on the growth of phytoplankton
(mainly cyanobacteria) in a shallow hypertrophic reservoir between November 2002 and December 2003. Nutrient enrichment bioassays
(NEBs) were conducted, along with analyses of seasonal ambient nutrients and phytoplankton taxa, in the reservoir. The average
DIN:TDP and TN:TP mass ratios in the ambient water were 90 (range: 17–187) and 34 (13–60), respectively, during the study
period. The dissolved inorganic phosphorus showed seasonal variation, but less than that of inorganic nitrogen. The TN:TP
ratios ranged from 13 to 46 (mean: 27 ± 6) during June–December when the cyanobacteria, Microcystis, dominated the phytoplankton composition. The NEBs showed that phytoplankton growth was mainly stimulated by the phosphorus
(all of total 17 cases), rather than the nitrogen concentration (8 of 17 cases). The rapid growth rate of cyanobacteria was
evident with TN:TP ratios less than 30. According to the results of the NEBs with different N concentrations (0.07, 0.7 and
3.5 mg l−1), but the same N:P ratios and when the nitrogen concentration was highest, the cyanobacterial growth reached a maximum at
N:P ratios <1. Overall, the response of cyanobacterial growth was a direct function of added phosphorus in the NEBs, and was
greater with increased N concentrations. Thus, cyanobacterial blooms favored relatively low N:P ratios in this hypertrophic
reservoir system.
An erratum to this article is available at . 相似文献
17.
Physiological Status and Community Composition of Microbial Mats of the Ebro Delta, Spain, by Signature Lipid Biomarkers 总被引:3,自引:0,他引:3
Navarrete A Peacock A Macnaughton SJ Urmeneta J Mas-Castellà J White DC Guerrero R 《Microbial ecology》2000,39(1):92-99
Abstract
Physiological status of microbial mats of the Ebro Delta (Tarragona, Spain) based on the extraction of lipids considered ``signature
lipid biomarkers' (SLB) from the cell membranes and walls of microorganisms has been analyzed. Data from a day–night cycle
show significant differences in viable cells countings (PLFA cells counts) ranging from 1.5 × 1010 to 5.0 × 1010 cells g−1 of sediment. Minimum values were observed at 18:00 and 6:00, when physicochemical conditions change drastically. The diversity
of the microbial community was assessed by GC/MS analysis of phospholipid fatty acids (PLFA). The ratio of PLFA, representative
of Gram-negative bacteria, comprises 47.8% of the total PLFA of the microbial mat community. The remaining PLFA was representative
of Gram-positive (10.0%), anaerobic (5.7%), and eukaryotic microorganisms (5.7%), and other common lipids. Two different approaches
were used as a comparative study to assess the physiological status of the microbial mats. Two parameters (cyclopropane fatty
acids/ω7c monoenoic fatty acids, and measurement of the trans/cis monoenoic PLFA ratio) showed a minimum at midnight, suggesting the highest microbial activity. Higher values were observed
at 18:00 and 6:00, coinciding with lower PLFA cell counts.
Received: 14 May 1999; Accepted: 6 September 1999; Online Publication: 24 March 2000 相似文献
18.
Sergey Dobretsov Raeid M. M. Abed Sultan M. S. Al Maskari Jamal N. Al Sabahi Reginald Victor 《Journal of applied phycology》2011,23(6):983-993
Polar (water) and non-polar (ethyl acetate) extracts from the cyanobacterial layer (top 1–3 mm) of four hot spring microbial
mats in the Sultanate of Oman were tested for their antibacterial, antidiatom and quorum-sensing inhibitory activities under
natural conditions. The chemical composition of the active extracts was analysed using gas chromatography–mass spectrometry
(GC-MS). Cyanobacteria within these mats were identified by direct microscopy while the total bacterial community composition
was compared using automated ribosomal intergenic spacer analysis (ARISA). Only the extracts from Bowshar and Nakhl mats showed
antibacterial properties against Bacillus sp., Micrococcus luteus, Shigella sonnei, Salmonella enterica and Klebsiella pneumoniae. All tested extracts inhibited the growth of the benthic diatom Amphora coffeaeformis. Extracts from Bowshar, Rustaq and Nakhl inhibited quorum-sensing of the reporter strains Chromobacterium violaceum CV017 and Agrobacterium tumefaciens NTL4. The highest bioactivity was recorded for ethyl acetate extracts from Nakhl mats, which had the lowest number of operational
taxonomic units (OTUs). Using GC-MS, 74 chemical compounds were obtained, however with different distribution among the four
mat extracts (similarity < 43%). Various cyanobacteria, belonging mainly to Chroococcus, Phormidium, Leptolyngbya, Spirulina and Lyngbya were detected in the different mats, and each mat had its unique bacterial community, as confirmed by ARISA profiles. We
conclude that antimicrobial and quorum-sensing inhibitory compounds can be produced by hot spring mat microorganisms under
natural conditions and the differences in these compounds could be attributed to the differences in the mats’ bacterial composition
as well as the physical–chemical conditions of the springs. 相似文献
19.
Characterization of salt-tolerant mutant for enhancement of l-threonine production in Escherichia coli 总被引:1,自引:0,他引:1
Escherichia coli strain HS3, metabolically engineered to have Met–, AHVr, IleL and AECr characteristics, produced 58.0 g/l of l-threonine, but it was neither salt-tolerant nor osmotolerant; and the growth and threonine production of the strain were
severely inhibited both by the addition of NaCl with a concentration higher than 2% and by the presence of glucose with a
concentration higher than 10%. Therefore, salt-tolerant mutants were isolated. The salt-tolerant mutants, HS454 and HS528
which were derived from strain HS3, were both tolerant to salt (2%) and hyperproductive. The growth and l-threonine production by the mutant strain HS454 were almost unaffected by a glucose concentration lower than 10%, but gradually
reduced with increasing glucose concentration, up to 15%. However, the mutant strain HS528 showed slightly enhanced growth
and l-threonine production with increasing glucose concentration, up to 10–12.5%. Strains HS454 and HS528 produced 69.8 g/l and
74.0 g/l of l-threonine, respectively in a 5-l jar fermentor.
Received: 21 January 2000 / Received revision: 31 March 2000 / Accepted: 5 May 2000 相似文献
20.
Naoki Hijii 《Ecological Research》1987,2(2):159-173
Seasonal changes in abundance and distribution pattern of soil micro-arthropods were studied in connection with a few environmental
factors in a Japanese cedar (Cryptomeria japonica
D. Don) plantation. The soil arthropods were sampled from three different depths at intervals of two months for two years. Of the
collected animals (total 51000–155000 m−2), Collembola (20000–76000 m−2), oribatid mites (19000–55000 m−2) and carnivorous mites (6200–21000 m−2) were the numerically dominant animal groups. Low seasonal variations in abundance indicated their seasonal stability in
population levels. The trends in seasonal fluctuation were similar among these groups and between the two years, showing bimodal
pattern with little peaks in early summer and winter. The pattern of seasonal fluctuation in abundance of carnivorous mites
(P
d) was significantly synchronized with that in the total abundance of Collembola and oribatid mites (P
τ). Thus, the number-ratios (P
d/P
τ) were fairly constant, ranging from 0.10 to 0.25. Seasonal changes in vertical distribution of the three animal groups showed
a similar pattern for both years. The downward migrations were shown to be more affected by low temperatures in winter accompanied
by snow coverage rather than by the desiccation of the surface soil in summer. All the three groups demonstrated as a whole
slightly aggregated patterns of horizontal distribution throughout the two years. Temporal increases in the patchiness indices
were observed from summer to autumn when the moisture content of the surface soil was low. 相似文献