Phototrophic purple sulfur bacteria oxidize sulfide to elemental sul- fur, which is .. Las bacterias fotótrofas rojas del azufre oxidan sulfuro a azu- fre elemental. Bacterias fototrofas (anaerobias). • Bacterias oxidadoras de hierro y azufre. ( quimiolitotrofía; autotrofía, ej. Beggiatoa). • Describió bacterias anaerobias fijadoras. La laguna Salada de Chiprana: Descripción de sus características fiicoquímicas como hábitat para sus singulares communidades de bacterias fototrofas.
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Microbial mats arising in the sand flats of the Ebro Delta Tarragona, Spain were investigated during the summer season, when the community was highly developed. These mats are composed of three pigmented layers of phototrophic organisms, an upper brown layer mainly composed of Lyngbya aestuarii and diatoms, an intermediate green layer of the cyanobacterium Microcoleus chthonoplastesand an underlying pink layer of a so-far unidentified purple sulfur bacterium.
In this laminated community, organic matter has an autochthonous origin, and photosynthesis is the most important source of organic carbon. Oxygen production reaches up to Their vertical zonation is due to the established steep bacteras gradients and to their own physiology, which results in the arrangement of fotohrofas layers typical of this kind of ecosystem.
Together with the photoautotrophic organisms, chemoautotrophic and heterotrophic bacteria coexist. Microbial mats are highly productive ecosystems . Cyanobacteria, developed in the upper layers, are usually the most important primary producers in this kind of environment. Due to their photosynthetic metabolism, cyanobacteria generate oxygen, which can diffuse a few millimeters into the mat, and synthesize organic carbon compounds that are available to the rest of the microbial populations by active excretion or cell lysis [20,27].
In the presence of suitable electron donors, anoxygenic photosynthesis and chemosynthesis play an important metabolic role. Anoxygenic phototrophic bacteria purple and green sulfur bacteriafound below the oxic layers in a narrow zone that contains sulfide and is reached by light, can fix inorganic carbon as a consequence of their photosynthetic metabolism, using sulfide as an electron donor. Chemolithoautotrophic organisms, usually found between oxygenic and anoxygenic phototrophs, where oxygen and sulfide coexist, are able to fix inorganic carbon independently from the light using different electron donors, such as hydrogen or reduced sulfur compounds, and oxygen as electron acceptor .
The study of photosynthetic generation of organic matter in these few-millimeter thick ecosystems has become easier with the aid of microsensors [8,23].
In addition to measuring the vertical distribution of several physicochemical variables, such as oxygen or sulfide, these sensors record the vertical distribution of photosynthetic activity with a high spatial resolution [8,24]. A description of the Ebro Delta microbial mats, including qualitative observations of different mat bacterisa, has already been published . In the present study, we report on the vertical biomass distribution of major phototrophic organisms and the primary production of microbial mats widely distributed in the southern spit of the Ebro Delta.
Sampling site description and sample collection. The studied microbial mat site P3 is located in the Alfacs Peninsula, at the southern spit of the Ebro Delta Spainin a temporarily inundated sand flat close to the inner coast of the Alfacs bay described earlier . Samples were collected during the summer season, when microbial mats were highly developed, using a 4. The corer was inserted into the mat, and uniform cylindrical cores were removed.
Alternatively, samples for pigment determination were frozen with liquid nitrogen in the field. In the laboratory, the different laminations were bacteriad separated and subsampled for bacterial counts and pigment determinations. For electrode analysis, the mat core was submerged in water from the sampling site. fototrocas
Physical and chemical analyses. Temperature, conductivity, and salinity were measured in the overlying water by means of a Yellow Springs Instrument S-C-T meter model A micropH Crison pH-meter was used to measure pH. Light intensity was measured with a Delta Ohm HD lux meter. Vertical sections of the mat were observed under an Olympus SZ40 dissecting microscope in order to determine the number and characteristics of the different layers.
To better understand the distribution of microorganisms within the mat, small pieces of each pigmented lamination were placed on a glass slide in one drop of water and observed by phase-contrast microscopy with an Olympus BH-2 microscope. Phototrophic bacteria were classified morphologically and each type was counted separately from phase-contrast microscopy images. From each layer, a total of 16 replicates were analyzed.
From each single microorganism, total area, diameter and length were measured with a digital planimeter. These final values were converted into biovolume units by approximation to the nearest geometrical figure. Chlorophyll a and bacteriochlorophyll a were measured in the different layers using methanol extracts according to the method of Mir et al.
Thesis, Autonomous University of Barcelona, Spain]. Absorption spectra of the extracts were obtained from to nm using a DU Beckman spectrophotometer. Microprofiles of needle electrodes. Microprofiles of oxygen and sulfide were determined using needle mini-electrodes according to the method of Van Gemerden et al.
Profiles were recorded in the sediment cores during stepwise lowering of the electrodes using a micromanipulator.
The outputs from the electrodes were read on a picoamperometer Keithley and a millivoltmeter Bioblockrespectively. Oxygen production and sulfide oxidation were calculated from the oxygen and sulfide profiles after dark and light exposition of the cores according to the method of Revsbech et al.
Description of the mat layers and vertical distribution of bacterial populations. Prior to measuring biomass, the chemical characteristics gacterias the mat were determined in the overlying water. Salinity, conductivity, and pH ranged from 60 to 70 bacetrias l – 1ms cm – 1and 8. The distribution of dominant phototrophic organisms was studied in the photic zone of the mat.
Lyngbya aestuarii and diatoms, together with different coccoid cyanobacteria and some filaments of Microcoleus chthonoplastescoated the surface of the mat as a 0. Below, a deep pink fohotrofas 1. This bottom layer was dominated by a new purple sulfur bacterium with morphological and ultrastructural characteristics that do not coincide with those of previously identified anoxygenic phototrophic bacteria.
Different brown sandy laminations underlay the black layer. Table 1 vototrofas the vertical biomass ftootrofas, expressed as biovolume, corresponding to major phototrophic organisms that inhabit the microbial mat studied. Diatoms, predominantly belonging to the genera AmphoraNaviculaand Nitzschiawere more abundant in the upper brown layer, where they reached values of 1.
Three groups of coccoid cyanobacteria could be distinguished, the Gloeocapsa group, the Cyanothece group, and the Gomphosphaerioideae subfamily.
All bacteriaz them were distributed along the entire photic zone; nevertheless, their concentrations were slightly increased in the green layer, with values of 1. With respect to the vertical biomass distribution of filamentous cyanobacteria, L.
The vertical biomass profile of the dominant purple sulfur bacterium showed that this new organism had a narrow distribution. Figure 1A shows depth distribution of chlorophyll a fototrifas, phaeophytin a and the ratios chl a: The maximum of chlorophyll a was found in the green layer 0. In relation to degradation forms, phaeophytin a maximum was located in the pink layer 0. As shown in Fig.
The ratio bchl a: In the surface and below 4 mm depth the ratio decreased. Below this depth, the amount of oxygen decreased, falling to zero at 3. The sulfide concentration increased with depth, reaching values of 3 mM at 5 mm in the black layer.
Oxygenic photosynthetic activity was detected from the surface down to 3 mm Fig. The maximum oxygen production From 3 mm, just below oxygen-sulfide interface, to 4.
The mean value of sulfide oxidation was The effect of light vs. During the first 2 fototrovas of illumination, fototroas production greatly increased.
The high slope indicates a very efficient photosynthetic process. From 2- 10 h of continuous light, no change in the oxygen production rate was detected.
Finally, after 10 h of light, there was a clear decrease in oxygen production. The vertical distribution of colored layers and major phototrophic populations found in the microbial mat samples analyzed in this study are similar to those observed in well developed mats reported earlier .
Depth profiles of photosynthetic biomass see Table 1 correlated with profiles of chlorophyll a and bacteriochlorophyll athe predominant pigments found in these mats. Diatoms made up Among all cyanobacteria evaluated, M.
These values are higher than those reported in other microbial mats located in marine environments, such as Mellum Island, and slightly higher than those found in Solar Lake or Spencer Gulf Table 2.
In all of these mats, M. The study of evolution of oxygenic photosynthetic activity along a simulated diel cycle was carried out under constant light intensity. Photosynthetic activity depends on proportion of sunlight that falls on the organism, the efficiency with which that light is harvested, and nutrient accessibility. Several stress factors can contribute to limit the process, such as irradiance excess or carbon dioxide depletion.
Nevertheless, the results obtained show that the system functions with high efficiency over a long period of time. These data support observations on the lack of photoinhibition in the field [2,25]. Under natural conditions, however, changes in light intensity during a diel cycle also contribute to prevent photoinhibition.
There are many microbial mats in which anoxygenic photosynthesis does not play a relevant role in primary production . In those cases, oxygen production is high enough to supersaturate pore water and to move the oxygen-sulfide interface down to layers not reached by light.
Under these conditions, sulfide will be oxidized mainly by chemotrophic bacteria . In Ebro Delta mats, sulfide oxidation in the light was estimated by the disappearance of sulfide in the illuminated mat. In summer, when the pink layer reached its maximal development, sulfide consumption was calculated to be This value is very similar to that found in mats from salterns of Salins-de-Giraud .
Considering that the pink layer is 1. Several studies have reported the contribution of anoxygenic phototrophic bacteria to the carbon cycle in such ecosystems. Thus, our study, as well as the other examples discussed, addresses the relevant role of anoxygenic phototrophic bacteria as primary producers in the illuminated layer of coastal microbial mats.
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There is little information available about the chemosynthetic carbon fixation in microbial mats. Carbon fixation in the dark has not been always taken into account in studies of organic matter generation.
In the Ebro Delta microbial mats, carbon fixation in the dark has not been evaluated; however, an indirect calculation can be made. Considering that the black layer is 3. The values obtained are similar to those found in other mats. For example, in mats from Eastern Passage, which consist mainly of Beggiatoa sp.