Signature lipid biomarkers of microbial mats of the ebro delta (Spain), camargue and Étang de berre (France): An assessment of biomass and activity

Chang Y., Peacock A.D., Long P.E., Stephen J.R., McKinley J.P., Macnaughton S.J., Hussain A.K., Saxton A.M., White D.C.

ABSTRACT Microbially mediated reduction and immobilization of U(VI) to U(IV) plays a role in both natural attenuation and accelerated bioremediation of uranium-contaminated sites. To realize bioremediation potential and accurately predict natural attenuation, it is important to first understand the microbial diversity of such sites. In this paper, the distribution of sulfate-reducing bacteria (SRB) in contaminated groundwater associated with a uranium mill tailings disposal site at Shiprock, N.Mex., was investigated. Two culture-independent analyses were employed: sequencing of clone libraries of PCR-amplified dissimilatory sulfite reductase (DSR) gene fragments and phospholipid fatty acid (PLFA) biomarker analysis. A remarkable diversity among the DSR sequences was revealed, including sequences from δ-Proteobacteria, gram-positive organisms, and the Nitrospira division. PLFA analysis detected at least 52 different mid-chain-branched saturate PLFA and included a high proportion of 10me16:0. Desulfotomaculum and Desulfotomaculum -like sequences were the most dominant DSR genes detected. Those belonging to SRB within δ-Proteobacteria were mainly recovered from low-uranium (≤302 ppb) samples. One Desulfotomaculum -like sequence cluster overwhelmingly dominated high-U (>1,500 ppb) sites. Logistic regression showed a significant influence of uranium concentration over the dominance of this cluster of sequences ( P = 0.0001). This strong association indicates that Desulfotomaculum has remarkable tolerance and adaptation to high levels of uranium and suggests the organism's possible involvement in natural attenuation of uranium. The in situ activity level of Desulfotomaculum in uranium-contaminated environments and its comparison to the activities of other SRB and other functional groups should be an important area for future research.

Myers R.T., Zak D.R., White D.C., Peacock A.

The composition and diversity of biotic communities are controlled by the availability of growth-limiting resources. Resource availability for microbial populations in soil is controlled by the amount and types of organic compounds entering soil from plant litter. Because plant communities differ in the amount and type of substrates entering soil, we reasoned that the composition and function of soil microbial communities should differ with the dominant vegetation. We tested this idea by studying two sugar maple (Acer saccharum Marsh.)-dominated and one oak (Quercus spp.)-dominated forest ecosystems in northern Lower Michigan that differ in rates of soil N cycling. We used phospholipid fatty acid (PLFA) analysis to gain insight into microbial community composition, and we used a subset of Biolog GN substrates found in root exudate to assess the metabolic capabilities soil microbial communities. Although microbial biomass did not differ among ecosystems, principal components analysis of bacterial, actinomycetal, and fungal PLFAs clearly separated the microbial communities of the three ecosystems. Similarly, principal components analysis separated microbial communities by differences in growth on carbohydrates, organic acids, and amino acids. Discrimination among microbial communities in the three ecosystems by PLFAs and substrate use occurred in spring, summer, and fall, but the individual PLFAs and substrates contributing to discrimination changed during the growing season. Our results indicate that floristically and edaphically distinct forest ecosystems also differ in microbial community composition and substrate use. This pattern was consistent across the growing season and repeatedly occurred across relatively large land areas.

Navarrete A., Peacock A., Macnaughton S.J., Urmeneta J., Mas-Castellà J., White D.C., Guerrero R.

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.

MacNaughton S.J., Stephen J.R., Venosa A.D., Davis G.A., Chang Y., White D.C.

ABSTRACT Three crude oil bioremediation techniques were applied in a randomized block field experiment simulating a coastal oil spill. Four treatments (no oil control, oil alone, oil plus nutrients, and oil plus nutrients plus an indigenous inoculum) were applied. In situ microbial community structures were monitored by phospholipid fatty acid (PLFA) analysis and 16S rDNA PCR-denaturing gradient gel electrophoresis (DGGE) to (i) identify the bacterial community members responsible for the decontamination of the site and (ii) define an end point for the removal of the hydrocarbon substrate. The results of PLFA analysis demonstrated a community shift in all plots from primarily eukaryotic biomass to gram-negative bacterial biomass with time. PLFA profiles from the oiled plots suggested increased gram-negative biomass and adaptation to metabolic stress compared to unoiled controls. DGGE analysis of untreated control plots revealed a simple, dynamic dominant population structure throughout the experiment. This banding pattern disappeared in all oiled plots, indicating that the structure and diversity of the dominant bacterial community changed substantially. No consistent differences were detected between nutrient-amended and indigenous inoculum-treated plots, but both differed from the oil-only plots. Prominent bands were excised for sequence analysis and indicated that oil treatment encouraged the growth of gram-negative microorganisms within the α-proteobacteria and Flexibacter-Cytophaga-Bacteroides phylum. α-Proteobacteria were never detected in unoiled controls. PLFA analysis indicated that by week 14 the microbial community structures of the oiled plots were becoming similar to those of the unoiled controls from the same time point, but DGGE analysis suggested that major differences in the bacterial communities remained.

White D.C., Flemming C.A., Leung K.T., Macnaughton S.J.

Numerous studies have established a relationship between soil, sediment, surface biofilm and subsurface contaminant pollution and a marked impact on the in situ microbial community in both microcosms and in the field. The impact of pollution on the in situ microbial community can now be quantitatively measured by molecular `fingerprinting' using `signature' biomarkers. Such molecular fingerprinting methods can replace classical microbiological techniques that relied on isolation and subsequent growth of specific microbes from the in situ microbial community. Classical methods often revealed less than 1% of the extant microbial communities. Molecular fingerprinting provides a quantitative measure of the in situ viable microbial biomass, community composition, nutritional status, relative frequency of specific functional genes, nucleic acid polymers of specific microbes, and, in some cases, the community metabolic activity can be inferred. Current research is directed at establishing correlations between contaminant disappearance, diminution in toxicity, and the return of the viable biomass, community composition, nutritional status, gene patterns of the in situ microbial community towards that of the uncontaminated soil, sediment or subsurface material with the original uncontaminated microniche environments. Compared to the current reliance on disappearance of pollutants and associated potentially toxic products for detection of effective and quantitative bioremediation, assessment of the in situ microbial community will be an additional and possibly more convincing risk assessment tool. The living community tends to accumulate and replicate toxic insults through multiple interactions within the community, which may then effect viable biomass, community composition, nutritional status, community metabolic activities, and specific nucleic acid polymer patterns.

Macnaughton S.J., Jenkins T.L., Alugupalli S., White D.C.

Standard methods for characterizing the microbial content of indoor air rely on detection of viable microbes that are collected in water or impacted onto growth substrata. Viable counts consistently underestimate microbial numbers in environmental samples by 90–99.9%. Assays of biochemical components characteristic of all cells provide an assessment method independent of the ability to culture the organisms. This article provides evidence that lipid analysis provides quantitative recovery of known volumes of culturable bacteria. Monocultures of Escherichia coli, Bacillus subtilis, and Legionella bozemanii and two mixtures of these organisms were deposited onto glass fiber filters using an air test stand constructed as a modification of the ASTM 1215 standard. Filter deposited biomass was determined by three methods: (1) viable counts of bacteria sampled using an impinger, (2) phospholipid ester-linked fatty acid (PLFA) analysis, and (3) hydroxy fatty acid (OH FA) analysis. PLFA and OH FA were quantified b...

White D., Stair J., Ringelberg D.

Kieft T.L., Fredrickson J.K., McKinley J.P., Bjornstad B.N., Rawson S.A., Phelps T.J., Brockman F.J., Pfiffner S.M.

Twenty-six subsurface samples were collected from a borehole at depths of 173.3 to 196.8 m in the saturated zone at the Hanford Site in south-central Washington State. The sampling was performed throughout strata that included fine-grained lacustrine (lake) sediments, a paleosol (buried soil) sequence, and coarse-grained fluvial (river) sediments. A subcoring method and tracers were used to minimize and quantify contamination to obtain samples that were representative of subsurface strata. Sediment samples were tested for total organic carbon, inorganic carbon, total microorganisms by direct microscopic counts, culturable aerobic heterotrophs by plate counts, culturable anaerobes by most-probable-number enumeration, basal respiration rates, and mineralization of (sup14)C-labeled glucose and acetate. Total direct microscopic counts of microorganisms were low, ranging from below detection to 1.9 x 10(sup5) cells g (dry weight)(sup-1). Culturable aerobes and anaerobes were below minimum levels of detection in most samples. Direct microscopic counts, basal respiration rates, and (sup14)C-glucose mineralization were all positively correlated with total organic carbon and were highest in the lacustrine sediments. In contrast to previous subsurface studies, these saturated-zone samples did not have higher microbial abundance and activities than unsaturated sediments sampled from the same borehole, the fine-textured lacustrine sediment had higher microbial numbers and activities than the coarse-textured fluvial sands, and the paleosol samples did not have higher biomass and activities relative to the other sediments. The results of this study expand the subsurface microbiology database to include information from an environment very different from those previously studied.

White D.C.

Caumette P., Matheron R., Raymond N., Relexans J.-.

Microbial mats that develop in the gypsum crust of the hypersaline ponds of Salins-de-Giraud (Camargue, France) were carefully investigated between 1989 and 1991. During the warm seasons, when these mats were fully developed, analyses of microbial activities and microprofiles of oxygen and sulfide have shown a great activity of the different kinds of bacteria found in the mat below the gypsum crust. Oxygen production could amount to 2 μmol cm−3 h−1 during the maximum daylight whereas the oxidation of sulfide in the light was calculated to be 12.7 μmol cm−3 h−1, i.e. 300 to 180 mmol m−2 day−1 assuming 8–10 hours of constant daylight and a sulfide oxidation zone of 3 mm in thickness. This sulfide oxidation consumes about 65–95% of the diel sulfide production which has been estimated to be 400 to 450 mmol m−2 day−1 originating from sulfate reduction which takes place in the 6 cm depth horizon of sediment plus mat. According to the amounts of sulfate precipitated at the sediment surface in the form of gypsum, sulfate reduction is never limited and was found to be among the highest values reported in the literature (average value of 8200 nmols cm−3 day−1). Completely covered by the gypsum crust, this ecosystem has been found to react as a closed system. Consequently, the sulfide does not escape and accumulate below the crust. It was detected up to the top of the mat after a few hours of darkness. It is reoxidized during the day by the photosynthetic organisms that from the mats. These latter mats were composed of 2 to 3 laminated layers of phototrophic organisms: an upper brown layer of the cyanobacterium Aphanothece, an intermediate green layer of the cyanobacterium Phormidium and an underlying red layer of purple sulfur-oxidizing bacteria from which two new halophilic species were isolated (Chromatium salexigens and Thiocapsa halophila). It has been found that the accumulated sulfide is oxidized not only by the phototrophic bacteria in the sulfide oxidation zone but also by the oxygen produced by the cyanobacteria which are able to photosynthesize in the presence of sulfide.

Guerrero R., Urmeneta J., Rampone G.

The distribution and types of microbial mats of the Ebro Delta (Catalonia, Spain) are described. The studied area is La Banya spit, formed by a narrow sand bar and a peninsula, located south of the main body of the Ebro Delta. Sea water can penetrate into the back shore through channel inlets, cutting the steeper coastal barrier of the open sea side of the spit or through the complex drainage channel system of the low-energy beaches in the inner Alfacs Bay. Sea water can stay in the back shore almost permanently, trapped in isolated depressions and lagoons. The surface distribution of microbial mats in La Banya spit has been studied by means of a detailed interpretation of vertical aerial photographs and field work consisting of mapping and sampling. The observed different ratios of cyanobacteria, as well as the presence and thickness of the layers of anoxygenic sulfur phototrophic bacteria, depend on the moisture content, the system stability, and the age of the microbial mat. Lyngbya, Oscillatoria, and Spirulina are the first cyanobacteria able to colonize the bare sediment. Lyngbya dominates in young microbial mats and in mats exposed to frequent desiccation. Microcoleus is the second most important colonist in the microbial succession. In relation to water, the alternation of emergence and submergence is optimal for the maximal development of Microcoleus-dominated microbial mats. We classify the microbial mats of the Ebro Delta into five main types: (i) Lyngbya-dominated type, in which the anoxygenic phototrophic bacteria are absent and the black layer of sulfate-reducers is very thin; (ii) Spirulina-dominated type; (iii) Oscillatoria-dominated type, which is found only at one site and covers a small area--this type, like the Spirulina-type mat, is not common in the Ebro Delta; (iv) Lyngbya/Microcoleus-transition type, in which Microcoleus and Lyngbya coexist in similar proportions--in the more developed mats of this group a layer of purple bacteria is usually present, and the black layer of sulfate-reducers is usually also well developed; and (v) Microcoleus-dominated type--in La Banya spit, this type is found in localities with relatively stable conditions. These areas are wet during most of the year. After appropriate conditions of diagenesis, the most highly developed microbial mats may be preserved as laminated hard sediments. The field study has been completed with cultivation, isolation, and identification of the main cyanobacterial genera under laboratory conditions.

Heipieper H.J., Diefenbach R., Keweloh H.

A trans unsaturated fatty acid was found as a major constituent in the lipids of Pseudomonas putida P8. The fatty acid was identified as 9-trans-hexadecenoic acid by gas chromatography, argentation thin-layer chromatography, and infrared absorption spectrometry. Growing cells of P. putida P8 reacted to the presence of sublethal concentrations of phenol in the medium with changes in the fatty acid composition of the lipids, thereby increasing the degree of saturation. At phenol concentrations which completely inhibited the growth of P. putida, the cells were still able to increase the content of the trans unsaturated fatty acid and simultaneously to decrease the proportion of the corresponding 9-cis-hexadecenoic acid. This conversion of fatty acids was also induced by 4-chlorophenol in nongrowing cells in which the de novo synthesis of lipids had stopped, as shown by incorporation experiments with labeled acetate. The isomerization of the double bond in the presence of chloramphenicol indicates a constitutively operating enzyme system. The cis-to-trans modification of the fatty acids studied here apparently is a new way of adapting the membrane fluidity to the presence of phenols, thereby compensating for the elevation of membrane permeability induced by these toxic substances.

Mir J., Martínez-Alonso M., Esteve I., Guerrero R.

Vertically stratified communities in a temporarily inundated sand flat at the Ebro Delta were studied. Three different microbial mats were compared using light microscopy, scanning electron microscopy and pigment analysis. The youngest mat had less layers than wellestablished mats and contained mostly filamentous cyanobaeteria belonging to the genus Spiruliaa . Diatoms, as well as coccoid cyanobacteria, could be found on the surface of this mat. The only pigmented layer present was green in color and the main pigment found, belonging to these oxygenic phototrophs, was chlorophyll a . Small amounts of bacteriochiorophyll a were present. Well-developed mats were vertically stratified into three distinct pigmented layers. In the up-permost yellow-brown layer, Nitzschia sp., Navicula sp. and Amphora sp. (diatoms) and coccoid cyanobacteria were dominant. The second layer was composed mostly of Microcoleus sp. and a few filaments of Lyngbya sp. and coccoid cyanobacteria. The principal pigment in both layers was chlorophyll a . Bacteriochlorophyll a , predominantly found in anoxTgenic phototrophic bacteria, increased with depth. The deepest layer, purple or orange in color depending on sampling site, was composed basically of anoxygenic phototrophic bacteria, i.e. Chromatium sp. and Thiocapsa sp. Several species of non phototrophic bacteria, i.e. spirochetes and other unidentified small rods and cocci, could be observed in these communities. Although it is not common to find eukaryotes, with the exception of diatoms, a eopepod and an unidentified nematode were present in these communities. The different mat populations occurred within a few millimeters where close contacts could be established among them. The extracellular polymer production in several microorganisms allowed their attachment to sediment particles.

Kaneda T.

Branched-chain fatty acids of the iso and anteiso series occur in many bacteria as the major acyl constituents of membrane lipids. In addition, omega-cyclohexyl and omega-cycloheptyl fatty acids are present in several bacterial species. These two types of fatty acids are synthesized by the repeated condensation of malonyl coenzyme A with one of the branched-chain and cyclic primers by the same enzyme system. The pathway of de novo branched-chain fatty acid synthesis differs only in initial steps of synthesis from that of the common straight-chain fatty acid (palmitic acid) present in most organisms. The cell membranes composed largely of iso-, anteiso-, and omega-alicyclic acids support growth of bacteria, which inhabit normal as well as extreme environments. The occurrence of these types of fatty acids as major cellular fatty acids is an important criterion used to aid identification and classification of bacteria.

Des Marais D.J.

Microbial mats have descended from perhaps the oldest and most widespread biological communities known. Mats harbor microbes that are crucial for studies of bacterial phylogeny and physiology. They illustrate how several oxygen-sensitive biochemical processes have adapted to oxygen, and they show how life adapted to dry land long before the rise of plants. The search for the earliest grazing protists and metazoa in stromatolites is aided by observations of mats: in them, organic compounds characteristic of ancient photosynthetic protists can be identified. Recent mat studies suggest that the 13C/12C increase observed over geological time in stromatolitic organic matter was driven at least in part by a long-term decline in atmospheric carbon dioxide levels.

Paisse S., Duran R., Coulon F., Goñi-Urriza M.

The diversity of alkB-related alkane hydroxylase sequences and the relationship between alkB gene expression and the hydrocarbon contamination level have been investigated in the chronically polluted Etang-de-Berre sediments. For this purpose, these sediments were maintained in microcosms and submitted to a controlled oil input miming an oil spill. New degenerated PCR primers targeting alkB-related alkane hydroxylase sequences were designed to explore the diversity and the expression of these genes using terminal restriction fragment length polymorphism fingerprinting and gene library analyses. Induction of alkB genes was detected immediately after oil addition and their expression detected only during 2 days, although the n-alkane degradation was observed throughout the 14 days of incubation. The alkB gene expression within triplicate microcosms was heterogeneous probably due to the low level of alkB transcripts. Moreover, the alkB gene expression of dominant OTUs has been observed in unoiled microcosms indicating that the expression of this gene cannot be directly related to the oil contamination. Although the dominant alkB genes and transcripts detected were closely related to the alkB of Marinobacter aquaeolei isolated from an oil-producing well, and to alkB genes related to the obligate alkanotroph Alcanivorax borkumensis, no clear relationship between the oil contamination and the expression of the alkB genes could be established. This finding suggests that in such coastal environments, alkB gene expression is not a function relevant enough to monitor bacterial response to oil contamination.

Villanueva L., del Campo J., Guerrero R., Geyer R.

Microbial mats are stratified microbial communities composed by highly inter-related populations and therefore are frequently chosen as model systems to study diversity and ecophysiological strategies. The present study describes an integrated approach to analyze microbial quinones and intact polar lipids (IPLs) in microbial mats within layers as thin as 500 µm by liquid chromatography–tandem mass spectrometry. Quinone profiles revealed important depth-related differences in community composition in two mat systems. The higher abundance of ubiquinones, compared to menaquinones, reflected the clear predominance of microorganisms belonging to aerobic α-, β-, and γ-Proteobacteria in Ebro delta estuarine mats. Hypersaline photosynthetic Camargue mats (France) showed a predominance of menaquinone-9 at the top of the mat, which is consistent with an important contribution of facultative aerobic or anaerobic bacteria in its photic zone. Quinone indices also indicated a higher diversity of non-phototrophs and a more anaerobic character in the hypersaline mats. Besides, the dissimilarity index suggested that the samples were greatly influenced by a depth-related redox state gradient. In the analysis of IPLs, there was a predominance of phosphatidylglycerols and sulfoquinovosyldiacylglycerols, the latter being an abundant biomarker of Cyanobacteria. This combined approach based on quinone and IPL analysis has proven to be a useful method to establish differences in the microbial diversity and redox state of highly structure microbial mat systems at a fine-scale level.

Villanueva L., Navarrete A., Urmeneta J., White D.C., Guerrero R.

Microbial mats are prokaryotic communities that provide model systems to analyze microbial diversity and ecophysiological interactions. Community diversity of microbial mat samples was assessed at 8:00 a.m. and 3:00 p.m. in a combined analysis consisting of 16S rRNA-denaturing gradient gel electrophoresis (DGGE) and phospholipid fatty acid (PLFA) profiles. The divergence index determined from PLFA and DGGE data showed that depth-related differences have a greater influence on diversity than temporal variations. Shannon and Simpson indices yielded similar values in all samples, which suggested the stable maintenance of a structurally diverse microbial community. The increased diversity observed at 3:00 p.m. between 2.5 and 4 mm can be explained mainly by diversification of anaerobic microorganisms, especially sulfate-reducing bacteria. In the afternoon sampling, the diversity index reflected a higher diversity between 4 and 5.5 mm depth, which suggested an increase in the diversity of strict anaerobes and fermenters. The results are consistent with the conclusion that hypersaline microbial mats are characterized by high degree of diversity that shifts in response to the photobiological adaptations and metabolic status of the microbial community.

Nocker A., Lepo J.E., Martin L.L., Snyder R.A.

The information content and responsiveness of microbial biofilm community structure, as an integrative indicator of water quality, was assessed against short-term changes in oxygen and nutrient loading in an open-water estuarine setting. Biofilms were grown for 7-day periods on artificial substrates in the Pensacola Bay estuary, Florida, in the vicinity of a wastewater treatment plant (WWTP) outfall and a nearby reference site. Substrates were deployed floating at the surface and near the benthos in 5.4 m of water. Three sampling events covered a 1-month period coincident with declining seasonal WWTP flow and increasing dissolved oxygen (DO) levels in the bottom waters. Biomass accumulation in benthic biofilms appeared to be controlled by oxygen rather than nutrients. The overriding effect of DO was also seen in DNA fingerprints of community structure by terminal restriction fragment length polymorphism (T-RFLP) of amplified 16S rRNA genes. Ribotype diversity in benthic biofilms at both sites dramatically increased during the transition from hypoxic to normoxic. Terminal restriction fragment length polymorphism patterns showed pronounced differences between benthic and surface biofilm communities from the same site in terms of signal type, strength, and diversity, but minor differences between sites. Sequencing of 16S rRNA gene clone libraries from benthic biofilms at the WWTP site suggested that low DO levels favored sulfate-reducing prokaryotes (SRP), which decreased with rising oxygen levels and increasing overall diversity. A 91-bp ribotype in the CfoI-restricted 16S rRNA gene T-RFLP profiles, indicative of SRP, tracked the decrease in relative SRP abundance over time.

Villanueva L., Navarrete A., Urmeneta J., Geyer R., White D.C., Guerrero R.

Microbial mats are highly productive microbial systems and a source of not-yet characterized microorganisms and metabolic strategies. In this article, we introduced a lipid biomarker/microbial isolation approach to detect short-term variations of microbial diversity, physiological and redox status, and also characterize lipid biomarkers from specific microbial groups that can be further monitored. Phospholipid fractions (PLFA) were examined for plasmalogens, indicative of certain anaerobes. The glycolipid fraction was processed for polyhydroxyalkanoates (PHA) and the neutral lipid fraction was used to evaluate respiratory quinone content. Data demonstrate an increase in the metabolic stress, unbalanced growth, proportion of anaerobic bacteria and respiratory rate after the maximal photosynthetic activity. Higher accumulation of polyhydroxyalkanoates at the same sampling point also suggested a situation of carbon storage by heterotrophs closely related to photosynthetic microorganisms. Besides, the characterization of lipid biomarkers (plasmalogens, sphingolipids) from specific microbial groups provided clues about the dynamics and diversity of less-characterized mat members. In this case, lipid analyses were complemented by the isolation and characterization of anaerobic spore formers and sulfate reducers to obtain insight into their affiliation and lipid composition. The results revealed that temporal shifts in lipid biomarkers are indicative of an intense change in the physiology, redox condition, and community composition along the diel cycle, and support the hypothesis that interactions between heterotrophs and primary producers play an important role in the carbon flow in microbial mats.

Villanueva L., Navarrete A., Urmeneta J., White D.C., Guerrero R.