Mercury Tolerance of Thermophilic <Emphasis Type="Italic">Bacillus</Emphasis> sp. and <Emphasis Type="Italic">Ureibacillus</Emphasis> sp

Although resistance of microorganisms to Hg(II) salts has been widely investigated and resistant strains have been reported from many eubacterial genera, there are few reports of mercuric ion resistance in extremophilic microorganisms. Moderately thermophilic mercury resistant bacteria were selected by growth at 62 °C on Luria agar containing HgCl₂. Sequence analysis of 16S rRNA genes of two isolates showed the closest matches to be with Bacillus pallidus and Ureibacillus thermosphaericus. Minimum inhibitory concentration (MIC) values for HgCl₂ were 80 μg/ml and 30 μg/ml for these isolates, respectively, compared to 10 μg/ml for B. pallidus H12 DSM3670, a mercury-sensitive control. The best-characterised mercury-resistant Bacillus strain, B. cereus RC607, had an MIC of 60 μg/ml. The new isolates had negligible mercuric reductase activity but removed Hg from the medium by the formation of a black precipitate, identified as HgS by X-ray powder diffraction analysis. No volatile H₂S was detected in the headspace of cultures in the absence or presence of Hg²⁺, and it is suggested that a new mechanism of Hg tolerance, based on the production of non-volatile thiol species, may have potential for decontamination of solutions containing Hg²⁺ without production of toxic volatile H₂S.     

Synergistic utilization of dichloroethylene as sole carbon source by bacterial consortia isolated from contaminated sites in Africa

The widespread use and distribution of chloroethylene organic compounds is of serious concern owing to their carcinogenicity and toxicity to humans and wildlife. In an effort to develop active bacterial consortia that could be useful for bioremediation of chloroethylenecontaminated sites in Africa, 16 combinations of 5 dichloroethylene (DCE)-utilizing bacteria, isolated from South Africa and Nigeria, were assessed for their ability to degradecis- andtrans-DCEs as the sole carbon source. Three combinations of these isolates were able to remove up to 72% of the compounds within 7 days. Specific growth rate constants of the bacterial consortia ranged between 0.465 and 0.716 d⁻¹ while the degradation rate constants ranged between 0.184 and 0.205 d⁻¹, with 86.36–93.53 and 87.47–97.12% of the stoichiometric-expected chloride released during growth of the bacterial consortia, incis- andtrans-DCE, respectively. Succession studies of the individual isolates present in the consortium revealed that the biodegradation process was initially dominated byAchromobacter xylosoxidans and subsequently byAcinetobacter sp. andBacillus sp., respectively. The results of this study suggest that consortia of bacteria are more efficient than monocultures in the aerobic biodegradation of DCEs, degrading the compounds to levels that are up to 60% below the maximum allowable limits in drinking water.     

Characteristics of stress response in a mushroom-pathogenic bacterium,Pseudomonas tolaasii, during the interaction withPleurotus ostreatus and carbon/nitrogen starvation in vitro

A brown blotch bacterium,Pseudomonas tolaasii strain PT814, expresses a high degree of cross-protection against generalized stress imposed by physical/chemical treatment, H₂O₂, UV, high temperature, ethanol and NaCl during the interaction withPleurotus ostreatus. Stress resistance was also noted in the bacterium in vitro under limited carbon and nitrogen sources. In addition, changes in cell morphology from a “metabolically active” rod to an “energy-saving” spherical shape were detected during starvation and the interaction. All the changes under stress were reversible. A homologue ofrpoS (σ ^S), a regulator that controls such physiological status during starvation in other bacteria, was identified inP. tolaasii strain PT814. Data suggest that the bacterium is able to withstand a complex stress environment for its survival through changes in its metabolic pattern.     

Antifungal action of alkoxy ethyl mercuric acetates

The fungitoxic action of alkoxy ethyl mercuric acetates and phenyl mercuric acetate was studied withAspergillus niger, Penicillium italicum andUstilago maydis as test moulds. Concentrations of mercurials from 10^–3 m to 10^–5 m were used in each experiment. The inhibitory action was about the same for each of the compounds tested.     

Growth ofPseudomonas putida andP. fluorescens on silicome oils

Growth ofP. putida andP. fluorescens on organic silicon compounds was investigated. Both strains could grow on low-molar-mass oligomeric organo-silicon compounds of M₂D up to M₂D₅ type and on polydimethylsiloxanes with a viscosity higher than 1.46 Pa s (20 °C). Linear α, ω-polydimethylsiloxanediols were attacked only by a mixed culture of the two bacteria. Dodecaethoxypen-tasiloxane and tetraethoxysilane were rapidly degraded, yielding ethanol, trimethoxysilane was transformed to trimethylsilanol. Organosilicon compounds can thus be transformed by a specific microflora and in the natural environment degraded by a mechanism similar to that of other organic compounds.     

The microbial production of poly(hydroxyalkanoates) from tallow

The bacteria Pseudomonas oleovorans, P. resinovorans, P. putida, and P. citronellolis were evaluated for their ability to grow and produce poly(hydroxyalkanoates) (PHA) using tallow free fatty acids and tallow triglyceride as carbon substrates. Tallow free fatty acids supported cell growth and PHA production for all four organisms, yielding PHA contents of 18%, 15%, 19% and 3% of their cell dry weights for P. oleovorans, P.␣resinovorans, P. putida, and P. citronellolis respectively. Only P. resinovorans, however, was able to grow and produce PHA polymer, with cells attaining a PHA content of 15% of their cell dry weight, using unhydrolyzed tallow as the substrate. Extracts from 46-h cultures of P. resinovorans were found to have a higher esterase activity (12.80 units μl⁻¹min⁻¹) compared to the activities found for cultures of P. oleovorans, P. citronellolis, and P. putida ( < 0.03 units μl⁻¹min⁻¹). Polymer repeat-unit compositions were determined by GC analysis of the β-hydroxymethyl esters of hydrolyzed PHA, and ranged in carbon-chain lengths from C₄ to C₁₄, with some mono-unsaturation in the C₁₂ and C₁₄ side-chains. PHA compositions were similar for the polymers obtained from all four organisms, with repeat units of chain lengths C₈ and C₁₀ predominating. Received: 16 February 1996 / Received revision: 23 May 1996 / Accepted: 10 June 1996     

Interaction of bacteria with mercuric compounds

We investigated the interaction of mercuric compounds with the bacteria Corynebacterium ammoniagenes, Micrococcus luteus, and Mycobacterium smegmatus capable of producing hydroxylamines (R-NOH) and 2-C-methyl-D-erythritol-2,4-cyclopyrophosphate (MECP), which are prone to form free radicals. The interaction of these substances with Hg2+ ions and their dynamics during the mercuric poisoning of bacteria was studied by EPR and NMR. Under stress conditions induced by lowering pH or generation of active oxygen species, the bacteria and, especially, their mutants with enhanced sensitivity to oxidative stress, were found to respond to exposure to 1-3 micrograms/ml HgCl2 and p-chloromercuribenzoate by a several-fold increase in their viability. The data obtained were interpreted in terms of the involvement of the sulfhydryl groups of bacterial surface proteins in this phenomenon. The interaction of bacteria with mercuric compounds may affect the pathogenesis of tuberculosis and other diseases.     

Depletion of adenosine triphosphate inDesulfovibrio by oxyanions of group VI elements

Oxyanions of elements from group VI of the periodic table, i.e., analogs of SO₄ ²⁻, destroyed adenosine 5′-triphosphate (ATP) in cells of sulfate-respiring bacteria (Desulfovibrio spp.), probably via the ATP sulfurylase reaction. The approximate order of effectiveness was CrO₄ ²⁻> MoO₄ ²⁻=WO₄ ²⁻>SeO₄ ²⁻. Cultures of aerobically grown or nitrate-respiring bacteria were less susceptible and with fermentatively grownEscherichia coli the oxyanions even appeared to stimulate ATP levels. The selective depletion of ATP in sulfate-respiring bacteria might provide the basis for a rapid and simple assay of their biomass in mixed cultures or environmental samples.     

Contribution of the allelicMtz 3 andMtz 4 allotype genes to the formation of individual rabbit serum α2-macroglobulin molecules

The contribution of the allelicMtz ³ andMtz ⁴ genes to the formation of individual rabbit serum α₂-macroglobulin (α₂M) molecules was examined by precipitation of α₂M from rabbits of known genotype with antiallotype antisera. The α₂M was isolated fromz ³z³ andz ⁴z⁴ homozygous andz ³z⁴ heterozygous rabbits, iodinated with I¹²⁵ and precipitated by sequential reactions with antiallotype antiserum and goat anti-rabbit IgG. Purified unlabeled α₂M or α₂M in serum was used to inhibit competitively the reaction of antiallotype antiserum and labeled α₂M. Nearly all α₂M molecules have z3 or z4 antigenic determinants; approximately 50% of α₂M molecules in heterozygotes have both. Altogether, the z3, z3,4, and z4 molecules in heterozygotes have approximately 60% of the number of z3 and 40% of the number of z4 determinants as compared to the respective homozygotes. Unlike all other known allelic blood protein systems of rabbits, allelic exclusion does not occur in α₂M molecules of heterozygotes; rather, hybrid molecules are formed. Presented in part at the Fifty-fourth and Fifty-fifth Annual Meetings of the Federation of American Societies for Experimental Biology, Atlantic City, New Jersey, April 12–17, 1970, and Chicago, Illinois, April 12–17, 1971. This investigation was supported in part by U.S. Public Health Service Grants AI-09241 and AI-07043. B.H.B. performed this investigation in partial fulfillment of the requirements for the Doctor of Philosophy Degree in the Graduate College; he is supported by a postdoctoral fellowship from the Schweppe Foundation. K.L.K. is the recipient of U.S. Public Health Service Research Career Development Award AI-28687.     

Evidence for a periodic excretion of nitrogen by roots of grass-legume associations

Diurnal variation in ion content of the solution bathing roots of two plants growing together in sand culture was analysed for three pairs of grass-legume species (Lolium multiflorum andTrifolium pratense; Zea mays andGlycine hispida; Avena sativa andVicia sativa) and their monospecific controls. Biomass and nitrogen content of plants were determined. Ion concentration (NO ₃ ⁻ , NO ₂ ⁻ , NH ₄ ⁺ , and K⁺) and pH of root solutions were measured for Lolium-Trifolium plant pairs and controls at 6 hours intervals over 36 h, starting at 8 am within a circadian cycle. Root solutions were regularly depleted in NO ₃ ⁻ by the grasses (Lolium-Lolium control) throughout the cycle. For associations involving the legume (Lolium-Trifolium and Trifolium-Trifolium), NO ₃ ⁻ depletion was followed by NO ₃ ⁻ enrichment at night, from late afternoon to early morning; the enrichment was more marked for the Lolium-Trifolium association. Solutions which did not contain NO ₂ ⁻ ions, were enriched by trace amounts of NH ₄ ⁺ ions, largely depleted in K⁺ and alkalanized for all associations throughout the cycle. Repeating the experiment with the three pairs of species at the vegetative phase of development confirmed the previous results: NO ₃ ⁻ enrichment during the night for associations with legumes. When the experiment was repeated with older plants which had almost completed their flowering stage, depletion only was observed and no NO ₃ ⁻ enrichment. These data suggest that NO ₃ ⁻ enrichment results from N excretion from active nodulated roots of the legume, accounting for the increase in both biomass and nitrogen content of the companion grass in grass-legume association. The quantitative importance and periodicity of nitrogen excretion as well as the origin of nitrate enrichment are discussed.     

Metabolism during starvation/dehydration stress in two species of galagos

Two species of galagos (G. senegalensis moholi andG. garnettii) were subjected to dehydration and starvation stress in order to determine whether, as is common in other animals, these hypometabolic prosimians would lower their metabolic rate even further. Dehydration was confirmed by losses in body mass, a decrease in fecal water content and a rise in urine osmolality. At the height of dehydration, 20 to 25% reduction in body mass, 30 to 40% reduction in fecal water content and urine osmolality ranging from 1.8 to 3.5 Osmol kg⁻¹ H₂O, were recorded in some of the animals. Basal metabolic rate of 0.536 ml O₂ (g·h)⁻¹ inG. s. moholi and 0.302 ml O₂ (g·h)⁻¹ inG. garnettii were recorded, representing 50 to 42% reduction in metabolic rate, respectively, compared with mass specific values. In none of the tested animals did we observe significant reduction in basal metabolism during dehydration/starvation stress compared with the rates observed during the control period. Basal metabolism in the bushbabies seems to have reached the lowest level and no further adjustment is apparently possible as a strategy for energy saving during starvation and/or dehydration stress.     

Studies in imitative behavior: A generalization of the rashevsky model; Its mathematical properties

This paper is based on N. Rashevsky's theory of imitative behavior, the underlying idea being that performance of one reaction by a given individual produces an increased stimulation (or tendency) toward the same reaction in other individuals. For simplicity, consideration is limited to cases in which each individual may choose only between two (or two main categories of) reactions, denoted byA andB in the following. However, upon suggestion from Dr. Rashevsky and certainly in better agreement with actual facts, the strength of imitative interaction is assumed to vary from individual to individual. More precisely, if Ψ_i denotes the additional excitation caused by imitation in theith individual,PA_i the probability for performance of reactionA, andPB_i the probability for performance of reactionB by theith individual, we postulate that where the constants α _ik ^′ and β _ik ^′ (coefficients of imitative interaction) measure the amount of imitative influence exerted by thekth individual upon theith,N being the total number of individuals in the population. The term — α_i Ψ_i accounts for the spontaneous decay of excitation, and the quantities α _ik ^′ and α _ik ^′ are assumed to benon-negative. The expressions forPA_i andPB_i are obtained from H. D. Landahl's theory of conflicting stimuli; they depend non-linearly on the values Ψ_i. It is implicit in this formulation that the theory can only be applied if the frequency of contacts between individuals is not too small. Some further shortcomings and limitations of the model are outlined, and the discussion includes suggestions for reinterpretation and improvement of the theory. If all the quantities α _ik ^′ and α _ik ^′ have the same value, sayA, we return to the case treated by Rashevsky (and Landau, 1950); these authors, however, replace the sums in the equation above by integrals, which automatically restricts the validity of their results to very large values ofN. Their work may therefore be characterized by the assumption of uniform interaction in large populations. Our equations, on the other hand, are applicable even to very small groups, and therein lies one of their main advantages. In this paper the mathematical properties of the non-linear system of equations above are studied with particular reference to the existence and stability of steady states [dΨ_i/dt ≡ 0;, i = 1 , 2, . . . N]. A sufficient condition for the existence of only one stable steady state is derived. It may be formulated roughly by stating that all the coefficients of interaction should be sufficiently small. It that is not the case, there may exist a greater number of stationary states. In particular, two of them (called “extremal”) have the following properties: they arestable and such that the average number of individuals in the group performing one or the other reaction is the largest (or smallest) possible as compared with the other steady states. Hence the situation is qualitatively similar to that found by Rashevsky and Landau.Quantitatively, however, important differences may arise, depending on the nature of the matrix specifying the interaction. A stable state may be approached through damped oscillations, but this effect is important only if the damping is sufficiently small for the oscillations to become practically observable. Little information could be obtained on this point, due to mathematical difficulties. As mentioned above, the most interesting applications of this theory will be with respect to small populations or to populations partitioned into subgroups with varying amounts of imitative interaction within as well as between groups.     

Inoculation of forage grasses with N2-fixing Enterobacteriaceae

Summary Previous investigations indicated some forage grass roots in Texas are heavily colonized with N₂-fixing bacteria. The most numerous N₂-fixing bacteria were in the genera Klebsiella and Enterobacter. In the present investigation inoculation experiments were conducted using 18 isolates of these bacteria to determine if a N₂-fixing association could be established between the bacteria and the grassesCynodon dactylon andPanicum coloratum. Plants were grown in soil for approximately 5 months in a greenhouse and were measured periodically for dry matter, nitrogen accumulation, and acetylene reduction activity. Results of the investigation indicated that 25% of the plant-soil systems were active in acetylene reduction and the activity was high enough to indicate agronomically significant quantities of N₂ were being fixed (>8kg N ha⁻¹). However, plant systems extrapolated to fix>8 kg N ha⁻¹ contained less nitrogen and accumulated less dry matter than plants less active in acetylene reduction. Inocula could not be re-isolated from healthy grass roots indicating that the N₂-fixing activity may have not have been closely assiciated with plant roots. Future research is needed to determine factors limiting colonization of grass roots.     

Pharmacophore modeling and 3D-QSAR analysis of phosphoinositide 3-kinase p110α inhibitors

Pharmacophore modeling studies were undertaken for a series of compounds belonging several groups of phosphoinositide 3-kinase (PI3K) p110α inhibitors: 4-morpholino-2-phenylquinazolines derivatives, pyrido[3′,2′:4,5]furo-[3,2-d]pyrimidine derivatives, imidazo[1,2-a]pyridine derivatives, sulfonylhydrazone substituted imidazo[1,2-a]pyridines, and LY294002. A five-point pharmacophore with three hydrogen bond acceptors (A), one hydrophobic group (H), and one aromatic ring (R) as pharmacophore features was developed. The pharmacophore hypothesis yielded a statistically significant 3D-QSAR model, with a correlation coefficient of R ² = 0.95 for training set compounds. The model generated showed excellent predictive power, with a correlation coefficient of Q ² = 0.88 and r _pret² = 0.95 for a test set of 14 compounds. Furthermore, the structure–activity relationships of PI3K p110α inhibitors were elucidated and the activity differences between them discussed. Docking studies were also carried out wherein active and inactive compounds were docked into the active site of the PI3K p110α crystal structure to analyze PI3K p110α–inhibitor interactions. The results provide insights that will aid optimization of these classes of PI3K p110α inhibitors for better activity, and may prove helpful for further lead optimization and virtual screening.     

Choline and acetylcholine: novel cationic osmolytes in Lactobacillus plantarum

The aim of this work was to study the physiological response of Lactobacillus plantarum subjected to osmotic stress in the presence of three structurally related compatible solutes. Either betaine, choline or acetylcholine was accumulated by osmotically stressed cells when provided in the chemically defined medium. Choline and acetylcholine were accumulated to maximum concentrations of 139 and 222 μmol g (dry weight) of cells⁻¹ respectively and were not converted to betaine. Addition of 0.5 mM choline or 0.5 mM acetylcholine to the medium increased the growth rates of cells in media with various amounts of added sodium chloride. Both choline and acetylcholine are positively charged compounds; therefore, it was presumed that charged intracellular solutes could counterbalance the excess of positive charge. Intracellular inorganic ion levels (K⁺, SO²⁻ ₄, PO³⁻ ₄ and Cl⁻) of cells cultured under conditions of osmotic stress remained similar in the presence of either betaine, choline or acetylcholine. However, cells cultured in the presence of choline or acetylcholine accumulated an additional quantity of approximately 125 or 200 μmol.glutamate (dry weight) cells⁻¹ respectively, as compared to cells grown in the presence of betaine. Hence glutamate appears to be the counterion for choline and acetylcholine. This is the first study demonstrating accumulation of choline and acetylcholine in lactic acid bacteria subjected to osmotic stress. Received: 5 February 1997 / Received revision: 15 April 1997 / Accepted: 19 April 1997     

Thermophilic biodegradation of BTEX by two consortia of anaerobic bacteria

Two thermophilic anaerobic bacterial consortia (ALK-1 and LLNL-1), capable of degrading the aromatic fuel hydrocarbons, benzene, toluene, ethylbenzene, and the xylenes (BTEX compounds), were developed at 60 °C from the produced water of ARCO'S Kuparuk oil field at Alaska and the subsurface water at the Lawrence Livermore National Laboratory gasoline-spill site, respectively. Both consortia were found to grow at 45–75 °C on BTEX compounds as their sole carbon and energy sources with 50 °C being the optimal temperature. With 3.5 mg total BTEX added to sealed 50-ml serum bottles, which contained 30 ml mineral salts medium and the consortium, benzene, toluene, ethylbenze, m-xylene, and an unresolved mixture of o- and p-xylenes were biodegraded by 22%, 38%, 42%, 40%, and 38%, respectively, by ALK-1 after 14 days of incubation at 50 °C. Somewhat lower, but significant, percentages of the BTEX compounds also were biodegraded at 60 °C and 70 °C. The extent of biodegradation of these BTEX compounds by LLNL-1 at each of these three temperatures was slightly less than that achieved by ALK-1. Use of [ring-¹⁴C]toluene in the BTEX mixture incubated at 50 °C verified that 41% and 31% of the biodegraded toluene was metabolized within 14 days to water-soluble products by ALK-1 and LLNL-1, respectively. A small fraction of it was mineralized to ¹⁴CO₂. The use of [U-¹⁴C]benzene revealed that 2.6%–4.3% of the biodegraded benzene was metabolized at 50 °C to water-soluble products by the two consortia; however, no mineralization of the degraded [U-¹⁴C]benzene to ¹⁴CO₂ was observed. The biodegradation of BTEX at all three temperatures by both consortia was tightly coupled to sulfate reduction as well as H₂S generation. None was observed when sulfate was omitted from the serum bottles. This suggests that sulfate-reducing bacteria are most likely responsible for the observed thermophilic biodegradation of BTEX in both consortial cultures. Received: 12 July 1996 / Received revision: 31 December 1996 / Accepted: 31 January 1997     

The ecology of mercury-resistant bacteria in Chesapeake Bay

Total ambient mercury concentrations and numbers of mercury resistant, aerobic heterotrophic bacteria at six locations in Chesapeake Bay were monitored over a 17 month period. Mercury resistance expressed as the proportion of the total, viable, aerobic, heterotrophic bacterial population reached a reproducible maximum in spring and was positively correlated with dissolved oxygen concentration and sediment mercury concentration and negatively correlated with water turbidity. A relationship between mercury resistance and metabolic capability for reduction of mercuric ion to the metallic state was established by surveying a number of HgCl₂-resistant cultures. The reaction was also observed in microrganisms isolated by differential centrifugation of water and sediment samples. Mercuric ion exhibited an average half-life of 12.5 days in the presence of approximately 10⁵ organisms/ml. Cultures resistant to 6 ppm of mercuric chloride and 3 ppm of phenylmercuric acetate (PMA) were classified into eight generic categories.Pseudomonas spp. were the most numerous of those bacteria capable of metabolizing both compounds; however, PMA was more toxic and was more selective forPseudomonas. The mercury-resistant generic distribution was distinct from that of the total bacterial generic distribution and differed significantly between water and sediment, positionally and seasonally. The proportion of nonglucose-utilizing mercury-resistantPsuedomonas spp. was found to be positively correlated with total bacterial mercury resistance. It is concluded from this study that numbers of mercury-resistant bacteria as established by plate count can serve as a valid index ofin situ Hg²⁺ metabolism.     

Reduction of the nitrogen and carbon content in swine waste with algae and bacteria

Animal waste causes environmental problems like eutrophication of ground and surface water or the pollution of the atmosphere because of its high NH₄ ⁺ content. The aim of our study was to fix the nitrogen of swine waste as biomass. Therefore, an isolated alga, Chlorella sp., and bacteria naturally living in liquid manure were grown in batch cultures (containing diluted swine waste supplied with a nutrient solution) and continuous cultures (undiluted liquid manure) to achieve reduction of NH₄ ⁺ and total organic carbon (TOC) contents. For continuous cultivation, a photobioreactor of our own design was used. The batch cultivation of Chlorella sp. and bacteria in swine waste resulted in good growth of both groups of organisms and in a reduction of 25% NH₄ ⁺ and 80% TOC. In the continuous cultivation a steady state was not achieved owing to a change in the composition of the bacterial population. NH₄ ⁺ was totally removed, but NO₂ ⁻ (up to 100 mM) was transiently released. NO₃ ⁻ was not detected. These effects might be explained by the presence of heterotrophic nitrifiers, which are able to oxidize NH₄ ⁺ to NO₂ ⁻ and to reduce NO₂ ⁻ to gaseous compounds. Received: 21 January 1999 / Received revision: 9 March 1999 / Accepted: 14 March 1999     

Impact of feeding and short-term temperature stress on the content and isotopic signature of fatty acids,sterols, and alcohols in the scleractinian coral <Emphasis Type="Italic">Turbinaria reniformis</Emphasis>

This study assesses the combined effect of feeding and short-term thermal stress on various physiological parameters and on the fatty acid, sterol, and alcohol composition of the scleractinian coral Turbinaria reniformis. The compound-specific carbon isotope composition of the lipids was also measured. Under control conditions (26°C), feeding with Artemia salina significantly increased the symbiont density and chlorophyll content and the growth rates of the corals. It also doubled the concentrations of almost all fatty acid (FA) compounds and increased the n-alcohol and sterol contents. δ¹³C results showed that the feeding enhancement of FA concentrations occurred either via a direct pathway, for one of the major polyunsaturated fatty acid (PUFA) compounds of the food (18:3n-3 FA), or via an enhancement of photosynthate transfer (indirect pathway), for the other coral FAs. Cholesterol (C₂₇Δ⁵) was also directly acquired from the food. Thermal stress (31°C) affected corals, but differently according to their feeding status. Chlorophyll, protein content, and maximal photosynthetic efficiency of photosystem II (PSII) decreased to a greater extent in starved corals. In such corals, FA concentrations were reduced by 33%, (especially C16, C18 FAs, and n-3 PUFA) and the sterol content by 27% (especially the C₂₈∆^5,22 and C₂₈∆⁵). The enrichment in the δ¹³C signature of the storage and structural FAs suggests that they were the main compounds respired during the stress to maintain the coral metabolism. Thermal stress had less effect on the lipid concentrations of fed corals, as only FA levels were reduced by 13%, with no major changes in their isotope carbon signatures. In conclusion, feeding plays an essential role in sustaining T. reniformis metabolism during the thermal stress.