Biological By-products Research Articles

Biogenic silver nanoparticle synthesis using orange peel extract and its multifaceted biomedical application.

The aim of this study was to employ an agro-industrial byproduct, specifically Citrus sinensis peels, as a reservoir of polyphenols. The natural chemicals present in C. sinensis peels serve as reducing agents in an environmentally benign method for synthesizing silver nanoparticles (AgNPs). This methodology not only provides a more environmentally friendly method for synthesizing nanoparticles but also enhances the value of agricultural waste, emphasizing the sustainable utilization of resources. In our study, AgNPs were successfully synthesized using peel aqueous exact of C. sinensis and then their various biological activity has been investigated. The synthesized AgNPs were characterized by UV-vis spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM) analysis. Furthermore, their effectiveness in inhibiting growth and biofilm formation of Escherichia coli, Staphylococcus aureus, and Candida albicans has been investigated. The minimum inhibitory concentrations (MIC) for E. coli and S. aureus were both 32μg/mL, and for C. albicans, it was 128µg/mL. At 250µg/mL of AgNPs, 94% and 92% biofilm inhibition were observed against E. coli and S. aureus, respectively. Furthermore, AgNPs demonstrated significant toxic effects against human prostate cancer cell line DU145 as investigated by anti-apoptotic, 4',6-diamidino-2-phenylindole (DAPI), reactive oxygen species (ROS), and acridine orange/ethidium bromide (AO/EtBr) assays. We also conducted uptake analysis on these pathogens and cancer cell lines to preliminarily investigate the mechanisms underlying their toxic effects. These findings confirm that AgNPs can serve as a cost-effective, non-toxic, and environmentally friendly resource for green synthesis of medicinal AgNPs. Moreover, this approach offers an alternative recycling strategy that contributes to the sustainable use of biological by-products.

Phytochemicals Modify the Action of Cancer Cells Mitochondrial Drug-Resistance Mechanism

The genesis and evolution of cancer are known to be significantly influenced by mitochondria, and recent studies have indicated that mitochondrial modifications may potentially contribute to the emergence of treatment resistance. Additionally, drug-resistant cancer cells may also display modifications in mitochondrial metabolism, such as changes in the generation of reactive oxygen species (ROS), which are biological byproducts of mitochondrial respiration. These changes can alter the cell's sensitivity to chemotherapy drugs and contribute to drug resistance. The expression of specific genes or proteins that are crucial in the control of cell growth and survival may be altered by mitochondrial mutations, which may also contribute to medication resistance. Phytochemicals are naturally occurring, biologically active substances found in plants that have been demonstrated to offer a variety of health advantages, including anti-cancer effects. It has been demonstrated that phytochemicals target these altered mitochondrial pathways in cancer cells, increasing the potency of chemotherapy medications and overcoming drug resistance. For instance, it has been demonstrated that some phytochemicals, including curcumin, resveratrol, and quercetin, can block the function of mitochondrial membrane proteins that lead to drug resistance in cancer cells. Other phytochemicals, including berberine and epigallocatechin gallate (EGCG), have been demonstrated to directly interfere with mitochondrial activity, inducing apoptosis (programmed cell death) in cancer cells. Overall, the capacity of phytochemicals to modify the functioning of cancer cell mitochondrial drug-resistance systems is a viable strategy for the creation of novel anti-cancer treatments.

Review Insights on Salivary Proteomics Biomarkers in Oral Cancer Detection and Diagnosis.

Early detection is crucial for the treatment and prognosis of oral cancer, a potentially lethal condition. Tumor markers are abnormal biological byproducts produced by malignant cells that may be found and analyzed in a variety of bodily fluids, including saliva. Early detection and appropriate treatment can increase cure rates to 80-90% and considerably improve quality of life by reducing the need for costly, incapacitating medicines. Salivary diagnostics has drawn the interest of many researchers and has been proven to be an effective tool for both medication monitoring and the diagnosis of several systemic diseases. Since researchers are now searching for biomarkers in saliva, an accessible bodily fluid, for noninvasive diagnosis of oral cancer, measuring tumor markers in saliva is an interesting alternative to blood testing for early identification, post-treatment monitoring, and monitoring high-risk lesions. New molecular markers for oral cancer detection, treatment, and prognosis have been found as a result of developments in the fields of molecular biology and salivary proteomics. The numerous salivary tumor biomarkers and how they relate to oral cancer and pre-cancer are covered in this article. We are optimistic that salivary protein biomarkers may one day be discovered for the clinical detection of oral cancer because of the rapid advancement of proteomic technology.

Insight into variations of DOM fractions in different latitudinal rural black-odor waterbodies of eastern China using fluorescence spectroscopy coupled with structure equation model

The structural compositions of dissolved organic matter (DOM) could profoundly affect formation and evolution of black-odor waterbodies (BOWs). In this study, 81 samples of BOWs were collected from three different latitudinal rural regions in eastern China, including low, middle and high latitude regions. Based on fluorescence index (FI) and biological index (BIX) deduced from excitation-emission matrices (EEMs) of rural BOWs, biological source of DOM was dominant in low latitude, while DOM derived from both biological and terrestrial in mid-latitude and high-latitude. Furthermore, humification degree of DOM in the former was lower than those in the latter based on humification index (HIX) deduced from EEMs. Seven fluorescence components of DOM were extracted by EEMs combined with parallel factor analysis: components 1 and 2 (C1 and C2) known as tryptophan-like substances, C3 and C4 associated with tyrosine-like, C5 related with biological byproducts, C6 relative to fulvic-like, and C7 referred as humic-like. The roughly decreasing order of percentages in DOM fractions from the rural BOWs was tyrosine-like > tryptophan-like > fulvic-like > microbial byproduct > humic-like in three regions. According to hierarchical cluster analysis and redundancy analysis, the autochthonous fresh DOM was dominant in low latitudinal rural BOWs, which was relative to actions of phytoplankton and microorganisms. However, humification degree of DOM increased with a rise in latitude, which could attribute to variations of climate and agriculture industrial structure. Based on structure equation model, the C5 and FI were the potential factors of the rural BOWs, which suggested that microbial activity and pollution sources should affect formation and evolution of rural BOWs. These findings are conductive to reveal composition and fluorescence properties of DOM and in recognizing the potential factors of forming mechanism in rural BOWs, which could provide basic theoretical support for policymakers to regulate and treat it.

Rice Bran Fermentation Using Lactiplantibacillus plantarum EM as a Starter and the Potential of the Fermented Rice Bran as a Functional Food.

Rice bran was fermented using a functional starter culture of Lactiplantibacillus plantarum EM, which exhibited high cholesterol removal and strong antimicrobial activity. Highest viable cell counts (9.78 log CFU/mL) and strong antimicrobial activity were obtained by fermenting 20% rice bran supplemented with 1% glucose and 3% corn steep liquor (pH 6.0) at 30 °C for 48 h. The fermented rice bran slurry was hot air-dried (55 °C, 16 h) and ground (HFRB). HFRB obtained showed effective cholesterol removal (45–68%) and antimicrobial activities (100–400 AU/mL) against foodborne pathogenic bacteria and food spoilage fungi. Phytate levels were significantly reduced during fermentation by 53% due to the phytase activity of L. plantarum EM, indicating HFRB does not present nutrient deficiency issues. In addition, fermentation significantly improved overall organoleptic quality. Our results indicate that HFRB is a promising functional food candidate. Furthermore, HFRB appears to satisfy consumer demands for a health-promoting food and environmental and legal requirements concerning the re-utilization of biological byproducts.

Development of Sustainable Masonry Bricks Using Biological By-Products and Wastes

AbstractMinimizing the use of nonreplaceable natural resources and relying on renewable materials that generate less waste is a key step in converting masonry manufacturing to a sustainable industr...

Percutaneous Anterior Cruciate Ligament Repair With Needle Arthroscopy and Biological Augmentation

Recent advancements in orthopaedic devices have instilled a renewed interest in repair of the anterior cruciate ligament. Biological augmentation of the repair has also recently been investigated with the hopes of improving repair outcomes and improving biological healing. The advent of needle arthroscopy allows for potentially decreased recovery times and potentially reduced complication rates compared with traditional arthroscopy. The purpose of this article is to present a percutaneous technique to repair the anterior cruciate ligament with suture tape augmentation while also augmenting with the biological byproducts from the native effusion using needle arthroscopy.

Determination of Antibiotic and Heavy Metal Resistance in Paenibacillus lautus 51ATA

Microbial and chemical contamination is one of the biggest environmental problems since exposure to pathogenic microorganisms, such as food poisoning bacteria and their biological by-products, are often associated with disease and allergic reactions. Paenibacillus lautus is an aerobic or facultative anaerobic opportunistic bacterial pathogen, which is found in a variety of sources. In this study, we isolated and characterized P. lautus from Niğde Province, which is a wastewater disposal area and therefore presents a great source of contamination. The bacterial isolate was grown, colony morphology and Gram-reactions were observed. Bacteria were identified by 16S rDNA sequencing analysis, which was performed using DNA samples isolated from pure cultures and amplified by polymerase chain reaction (PCR). Sequencing results were compared against known bacterial strains using BLAST (Basic Local Alignment Search Tool) across databases. Antibiotic resistance against 20 different antibiotics and heavy metal resistance against different concentrations of zinc, copper, iron, cobalt, chromium and silver containing compounds were tested via disk diffusion method. Inhibition zones were examined and minimum inhibitory concentrations were recorded. Our results indicated that P. lautus was resistant to a certain set of antibiotics, while it was sensitive against others. Similarly, the bacteria were resistant against high concentrations of most metals tested. In summary, this study provided the first data regarding the isolation and characterization of Paenibacillus lautus strain from a local source in Turkey, which will account as preliminary data and guide our future efforts to fight against microbial contaminations.

In vitro toxicological evaluation of surgical smoke from human tissue

BackgroundOperating room personnel have the potential to be exposed to surgical smoke, the by-product of using electrocautery or laser surgical device, on a daily basis. Surgical smoke is made up of both biological by-products and chemical pollutants that have been shown to cause eye, skin and pulmonary irritation.MethodsIn this study, surgical smoke was collected in real time in cell culture media by using an electrocautery surgical device to cut and coagulate human breast tissues. Airborne particle number concentration and particle distribution were determined by direct reading instruments. Airborne concentration of selected volatile organic compounds (VOCs) were determined by evacuated canisters. Head space analysis was conducted to quantify dissolved VOCs in cell culture medium. Human small airway epithelial cells (SAEC) and RAW 264.7 mouse macrophages (RAW) were exposed to surgical smoke in culture media for 24 h and then assayed for cell viability, lactate dehydrogenase (LDH) and superoxide production.ResultsOur results demonstrated that surgical smoke-generated from human breast tissues induced cytotoxicity and LDH increases in both the SAEC and RAW. However, surgical smoke did not induce superoxide production in the SAEC or RAW.Conclusion These data suggest that the surgical smoke is cytotoxic in vitro and support the previously published data that the surgical smoke may be an occupational hazard to healthcare workers.

Adventurous Upcrafting Ventures

Since 2015, the Research Institute of Organic Treasures (R.I.O.T.) has combined fermentation practices and social experimentation in Hong Kong to give biological byproducts from human and urban metabolisms a regenerative purpose. Here putrescible wastes emitted from our kitchens, toilets, and bodies are considered our most foundational design material that contributes to a “world of eaters” (DuPuis 2015). In this applied design work, the concept of upcycling is socio-materially extended into shared forms of upskilling, and therefore referred to as upcrafting. In an effort to combine practical outcomes with long-term welfare creation, R.I.O.T. brings together laypersons, natural scientists, and artists, into open-ended explorations of alternative knowledge and change making, or what Melanie DuPuis calls “extended peer communities” (ibid. 155).

The Potential Incorporation of Biochar into a Char-Water Fuel — Study of Chemical and Physical Properties

Biochar has the potential to be used for a wide range of applications. One of these includes utilisation as a char-water fuel, with the aim of substituting less sustainable fuels in the future. This paper reports the chemical and physical properties of biochar produced from sugarcane bagasse for use as a char-water fuel. Sugarcane bagasse was pre-treated with diammonium phosphate (DAP) and pyrolysed to increase the yield of biochar. An untreated sample of bagasse was also converted to biochar for comparison. The treated samples were formulated into char-water fuel and analysed for rheological behaviour. Viscosities were comparable to that reported for coal-water slurry fuels and, in some cases, other biological by-products (i.e. biooils), but were higher than diesel or gasoline. Thermal gravimetric analysis (TGA) and particle size distribution were conducted on the char samples and the energy content was measured using bomb calorimetry. The energy content of the char-water fuel would be similar to that of coal-water fuels if beneficiation of the biochar to remove ash components can be performed.

The shadow of dichloroacetonitrile (DCAN), a typical nitrogenous disinfection by-product (N-DBP), in the waterworks and its backwash water reuse

Dichloroacetonitrile (DCAN) is one of nitrogenous disinfection by-products (N-DBPs) with strong cytotoxicity and genotoxicity. In this study, the formation potential (FP) of DCAN was investigated in the samples of six important water sources located in the Yangtze River Delta. The highest formation concentration of DCAN was 9.05 μg/L in the water sample taken from Taihu Lake with the lowest SUVA value. After the NOM fractionation, the conversion rate of hydrophilic fraction to DCAN was found the highest. Subsequently, a waterworks using Taihu Lake as water source was chosen to research the FP variations of DCAN in the treatment process and backwash water. The results showed that, compared to the conventional treatment process, O/biological activated carbon (BAC) process increased the removal efficiency of DCAN from 21.89% to 50.58% by removing aromatic protein and soluble biological by-products as main precursors of DCAN. The DCAN FP in the effluent of BAC filters using old granular activated carbon was higher than that in the influent and the DCAN FP of its backwash water was lower than that in raw water. In the backwash water of sand filters, the DCAN FP higher than raw water required the recycle ratio less than 5% to avoid the accumulation of DCAN.

Comparative Evaluation of Pre-treatment Methods to Enhance Phosphorus Release from Digestate

This paper aims to evaluate various pre-treatment methods to improve the release of phosphorus (P) in the liquid fraction after solid–liquid separation of digestate (input: (dairy) manure and organic biological by-products provided by the food industry). As such, the P recovery potential from the liquid fraction as concentrated fertilizer product can be increased, whereas soil organic carbon can be maintained through local recycling of the resulting thickened fraction. Four different mechanical pre-treatments (microwave heating, conventional heating, ultrasonic treatment, and orbital shaking) were tested in combination with the chemical dosing of three different acids (citric acid, formic acid, and HCl) down to pH 4, 5, and 6. The pre-treatments released 13–28 % soluble ortho-P relative to total P. When balancing the recovery efficiency with the acid costs, the addition of HCl down to pH 4 under microwave heating was most feasible. Nevertheless, if no pasteurization is required for fertilizer marketing, then orbital shaking (mixing in practice) with HCl addition may be more attractive.

Fate of Environmental Pollutants.

This annual review covers the literature published in 2014 on topics related to the occurrence and fate of emerging environmental pollutants in wastewater. Due to the vast amount of literature published on this topic, I have discussed only a fraction of the quality research publications, up to maximum 15 relevant articles per section, due to limitation of space. The abstract search was carried out using Web of Science, and the abstracts were selected based on their relevance. In few cases, full-text articles were referred to better understand new findings. This review is divided into the following sections: biological agents, disinfection by-products (DBPs), halogenated compounds, pharmaceuticals and personal care products (PPCPs), and other emerging contaminants.

Modeling and simulation of an aquatic habitat for bioregenerative life support research

Long duration human spaceflight poses challenges for spacecraft autonomy and the regeneration of life support consumables, such as oxygen and water. Bioregenerative life support systems (BLSS), which make use of biological processes to transform biological byproducts back into consumables, have the ability to recycle organic byproducts and are the preferred option for food production. A limitation in BLSS research is in the non-availability of small-scale experimental capacities that may help to better understand the challenges in system closure, integration, and control. Ground-based aquatic habitats are an option for small-scale research relevant to bioregenerative life support systems (BLSS), given that they can operate as self-contained systems enclosing a habitat composed of various species in a single volume of water. The purpose of this paper is to present the modeling and simulation of a reconfigurable aquatic habitat for experiments in regenerative life support automation; it supports the use of aquatic habitats as a small-scale approach to experiments relevant to larger-scale regenerative life support systems. It presents ground-based aquatic habitats as an option for small-scale BLSS research focusing on the process of respiration, and elaborates on the description of biological processes by introducing models of ecophysiological phenomena for consumers and producers: higher plants of the species Bacopa monnieri produce O2 for snails of the genus Pomacea; the snails consume O2 and generate CO2, which is used by the plants in combination with radiant energy to generate O2 through the process of photosynthesis. Feedback controllers are designed to regulate the concentration of dissolved oxygen in the water. This paper expands the description of biological processes by introducing models of ecophysiological phenomena of the organisms involved. The model of the plants includes a description of the rate of CO2 assimilation as a function of irradiance. Simulations and validation runs with hardware show how these phenomena may act as disturbances to the control mechanisms that maintain safe concentration levels of dissolved oxygen in the habitat.

How Cardiomyocytes Make the Heart Old

Naturally occurring decline in cardiovascular reserve with age associates with a combination of the reduction in cardiomyocyte number and altered cardiomyocyte function. Recent investigations suggested that about half of the cardiomyocytes is the same as at birth, while the other half of the cardiomyocytes is the result of cardiomyocyte renewal in the senescent heart. In addition, the total number of cardiomyocytes is estimated to be less by one third in the old heart than the number of cardiomyocytes at birth. Thus, the reduction in cardiomyocyte number of the aging heart cannot be fully compensated by cardiomyocyte renewal. Aging of long-lived differentiated myocardial cells, as well as of cardiac progenitor stem cells may contribute to an increased rate of apoptosis, and decreased capacity of cell duplication and/or differentiation. In addition, differentiated cardiomyocytes are prone for accumulating biological by-products of cellular metabolism and of incompletely processed oxidative insults. In this context, interactions between lysosomes and mitochondria may provide a mechanistic background for the age-dependent alterations in cardiac macromolecules. This reasoning postulates a direct relationship between the number of pro-oxidative, ill-functioning mitochondria and the amount of ballast- overloaded lysosomes in long-lived cardiomyocytes. Accumulation of biological garbage and telomere shortening might be considered as hallmarks of cardiomyocyte aging with implications for depressed cardiac function and cardiomyocyte renewal. Changes in protein expression together with posttranslational modifications of myocardial proteins affect excitation-contraction coupling and explain the declining mechanical function of the cardiomyocytes. Altogether, these changes represent a significant part of the reduced cardiovascular reserve in aged individuals. Keywords: Aging, cardiomyocyte cell death, cardiomyocyte renewal, telomere

How Cardiomyocytes Make the Heart Old

Naturally occurring decline in cardiovascular reserve with age associates with a combination of the reduction in cardiomyocyte number and altered cardiomyocyte function. Recent investigations suggested that about half of the cardiomyocytes is the same as at birth, while the other half of the cardiomyocytes is the result of cardiomyocyte renewal in the senescent heart. In addition, the total number of cardiomyocytes is estimated to be less by one third in the old heart than the number of cardiomyocytes at birth. Thus, the reduction in cardiomyocyte number of the aging heart cannot be fully compensated by cardiomyocyte renewal. Aging of long-lived differentiated myocardial cells, as well as of cardiac progenitor stem cells may contribute to an increased rate of apoptosis, and decreased capacity of cell duplication and/or differentiation. In addition, differentiated cardiomyocytes are prone for accumulating biological by-products of cellular metabolism and of incompletely processed oxidative insults. In this context, interactions between lysosomes and mitochondria may provide a mechanistic background for the age-dependent alterations in cardiac macromolecules. This reasoning postulates a direct relationship between the number of pro-oxidative, ill-functioning mitochondria and the amount of ballast- overloaded lysosomes in long-lived cardiomyocytes. Accumulation of biological garbage and telomere shortening might be considered as hallmarks of cardiomyocyte aging with implications for depressed cardiac function and cardiomyocyte renewal. Changes in protein expression together with posttranslational modifications of myocardial proteins affect excitation-contraction coupling and explain the declining mechanical function of the cardiomyocytes. Altogether, these changes represent a significant part of the reduced cardiovascular reserve in aged individuals.

Revisiting the agronomic benefits of manure: a correct assessment and exploitation of its fertilizer value spares the environment

The ongoing disintegration of agriculture into specialized farms, specialized regions and even specialized countries, has disrupted local nutrient cycles. This process is promoted and sustained by the use of mineral fertilizers. Ample availability of mineral fertilizers has changed farmers' perception and appreciation of manure. By now, manure is looked upon as `waste' in some regions. It is a contradiction in terms, however, to regard biological by-products as `waste'. Apart from this cultural aspect, economical and environmental considerations per se, justify a rehabilitation of manure. First of all a correct assessment of the fertilizer value is required. The present paper explaines how to determine the nitrogen fertilizer value (NFV) of manures in a unbiassed manner. Subsequently, recommendations are made on how to exploit the potential NFV as good as possible. Undeniably, it is easier to manage mineral fertilizers than manure. However, when proper attention is given to the composition of manure and decisions on rates, timing and placement are made correspondingly, the NFV can be enhanced. This should lead to a drastic reduction of mineral fertilizer use, nutrient surpluses and environmental pollution. Under such conditions, `manure', `precision farming' and `environment' can become reconciled again.

ENHANCING ENVIRONMENTAL QUALITY IN AGRICULTURAL SYSTEMS

Greenhouses have been extremely successful in providing abundant, cheap and high-quality produce, by using resources (water, minerals, pesticides) with a very high economic efficiency. Marginal agricultural land is being rapidly converted into protected cultivation in many (semi-arid) regions of the world, hoping to pros-per both from primary and secondary activities. Water use efficiency of greenhouse production is about five times as high as field production of vegetables. However, in spite of using resources more efficiently, greenhouse areas have an enormous visual and environmental impact: diversion of limited good water resources; contamina-tion due to pollutants released with over-abundant irrigation; production of plastic and mineral waste and biological by-products; contamination due to plant protec-tion chemicals and emission of ?greenhouse? gases (CO2) by heating with fossil fuels in Northern countries. In addition, greenhouse production has an ?image? problem: there is a general perception among European consumers that such an ?industrial? production of food is non-natural and unhealthy, although in the Americas, for instance, the ?cleanliness? of the production process is considered an advantage. Since, the ?polluter pays? very seldom, environment-friendly production is more expensive. Therefore a large market in ?eco-labels? has developed in response to consumers? misgivings and in the hope of recovering (part of) the costs through higher prices. However, there is little clarity about agricultural practices associated to each label and there are doubts about enforcement. This paper analyses advan-tages and draw-backs of greenhouse production, and attempts to review the items where improvement is necessary in order to ensure that greenhouse production is sustainable, yet profitable also in the future.

The Gaia Hypothesis: Conjectures and Refutations

The uncertainties surrounding global climate change provide ample evidence, if any were necessary, of the need for a whole-system view of the Earth. Arguably the most visible - and controversial - attempt to understand Earth as a system has been Lovelock's Gaia theory. Gaia has been a fruitful hypothesis generator, and has prompted many intriguing conjectures about how biological processes might contribute to planetary-scale regulation of atmospheric chemistry and climate. In many important cases, however, these conjectures are refuted by the available data. For example, Gaia theory predicts that the composition of the atmosphere should be tightly regulated by biological processes, but rates of carbon uptake into the biosphere have accelerated by only about 2% in response to the 35% rise in atmospheric CO2 since pre-industrial times. Gaia theory would predict that atmospheric CO2 should be more sensitively regulated by terrestrial ecosystem uptake (which is biologically mediated) than by ocean uptake (which is primarily abiotic), but both processes are about equally insensitive to atmospheric CO2 levels. Gaia theory predicts that biological feedbacks should make the Earth system less sensitive to perturbation, but the best available data suggest that the net effect of biologically mediated feedbacks will be to amplify, not reduce, the Earth system's sensitivity to anthropogenic climate change. Gaia theory predicts that biological by-products in the atmosphere should act as planetary climate regulators, but the Vostok ice core indicates that CO2, CH4, and dimethyl sulfide - all biological by-products - function to make the Earth warmer when it is warm, and colder when it is cold. Gaia theory predicts that biological feedbacks should regulate Earth's climate over the long term, but peaks in paleotemperature correspond to peaks in paleo-CO2 in records stretching back to the Permian; thus if CO2 is biologically regulated as part of a global thermostat, that thermostat has been hooked up backwards for at least the past 300 million years. Gaia theory predicts that organisms alter their environment to their own benefit, but throughout most of the surface ocean (comprising more than half of the globe), nutrient depletion by plankton has almost created a biological desert, and is kept in check only by the nutrient starvation of the plankton themselves. Lastly, where organisms enhance their environment for themselves, they create positive feedback; thus Gaia theory's two central principles - first, that organisms stabilize their environment, and second, that organisms alter their environment in ways that benefit them - are mutually incon- sistent with one another. These examples suggest that the further development of Gaia theory will require more deliberate comparison of theory and data.