Carbon Storage Material Research Articles

A Review of Algae-Based Carbon Capture, Utilization, and Storage (Algae-Based CCUS)

Excessive emissions of greenhouse gases, primarily carbon dioxide (CO2), have garnered worldwide attention due to their significant environmental impacts. Carbon capture, utilization, and storage (CCUS) techniques have emerged as effective solutions to address CO2 emissions. Recently, direct air capture (DAC) and bioenergy with carbon capture and storage (BECCS) have been advanced within the CCUS framework as negative emission technologies. BECCS, which involves cultivating biomass for energy production, then capturing and storing the resultant CO2 emissions, offers cost advantages over DAC. Algae-based CCUS is integral to the BECCS framework, leveraging algae’s biological processes to capture and sequester CO2 while simultaneously contributing to energy production and potentially achieving net negative carbon emissions. Algae’s high photosynthetic efficiency, rapid growth rates, and ability to grow in non-arable environments provide significant advantages over other BECCS methods. This comprehensive review explores recent innovations in algae-based CCUS technologies, focusing on the mechanisms of carbon capture, utilization, and storage through algae. It highlights advancements in algae cultivation for efficient carbon capture, algae-based biofuel production, and algae-based dual carbon storage materials, as well as key challenges that need to be addressed for further optimization. This review provides valuable insights into the potential of algae-based CCUS as a key component of global carbon reduction strategies.

The fundamental role of pH in CH4 bioconversion into polyhydroxybutyrate in mixed methanotrophic cultures

Climate change and plastic pollution are likely the most relevant challenges for the environment in the 21st century. Developing cost-effective technologies for the bioconversion of methane (CH4) into polyhydroxyalkanoates (PHAs) could simultaneously mitigate CH4 emissions and boost the commercialization of biodegradable polymers. Despite the fact that the role of temperature, nitrogen deprivation, CH4:O2 ratio or micronutrients availability on the PHA accumulation capacity of methanotrophs has been carefully explored, there is still a need for optimization of the CH4-to-PHA bioconversion process prior to becoming a feasible platform in future biorefineries. In this study, the influence of different cultivation broth pH values (5.5, 7, 8.5 and 10) on bacterial biomass growth, CH4 bioconversion rate, PHA accumulation capacity and bacterial community structure was investigated in a stirred tank bioreactor under nitrogen deprivation conditions. Higher CH4 elimination rates were obtained at increasing pH, with a maximum value of 50.4 ± 2.7 g CH4·m−3·h−1 observed at pH 8.5. This was likely mediated by an increased ionic strength in the mineral medium, which enhanced the gas-liquid mass transfer. Interestingly, higher PHB accumulations were observed at decreasing pH, with the highest PHB contents recorded at a pH 5.5 (43.7 ± 3.4 %w·w−1). The strong selective pressure of low pH towards the growth of Type II methanotrophic bacteria could explain this finding. The genus Methylocystis increased its abundance from 34 % up to 85 and 90 % at pH 5.5 and 7, respectively. On the contrary, Methylocystis was less abundant in the community enriched at pH 8.5 (14 %). The accumulation of intracellular PHB as energy and carbon storage material allowed the maintenance of high CH4 biodegradation rates during 48 h after complete nitrogen deprivation. The results here obtained demonstrated for the first time a crucial and multifactorial role of pH on the bioconversion performance of CH4 into PHA.

Methodology for Evaluating the CO2 Sequestration Capacity of Waste Ashes.

The concentration of CO2 in the atmosphere is constantly increasing, leading to an increase in the average global temperature and, thus, affecting climate change. Hence, various initiatives have been proposed to mitigate this process, among which CO2 sequestration is a technically simple and efficient approach. The spontaneous carbonation of ashes with atmospheric CO2 is very slow, and this is why accelerated carbonation is encouraged. However, not all ashes are equally suitable for this process, so a methodology to evaluate their potential should be developed. Such a methodology involves a combination of techniques, from theoretical calculations to XRF, XRD, DTA-TG, and the calcimetric determination of the CaCO3 content. The present study followed the approach of exposing ashes to accelerated carbonation conditions (4% v/v CO2, 50-55% and 80-85% RH, 20 °C) in a closed carbonation chamber for different periods of time until the maximum CO2 uptake is reached. The amount of sequestered CO2 was quantified by thermogravimetry. The results show that the highest CO2 sequestration capacity (33.8%) and carbonation efficiency (67.9%) were obtained for wood biomass bottom ash. This method was applied to eight combustion ashes and could serve to evaluate other ashes or comparable carbon storage materials.

Semi-continuous production of polyhydroxybutyrate (PHB) in the Chlorophyta Desmodesmus communis

Polyhydroxyalkanoates (PHAs) are promising alternatives that accumulate as energy and carbon storage material in various microorganisms, including bacteria and microalgae, being biodegradable and suitable for a wide variety of applications. Among these compounds, the most prevalent and well-characterized biopolymer is polyhydroxybutyrate (PHB), which belongs to the short-chain PHAs.The present study was designed to evaluate algae-based PHB production in two Chlorophyta (Desmodesmus communis and Chlorella vulgaris) under a two-phase nutritional mode of cultivation, namely a phototrophic growth phase (PGP) and a mixotrophic stress phase (MSP) with N,P-depleted media and organic carbon supply (i.e., glucose or sodium acetate, NaOAc). The highest PHB productivity (0.11 g PHB/g biomass/d; 0.015 g PHB/L/d), corresponding to 32.1 % w/w of intracellular PHB, was observed for D. communis after 3 days of cultivation under mixotrophic conditions in batch cultures (e.g., low light, phosphorus-free medium, 1 g/L of NaOAc). A scaled-up cultivation (10 L) was set up to evaluate for the first time PHB yields and biomass composition in a semi-continuous system. A PHB content of 34 % w/w was achieved on day 8, corresponding to a maximum PHB productivity of 0.10 g PHB/g biomass/d (or 0.011 g PHB/L/d), which increased up to 54 % w/w on day 15. The biomass was composed of about 30 % w/w proteins, 6 % w/w polysaccharides, and 11 % w/w lipids, which can be valorised from a biorefinery perspective. The scaled-up D. communis cultivation in 10 L PBRs confirmed the potential utilization of this algal species for PHB production with productivity up to 2-times higher than those reported for several cyanobacterial species and similar to the maximum value obtained with batch cultures in previous works performed with Scenedesmaceae.

Emerging Engineered Wood for Building Applications.

The building sector, including building operations and materials, was responsible for the emission of ∼11.9 gigatons of global energy-related CO2 in 2020, accounting for 37% of the total CO2 emissions, the largest share among different sectors. Lowering the carbon footprint of buildings requires the development of carbon-storage materials as well as novel designs that could enable multifunctional components to achieve widespread applications. Wood is one of the most abundant biomaterials on Earth and has been used for construction historically. Recent research breakthroughs on advanced engineered wood products epitomize this material's tremendous yet largely untapped potential for addressing global sustainability challenges. In this review, we explore recent developments in chemically modified wood that will produce a new generation of engineered wood products for building applications. Traditionally, engineered wood products have primarily had a structural purpose, but this review broadens the classification to encompass more aspects of building performance. We begin by providing multiscale design principles of wood products from a computational point of view, followed by discussion of the chemical modifications and structural engineering methods used to modify wood in terms of its mechanical, thermal, optical, and energy-related performance. Additionally, we explore life cycle assessment and techno-economic analysis tools for guiding future research toward environmentally friendly and economically feasible directions for engineered wood products. Finally, this review highlights the current challenges and perspectives on future directions in this research field. By leveraging these new wood-based technologies and analysis tools for the fabrication of carbon-storage materials, it is possible to design sustainable and carbon-negative buildings, which could have a significant impact on mitigating climate change.

From Organic Wastes and Hydrocarbons Pollutants to Polyhydroxyalkanoates: Bioconversion by Terrestrial and Marine Bacteria

The use of fossil-based plastics has become unsustainable because of the polluting production processes, difficulties for waste management sectors, and high environmental impact. Polyhydroxyalkanoates (PHA) are bio-based biodegradable polymers derived from renewable resources and synthesized by bacteria as intracellular energy and carbon storage materials under nutrients or oxygen limitation and through the optimization of cultivation conditions with both pure and mixed culture systems. The PHA properties are affected by the same principles of oil-derived polyolefins, with a broad range of compositions, due to the incorporation of different monomers into the polymer matrix. As a consequence, the properties of such materials are represented by a broad range depending on tunable PHA composition. Producing waste-derived PHA is technically feasible with mixed microbial cultures (MMC), since no sterilization is required; this technology may represent a solution for waste treatment and valorization, and it has recently been developed at the pilot scale level with different process configurations where aerobic microorganisms are usually subjected to a dynamic feeding regime for their selection and to a high organic load for the intracellular accumulation of PHA. In this review, we report on studies on terrestrial and marine bacteria PHA-producers. The available knowledge on PHA production from the use of different kinds of organic wastes, and otherwise, petroleum-polluted natural matrices coupling bioremediation treatment has been explored. The advancements in these areas have been significant; they generally concern the terrestrial environment, where pilot and industrial processes are already established. Recently, marine bacteria have also offered interesting perspectives due to their advantageous effects on production practices, which they can relieve several constraints. Studies on the use of hydrocarbons as carbon sources offer evidence for the feasibility of the bioconversion of fossil-derived plastics into bioplastics.

Toward Carbon-Neutral Concrete through Biochar–Cement–Calcium Carbonate Composites: A Critical Review

High-density, high-permanence forms of carbon storage are in demand to save storage space on land or at sea while allowing the world to reach its climate targets. Biochar and calcium carbonate are two such forms that have been considered largely separately in the literature for carbon storage. In this paper, we consider how biochar and calcium carbonate might interact when they are used together with cement as part of a carbon storage system, ideally to form a carbon-neutral concrete. The carbon storage system stores atmospherically absorbed CO2 within concrete, thereby reducing carbon in the atmosphere. In addition, such a system will help in reducing cement usage, thus reducing the need for clinker in cement manufacturing and directly reducing CO2 emissions that result from limestone calcination during clinker manufacturing. Another benefit of such a composite storage system is its use in building structures, a use that has positive environmental and social impact. Thus, further research on the properties of this composite material is warranted. This paper explores the literature on the use of biochar combined with calcium carbonate and cement as carbon storage material. The use of recycled carbon aggregates (RCAs) and LC3 concrete as part of this approach is reviewed. The paper also addresses the possible compressive strength range of the biochar–cement–calcium carbonate composite material, along with other performance expectations. Obstacles to scaling the use of carbon-neutral concrete are identified and an array of research directions are presented, with the goal of improving carbon-neutral concrete and its use.

Accumulation of PHA in the Microalgae Scenedesmus sp. under Nutrient-Deficient Conditions.

Traditional plastics have undoubted utility and convenience for everyday life; but when they are derived from petroleum and are non-biodegradable, they contribute to two major crises today’s world is facing: fossil resources depletion and environmental degradation. Polyhydroxyalkanoates are a promising alternative to replace them, being biodegradable and suitable for a wide variety of applications. This biopolymer accumulates as energy and carbon storage material in various microorganisms, including microalgae. This study investigated the influence of glucose, N, P, Fe, and salinity over the production of polyhydroxyalkanoate (PHA) by Scenedesmus sp., a freshwater microalga strain not previously explored for this purpose. To assess the effect of the variables, a fractional Taguchi experimental design involving 16 experimental runs was planned and executed. Biopolymer was obtained in all the experiments in a wide range of concentrations (0.83–29.92%, w/w DW), and identified as polyhydroxybutyrate (PHB) by FTIR analysis. The statistical analysis of the response was carried out using Minitab 16, where phosphorus, glucose, and iron were identified as significant factors, together with the P-Fe and glucose-N interactions. The presence of other relevant macromolecules was also quantified. Doing this, this work contributes to the understanding of the critical factors that control PHA production and present Scenedesmus sp. as a promising species to produce bio-resources in commercial systems.

Molecular Profiling and Optimization Studies for Growth and PHB Production Conditions in Rhodobacter sphaeroides

In the recent climate change regime, industrial demand for renewable materials to replace petroleum-derived polymers continues to rise. Of particular interest is polyhydroxybutyrate (PHB) as a substitute for polypropylene. Accumulating evidence indicates that PHB is highly produced as a carbon storage material in various microorganisms. The effects of growth conditions on PHB production have been widely studied in chemolithotrophs, particularly in Rhodobacter. However, the results on PHB production in Rhodobacter have been somewhat inconsistent due to different strains and experimental conditions, and it is currently unclear how diverse environmental factors are linked with PHB production. Here, we report optimized growth conditions for PHB production and show that the growth conditions are closely related to reactive oxygen species (ROS) regulation. PHB accumulates in cells up to approximately 50% at the highest level under dark-aerobic conditions as opposed to light aerobic/anaerobic conditions. According to the time-course, PHB contents increased at 48 h and then gradually decreased. When observing the effect of temperature and medium composition on PHB production, 30 °C and a carbon/nitrogen ratio of 9:1 or more were found to be most effective. Among PHB biosynthetic genes, PhaA and PhaB are highly correlated with PHB production, whereas PhaC and PhaZ showed little change in overall expression levels. We found that, while the amount of hydrogen peroxide in cells under dark conditions was relatively low compared to the light conditions, peroxidase activities and expression levels of antioxidant-related genes were high. These observations suggest optimal culture conditions for growth and PHB production and the importance of ROS-scavenging signaling with regard to PHB production.

Pyrolysis performance of peat moss: A simultaneous in-situ thermal analysis and bench-scale experimental study

Peat moss in drained peatlands has become a non-negligible source of greenhouse gases (GHG) emission. Pyrolysis is a potential technique to convert carbon-emitting peat moss to carbon-storage materials. This work investigates the behavior of peat moss pyrolysis by a combined in-situ thermal analysis and bench-scale pyrolysis experiment methodology. The simultaneous thermal analyzer, which provides the simultaneous TG/DTA analysis, was employed to reveal the thermal decomposition behavior of peat moss. The samples were heated up to 900 °C with different heating rates of 10, 15, and 20 °C/min. Thereafter, pyrolysis experiments with peak temperatures of 450, 500, 550 and 600 °C were performed in a bench-scale pyrolyzer. It was found that there are four main stages and two micro stages of mass loss during peat moss pyrolysis from room temperature to 900 °C. Also, kinetic parameters were calculated based on the results of TG and DTG by the Kissinger-Akahira-Sunose (KAS) method and the Coats-Redfern (CR) method. In the bench-scale pyrolysis experiments, four phases, i.e., char, tar, aqueous phase, and gas, were obtained and characterized. The carbon distribution and the GHG emission from peat moss pyrolysis were determined.

In silico analysis of phag-like protein in Ralstonia Euthropa H16, potentially involved in polyhydroxyalkanoates synthesis

Polyhydroxyalkanoates (PHA) are synthesised by bacteria as carbon storage material. The protein PhaG directs carbon from non-related carbon sources such as glycerol, metabolised through fatty acid de novo synthesis (FAS) pathway, with PHA synthesis. The gene that codifies for this protein has not yet been found in the genome of Ralstonia eutropha H16, a model organism. By bioinformatic comparison to already known PhaG proteins, a PhaG-like protein was found codified by gene H16_A0147 and presence of the gene was preliminary confirmed by PCR. This is the first study that shows the presence and characteristics of a PhaG-like protein in R. eutropha H16 and represents the first step for the identification of a connection between FAS and PHA pathways in this model bacterium. Further gene deletion and enzymatic activity studies are necessary to confirm this potential relationship, which could improve industrial PHA production and utilisation of agro-industrial residues such as glycerol.

Mechanisms of biochar assisted immobilization of Pb2+ by bioapatite in aqueous solution

Bioapatite (BAp) is regarded as an effective material to immobilize lead (Pb2+) via the formation of stable pyromorphite. However, when applied in contaminated soil, due to its low surface area and low adsorption capacity, BAp might not sufficiently contact and react with Pb2+. Biochar, a carbon storage material, typically has high surface area and high adsorption capacity. This study investigated the feasibility of using biochar as a reaction platform to enhance BAp immobilization of Pb2+. An alkaline biochar produced from wheat straw pellets (WSP) and a slightly acidic biochar produced from hardwood (SB) were selected. The results of aqueous adsorption showed the combination of biochar (WSP or SB) and BAp effectively removed Pb2+ from the aqueous solution containing 1000 ppm Pb2+. XRD, ATR-IR, and SEM/EDX results revealed the formation of hydroxypyromorphite on both biochars’ surfaces. This study demonstrates that biochars could act as an efficient reaction platform for BAp and Pb2+ in aqueous solution due to their high surface area, porous structure, and high adsorption capacity. Therefore, it is mechanistically feasible to apply biochar to enhance BAp immobilization of Pb2+ in contaminated soil.

Unveiling the 30-year mystery of polyhydroxyalkanoate (PHA) synthase.

See accompanying articles by Jieun Kim et al. DOI 10.1002/biot.201600648 & Yeo-Jin Kim et al. DOI 10.1002/biot.201600649 It has been my great pleasure to read the two papers entitled ”Crystal structure of Ralstonia eutropha polyhydroxyalkanoate synthase C-terminal domain and reaction mechanisms“ by Kim et al. 1, and ”Structure and function of the N-terminal domain of Ralstonia eutropha polyhydroxyalkanoate synthase, and the proposed structure and mechanisms of the whole enzyme“ by Kim et al. 2. Polyhydroxyalkanoates (PHAs) are diverse biopolyesters accumulated by many bacteria as energy and carbon storage materials. PHAs have been exploited as biodegradable and biocompatible thermal plastics (also called Bioplastics). PHA synthase plays important roles in determining the general characteristics of PHAs produced, including molecular weight, polydispersity, monomer composition, and productivity. Global efforts have been made to understand PHA synthase via revealing its crystal structure (short as PhaC) without success over the last 30 years; however, Prof. Sang Yup Lee and his colleagues unveil the mystery in these two studies. Kim et al. 1 firstly demonstrate the crystal structure of PHA synthase from Ralstonia eutropha, the best studied bacterium for PHA production, and report the structural basis for the detailed molecular mechanisms of PHA biosynthesis. Kim et al. 2 then for the first time report the 3D reconstructed model of full length PHA synthase from R. eutropha, and performed several biochemical studies. These two studies provide feasibility for rational engineering of PHA synthase toward more efficient production of bioplastics, more broad PHA structure diversity and possibly controllable PHA molecular weights. If the mechanism is better understood, we may even be able to develop artificial synthases for synthesis of other non-PHA polyesters. With the PHA synthase structure revealed now, we are moving more close to tailor-made PHA to meet various needs. The author declares no financial or commercial conflict of interest.

Application of polyhydroxyalkanoate (PHA) synthesis regulatory protein PhaR as a bio-surfactant and bactericidal agent

Polyhydroxyalkanoates (PHA), a family of diverse bio-polyesters, are produced by many bacteria as an energy and carbon storage material. PHA synthesis regulatory protein PhaR was reported to attach on the surface of intracellular PHA granules for convenience of synthesis regulation. PhaR was found to have an amphiphilic property. However, no study was conducted to exploit this property for applications as bio-surfactant and bactericide agent. Purified PhaR showed a higher emulsification ability than that of the widely used chemical surfactants including SDS, Tween 20, sodium oleate, and liquefied detergent (LD). PhaR also showed a higher emulsification ability than bio-surfactants rhamnose and PHA granules associated protein termed phasin or PhaP. Non-purified PhaR, namely, the native inclusion bodies and cell lysates, also demonstrated to be an excellent surfactant. PhaR was found highly stable even at 95°C. In addition, PhaR was revealed to be a promising bactericidal agent against Gram positive and negative bacteria. PhaR can be conveniently produced by recombinant Escherichia coli. It has shown to be a bio-surfactant with excellent emulsification ability and strong bactericidal capacity at elevated temperature as high as 95°C. Therefore, PhaR could be used in areas including food, beverage, pharmaceutical and cosmetics industries.

Studies on the production of branched-chain alcohols in engineered Ralstonia eutropha

Wild-type Ralstonia eutropha H16 produces polyhydroxybutyrate (PHB) as an intracellular carbon storage material during nutrient stress in the presence of excess carbon. In this study, the excess carbon was redirected in engineered strains from PHB storage to the production of isobutanol and 3-methyl-1-butanol (branched-chain higher alcohols). These branched-chain higher alcohols can directly substitute for fossil-based fuels and be employed within the current infrastructure. Various mutant strains of R. eutropha with isobutyraldehyde dehydrogenase activity, in combination with the overexpression of plasmid-borne, native branched-chain amino acid biosynthesis pathway genes and the overexpression of heterologous ketoisovalerate decarboxylase gene, were employed for the biosynthesis of isobutanol and 3-methyl-1-butanol. Production of these branched-chain alcohols was initiated during nitrogen or phosphorus limitation in the engineered R. eutropha. One mutant strain not only produced over 180 mg/L branched-chain alcohols in flask culture, but also was significantly more tolerant of isobutanol toxicity than wild-type R. eutropha. After the elimination of genes encoding three potential carbon sinks (ilvE, bkdAB, and aceE), the production titer improved to 270 mg/L isobutanol and 40 mg/L 3-methyl-1-butanol. Semicontinuous flask cultivation was utilized to minimize the toxicity caused by isobutanol while supplying cells with sufficient nutrients. Under this semicontinuous flask cultivation, the R. eutropha mutant grew and produced more than 14 g/L branched-chain alcohols over the duration of 50 days. These results demonstrate that R. eutropha carbon flux can be redirected from PHB to branched-chain alcohols and that engineered R. eutropha can be cultivated over prolonged periods of time for product biosynthesis.

Application of Polyhydroxyalkanoate Granules for Sizing of Paper

Polyhydroxyalkanoates (PHAs) are characterized by the chemistry of the biodegradable inclusions inside the microbial membrane. They are produced by a wide variety of bacteria, where they function as energy and carbon storage materials. This intracellular Bioplastic forms a stable latex suitable for surface treatments of paper such as sizing and coating. In this work, we compare native granules and artificial granules made from market poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-hydroxyvalerate), P(3HB-co-3HV), for their ability as sizing agent. Paper sizing was assayed by measuring the resistance of sized paper to penetration by aqueous fluids. Our results indicate that the sizing effect of PHAs is dependent on several factors, such as, paper drying temperature, drying time, pressure, and polymer composition, that is, homopolymer, random copolymer, and texture of granules. The sizing efficiency of the copolymer is generally poor compared to the PHB homopolymer. In addition to water permeability, the tensile strength of sized paper was measured and physical properties of granule suspensions were recorded using SEM microscopy, X-ray diffraction, and dynamic light scattering.

Polyhydroxyalkanoate synthesis using different carbon sources by two enhanced biological phosphorus removal microbial communities

Polyhydroxyalkanoate (PHA) is a biodegradable plastic synthesised by bacteria as energy and carbon storage material. PHA production is mostly based on pure cultures operated under sterile conditions, which increase the costs of this biopolymer. The use of inexpensive mixed culture biomass, such as activated sludge, to produce biodegradable plastics from renewable waste streams has been proposed as an alternative. The effect of carbon sources (acetate, propionate, butyrate and glucose) on the type and quantity of PHA synthesis obtained with different enhanced biological phosphorus removal (EBPR) microbial communities enriched with acetate and propionate are reported in this work. Two sequencing batch reactors (SBRs) were seeded with biomass withdrawn from a non-EBPR wastewater treatment plant (WWTP). The same operational conditions were kept, but using acetate or propionate as the sole carbon source of each reactor. These conditions produced two microbial communities with different P-removal capacity. The results presented in this study show the effect of the carbon source on the PHA composition (amount of polyhydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxy-2-methylvalerate (PH2MV)), which differed not just between substrates but also between the two EBPR communities used. In addition, some monomers not always analysed contribute significantly to the total amount of PHA, especially when using butyrate, showing that if they are not considered this can lead to erroneous calculated yields.

Occurrence of Polyhydroxyalkanoate as Temporal Carbon Storage Material in Activated Sludge during The Removal of Organic Pollutants

The amounts of temporal carbon storage material, polyhydroxyalkanoate (PHA), were quantified in the course of wastewater treatment by different activated sludge reactors operated at Beijing University of Technology, Beijing, China. The studied reactors were five continuous ones and two sequencing batch ones. In all the reactors, PHA was detected, and its contents within activated sludge ranged between 0.2% and 3.2%. Soluble organic matters loaded to the reactors were mainly removed in the first anaerobic or microaerophilic tank and one fifth to all of removed soluble organic matters were tentatively stored as PHA in the studied reactors. It was concluded that not a small part of soluble organic matters in sewage is converted to PHA in the course of their removal by activated sludge.

Salinity-induced accumulation of poly-β-hydroxybutyrate in rhizobia indicating its role in cell protection

Poly β-hydroxybutyrate (PHB) is an energy and carbon storage material accumulated in response to the limitation of an essential nutrient. The effect of different salt concentrations on growth and PHB accumulation of four different Sinorhizobium strains was examined. Irrespective of the strain, a defined trend in the accumulation of PHB inside the cells was observed. While minimum PHB content was accumulated at low or zero salinity, maximum was observed by the salt-tolerant strains at higher salt concentrations. This suggests a definite role for PHB in cell protection in saline conditions.

Cell lysis and release of particulate polysaccharides in extensive marine mucilage assessed by lipid biomarkers and molecular probes

During the massive mucllage event in the northern Adriatic Sea in July 1991 samples of macroaggregate were fixed in different ways: with formaldehyde, deep frozen and freeze-dried. Conventional microscopy (light and epifluorescence) revealed different autotrophic species embedded in gelatinous matl-ix. Cyanobacteria and heterotrophic bacteria were also identified. Scanning confocal laser microscopy (SCLMI and fluorescent molec~~ la r p obes (the lectins concanavalin A and UEA-I) showed wall-free cytoplasm and particulate polysacchar~des leaklng from the envelopes of broken cells in the matrix. The extensive cell lysis was supported by the observation of cytoplasn1-free cytoskeletons, stained by the molecular probe phalloidin High concentrations of triglycerides (30Y0 of total lipids) and free fatty aclds (22'2%) along with very low concentrations of phospholipids ( 2 % ) also indicated massive cell degradation in freeze-dried material. The mucllage observations were compared with those of a natural plankton community grown under hlgh nutrlent conditions using the same techniques. Free polysaccharides were observed as globular flocs (marine snow) during in situ enrichment experiments and inti-acellular polysaccharides as carbon storage materials In autotrophic organisms. No strings, filaments, layers, cell lysis or lipid classes indicating strong cell biodeterioration were observed in a 1 mo controlled experiment during an algal bloom.