Impact of organic carbon acquisition on growth and functional biomolecule production in diatoms

Diatoms are unicellular photosynthetic protists which constitute one of the most successful microalgae contributing enormously to global primary productivity and nutrient cycles in marine and freshwater habitats. Though they possess the ability to biosynthesize high value compounds like eicosatetraenoic acid (EPA), fucoxanthin (Fx) and chrysolaminarin (Chrl) the major bottle neck in commercialization is their inability to attain high density growth. However, their unique potential of acquiring diverse carbon sources via varied mechanisms enables them to adapt and grow under phototrophic, mixotrophic as well as heterotrophic modes. Growth on organic carbon substrates promotes higher biomass, lipid, and carbohydrate productivity, which further triggers the yield of various biomolecules. Since, the current mass culture practices primarily employ open pond and tubular photobioreactors for phototrophic growth, they become cost intensive and economically non-viable. Therefore, in this review we attempt to explore and compare the mechanisms involved in organic carbon acquisition in diatoms and its implications on mixotrophic and heterotrophic growth and biomolecule production and validate how these strategies could pave a way for future exploration and establishment of sustainable diatom biorefineries for novel biomolecules.

Сyanoprokaryota cultivation with the lighting unit under different light regimes

The continuous phototrophic growth and light / dark cycled regime showed comparable OTR, max. µ 0.06 h-1, biomass concentration ca. 0.8 g‧L-1. During growth with 1.5 g‧L-1 glucose compared to the phototrophic showed the higher OTR.

Synthesis of glycogen by Chlorobium limicola IMV K-8 while growth in wastewater

Due to the high content of organic compounds, the distillery wastewater can be a good substrate for the production of glycogen during cultivation of green photosynthetic bacteria. Green photosynthetic bacteria Chlorobium limicola IMV K-8 are producers of glycogen and show exoelectrogenic properties when grown alone or inside the co-culture with heterotrophic bacteria-exoelectrogens in wastewater of various origins. In our previous works it was found that due to the phototrophic growth of C. limicola IMV K-8 in the distillery wastewater significantly reduces the content of compounds of nitrogen, sulfur, Ca2+, Mg2+ and others. The study of the patterns of glycogen synthesis by green photosynthetic bacteria during growth in such an extreme environment as the wastewater of a distillery has prospects for the development of biotechnology for the production of this polysaccharide. The aim of the study was to investigate the glycogen content in C. limicola IMV K-8 cells under different growth conditions in the wastewater of the distillery. Bacteria were grown in the wastewater of the distillery under light (phototrophic growth) and without light exposure (heterotrophic growth). Bacterial cells grown on GSB medium under light (phototrophic growth) and without light (heterotrophic growth) exposure were used as controls. Glycogen content was determined at 7, 14, 21 and 30 days of growth by the glucose oxidase method. Glucose or glycogen in the wastewater of the distillery without the introduction of bacteria was not detected. It was found that the content of glycogen in cells of C. limicola IMV K-8 grown in the wastewater of the distillery, under light exposure increased from 3.8 % to 39.8 % of cells dry weight from the seventh to third day of growth during 30 days of cultivation and was 2 times higher the glycogen content of cells on GSB medium. It is assumed that the bacteria C. limicola IMV K-8 use available in the water sources of carbon and other compounds necessary for cell metabolism along with glycogen biosynthesis and bioremediation of wastewater. During C. limicola IMV K-8 growth in the darkness there is an assimilation of organic sources of carbon (acetate, pyruvate and probably organic compounds of wastewater), which allows cells to remain viable for 30 days without additional sources of carbon, nitrogen, etc., but significant glycogen synthesis does not occur. The glycogen formed under phototrophic conditions can be further a source of carbon or a substrate for electric current generation by exoelectrogenic bacteria.

Adaptation to Photooxidative Stress: Common and Special Strategies of the Alphaproteobacteria Rhodobacter sphaeroides and Rhodobacter capsulatus

Photosynthetic bacteria have to deal with the risk of photooxidative stress that occurs in presence of light and oxygen due to the photosensitizing activity of (bacterio-) chlorophylls. Facultative phototrophs of the genus Rhodobacter adapt the formation of photosynthetic complexes to oxygen and light conditions, but cannot completely avoid this stress if environmental conditions suddenly change. R. capsulatus has a stronger pigmentation and faster switches to phototrophic growth than R. sphaeroides. However, its photooxidative stress response has not been investigated. Here, we compare both species by transcriptomics and proteomics, revealing that proteins involved in oxidation–reduction processes, DNA, and protein damage repair play pivotal roles. These functions are likely universal to many phototrophs. Furthermore, the alternative sigma factors RpoE and RpoHII are induced in both species, even though the genetic localization of the rpoE gene, the RpoE protein itself, and probably its regulon, are different. Despite sharing the same habitats, our findings also suggest individual strategies. The crtIB-tspO operon, encoding proteins for biosynthesis of carotenoid precursors and a regulator of photosynthesis, and cbiX, encoding a putative ferrochelatase, are induced in R. capsulatus. This specific response might support adaptation by maintaining high carotenoid-to-bacteriochlorophyll ratios and preventing the accumulation of porphyrin-derived photosensitizers.

Overproduction of the Flv3B flavodiiron, enhances the photobiological hydrogen production by the nitrogen-fixing cyanobacterium Nostoc PCC 7120

Background: The ability of some photosynthetic microorganisms, particularly cyanobacteria and microalgae, to produce hydrogen (H2) is a promising alternative for renewable, clean-energy production. However, the most recent, related studies point out that much improvement is needed for sustainable cyanobacterial-based H2 production to become economically viable. In this study, we investigated the impact of induced O2-consumption on H2 photoproduction yields in the heterocyte-forming, N2-fixing cyanobacterium Nostoc PCC7120. Results: The flv3B gene, encoding a flavodiiron protein naturally expressed in Nostoc heterocytes, was overexpressed. Under aerobic and phototrophic growth conditions, the recombinant strain displayed a significantly higher H2 production than the wild type. Nitrogenase activity assays indicated that flv3B overexpression did not enhance the nitrogen fixation rates. Interestingly, the transcription of the hox genes, encoding the NiFe Hox hydrogenase, was significantly elevated, as shown by the quantitative RT-PCR analyses. Conclusion: We conclude that the overproduced Flv3B protein might have enhanced O2-consumption, thus creating conditions inducing hox genes and facilitating H2 production. The present study clearly demonstrates the potential to use metabolic engineered cyanobacteria for photosynthesis driven H2 production.

A Modified System of Nonlinear Fractional-Order Differential Equations in the Study of the Dynamics of Marital Relationships and their Behavioural Features

Our theory includes generalized explanations of how nature works, confirmed by pieces of evidence, cover predictions for further technological developments towards economically and environmentally sustainable industrial processes as well as provides the role of bioenergy accumulation and transformation for improved understanding about evolution, influences of anthropogenic activity, decision-makers errors, technological choices, pandemics prevention and the necessary skills toward the innovation algae-based system. The possibility of origination and evolution of the landforms of life were the results of bioenergy accumulation by microalgae and at present, the contribution of algae remains dominant in reducing CO2 and maintaining O2 level in the atmosphere. Population growth stimulates the accumulation of air carbon and bioenergy. The production and application of fertilizers originated large GHG emissions and it is a big conceptual need to shift on organic agriculture including algae fertilization of soil to contribute long-term sustainability. The used technologies for 1G biofuels production, as well as microalgae to biofuel based on biomass phototrophic growth by the use of fertilizers, are induced aggressively increasing GHG emission instead of their mitigation. Microalgae biofuel has big potential in case the use of wastewaters and food waste for biomass growth. The priority strategy for dealing with future pandemics treats such as COVID-19, etc. must be increasing the stability of immunity system of humans and animals to infections and due to a high concentration of physiologically active compounds in microalgae they application can be the best decision. Analyses of the Kyoto Protocol, Paris Climate Agreement, etc. results provide that their application has many disadvantages. The New policy must be founded on the admitting of the Life Conserve industry as the new part of the production. Keywords: bioenergy, biofuel, environmental policy evaluation, evolution, climate change, Malthusian theory, microalgae, agriculture, pandemics, waste

Optimal proteome allocation strategies for phototrophic growth in a light-limited chemostat

Background Cyanobacteria and other phototrophic microorganisms allow to couple the light-driven assimilation of atmospheric $$\text {CO}_{2}$$ CO 2 directly to the synthesis of carbon-based products, and are therefore attractive platforms for microbial cell factories. While most current engineering efforts are performed using small-scale laboratory cultivation, the economic viability of phototrophic cultivation also crucially depends on photobioreactor design and culture parameters, such as the maximal areal and volumetric productivities. Based on recent insights into the cyanobacterial cell physiology and the resulting computational models of cyanobacterial growth, the aim of this study is to investigate the limits of cyanobacterial productivity in continuous culture with light as the limiting nutrient. Results We integrate a coarse-grained model of cyanobacterial growth into a light-limited chemostat and its heterogeneous light gradient induced by self-shading of cells. We show that phototrophic growth in the light-limited chemostat can be described using the concept of an average light intensity. Different from previous models based on phenomenological growth equations, our model provides a mechanistic link between intracellular protein allocation, population growth and the resulting reactor productivity. Our computational framework thereby provides a novel approach to investigate and predict the maximal productivity of phototrophic cultivation, and identifies optimal proteome allocation strategies for developing maximally productive strains. Conclusions Our results have implications for efficient phototrophic cultivation and the design of maximally productive phototrophic cell factories. The model predicts that the use of dense cultures in well-mixed photobioreactors with short light-paths acts as an effective light dilution mechanism and alleviates the detrimental effects of photoinhibition even under very high light intensities. We recover the well-known trade-offs between a reduced light-harvesting apparatus and increased population density. Our results are discussed in the context of recent experimental efforts to increase the yield of phototrophic cultivation.