Optimal iron concentrations for growth-associated polyhydroxyalkanoate biosynthesis in the marine photosynthetic purple bacterium Rhodovulum sulfidophilum under photoheterotrophic condition

Light/dark cycles and iron supplementation to enhance the simultaneous production of polyhydroxyalkanoates, 5-aminolevulinic acid, coenzyme Q10, and pigments through photofermentation

This study aimed to obtain 5-aminolevulinic acid (5-ALA), Coenzyme Q10 (CoQ10), polyhydroxyalkanoates (PHA), carotenoids, and bacteriochlorophylls (Bchl) through the photofermentation of residual wine lees. Light/dark cycles and iron supplementation were evaluated. Under 12-hour light/dark cycles, the production of 5-ALA, CoQ10, carotenoids, and Bchl increased by 1.7, 2.8, 1.7, and 2.4 times, respectively, compared to the continuous illumination control, while PHA production decreased from 511 to 445 mg/L. Combining light/dark cycles with iron supplementation enhanced the biomass production rate. The CoQ10 content increased by 4.9 times (reaching 8.8 mg/g-dw), carotenoids by 3.7 times (6.4 mg/g-dw), and Bchl by 6.4 times (17.9 mg/g-dw) compared to the control treatment, while maintaining 5-ALA at 5.3 µmol/L and PHA at 377 mg/L. The combination of light/dark cycles and iron provides a triple benefit: increased production of value-added substances, enhanced biomass production rate, and improved organic matter removal, making it an attractive option for winery effluent treatment and valorization.

The Biology of Natural Polymers Accelerates and Expands the Science of Biomacromolecules: A Focus on Structural Proteins

This Perspective explores the use of biomacromolecules in natural materials synthesized by living organisms, such as spider silk, in the development of sustainable synthetic materials. Currently employed synthetic polymers lack the hierarchical complexity and unique properties of natural materials composed of biomacromolecules. By understanding the composition of these natural materials, it may be able to reproduce their properties synthetically. Additionally, research directions involving the use of renewable resources such as nitrogen and carbon dioxide from the air and seawater to develop biomacromolecules such as spider silk and biopolyester via photosynthetic organisms are reviewed. Next-generation biomacromolecule research will aid in the creation of a sustainable global society, advancing fields such as biomanufacturing, agriculture, aquaculture, and other industries.

Production efficiency and properties of poly(3hydroxybutyrate-co-3hydroxyvalerate) generated via a robust bacterial consortium dominated by Zoogloea sp. using acidified discarded fruit juices as carbon source

In the current study, a mixed microbial culture (MMC) of polyhydroxyalkanoates (PHAs) producers was developed under nutrient stress and was assessed as biocatalyst for the production of high-yielding PHAs from fermented (acidified) discarded fruit juices (DFJ). The structure of the MMC was analyzed periodically to determine its microbial dynamics, revealing that Zoogloae sp. dominated throughout the operation of the system. The efficiency of PHAs production from the MMC was further optimized in batch mode by altering the ratio of C to N, the ratio of carbon sources (propionate and butyrate), and the initial pH, and subsequently different fermentation mixtures of acidified DFJ were assessed as substrates at optimal conditions. Upon solvent extraction, the properties of recovered PHAs were analyzed, showing that in all cases P(3HB-co-3HV) was produced, with T_m ranging from 90.5 to 168.8 °C, and maximum obtained yields 54.61 ± 4.31 % and 43.27 ± 2.13 %, from synthetic substrates and DFJ, respectively. Overall, it was shown that the developed MMC can be efficiently applied as biocatalyst for the exploitation of sugary wastewaters, such as DFJ, towards bio-based and biodegradable plastics bearing the required properties to substitute fossil plastics, into the concept of a circular economy.

Microbial autotrophic biorefineries: Perspectives for biopolymer production

The use of autotrophic microorganisms to fabricate biochemical products has attracted much attention in both academia and industry. Unlike heterotrophic microorganisms that require carbohydrates and amino acids for growth, autotrophic microorganisms have evolved to utilize either light (photoautotrophs) or chemical compounds (chemolithotrophs) to fix carbon dioxide (CO2) and drive metabolic processes. Several biotechnological approaches, including synthetic biology and metabolic engineering, have been proposed to harness autotrophic microorganisms as a sustainable/green production platform for commercially essential products such as biofuels, commodity chemicals, and biopolymers. Here, we review the recent advances in natural autotrophic microorganisms (photoautotrophic and chemoautotrophic), focusing on the biopolymer production. We present current state-of-the-art technologies to engineer autotrophic microbial cell factories for efficient biopolymer production.

Engineered Mutants of a Marine Photosynthetic Purple Nonsulfur Bacterium with Increased Volumetric Productivity of Polyhydroxyalkanoate Bioplastics

Polyhydroxyalkanoates (PHAs) are green and sustainable bioplastics that could replace petrochemical synthetic plastics without posing environmental threats to living organisms. In addition, sustainable PHA production could be achieved using marine photosynthetic purple nonsulfur bacteria (PNSBs) that utilize natural seawater, sunlight, carbon dioxide gas, and nitrogen gas for growth. However, PHA production using marine photosynthetic PNSBs has not been economically feasible yet due to its high cost and low productivity. In this work, strain improvement, using genome-wide mutagenesis coupled with high-throughput screening via fluorescence-activated cell sorting, we were able to create Rhodovulum sulfidophilum mutants with enhanced volumetric PHA productivity, with an up to 1.7-fold increase. The best selected mutants (E6 and E6M4) reached the stationary growth phase 1 day faster and accumulated the maximum PHA content 2 days faster than the wild type. Maximizing volumetric PHA productivity before the stationary growth phase is indeed an additional advantage for R. sulfidophilum as a growth-associated PHA producer.

Insightful Advancement and Opportunities for Microbial Bioplastic Production

Impetuous urbanization and population growth are driving increased demand for plastics to formulate impeccable industrial and biomedical commodities. The everlasting nature and excruciating waste management of petroleum-based plastics have catered to numerous challenges for the environment. However, just implementing various end-of-life management techniques for assimilation and recycling plastics is not a comprehensive remedy; instead, the extensive reliance on finite resources needs to be reduced for sustainable production and plastic product utilization. Microorganisms, such as bacteria and algae, are explored substantially for their bioplastic production repertoire, thus replacing fossil-based plastics sooner or later. Nevertheless, the utilization of pure microbial cultures has led to various operational and economical complications, opening the ventures for the usage of mixed microbial cultures (MMCs) consisting of bacteria and algae for sustainable production of bioplastic. The current review is primarily focuses on elaborating the bioplastic production capabilities of different bacterial and algal strains, followed by discussing the quintessence of MMCs. The present state-of-the-art of bioplastic, different types of bacterial bioplastic, microalgal biocomposites, operational factors influencing the quality and quantity of bioplastic precursors, embracing the potential of bacteria-algae consortia, and the current global status quo of bioplastic production has been summarized extensively.

Insights into the bacterial community composition of farmed Caulerpa lentillifera: A comparison between contrasting health states

The bacterial communities of Caulerpa lentillifera were studied during an outbreak of an unknown disease in a sea grape farm from Vietnam. Clear differences between healthy and diseased cases were observed at the order, genus, and Operational Taxonomic Unit (OTU) level. A richer diversity was detected in the diseased thalli of C. lentillifera, as well as the dominance of the orders Flavobacteriales (phylum Bacteroidetes) and Phycisphaerales (Planctomycetes). Aquibacter, Winogradskyella, and other OTUs of the family Flavobacteriaceae were hypothesized as detrimental bacteria, this family comprises some well-known seaweed pathogens. Phycisphaera together with other Planctomycetes and Woeseia were probably saprophytes of C. lentillifera. The Rhodobacteraceae and Rhodovulum dominated the bacterial community composition of healthy C. lentillifera. The likely beneficial role of Bradyrhizobium, Paracoccus, and Brevundimonas strains on nutrient cycling and phytohormone production was discussed. The bleaching of diseased C. lentillifera might not only be associated with pathogens but also with an oxidative response. This study offers pioneering insights on the co-occurrence of C. lentillifera-attached bacteria, potential detrimental or beneficial microbes, and a baseline for understanding the C. lentillifera holobiont. Further applied and basic research is urgently needed on C. lentillifera microbiome, shotgun metagenomic, metatranscriptomic, and metabolomic studies as well as bioactivity assays are recommended.

Poly-β-Hydroxybutyrate Production by Rhodopseudomonas sp. Grown in Semi-Continuous Mode in a 4 L Photobioreactor

The synthesis of polyhydroxybutyrate (PHB) by photosynthetic non-sulfur bacteria is a potential approach for producing biodegradable plastics. In this work, acetate was used as a single carbon source to study the effect on PHB formation in Rhodopseudomonas sp. cultured in a cylindrical four-liter photobioreactor under semi-continuous mode. The cultivation process is divided into a symmetrical growth phase and a PHB accumulation phase separated temporally. The symmetrical growth phase (nutrient sufficient conditions) was followed by a sulfur-limited phase to promote PHB accumulation. The main novelty is the progressive lowering of the sulfur concentration into Rhodopseudomonas culture, which was obtained by two concomitant conditions: (1) sulfur consumption during the bacterial growth and (2) semi-continuous growth strategy. This caused a progressive lowering of the sulfur concentration into Rhodopseudomonas culturedue to the sulfur-free medium used to replace 2 L of culture (50% of the total) that was withdrawn from the photobioreactor at each dilution. The PHB content ranged from 9.26% to 15.24% of cell dry weight. At the steady state phase, the average cumulative PHB was >210 mg/L. Sulfur deficiency proved to be one of the most suitable conditions to obtain high cumulative PHB in Rhodopseudomonas culture.

Bioplastic production by feeding the marine Rhodovulum sulfidophilum DSM-1374 with four different carbon sources under batch, fed-batch and semi-continuous growth regimes

In the present study, the ability of the marine bacterium Rhodovulum sulfidophilum DSM-1374 to convert, via photo-fermentative process, certain organic acids such as single carbon source (acetate, lactate, malate and succinate) into polyhydroxyalkanoate accumulations within bacterial cells is evaluated. The main goal of the investigation was poly-3-hydroxybutyrate (P3HB) synthesis by a photo-fermentative process. Of the four carbon sources, only succinate simultaneously produced P3HB and H₂ (268 mg/L and 1085 mL/L respectively). Malate was the least productive source for P3HB; the other carbon sources (acetate and lactate) produced a significant amount of polymer (596 mg P3HB/L for acetate and 716 mg P3HB/L for lactate) when R. sulfidophilum was cultured in batch growth conditions. Cumulative P3HB increased significantly when the bacterium was grown under two steps: nutrient sufficient conditions (step 1) followed by macronutrient deficient conditions (step 2). The highest cumulative P3HB was observed at the end of step 2 (1000 mg/L) when R. sulfidophilum was fed with lactate under phosphorus starvation. When grown over 1200 h, under a semi-continuous regimen, the harvested dry-biomass reached a constant content of P3HB (39.1 ± 1.6 % of cell dry-weight), in the semi-steady state condition. Since lactate is an abundant byproduct of world industries, it can be used to mitigate the environmental impact in a modern circular bio-economy.

An overview of anoxygenic phototrophic bacteria and their applications in environmental biotechnology for sustainable Resource recovery

Anoxygenic phototrophic bacteria (APB) are a phylogenetically diverse group of organisms that can harness solar energy for their growth and metabolism. These bacteria vary broadly in terms of their metabolism as well as the composition of their photosynthetic apparatus. Unlike oxygenic phototrophic bacteria such as algae and cyanobacteria, APB can use both organic and inorganic electron donors for light-dependent fixation of carbon dioxide without generating oxygen. Their versatile metabolism, ability to adapt in extreme conditions, low maintenance cost and high biomass yield make APB ideal for wastewater treatment, resource recovery and in the production of high value substances. This review highlights the advantages of APB over algae and cyanobacteria, and their applications in photo-bioelectrochemical systems, production of poly-β-hydroxyalkanoates, single-cell protein, biofertilizers and pigments. The ecology of ABP, their distinguishing factors, various physiochemical parameters governing the production of high-value substances and future directions of APB utilization are also discussed.

Peptide-Mediated Gene Transfer into Marine Purple Photosynthetic Bacteria

Use of photosynthetic organisms is one of the sustainable ways to produce high-value products. Marine purple photosynthetic bacteria are one of the research focuses as microbial production hosts. Genetic transformation is indispensable as a biotechnology technique. However, only conjugation has been determined to be an applicable method for the transformation of marine purple photosynthetic bacteria so far. In this study, for the first time, a dual peptide-based transformation method combining cell penetrating peptide (CPP), cationic peptide and Tat-derived peptide (dTat-Sar-EED) (containing D-amino acids of Tat and endosomal escape domain (EED) connected by sarcosine linkers) successfully delivered plasmid DNA into Rhodovulum sulfidophilum, a marine purple photosynthetic bacterium. The plasmid delivery efficiency was greatly improved by dTat-Sar-EED. The concentrations of dTat-Sar-EED, cell growth stage and recovery duration affected the efficiency of plasmid DNA delivery. The delivery was inhibited at 4 °C and by A22, which is an inhibitor of the actin homolog MreB. This suggests that the plasmid DNA delivery occurred via MreB-mediated energy dependent process. Additionally, this peptide-mediated delivery method was also applicable for E. coli cells. Thus, a wide range of bacteria could be genetically transformed by using this novel peptide-based transformation method.

A marine photosynthetic microbial cell factory as a platform for spider silk production

Photosynthetic microorganisms such as cyanobacteria, purple bacteria and microalgae have attracted great interest as promising platforms for economical and sustainable production of bioenergy, biochemicals, and biopolymers. Here, we demonstrate heterotrophic production of spider dragline silk proteins, major ampullate spidroins (MaSp), in a marine photosynthetic purple bacterium, Rhodovulum sulfidophilum, under both photoheterotrophic and photoautotrophic growth conditions. Spider silk is a biodegradable and biocompatible material with remarkable mechanical properties. R. sulfidophilum grow by utilizing abundant and renewable nonfood bioresources such as seawater, sunlight, and gaseous CO₂ and N₂, thus making this photosynthetic microbial cell factory a promising green and sustainable production platform for proteins and biopolymers, including spider silks.

Foong et al. demonstrate production of spider dragline silk proteins in Rhodovulum sulfidophilum, a marine photosynthetic purple bacterium. This platform generates promise for the sustainable production of valuable biocompounds in photosynthetic organisms.

How to define and study structural proteins as biopolymer materials

Structural proteins, including silk fibroins, play an important role in shaping the skeletons and structures of cells, tissues, and organisms. The amino acid sequences of structural proteins often show characteristic features, such as a repeating tandem motif, that are notably different from those of functional proteins such as enzymes and antibodies. In recent years, materials composed of or containing structural proteins have been studied and developed as biomedical, apparel, and structural materials. This review outlines the definition of structural proteins, methods for characterizing structural proteins as polymeric materials, and potential applications.

Method for the facile transformation of marine purple photosynthetic bacteria using chemically competent cells

Marine purple photosynthetic bacteria are ideal organisms for the production of useful materials at reduced costs and contributing to a sustainable society because they can utilize sunlight, seawater, and components of air, including carbon dioxide and nitrogen gases, for their growth. However, conjugation is the only applicable method for the transformation of marine purple photosynthetic bacteria so far. Here, we examined a calcium chloride‐mediated method for the transformation of marine purple photosynthetic bacteria. Plasmid DNAs containing the kanamycin resistance gene were successfully transferred into chemically competent cells of two strains of marine purple photosynthetic bacteria (Rhodovulum sulfidophilum and Roseospira marina). Heat shock treatment increased the transformation efficiency in R. sulfidophilum, whereas the addition of cell‐penetrating peptide did not improve it. We also found that prolonged incubation in agar plates containing kanamycin led to spontaneous mutation of the 16S rRNA, resulting in kanamycin resistance in R. marina. Thus, we developed an efficient and facile transformation method using chemically competent cells of marine purple photosynthetic bacteria with calcium chloride.

Marine Purple Photosynthetic Bacteria as Sustainable Microbial Production Hosts

Photosynthetic microorganisms can serve as the ideal hosts for the sustainable production of high-value compounds. Purple photosynthetic bacteria are typical anoxygenic photosynthetic microorganisms and are expected to be one of the suitable microorganisms for industrial production. Purple photosynthetic bacteria are reported to produce polyhydroxyalkanoate (PHA), extracellular nucleic acids and hydrogen gas. We characterized PHA production as a model compound in purple photosynthetic bacteria, especially focused on marine strains. PHA is a family of biopolyesters synthesized by a variety of microorganisms as carbon and energy storage materials. PHA have recently attracted attention as an alternative to conventional petroleum-based plastics. Production of extracellular nucleic acids have been studied in Rhodovulum sulfidophilum, a marine purple non-sulfur bacterium. Several types of artificial RNAs have been successfully produced in R. sulfidophilum. Purple photosynthetic bacteria produce hydrogen via nitrogenase, and genetic engineering strategies have been investigated to enhance the hydrogen production. This mini review describes the microbial production of these high-value compounds using purple photosynthetic bacteria as the host microorganism.