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

Microbes and us: microbiology literacy in Greece

Microbes are ubiquitous and provide numerous services to humans and our planet. However, a query arises as to whether these microbial services are valued by the general public especially after unprecedented conditions like the COVID-19 pandemic. In this context a survey was conducted to investigate the concept of microbe in Greece. Thematic analysis of 672 anonymous responses (age range 4-75yo) received for the open-ended prompt "What is the first thing that comes to mind when you hear the word microbe?" revealed five thematic categories: Negative emotions, Fuzzy associations, Biology, Entities and Health. Almost 80% of responses fell under "Biology" and "Health" and the general pattern of answers was the same across all age groups. Microbes took a variety of forms in the minds of respondents, however, the concept of "microbe" seems to be more unshaped at younger ages (4-11yo), as revealed in children's language choices. Overall, the often-negative perception of microorganisms seems to be confirmed in this study. Although this research was limited to participants from Greece, it remains relevant to other countries around the world as well. We discuss the reasons behind this negative perception and offer suggestions for reversing it.

Polyhydroxyalkanoates and 5-aminolevulinic acid production by a mixed phototrophic culture using medium-chain carboxylic acids from winery effluents

This work aimed to obtain polyhydroxyalkanoates (PHA) and 5-aminolevulinic acid (5-ALA) from medium-chain carboxylic acids (MCCA) using a mixed culture enriched in Rhodopseudomnas palustris. MCCA, obtained from residual wine lees, were tested in batch photofermentation experiments. First, the influence of individual MCCA (hexanoic, heptanoic, and octanoic acids) was evaluated; then, the MCCA coming directly from a fermentation reactor (LC-effluent) or after acids extraction (HC-effluent) were studied. Nutrient supplementation, bicarbonate, and acetic acid addition were also tested. Results showed that PHA production was higher in hexanoic (328 mg PHA/L) compared to heptanoic (152 mg PHA/L) and octanoic (164 mg PHA/L) acids. Bicarbonate addition and acetic acid as co-substrate improved the MCCA consumption, the PHA content and production rate. The HC-effluent, without nutrient supplementation, was allowed to increase 2.5 times the PHA content (reaching 40 % w/w and 584 mg/L) and to double 5-ALA production (7.6 µM) compared to the LC-effluent condition.

Purple non-sulfur bacteria as cell factories to produce a copolymer as PHBV under light/dark cycle in a 4-L photobioreactor

The present study reports a strategy to produce polyhydroxyalkanoates (PHAs) by culturing the marine bacterium Rhodovulum sulfidophilum DSM-1374. The study was carried out by growing the bacterium anaerobically for 720 h under 16/8 light/dark cycle. Two analytical techniques such as proton magnetic nuclear magnetic resonance (¹H NMR) and Fourier transform infrared spectroscopy (FT-IR) were used to determine that the polyester produced was poly-3-hydroxybutirate-co-3-hydroxyvalerate (PHBV). This study showed that the excess of lactate and the limitation of N-P nutrients under a light-dark cycle enhanced PHBV synthesis and achieved a PHBV concentration of 330 mg/L in the R. sulfidophilum culture. During the 30 days of bacterial cultivation, the percentage of polymer in the six harvested dry biomasses gradually increased from 13.7% to 23.4%. In addition, the study showed that PHBV synthesis stopped during the 8-h dark phase and restarted in the light. The light-dark cycle study also showed that R. sulfidophilum DSM-1374 can be grown outdoors because the cells are exposed to the natural light-dark cycle.

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.

Extraction of Polyhydroxyalkanoates from Purple Non-Sulfur Bacteria by Non-Chlorinated Solvents

In this study, non-chlorinated solvents such as cyclohexanone (CYC) and three ionic liquids, (ILs) (1-ethyl-3-methylimidazolium dimethylphosphate, [EMIM][DMP], 1-ethyl-3-methylimidazolium diethylphosphate, [EMIM][DEP] and 1-ethyl-3-methylimidazolium methylphosphite, [EMIM][MP]) were tested to extract polyhydroxyalkanoates (PHAs) from the purple non-sulfur photosynthetic bacterium (PNSB) Rhodovulumsulfidophilum DSM-1374. The photosynthetic bacterium was cultured in a new generation photobioreactor with 4 L of working volume using a lactate-rich medium. The extracted PHAs were characterized using a thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy, proton nuclear magnetic resonance and gel permeation chromatography. The most promising results were obtained with CYC at 125 °C with an extraction time of above 10 min, obtaining extraction yields higher than 95% and a highly pure poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV) with around 2.7 mol% of hydroxylvalerate (HV). A similar yield and purity were obtained with chloroform (CHL) at 10 °C for 24 h, which was used as the referent solvent Although the three investigated ILs at 60 °C for 4 and 24 h with biomass/IL up to 1/30 (w/w) obtained PHAs strongly contaminated by cellular membrane residues, they were not completely solubilized by the investigated ILs.

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.

Photoautotrophs-Bacteria Co-Cultures: Advances, Challenges and Applications

Photosynthetic microorganisms are among the fundamental living organisms exploited for millennia in many industrial applications, including the food chain, thanks to their adaptable behavior and intrinsic proprieties. The great multipotency of these photoautotroph microorganisms has been described through their attitude to become biofarm for the production of value-added compounds to develop functional foods and personalized drugs. Furthermore, such biological systems demonstrated their potential for green energy production (e.g., biofuel and green nanomaterials). In particular, the exploitation of photoautotrophs represents a concrete biorefinery system toward sustainability, currently a highly sought-after concept at the industrial level and for the environmental protection. However, technical and economic issues have been highlighted in the literature, and in particular, challenges and limitations have been identified. In this context, a new perspective has been recently considered to offer solutions and advances for the biomanufacturing of photosynthetic materials: the co-culture of photoautotrophs and bacteria. The rational of this review is to describe the recently released information regarding this microbial consortium, analyzing the critical issues, the strengths and the next challenges to be faced for the intentions attainment.