Exploring nutrient limitation for polyhydroxyalkanoates synthesis by newly isolated strains of Aeromonas sp. using biodiesel-derived glycerol as a substrate

Halomonas alkaliantarctica as a platform for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production from biodiesel-derived glycerol

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters produced by a wide range of microorganisms, including extremophiles. These unique microorganisms have gained interest in PHA production due to their ability to utilise low-cost carbon sources under extreme conditions. In this study, Halomonas alkaliantarctica was examined with regards to its potential to produce PHAs using crude glycerol from biodiesel industry as the only carbon source. We found that cell dry mass concentration was not dependent on the applying substrate concentration. Furthermore, our data confirmed that the analysed halophile was capable of metabolising crude glycerol into poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer within 24 h of the cultivation without addition of any precursors. Moreover, crude glycerol concentration affects the repeat units content in the purified PHAs copolymers and their thermal properties. Nevertheless, a differential scanning calorimetric and thermogravimetric analysis showed that the analysed biopolyesters have properties suitable for various applications. Overall, this study described a promising approach for the valorisation of crude glycerol as a future strategy of industrial waste management to produce high value microbial biopolymers.

Production and characterization of polyhydroxyalkanoates by Halomonas alkaliantarctica utilizing dairy waste as feedstock

Currently, the global demand for polyhydroxyalkanoates (PHAs) is significantly increasing. PHAs are produced by several bacteria that are an alternative source of synthetic polymers derived from petrochemical refineries. This study established a simple and more feasible process of PHA production by Halomonas alkaliantarctica using dairy waste as the only carbon source. The data confirmed that the analyzed halophile could metabolize cheese whey (CW) and cheese whey mother liquor (CWML) into biopolyesters. The highest yield of PHAs was 0.42 g/L in the cultivation supplemented with CWML. Furthermore, it was proved that PHA structure depended on the type of by-product from cheese manufacturing, its concentration, and the culture time. The results revealed that H. alkaliantarctica could produce P(3HB-co-3HV) copolymer in the cultivations with CW at 48 h and 72 h without adding of any precursors. Based on the data obtained from physicochemical and thermal analyses, the extracted copolymer was reported to have properties suitable for various applications. Overall, this study described a promising approach for valorizing of dairy waste as a future strategy of industrial waste management to produce high value microbial biopolymers.

Effect of short- and medium-chain fatty acid mixture on polyhydroxyalkanoate production by Pseudomonas strains grown under different culture conditions

Short- and medium-chain fatty acids (SMCFAs) derived from the acidogenic anaerobic mixed culture fermentation of acid whey obtained from a crude cheese production line and their synthetic mixture that simulates a real SMCFA-rich stream were evaluated for polyhydroxyalkanoate (PHA) production. Three individual Pseudomonas sp. strains showed different capabilities of growing and producing PHAs in the presence of a synthetic mixture of SMCFAs. Pseudomonas sp. GL06 exhibited the highest SMCFA tolerance and produced PHAs with the highest productivity (2.7 mg/L h). Based on these observations, this strain was selected for further investigations on PHA production in a fed-batch bioreactor with a SMCFA-rich stream extracted from the effluent. The results showed that PHA productivity reached up to 4.5 mg/L h at 24 h of fermentation together with the ammonium exhaustion in the growth medium. Moreover, the PHA monomeric composition varied with the bacterial strain and the type of the growth medium used. Furthermore, a differential scanning calorimetric and thermogravimetric analysis showed that a short- and medium-chain-length PHA copolymer made of 3-hydroxybutyric, -hexanoic, -octanoic, -decanoic, and -dodecanoic has promising properties. The ability of Pseudomonas sp. to produce tailored PHA copolymers together with the range of possible applications opens new perspectives in the development of PHA bioproduction as a part of an integrated valorization process of SMCFAs derived from waste streams.

Conversion of Short and Medium Chain Fatty Acids into Novel Polyhydroxyalkanoates Copolymers by Aeromonas sp. AC_01

Polyhydroxyalkanoates (PHAs) production by Aeromonas sp. AC_01 was investigated using synthetic and waste derived short and medium chain fatty acids (SMCFAs). The obtained results revealed that the analyzed bacterial strain was able to grow and synthesize PHAs using SMCFAs. The highest PHA productivity was observed in the cultivation supplemented with a mixture of acetic acid and butyric acid (3.89 mg/L·h). Furthermore, SMCFAs-rich stream, derived from acidogenic mixed culture fermentation of acid whey, was found to be less beneficial for PHA productivity than its synthetic mixture, however the PHA production was favored by the nitrogen-limited condition. Importantly, Aeromonas sp. AC_01 was capable of synthesizing novel scl-mcl copolymers of 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 3-hydroxytridecanoate (3HtriD) and/or 3-hydroxytetradecaonate (3HTD) with high 3HB and 3HV fractions. They were identified with alterable monomers composition depending on the culture conditions used. Moreover, in-depth thermal analyses proved that they are highly resistant to thermal degradation regardless of their monomeric composition. The obtained results confirm that Aeromonas sp. AC_01 is a promising candidate for the biotechnological production of PHAs from SMCFAs with thermal properties that can be tuned together with their chemical composition by the corresponding adjustment of the cultivation process.

Polyhydroxyalkanoates production from short and medium chain carboxylic acids by Paracoccus homiensis

The aim of this study was to evaluate an effect of short and medium chain carboxylic acids (CAs) rich stream derived from acidogenic mixed culture fermentation of acid whey on polyhydroxyalkanoates (PHAs) synthesis by Paracoccus homiensis and compare it with the impact of individual synthetic CAs. The obtained results confirmed that the analyzed bacterium is able to metabolize synthetic CAs as the only carbon sources in the growth medium with maximum PHAs production yields of 26% of cell dry mass (CDM). The replacement of the individual CAs by a CAs-rich residual stream was found to be beneficial for the Paracoccus homiensis growth. The highest biomass concentration reached about 2.5 g/L with PHAs content of 17% of CDM. The purified PHAs were identified as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by applying gas chromatography coupled with mass spectrometry, Fourier transform infrared spectroscopic spectra and UV–Vis spectra. Furthermore, a differential scanning calorimetric, thermogravimetric and water contact angle analysis proved that the extracted copolymers have useful properties. The obtained data are promising in the perspective of developing a microbial PHAs production as a part of an integrated valorization process of high CAs content waste-derived streams.

What Is New in the Field of Industrial Wastes Conversion into Polyhydroxyalkanoates by Bacteria?

The rising global consumption and industrialization has resulted in increased food processing demand. Food industry generates a tremendous amount of waste which causes serious environmental issues. These problems have forced us to create strategies that will help to reduce the volume of waste and the contamination to the environment. Waste from food industries has great potential as substrates for value-added bioproducts. Among them, polyhydroxyalkanaotes (PHAs) have received considerable attention in recent years due to their comparable characteristics to common plastics. These biodegradable polyesters are produced by microorganisms during fermentation processes utilizing various carbon sources. Scale-up of PHA production is limited due to the cost of the carbon source metabolized by the microorganisms. Therefore, there is a growing need for the development of novel microbial processes using inexpensive carbon sources. Such substrates could be waste generated by the food industry and food service. The use of industrial waste streams for PHAs biosynthesis could transform PHA production into cheaper and more environmentally friendly bioprocess. This review collates in detail recent developments in the biosynthesis of various types of PHAs produced using waste derived from agrofood industries. Challenges associated with this production bioprocess were described, and new ways to overcome them were proposed.

Complete genome sequence of Photobacterium ganghwense C2.2: A new polyhydroxyalkanoate production candidate

Polyhydroxyalkanoates (PHAs) are biodegradable bioplastics that can be manufactured sustainably and represent a promising green alternative to petrochemical-based plastics. Here, we describe the complete genome of a new marine PHA-producing bacterium-Photobacterium ganghwense (strain C2.2), which we have isolated from the Black Sea seashore. This new isolate is psychrotolerant and accumulates PHA when glycerol is provided as the main carbon source. Transmission electron microscopy, specific staining with Nile Red visualized via epifluorescence microscopy and gas chromatography analysis confirmed the accumulation of PHA. This is the only PHA-producing Photobacterium for which we now have a complete genome sequence, allowing us to investigate the pathways for PHA production and other secondary metabolite synthesis pathways. The de novo assembly genome, obtained using open-source tools, comprises two chromosomes (3.5, 2 Mbp) and a megaplasmid (202 kbp). We identify the entire PHA synthesis gene cluster that encodes a class I PHA synthase, a phasin, a 3-ketothiolase, and an acetoacetyl-CoA reductase. No conventional PHA depolymerase was identified in strain C2.2, but a putative lipase with extracellular amorphous PHA depolymerase activity was annotated, suggesting that C2.2 is unable to degrade intracellular PHA. A complete pathway for the conversion of glycerol to acetyl-CoA was annotated, in accordance with its ability to convert glycerol to PHA. Several secondary metabolite biosynthetic gene clusters and a low number of genes involved in antibiotic resistance and virulence were also identified, indicating the strain's suitability for biotechnological applications.

Proteomic Response of Pseudomonas putida KT2440 to Dual Carbon-Phosphorus Limitation during mcl-PHAs Synthesis

Pseudomonas putida KT2440, one of the best characterized pseudomonads, is a metabolically versatile producer of medium-chain-length polyhydroxyalkanoates (mcl-PHAs) that serves as a model bacterium for molecular studies. The synthesis of mcl-PHAs is of great interest due to their commercial potential. Carbon and phosphorus are the essential nutrients for growth and their limitation can trigger mcl-PHAs' production in microorganisms. However, the specific molecular mechanisms that drive this synthesis in Pseudomonas species under unfavorable growth conditions remain poorly understood. Therefore, the proteomic responses of Pseudomonas putida KT2440 to the limited carbon and phosphorus levels in the different growth phases during mcl-PHAs synthesis were investigated. The data indicated that biopolymers' production was associated with the cell growth of P. putida KT2440 under carbon- and phosphorus-limiting conditions. The protein expression pattern changed during mcl-PHAs synthesis and accumulation, and during the different physiological states of the microorganism. The data suggested that the majority of metabolic activities ceased under carbon and phosphorus limitation. The abundance of polyhydroxyalkanoate granule-associated protein (PhaF) involved in PHA synthesis increased significantly at 24 and 48 h of the cultivations. The activation of proteins belonging to the phosphate regulon was also detected. Moreover, these results indicated changes in the protein profiles related to amino acids metabolism, replication, transcription, translation, stress response mechanisms, transport or signal transduction. The presented data allowed the investigation of time-course proteome alterations in response to carbon and phosphorus limitation, and PHAs synthesis. This study provided information about proteins that can be potential targets in improving the efficiency of mcl-PHAs synthesis.

Polyhydroxyalkanoates Synthesized by Aeromonas Species: Trends and Challenges

The negative effects of petrochemical-derived plastics on the global environment and depletion of global fossil fuel supplies have paved the way for exploring new technologies for the production of bioplastics. Polyhydroxyalkanoates (PHAs) are considered an alternative for synthetic polymers because of their biodegradability, biocompatibility, and non-toxicity. Many bacteria have been reported to have the ability to synthesize PHAs. Among them, the Aeromonas species seem to be ideal hosts for the industrial production of these biopolyesters due to their robust growth, simple growth requirements, their ability for the synthesis of homopolymers, co-polymers, and terpolymers with unique material properties. Some Aeromonas strains were able to produce PHAs in satisfactory amounts from simple carbon sources. Efforts have been made to use genetically modified Aeromonas strains for enhanced PHAs and to obtain bacteria with modified compositions and improved properties. This review discusses the current state of knowledge of polyhydroxyalkanoates synthesized by Aeromonas species, with a special focus on their potential, challenges, and progress in PHA synthesis.