Risk assessment framework for microplastic in marine environments

Constantly raising microplastic (MP) contamination of water sources poses a direct threat to the gentle balance of the marine environment. This study focuses on a multifactor hazard evaluation of conventional (polyethylene - PE, polypropylene - PP, and polystyrene - PS) and alternative (polyethylene terephthalate with 25 % or 50 % recycled material and polylactic acid) plastics. The risk assessment framework explored included MP abundance, water acidification potential, surface oxidation, fragmentation, and bacterial growth inhibition. Based on MP monitoring campaigns worldwide, we conclude that PE-based plastics are the most abundant MPs in water samples (comprise up to 82 % the MP in those samples). A year-long weathering experiment showed that PS-based and PP-based plastics were oxidized to a higher extent, resulting in the highest water acidification with pH reduction of up to three orders of magnitude. Finally, our laboratory experiments showed that weathered PS was the most fragile plastic during mechanical degradation, while both PP- and PS-based plastic extracts showed a significant growth inhibition toward the marine microorganisms (Bacillus sp. and Pseudoaltermonas sp). Using the examined factors as weighted inputs into our framework, this holistic evaluation of hazards suggest that PP-based plastic products were the most hazardous compared to the other conventional and alternative plastic types.

Avocado seed waste bioconversion into poly(3-hydroxybutyrate) by using Cobetia amphilecti and ethyl levulinate as a green extractant

The avocado processing industry produces up to 1.3M tons of agro-waste annually. Chemical analysis of avocado seed waste (ASW) revealed that it is rich in carbohydrates (464.7 ± 21.4 g kg^-1) and proteins (37.2 ± 1.5 g kg^-1). Optimized microbial cultivation of Cobetia amphilecti using an acid hydrolysate of ASW, generated poly(3-hydroxybutyrate) (PHB) in a 2.1 ± 0.1 g L^-1 concentration. The PHB productivity of C. amphilecti cultivated on ASW extract was 17.5 mg L^-1 h^-1. The process in which a novel ASW substrate was utilized has been further augmented by using ethyl levulinate as a sustainable extractant. This process achieved 97.4 ± 1.9 % recovery yield and 100 ± 1 % purity (measured by TGA, NMR, and FTIR) of the target PHB biopolymer, along with a high and relatively uniform PHB molecular weight (M_w = 1831 kDa, M_n = 1481 kDa, M_w/M_n = 1.24) (measured by gel permeation chromatography), compared to PHB polymer extracted by chloroform (M_w = 389 kDa, M_n = 297 kDa, M_w/M_n = 1.31). This is the first example of ASW utilization as a sustainable and inexpensive substrate for PHB biosynthesis and ethyl levulinate as an efficient and green extractant of PHB from a single bacterial biomass.

Turning mannitol-rich agricultural waste to poly(3-hydroxybutyrate) with Cobetia amphilecti fermentation and recovery with methyl levulinate as a green solvent

The present study explored the use of mannitol and mannitol-rich agro-industrial wastes as substrates for PHB production by Cobetia amphilecti isolated from the green Ulva sp. seaweed. Cultivation of C. amphilecti on mannitol, celery, and olive leaves (OLs) waste led to 4.20, 6.00, and 5.16 g L^-1 of cell dry mass (CDM), 76.3, 25.5, and 12.0% of PHB content in CDM and 3.2, 1.53, and 0.62 g L^-1 of PHB concentration, respectively; which suggested that they can be exploited as carbon substrates for the production of PHB. Extraction of PHB from C. amphilecti cultures by solubilization in the green solvent methyl levulinate (ML) (2% w/w, 140 °C, 1 h) indicated that the recovery yield and purity of PHB are above 97 and 90% w/w, respectively. The use of ML could be an attractive method for the recovery of PHB when safe and non-toxic solvents are required.

Marine bacteria associated with the green seaweed Ulva sp. for the production of polyhydroxyalkanoates

This work aimed to isolate a series of bacterial strains associated with the green seaweed Ulva sp. and evaluate their capability to manufacture PHA. The effect of the type of supplemented sugars found to be in macroalgae, on the growth and PHA productivity of the strains was studied. Analysis of the 16S rRNA gene sequence of the isolated strains revealed that the PHA-producing bacteria were phylogenetically related to the genus Cobetia, Bacillus, Pseudoaltermonas and Sulfitobacter, which showed high PHA contents among the isolates. The highest PHA content was observed in the case of Cobetia strain, with up to 61% w/w in the presence of mannitol and 12% w/w on Ulva sp. acid hydrolysate as a substrate.

Detection and differentiation of bacteria by electrical bioimpedance spectroscopy

Detecting bacteria in samples and differentiating between Gram-negative and Gram-positive species is an important challenge, and the most common method, Gram staining, is very time consuming. The aim of this study was to evaluate the electrical bioimpedance spectroscopy (EBIS) technique as an inexpensive and practical tool for real-time detection of bacteria and differentiation between Gram-positive and Gram-negative species. The relevant sensitivity for differentiating between species was found in the magnitude and phase at frequencies of 158,489 and 5248 Hz, respectively, at a bacterial concentration of 1 μg/μl. Subsequently, the sensitivity was estimated as a function of bacterial concentration. Our results demonstrated that EBIS can potentially distinguish between presence and absence of bacteria as well as between different types of bacteria.

Label-Free cDNA Detection Based on Radiofrequency Scattering Parameters: A New Approach for an Inexpensive Gene Sensor

A new gene detection technique that is fast, inexpensive, and easy-to-use is urgently needed in hospitals, clinics, and laboratories without access to expensive equipments. The lack of a practical, minimally invasive, and economical method constitutes the main impediment to the promotion of genetic medicine in developing countries. Radiofrequency scattering parameters are an inexpensive gene sensor potentially capable of noninvasively identifying biological materials. They represent a quantitative value for the electromagnetic reflection/transmission characteristics of certain molecular markers in a given frequency domain. The S21 parameter is the difference between the signal received and that transmitted. The aim of this study is to evaluate the S21 transmittance parameters (magnitude and phase) as an indirect impedance measurement for detecting the label-free complementary deoxyribonucleic acid (cDNA) amplification of the 16S ribosomal subunit gene. S21 values showed differences associated with distinct cDNA concentrations. Hence, this technique could possibly facilitate the design of an inexpensive, label-free, and easy-to-use gene sensor.

Macroalgal biomass subcritical hydrolysates for the production of polyhydroxyalkanoate (PHA) by Haloferax mediterranei

Non-conventional carbon sources, such as macroalgae, are sustainable alternatives for large-scale production of biopolymers. The present study examined macroalgae-derived carbohydrates, as carbon sources for the production of polyhydroxyalkanoates (PHAs) by Haloferax mediterranei. Simulants of the hydrolysates of seven different macroalgal biomasses were prepared and the PHA production was studied. A maximum biomass concentration with maximum PHA content was detected in medium prepared from green macroalgae. The highest cell dry weight and PHA concentrations were 3.8 ± 0.2 g·L^-1 and 2.2 ± 0.12 g·L^-1 respectively when Haloferax mediterranei was grown in 25% (w/w) of Ulva sp. hydrolysate, at 42 °C temperature and initial pH of 7.2. Poly(3-hydroxy-butyrate-co-3-hydroxyvalerate was the major PHA constituent. The present study demonstrated that Ulva sp. is a promising feedstock for PHA production.