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Plastics are widely used for diverse applications due to their versatility. However, their negative impact on ecosystems is undeniable due to their long-term degradation. Thus, there is a rising need for developing eco-friendlier alternatives to substitute fossil-based plastics, like biopolymers. PHA are synthesized intracellularly by microorganisms under stressful conditions of growth and have similar characteristics to conventional polymers, like their melting point, transition temperatures, crystallinity, and flexibility. Although it is feasible to use biopolymers for diverse industrial applications, their elevated production cost due to the supplies needed for microbiological procedures and the low productivity yields obtained have been the main limiting factors for their commercial success. The present study assessed the ability of Bacillus megaterium strain MNSH1-9K-1 to produce biopolymers using low-cost media from different kinds of fruit-peel residues. The results show that MNSH1-9K-1 can produce up to 58 g/L of PHB when grown in a medium prepared from orange-peel residues. The data obtained provide information to enhance the scalability of these kinds of biotechnological processes.

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The presence of colonial and solitary ciliated peritrichous protozoa was determined in a Sequencing Batch Reactor system filled with tezontle, a volcanic rock, economic, and abundant material that can be found in some parts of the world, like Mexico. The presence of these protozoa was related to the removal efficiencies of organic matter. Also, two novel staining techniques are proposed for staining both colonial and solitary peritrichous protozoa. The results show that tezontle promotes the growth of solitary and colonial ciliated peritrichous protozoa, which, once identified, could be used as indicators of the efficiency of the wastewater treatment process. Additionally, the staining techniques established in the current study allowed the precise observation of protozoan nuclei. They can represent a useful complementary methodology for identifying protozoan species present in water treatment processes, along with the already existing identification techniques. The number and variety of protozoa found in the system may be considered potential bioindicators of water quality during biological treatments.

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Hydroxyapatite (HAp) nanoparticles with a homogeneous rod morphology were successfully synthesized using the hydrothermal method. The powders were characterized using Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The antibacterial and dermal irritation analyses of the samples were performed and discussed. The use of cationic and anionic surfactants, namely, cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), respectively, at a low concentration (2.5 mol%) modified the length/diameter (L/D) ratio of the HAp rods. Structural characterizations of hydroxyapatite synthesized without surfactant (HA), with 2.5 and 5 mol% of SDS (SDS- and SDS+, respectively), and with 2.5 and 5 mol% of CTAB (CTAB- and CTAB+, respectively) revealed well-crystallized samples in the hexagonal phase. The CTAB- sample presented antibacterial activity against Pseudomonas aeruginosa, Escherichia coli, Streptococcus anginosus, Staphylococcus aureus, Micrococcus luteus, and Klebsiella pneumoniae, suggesting that antimicrobial susceptibility was promoted by the bacterial nature and the use of the surfactant. Dermal irritation showed no clinical signs of disease in rabbits during the study, where there was neither erythema nor necrosis at the inoculation sites.

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In the bacterial processes involved in the mitigation of nitrogen pollution, an adequately high carbon-to-nitrogen (C : N) ratio is key to sustain denitrification. We evaluated three natural materials (woodchips, barley grains, and peanut shells) as carbon sources for low C : N wastewater. The amount of organic matter released from these materials to aqueous media was evaluated, as well as their pollution swapping potential by measuring the release of total Kjeldahl nitrogen, N-NH4 (+), NO2 (-), and NO3 (-), and total phosphorous. Barley grains yielded the highest amount of organic matter, which also showed to be the most easily biodegradable. Woodchips and peanut shells released carbon rather steadily and so they would not require frequent replenishment from biological reactors. These materials produced eluates with lower concentrations of nutrients than the leachates from barley grains. However, as woodchips yielded lower amounts of suspended solids, they constitute an adequate exogenous source for the biological treatment of carbon-deficient effluents.

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