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Background Biohydrogen production from agro-industrial wastes through dark fermentation offers several advantages including eco-friendliness, sustainability, and the simplicity of the process. This study aimed to produce biohydrogen from fruit and vegetable peel wastes (FVPWs) by anaerobic fermentative bacteria isolated from domestic wastewater. Kinetic analysis of the produced biohydrogen by five isolates on a glucose medium was analyzed using a modified Gompertz model (MGM). Besides, the feasibility of hydrogen production by Clostridium butyricum NE95 using FVPWs as substrates was investigated. Results The bacterial isolate NE95 was selected as the highest biohydrogen producer with maximum biohydrogen production (H max ) of 1617.67 ± 3.84 mL/L, R max (MGM) of 870.77 mL/L/h and lag phase (λ) of 28.37 h. NE95 was phenotypically and genetically identified as C. butyricum and its 16 S rRNA gene sequence was deposited in the GenBank under the accession number PP581833. The genetic screening of hydrogenase gene clusters indicated the presence of Fe-Fe hydrogenase gene in C. butyricum NE95. C. butyricum NE95 showed the ability to produce biohydrogen from different FVPWs, with watermelon and melon peels being the most promising feedstocks for fermentation. It was revealed that using a mixture (1:1, w/w) of watermelon and melon peels as a substrate for C. butyricum NE95 significantly increased biohydrogen yield with H max of 991.00 ± 10.54 mL/L, R max of 236.31 mL/L/h, λ of 33.92 h and a high accuracy of R 2 (0.997). Conclusions The study highlights the effectiveness of C. butyricum NE95 on the valorization of FVPWs and generates a sustainable source of biohydrogen production.

Background Biohydrogen production from agricultural waste is a promising strategy to address climate change and energy challenges. This study aimed to optimize the process parameters for biohydrogen production from watermelon peels (WMP) by Clostridium butyricum NE133 using statistical optimization techniques. Initial screening of eight significant variables influencing hydrogen production including, initial pH, incubation temperature, WMP concentration, inoculum volume, yeast extract, tryptone, sodium acetate, and ammonium acetate concentration was conducted by a Plackett–Burman (PB) design. Results The results showed that four variables including, initial pH ( P  < 0.001), WMP concentration ( P  < 0.001), sodium acetate ( P  = 0.023), and ammonium acetate ( P  = 0.048) had statistically significant effects on hydrogen production. The model curvature ( P  = 0.040) indicated that it was significant. Box–Behnken (BB) design under response surface methodology (RSM) was employed to optimize the four selected variables to maximize hydrogen production. The optimal conditions for maximizing hydrogen production from WMP by C. butyricum were: initial pH of 8.98, WMP concentration of 44.75%, sodium acetate 4.49 gL −1 , and ammonium acetate 1.15 gL −1 at with predicted H max of 4703.23 mLL −1 . The determination coefficient R 2 of the model was 0.9902 with the lack of fit F-value was 1.86. Conclusions The confirmation experiment revealed only a 0.59% difference between the predicted and experimental hydrogen production, indicating that the optimum conditions were actual with the least error. Improvement of about 103.25% in hydrogen production from WMP by C. butyricum NE133 was achieved after the optimization process. Graphical Abstract

Approximately 6% of the world’s total land area and 20% of the irrigated land are affected by salt stress. Egypt is one such country affected by salt-stress problems. This paper focuses on the role of isolated bacteria, such as Bacillus subtilis and Pseudomonas fluorescens , in alleviating the harmful effects of salt stress. The results show that the irrigation of plants with different concentrations of saline water (0, 75, and 150 mM NaCl) leads to significantly decreased growth criteria, photosynthetic pigments (i.e., chl a, chl b, and carotenoids), and membrane stability index (MSI) values. Moreover, malondialdehyde (MDA), glutathione content, endogenous proline, the antioxidant defense system, 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase (ACS), ACC oxidase (ACO), and Na + content were significantly increased under NaCl-stress exposure. On the contrary, treatment with endophytic bacteria significantly increased the resistance of pea plants to salt stress by increasing the enzymatic antioxidant defenses (i.e., superoxide dismutase, catalase, peroxidase, and glutathione reductase), non-enzymatic antioxidant defenses (i.e., glutathione), osmolyte substances such as proline, and antioxidant enzyme gene expression. As a result, endophytic bacteria’s use was significantly higher compared to control values for indole-3-acetic acid (IAA), gibberellic acid GA 3 , MSI, and photosynthetic pigments. The use of endophytic bacteria significantly decreased Na + accumulation while, at the same time, promoting K + uptake. In conclusion, the induction of endophytic bacterium-induced salt tolerance in pea plants depends primarily on the effect of endophytic bacteria on osmoregulation, the antioxidant capacity, and ion uptake adjustment by limiting the uptake of Na + and, alternatively, increasing the accumulation of K + in plant tissue.

Antibiotic resistance is a growing problem that can be ameliorated by the discovery of novel drug candidates. Bacterial associates are often the source of pharmaceutically active natural products isolated from marine invertebrates, and thus, important targets for drug discovery. While the microbiomes of many marine organisms have been extensively studied, microbial communities from chemically-rich nudibranchs, marine invertebrates that often possess chemical defences, are relatively unknown. We applied both culture-dependent and independent approaches to better understand the biochemical potential of microbial communities associated with nudibranchs. Gram-positive microorganisms isolated from nudibranchs collected in the Red Sea were screened for antibacterial and antitumor activity. To assess their biochemical potential, the isolates were screened for the presence of natural product biosynthetic gene clusters, including polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) genes, using PCR. The microbiomes of the nudibranchs were investigated by high-throughput sequencing of 16S rRNA amplicons. In screens against five model microorganisms, 51% of extracts displayed antimicrobial activity against more than one organism, and 19% exhibited antitumor activity against Ehrlich's ascites carcinoma. Sixty-four percent of isolates contained PKS and NRPS genes, suggesting their genomes contain gene clusters for natural product biosynthesis. Thirty-five percent were positive for more than one class of biosynthetic gene. These strains were identified as belonging to the Firmicutes and Actinobacteria phyla via 16S rRNA gene sequencing. In addition, 16S rRNA community amplicon sequencing revealed all bacterial isolates were present in the uncultured host-associated microbiome, although they were a very small percentage of the total community. Taken together, these results indicate that bacteria associated with marine nudibranchs are potentially a rich source of bioactive compounds and natural product biosynthetic genes.