As the search for new antibiotics continues, the resistance to known antimicrobial compounds continues to increase. Many researchers around the world, in response to antibiotics resistance, have continued to search for new antimicrobial compounds in different ecological niches such as the marine environment. Marine habitats are one of the known and promising sources for bioactive compounds with antimicrobial potentials against currently drug-resistant strains of pathogenic microorganisms. For more than a decade, numerous antimicrobial compounds have been discovered from marine environments, with many more antimicrobials still being discovered every year. So far, only very few compounds are in preclinical and clinical trials. Research in marine natural products has resulted in the isolation and identification of numerous diverse and novel chemical compounds with potency against even drug-resistant pathogens. Some of these compounds, which mainly came from marine bacteria and fungi, have been classified into alkaloids, lactones, phenols, quinones, tannins, terpenes, glycosides, halogenated, polyketides, xanthones, macrocycles, peptides, and fatty acids. All these are geared towards discovering and isolating unique compounds with therapeutic potential, especially against multidrug-resistant pathogenic microorganisms. In this review, we tried to summarize published articles from 2015 to 2019 on antimicrobial compounds isolated from marine sources, including some of their chemical structures and tests performed against drug-resistant pathogens.

In order to discover a broad-specificity and high stability chitinase, a marine fungus, Aspergillus fumigatus df347, was identified in the sediments of mangrove wetlands in Qinzhou Bay, China. The chitinase gene (AfChi28) from A. fumigatus df347 was cloned and heterologously expressed in Escherichia coli, and the recombinant enzyme AfChi28 was purified and characterized. AfChi28 is an acido-halotolerant- and temperature-resistant bifunctional enzyme with both endo- and exo-cleavage functions. Its enzymatic products are mainly GlcNAc, (GlcNAc)₂, (GlcNAc)₃ and (GlcNAc)₄. Na⁺, Mg²⁺, K⁺, Ca²⁺ and Tris at a concentration of 50 mM had a strong stimulatory effect on AfChi28. The crude enzyme and pure enzyme exhibited the highest specific activity of 0.737 mU/mg and 52.414 mU/mg towards colloidal chitin. The DxDxE motif at the end of strand β5 and with Glu154 as the catalytic residue was verified by the AlphaFold2 prediction and sequence alignment of homologous proteins. Moreover, the results of molecular docking showed that molecular modeling of chitohexaose was shown to bind to AfChi28 in subsites −4 to +2 in the deep groove substrate-binding pocket. This study demonstrates that AfChi28 is a promising chitinase for the preparation of desirable chitin oligosaccharides, and provides a foundation for elucidating the catalytic mechanism of chitinases from marine fungi.

Secondary metabolites from marine sources have a wide range of biological activity. Marine natural products are promising candidates for lead pharmacological compounds to treat diseases that plague humans, including cancer. Cancer is a life-threatening disorder that has been difficult to overcome. It is a long-term illness that affects both young and old people. In recent years, significant attempts have been made to identify new anticancer drugs, as the existing drugs have been useless due to resistance of the malignant cells. Natural products derived from marine sources have been tested for their anticancer activity using a variety of cancer cell lines derived from humans and other sources, some of which have already been approved for clinical use, while some others are still being tested. These compounds can assault cancer cells via a variety of mechanisms, but certain cancer cells are resistant to them. As a result, the goal of this review was to look into the anticancer potential of marine natural products or their derivatives that were isolated from January 2019 to March 2020, in cancer cell lines, with a focus on the class and type of isolated compounds, source and location of isolation, cancer cell line type, and potency (IC₅₀ values) of the isolated compounds that could be a guide for drug development.

The development of thermostable and pH-robust endo-polygalacturonases (endo-PGases) is crucial for industrial applications such as food processing. This study aimed to engineer the thermostability of an acidic, thermophilic endo-PGase (PoxaEnPG28B) by rigidifying its flexible regions. We employed an integrated computational strategy combining molecular dynamics (MD) simulations at elevated temperatures with in silico analyses of unfolding free-energy changes to identify and design stabilizing mutations. This approach successfully yielded the mutant D249K, which exhibited a 5 °C higher optimal temperature (70 °C) and a 68.8% longer half-life at 55 °C, and it retained over 76.8% activity at 75 °C. Notably, D249K maintained the wild-type’s optimal pH (5.0) and broad pH stability (3.0–8.0). Although it is not the absolute top performer in every single metric, D249K achieves the best overall balance between thermostability and pH robustness among all reported thermophilic endo-PGases. MD simulations revealed that its enhanced stability sems from reduced global and local flexibility and a more compact structure. In juice extraction applications, D249K increased yields by up to 98.5%, significantly surpassing the wild-type. This study demonstrates the efficacy of MD-guided flexible region engineering for the GH28 family and presents D249K as a highly promising industrial biocatalyst.

Chitin, the second most abundant polysaccharide, is poorly soluble and underutilized, whereas its monomer N-acetylglucosamine (GlcNAc) has broad pharmaceutical applications. Efficient enzymatic conversion of chitin to GlcNAc remains challenging. Chitinibacter mangrovi FCG-7 ^T , a novel chitinolytic strain isolated from mangrove sediments, exhibited exceptional chitin degradation, achieving a hydrolysis zone ratio (H/C) of 4.75 and maintained genetic stability over ten successive passages. Sequential optimization using One-Factor-at-a-Time (OFAT), Plackett-Burman designs (PBD), and Box–Behnken designs (BBD) enhanced chitinase production by 49.43-fold, yielding a final activity of 1.211 U/mL under optimized conditions (pH 7.4, 20 °C, 12 g/L powdered chitin). Purification yielded a 100 kDa bifunctional chitinase Cm Chi, exhibiting dual chitobiosidase and N-acetylglucosaminidase (NAGase) activities. The purified enzyme showed a specific activity of 7.96 U/mg toward colloidal chitin. Cm Chi demonstrated a high affinity for colloidal chitin with a K _m value of 0.24 mg/mL and retained over 80% stability across a broad pH range 4.0–11.0. Furthermore, Cm Chi completely converted colloidal chitin to N-acetylglucosamine (GlcNAc) within 48 h and demonstrated tolerance to various reagents, including 1% methanol, acetonitrile, Tween 20, and Tween 80 (v/v). Notably, in cyclophosphamide (CTX)-induced immunosuppressed mice, GlcNAc (200 mg/kg) significantly restored body weight, thymic/splenic indices, and tissue architecture while elevating serum TNF- α , IL-2, IgG, and IgM ( p < 0.05). This study establishes Cm Chi as an efficient biocatalyst for industrial GlcNAc production and validates the immunomodulatory potential of GlcNAc, highlighting its dual applicability in biotechnology and immunotherapy.