Recently, Tribonema sp., a kind of filamentous microalgae, has been studied for biofuel production due to its accumulation of triacylglycerols. However, the polysaccharides of Tribonema sp. and their biological activities have rarely been reported. In this paper, we extracted sulfated polysaccharides from Tribonema sp. (TSP), characterized their chemical composition and structure, and determined their immunostimulation and anticancer activities on RAW264.7 macrophage cells and HepG2 cells. The results showed that TSP is a sulfated polysaccharide with a M_w of 197 kDa. TSP is a heteropolysaccharide that is composed mainly of galactose. It showed significant immune-modulatory activity by stimulating macrophage cells, such as upregulating interleukin 6 (IL-6), interleukin 10 (IL-10), and tumor necrosis factor α (TNF-α). In addition, TSP also showed significant dose-dependent anticancer activity (with an inhibition rate of up to 66.8% at 250 µg/mL) on HepG2 cells as determined by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cycle analysis indicated that the anticancer activity of TSP is mainly the result of induced cell apoptosis rather than affecting the cell cycle and mitosis of HepG2 cells. These findings suggest that TSP might have potential as an anticancer resource, but further research is needed, especially in vivo experiments, to explore the anticancer mechanism of TSP.

Three marine macroalgae, i.e., Grateloupia filicina, Ulva pertusa and Sargassum qingdaoense, were selected as the deputies of Rhodophyta, Chlorophyta and Ochrophyta for comparative analysis of the molecular structures and biological activities of sulfated polysaccharides (SP). The ratio of water-soluble polysaccharides, the monosaccharide composition and the sulfated contents of three extracted SPs were determined, and their structures were characterized by Fourier transformation infrared spectroscopy. In addition, biological activity analysis showed that all three SPs had immune-modulatory activity both in vitro and in vivo, and SPs from S. qingdaoense had the best effect. Further bioassays showed that three SPs could not only enhance the immunity level stimulated by inactivated avian influenza virus (AIV) in vivo but also significantly inhibited the activity of activated AIV (H9N2 subtype) in vitro. G. filicina SP exhibited the strongest anti-AIV activity. These results revealed the variations in structural features and bioactivities among three SPs and indicated the potential adjuvants for immune-enhancement and anti-AIV.

As an environmentally friendly and efficient method, successive two-step fermentation has been applied for extracting chitin from shrimp shells. To screen out the microorganisms for fermentation, a protease-producing strain, Exiguobacterium profundum, and a lactic acid-producing strain, Lactobacillus acidophilus, were isolated from the traditional fermented shrimp paste. Chitin was extracted by successive two-step fermentation with these two strains, and 85.9 ± 1.2% of protein and 95 ± 3% of minerals were removed. The recovery and yield of chitin were 47.82 and 16.32%, respectively. Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy (SEM) were used to characterize the chitin. The crystallinity index was 54.37%, and the degree of deacetylation was 3.67%, which was lower than that of chitin extracted by the chemical method. These results indicated that successive two-step fermentation using these two bacterial strains could be applied to extract chitin. This work provides a suitable strategy for developing an effective method to extract chitin by microbial fermentation.

Kojic acid (KA) with antibacterial activities produced by fermentation was grafted onto konjac glucomannan oligosaccharide (KGO) composed of glucose and mannose linked by β-1,4 glycosidic bonds. A novel KGO derivative, konjac glucomannan oligosaccharide kojic acid (KGOK) possessing both moisture retention and antibacterial activities was synthesized. The structure of KGOK was characterized and analyzed by thermogravimetric analysis (TG), XRD, UV–vis absorption, FTIR, and ¹H NMR. The analysis results suggest that KA was linked to the KGO molecular chain through a covalent bond, and the reaction site of KA was the methylol group. The studies demonstrate that KGOK maintained the excellent moisture absorption and retention properties of KGO and the good antibacterial activities of KA. The minimum inhibitory concentration (MIC) of KGOK is 2 mg/mL for Staphylococcus aureus, Staphylococcus epidermidis, Shewanella putrefaciens, and Salmonella enterica, while its MIC is 3 mg/mL for Escherichia coli. The multi-functionality of the KGOK synthesized from natural sources provides a theoretical foundation for their potential applications in the preservation of food, beverage, aquatic, and cosmetic products.

Searching for natural products with antitumor and immune-enhancing activities is an important aspect of cancer research. Sargassum pallidum is an edible brown alga that has been used in Chinese traditional medicine for the treatment of tumors. However, the purification and application of its active components are still insufficient. In the present study, the polysaccharides from S. pallidum (SPPs) with antitumor and immune-enhancing activities were isolated and purified, and five polysaccharide fractions (SPP-0.3, SPP-0.5, SPP-0.7, SPP-1, and SPP-2) were obtained. The ratio of total saccharides, monosaccharide composition, and sulfated contents was determined, and their structures were analyzed by Fourier transform infrared spectroscopy. Moreover, bioactivity analysis showed that all five fractions had significant antitumor activity against three types of cancer cells (A549, HepG2, and B16), and can induce cancer cell apoptosis. In addition, the results indicated that SPPs can enhance the proliferation of immune cells and improve the expression levels of serum cytokines (IL-6, IL-1β, iNOS, and TNF-α). SPP-0.7 was identified as the most active fraction and selected for further purification, and its physicochemical properties and antitumor mechanism were further analyzed. Transcriptome sequencing result showed that SPP-0.7 can significantly induce the cell apoptosis, cytokine secretion, and cellular stress response process, and inhibit the normal physiological processes of cancer cells. Overall, SPPs and SPP-0.7 may be suitable for use as potential candidate agents for cancer therapy.

Excessive use of nitrogen fertilizer in intensively managed agriculture has resulted in abundant accumulation of nitrate in soil, which limits agriculture sustainability. How to reduce nitrate content is the key to alleviate secondary soil salinization. However, the microorganisms used in soil remediation cause some problems such as weak efficiency and short survival time. In this study, seaweed polysaccharides were used as stimulant to promote the rapid growth and safer nitrate removal of denitrifying bacteria. Firstly, the growth rate and NO₃⁻-N removal capacity of three kinds of denitrifying bacteria, Bacillus subtilis (BS), Pseudomonas stutzeri (PS) and Pseudomonas putida (PP), were compared. The results showed that Bacillus subtilis (BS) had a faster growth rate and stronger nitrate removal ability. We then studied the effects of Enteromorpha linza polysaccharides (EP), carrageenan (CA), and sodium alginate (AL) on growth and denitrification performance of Bacillus subtilis (BS). The results showed that seaweed polysaccharides obviously promoted the growth of Bacillus subtilis (BS), and accelerated the reduction of NO₃⁻-N. More importantly, the increased NH₄⁺-N content could avoid excessive loss of nitrogen, and less NO₂⁻-N accumulation could avoid toxic effects on plants. This new strategy of using denitrifying bacteria for safely remediating secondary soil salinization has a great significance.