[Effect of Tween 20 on enhancing extracellular polysaccharide synthesis by Pantoea alhagi NX-11].

Pantoea alhagi NX-11 exopolysaccharide (PAPS) is a novel microbial biostimulant that enhances crop resistance to salt and drought stress. It is biodegradable and holds promising applications in improving agricultural yield and efficiency. However, the fermentation process of PAPS exhibits a high viscosity due to low oxygen transfer efficiency, which hinders yield improvement and downstream processing. This study aimed to investigate the effects of seven oxygen carriers (Span 80, Span 20, Tween 80, Tween 20, glycerin, olive oil, and soybean oil) on fermentation yield. The results showed that the addition of 0.5% (V/V) Tween 20 significantly enhanced the production of PAPS. Moreover, the introduction of 0.5% (V/V) Tween 20 in a 7.5 L fermenter resulted in a PAPS titer of (16.85±0.50) g/L, which was 17.70% higher than that of the control group. Furthermore, the rheological characterization and the microstructure analysis of the polysaccharide products revealed that the characteristic structure of polysaccharides remained unchanged in the oxygen carrier treated group, but their viscosity increased. These findings may facilitate enhancing the biosynthesis efficiency of other polymer products.

Production and Characterization of New Biosurfactants/Bioemulsifiers from Pantoea alhagi and Their Antioxidant, Antimicrobial and Anti-Biofilm Potentiality Evaluations.

The present work aimed to develop rapid approach monitoring using a simple selective method based on a positive hemolysis test, oil spreading activity and emulsification index determinations. It is the first to describe production of biosurfactants (BS) by the endophytic Pantoea alhagi species. Results indicated that the new BS evidenced an E24 emulsification index of 82%. Fourier-transform infrared (FTIR) results mentioned that the described BS belong to the glycolipid family. Fatty acid profiles showed the predominance of methyl 2-hyroxydodecanoate in the cell membrane (67.00%) and methyl 14-methylhexadecanoate (12.05%). The major fatty acid in the BS was oleic acid (76.26%), followed by methyl 12-methyltetradecanoate (10.93%). Markedly, the BS produced by the Pantoea alhagi species exhibited antimicrobial and anti-biofilm activities against tested human pathogens. With superior antibacterial activity against Escherchia coli and Staphylococcus aureus, a high antifungal effect was given against Fusarium sp. with a diameter of zone of inhibition of 29.5 mm, 36 mm and 31 mm, obtained by BS dissolved in methanol extract. The DPPH assay indicated that the BS (2 mg/mL) showed a higher antioxidant activity (78.07 inhibition percentage). The new BS exhibited specific characteristics, encouraging their use in various industrial applications.

High-Efficiency Extraction of Pantoea alhagi Exopolysaccharides Driven by pH-Related Changes in the Envelope Structure.

Increasing numbers of exopolysaccharides and their properties have been explored. However, the difficulty of extracting high-viscosity exopolysaccharides has hindered their further industrialization. In this research, we explored a strategy based on encapsulated structure control under different pH to efficiently extract Pantoea alhagi exopolysaccharides (PAPS). Results showed that at pH levels of 6, 12, and 13, the extraction efficiency of PAPS was elevated, and the yield did not decrease. The rheological properties of the pH-12-treated PAPS were better than those of PAPS treated at pH 7, while the pH-6-treated PAPS decreased. The effects of pH-12-treated PAPS on soil macroaggregates and soil's water evaporation rate were similar to those of PAPS treated at pH 7. In addition, we observed that treatment at pH 12 produced a significantly reduced encapsulated structure compared with treatment at pH 7. The proportion of unsaturated fatty acids after treatment at pH 12 was higher than after treatment at pH 7, which may result in reduced encapsulated structure in pH-12 conditions. These results enrich the understanding of the effect that alters pH conditions on the encapsulated structure to improve the extraction efficiency of exopolysaccharides and provide a theoretical basis for the extraction of exopolysaccharides with extreme viscosity.

Structure characterization, antioxidant and emulsifying capacities of exopolysaccharide derived from Pantoea alhagi NX-11.

Pantoea alhagi exopolysaccharides (PAPS) have been shown to enhance crop resistance to abiotic stress. However, physicochemical properties and structure of PAPS have not yet been analyzed. In this study, two PAPSs, named PAPS1 and PAPS2, were isolated and purified from the P. alhagi NX-11. The results showed PAPS1 and PAPS2 were composed of glucose, galactose, glucuronic acid, glucosamine and mannose with average molecular weight of 1.326 × 106 Da and 1.959 × 106 Da, respectively. Moreover, the structure of PAPS1 and PAPS2 was investigated by FT-IR and NMR analysis. PAPS1 was identified to have the backbone structure of →4)-ß-D-GlcpA-(1→2)-α-D-Galp-(1→3)-ß-D-Galp-(1→3)-ß-D-GlcpN- (1→3)-α-D-Galp-(1→3)-ß-D-Galp-(1→. PAPS2 had the backbone structure of →4)-ß-D-GlcpA-(1→2)-α-D-Galp-(1→3)-ß-D-Glcp-(1→3)-ß-D-GlcpN-(1→3)-α-D-Galp-(1→3)-α-D-GlcpN-(1→. In addition, PAPS1 and PAPS2 had moderate antioxidant and emulsifying capacities. Overall, the structure analysis of PAPS may point out the direction for the subsequent study of PAPS-mediated microbial and plant interactions, and further exploration of the application of PAPS.

Effects of exopolysaccharide derived from Pantoea alhagi NX-11 on drought resistance of rice and its efficient fermentation preparation.

Exopolysaccharide (EPS) plays an important role in plant growth-promoting bacteria (PGPB)-mediated enhancement of plant abiotic stress resistance. In this study, it is found that EPS from Pantoea alhagi NX-11 foliar sprayed at 20, 50, and 100 ppm could significantly enhance drought resistance of rice seedlings. The fresh weight and relative water content of EPS sprayed were increased. In addition, malondialdehyde content reduced while total chlorophyll, proline and soluble sugar content, prominent enhanced. Meanwhile, the antioxidant enzymes, CAT, POD and SOD, were also significantly increased. The drought resistance of rice was most pronounced at the 50 ppm EPS dose. For the sake of commercializing the gram-negative EPS-producing PGPB which were difficult to preserve, it is vital to improve the EPS yield. First, the carbon source, nitrogen source and inorganic salt were optimized. Subsequently, the effect of three oxygen vectors, which could increase the efficiency of oxygen mass transfer, on EPS yield was studied by response surface methodology. The maximum EPS yield (19.27 g/L) was obtained, which is 51.7% higher than the initial yield of 12.7 g/L. Overall, it may provide a new way for the industrialization of PGPB to increase the yield of EPS.

The Endophyte Pantoea alhagi NX-11 Alleviates Salt Stress Damage to Rice Seedlings by Secreting Exopolysaccharides.

Endophytes have the potential to enhance the ability of plants to resist salt stress, improving crop development and yield. Therefore, in this study, we isolated an endophyte that produced large amounts of exopolysaccharides (EPSs) from the roots of sea rice and examined its effects on the physiological responses of rice (Oryza sativa L. ssp. japonica "Nipponbare") seedlings to salt stress using hydroponic experiments. The endophyte was named Pantoea alhagi NX-11 based on its morphological characteristics and 16S ribosomal DNA (rDNA) sequence alignment. Rice seedlings that had been inoculated with P. alhagi NX-11 exhibited a 30.3% increase in fresh weight, a 28.6% increase in root length, a 51.6% increase in shoot length, and a 26.3% increase in chlorophyll content compared with control seedlings under normal conditions. In addition, inoculated rice seedlings had a 37.5% lower malondialdehyde content, a 133% higher K+/Na+ ratio, and a 52.8% higher proline content after 7 days under salt stress, as well as up-regulated expression of proline synthase, down-regulated expression of proline dehydrogenase, and enhanced antioxidant enzyme activities. Interestingly, rice seedlings that were inoculated with an EPS-deficient strain named NX-11eps- that was obtained by atmospheric and room temperature plasma (ARTP) mutagenesis were damaged by salt stress and had similar physiological and biochemical indicators to the control group. Therefore, we speculate that the ability of P. alhagi NX-11 to enhance the salt tolerance of rice seedlings is related to the EPSs it produces.