Peptidoglycan recognition protein MsPGRP in largemouth bass (Micropterus salmoides) mediates immune functions with broad nonself recognition ability

Peptidoglycan (PGN) recognition proteins (PGRPs) are important immune factors in innate immunity that function in recognising pathogens and activating the immune system. These ubiquitous proteins are conserved in invertebrates and vertebrates. In this study, a PGRP gene (MsPGRP) from largemouth bass (Micropterus salmoides) was identified and characterised, and its transcription distribution was explored. Recombinant protein (rMsPGRP) exhibited dose-dependent binding to PGN and glucan (GLU), but weak binding to lipopolysaccharide (LPS). MsPGRP exhibited agglutinating activity against several Gram-negative bacteria, Gram-positive bacteria and fungi, and it promoted phagocytosis activity of leukocytes against Micrococcus luteus and Aeromonas hydrophila. The protein also possessed amidase activity in the presence of Zn²⁺, degraded PGN, and disrupted the M. luteus cell wall. The results suggest that MsPGRP plays an important role in pathogen recognition, and acts as a opsonin during immune system responses and elimination of invading pathogens.

Reductive soil disinfestation incorporated with organic residue combination significantly improves soil microbial activity and functional diversity than sole residue incorporation

Reductive soil disinfestation (RSD) is an effective agricultural practice to eliminate soil-borne pathogens that heavily relies on the organic substrate used. However, the influences of combined application of organic residues on disinfestation efficiency, soil microbiomes, and their associated functional characteristics are still not well-characterized. In this work, four treatments, i.e., untreated soil (CK), RSD with 15 t ha^-1 sugarcane bagasse (SB), bean dregs (BD), and their combinations (1:1, SB+BD), were conducted to investigate their influence on disinfestation efficiency, microbial functional diversity, community diversity, and composition using Biolog analysis, real-time PCR, and high-throughput sequencing. The SB+BD treatment had synergetic effects on soil microbial activity, metabolic activity, and functional diversity with similar efficacy in pathogen elimination and soil salinization alleviation, as compared to the SB and BD treatments. Moreover, the SB+BD treatment distinctly altered the structure and composition of bacterial and fungal communities, especially enriched the core microbiomes associated with soil general functions such as organic decomposition and nitrate removal. The SB+BD treatment also strengthened the soil specific functions including disease suppression through the regulation of unique microbiomes. In addition, the microbial richness, diversity, and evenness were significantly higher in the SB+BD-treated soil as compared to the SB- and BD-treated soils. Taken together, RSD incorporated with organic residue combination not only efficiently restore the degraded soils, but also considerably improve soil functions, which may benefit to the health for the future plant generations. KEY POINTS: • Organic residue combination effectively declines pathogen density. • Organic residue combination improves soil microbial activity and functional diversity. • The enriched core microbiome is responsible for soil general functions. • The induced unique microbiome is important for soil specific functions.

Influence of initial pH on bioleaching of river sediments to achieve deep dehydration

Acidification is one of the important methods of bioleaching and a rate-limiting steps in the reaction, with initial sediment pH having an important influence on bioleaching efficiency. Therefore, in this study, bioleaching treatments were assessed on river sediments with initial pH ranging from 3.0 to 11.0. Shake-flask tests were performed, using inoculated microorganisms and fresh river sediments in 500 mL Erlenmeyer bottles at a ratio of 1:9, with the addition of 5 g/L FeS₂ and 2 g/L S⁰ as energy sources. Erlenmeyer flasks were shaken for 72 h at 180 rpm and 28 °C, in a homeothermic oscillating water-bath. Results show that the bioleached sediment CST decreased from 39.10 s to between 10.3 s and 13.0 s. Sediment dewaterability reached a maximum level when the initial pH was 5 and the bioleaching duration was 36 h, with CST decreasing from 39.10 s to 10.30 s, a decrease in the CST rate by 82.25%, and moisture content was reduced to 57.5%. Illumina high-throughput sequencing results showed that the relative abundance of dominant microorganisms under different initial pH conditions had no significant difference at the phylum level. However, significant differences were apparent at the genus level. When the initial pH value increased from 3 to 5 in sediments, the relative abundances of the autotrophic bacteria Alicyclobacillus and Ferritrophicum and the heterotrophic bacteria Acidocella, which oxidize S⁰ and Fe²⁺, increase and dominate the microbial community, reaching abundances of 8.88%, 5.11%, and 4.87%, respectively. The heterotrophic bacteria Acidocella can biodegrade CLs products and eliminate their inhibitory effect on autotrophic bacteria Alicyclobacillus and Ferritrophicum with this synergistic effect improving the sediment dewatering performance. When the initial pH increased further to 9, the relative abundances of dominant bacteria decreased to varying degrees. In addition, variation in the initial pH conditions had no effect on the elimination efficiencies of pathogenic microorganism which were constantly > 98%. Graphical abstract .

Management of sewage sludge by composting using fermented water hyacinth

The goal of the present research work was to assess the management of sewage sludge (SS) by composting using fermented water hyacinth (WHferm) as an amendment. The water hyacinth was fermented, and a higher production of volatile fatty acids (VFAs) (782.67 mg L(-1)) and soluble organic carbon (CSOL) (4788.34 mg L(-1)) was obtained using a particle size of 7 mm compared to 50 mm. For composting, four treatments (10 kg fresh weight each) were evaluated: treatment A (100 % SS + 0 % WHferm), treatment B (75 % SS + 25 % WHferm), treatment C (50 % SS + 50 % WHferm), and treatment D (25 % SS + 75 % WHferm). The WHferm added to SS, especially in treatments C (50 %) and D (75 %), increased the initial contents of organic matter (OM), organic carbon (CORG), CSOL, the C/N ratio, and the germination index (GI). The heavy metal content (HMC) (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) at the beginning was below the maximum allowed by USEPA regulations. All of the samples were free of Salmonella sp. from the beginning. The reduction of the CORG, CSOL, total Kjeldahl nitrogen (TKN), and C/N ratio indicated the degradation of the OM by day 198. The treatments with WHferm (B, C, and D) yielded higher values of electrical conductivity, cation exchange capacity, and GI than SS at day 198. No significant differences were observed in GI among the treatments with WHferm. The fecal coliforms were eliminated (<3 MPN g(-1)) and the helminths were reduced to ≤5 eggs/2 g during the process. The competition for nutrients and the presence of suppressive fungi of the genera Penicillium, Rhizopus, Paecilomyces (penicillin producers), and Fusariella isolated from the compost may have promoted the elimination of pathogens since no thermophile temperatures were obtained. WHferm as an amendment in the composting of SS improved the characteristics of the final product, especially when it was used in proportions of 25 and 50 %. An excellent product was obtained in terms of HMC, and the product was B class in terms of pathogens.