Revealing the functional potential of microbial community of activated sludge for treating tuna processing wastewater through metagenomic analysis

Abstract

Reports regarding the composition and functions of microorganisms in activated sludge from wastewater treatment plants for treating tuna processing wastewater remains scarce, with prevailing studies focusing on municipal and industrial wastewater. This study delves into the efficiency and biological dynamics of activated sludge from tuna processing wastewater, particularly under conditions of high lipid content, for pollutant removal. Through metagenomic analysis, we dissected the structure of microbial community, and its relevant biological functions as well as pathways of nitrogen and lipid metabolism in activated sludge. The findings revealed the presence of 19 phyla, 1,880 genera, and 7,974 species, with Proteobacteria emerging as the predominant phylum. The study assessed the relative abundance of the core microorganisms involved in nitrogen removal, including Thauera sp. MZ1T and Alicycliphilus denitrificans K601, among others. Moreover, the results also suggested that a diverse array of fatty acid-degrading microbes, such as Thauera aminoaromatica and Cupriavidus necator H16, could thrive under lipid-rich conditions. This research can provide some referable information for insights into optimizing the operations of wastewater treatment and identify some potential microbial agents for nitrogen and fatty acid degradation.

Keywords: activated sludge; metagenomics; nitrogen removal; tuna processing; wastewater.

Figure 1

Microbial community composition of four kingdoms at the phylum, genus, and species levels. (A) Bacteria kingdom; (B) Eukaryota kingdom; (C) Archaea kingdom; (D) Viruses kingdom.

Figure 2

Potential function of genes detected in the activated sludge, annotated by KEGG database. The first level is displayed in black font, and the second level is displayed in color font.

Figure 3

KEGG pathway analysis of the top 20 outcomes of related microorganisms. The color gradient is depicted on the left and reflects the relative abundance of metabolic pathways. The bar chart on the right represents the abundance of the top three bacterial species associated with each metabolic pathway.

Figure 4

Nitrogen metabolism pathway of activated sludge. Functional genes involved in different processes are represented in different colors, with the abundance of the corresponding gene in parentheses. The symbol “**” represented the omitted genes. Ammonification: gudB/GLUD1_2/E1.4.1.4/GDH2, glutamate dehydrogenase. Nitrification: pmoA-amoA/pmoB-amoB/pmoC-amoC, methane/ammonia monooxygenase; hao, hydroxylamine dehydrogenase; narG/narH nitrate reductase/nitrite oxidoreductase. Denitrification: narG/narH/narl/napA/napB, nitrate reductase; nirK/nirS, nitrite reductase; norB/norC, nitric oxide reductase; nosZ, nitrous-oxide reductase. Assimilatory nitrate reduction: narB, ferredoxin-nitrate reductase; nasC, assimilatory nitrate reductase; nirA, ferredoxin-nitrite reductase. Dssimilatory nitrate reduction: narG/narH/narl/napA/napB, nitrate reductase; nirB/nirD/nrfA/nrfH, nitrite reductase. Nitrogen fixation: nifD/nifK/nifH, nitrogenase.

Figure 5

The abundance of each pathway in the lipid metabolism, annotated by KEGG ORTHOLOGY database.

Figure 6

Schematic diagram of fatty acid degradation pathways and the relative abundance of enzymes involved in each step. (A) The degradation process of saturated fatty acids under the action of key enzymes is mainly described, and other fatty acid degradation methods are briefly mentioned in the bottom half of the figure; (B) Heat map of relative abundance of functional genes and their encoded enzymes in fatty acid degradation.