Revealing the dissimilar structure of microbial communities in different WWTPs that treat fish-canning wastewater with different NaCl content

Studies that characterize the microbial communities in wastewater treatment plants (WWTPs) are numerous, yet similar studies in industrial WWTPs treating fish-canning effluents are limited. The microbial communities in samples of 4 fish-canning WWTPs that operated under different NaCl concentrations were investigated by qPCR and partial 16S rRNA gene Illumina sequencing. The absolute abundances of key microbial populations (Total Bacteria, Archaea and Fungi, ammonium oxidizing bacteria (AOB), Mycolata, Candidatus Microthrix, Ca. Accumulibacter and Ca. Competibacter) presented statistical differences among the WWTPs. The NaCl concentration negatively affected the absolute abundance of Bacteria and Fungi, filamentous, and phosphate (PAO) and glycogen (GAO) accumulating bacteria, while AOB and Ca. Microthrix populations were statistically higher in the WWTP with higher NaCl contents. On the other hand, the main bacterial operational taxonomic units (OTUs) were classified as members of Kouleothrix (Chloroflexia, Chloroflexi) and Tetrasphaera (Actinomycetia, Actinobacteria), family Beijerinckiaceae (Alphaproteobacteria, Proteobacteria), order Betaproteobacteriales (Gammaproteobacteria, Proteobacteria), Sphingobacteriales (Sphingobacteriia, Bacteroidetes) and Frankiales (Actinobacteria, Actinobacteria), class Anaerolineae (Chloroflexi), phylum Chloroflexi and Bacteria_unclassified. The structure of the bacterial community was highly dissimilar among the 4 WWTPs, as the identities of the dominant OTUs differed significantly among them. Therefore, the individual characteristics of the different WWTPs, mainly NaCl concentration, were responsible for the narrow assemblage of the bacterial communities. Different OTUs belonging to the phyla Actinobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes and Proteobacteria were revealed as salt-tolerant. Taking into account these results, NaCl content was an important driver of the abundance of microbial populations and the bacterial community structure in the analysed industrial facilities.