Salinity is the major driver of the global eukaryotic community structure in fish-canning wastewater treatment plants

Metagenomic insights into the response of microbial metabolic function and extracellular polymeric substances from microalgae-bacteria consortia to fluoroquinolone antibiotics

Microalgae-bacteria consortia (MBC) are considered a promising bioremediation technology for removing pollutants from swine wastewater. However, the overuse of antibiotics poses challenges to the effective functioning of MBC. In this study, the removal efficiency of nutrients in wastewater by MBC under different antibiotic concentrations (0, 1, 5, 10 and 50 mg/L) was evaluated. The changes of functional microbial abundance were elucidated and the response mechanism of MBC against antibiotics was investigated. Antibiotics inhibited the accumulation of MBC biomass and reduced the removal efficiency of ammonia nitrogen and total phosphorus in wastewater by 8.39 % and 8.74 % respectively. In addition, antibiotics affected the relative abundance of microorganisms (Raineyella, from 30.72 % to 15.96 %) and functional genes (glnA, gudB, NirK, NirBD, NarB, NapAB, NorBC and NosZEPS) involved in N metabolism. MBC could defend against the adverse effects of antibiotics by regulating the content of proteins in the extracellular polymeric substances.

Salinity levels influence treatment performance and the activity of electroactive microorganisms in a microbial fuel cell system for wastewater treatment

There is growing interest in developing effective treatment technologies to mitigate the environmental impact of saline wastewater while also potentially recovering valuable resources from it. However, it remains largely unknown how different salinity levels impact treatment performance, energy generation, and the diversity and composition of electroactive microorganisms in MFCs treating real effluents such as urban wastewater. This study explores the impact of three salinity levels (3.5, 7, and 15 g/L NaCl) on current production, organic removal rates, and bacterial community dynamics in a continuous-flow microbial fuel cell (MFC) fed with urban wastewater. Using metagenomics and metatranscriptomics, we explored variations in the abundance and expression of extracellular electron transfer (EET) genes and those involved in other general metabolisms. We found that low salinity (3.5 g/L NaCl) enhanced both current production and organic removal efficiency compared to higher salinity levels. This improvement was linked to an increased abundance and activity of electroactive microorganisms, particularly taxa within the Ignavibacteria class, which possess genes coding for outer membrane cytochromes and porin cytochromes. Additionally, salinity influenced general metabolic genes and microbial community composition, with higher salinity levels limiting bacterial growth and diversity. This research provides valuable insights into the interplay between salinity stress and microbial adaptation, contributing to the optimization of MFC technologies for enhanced environmental and bioengineering applications.

Inoculum selection and hydraulic retention time impacts in a microbial fuel cell treating saline wastewater

Microbial fuel cell (MFC) technology has received increased interest as a suitable approach for treating wastewater while producing electricity. However, there remains a lack of studies investigating the impact of inoculum type and hydraulic retention time (HRT) on the efficiency of MFCs in treating industrial saline wastewater. The effect of three different inocula (activated sludge from a fish-canning industry and two domestic wastewater treatment plants, WWTPs) on electrochemical and physicochemical parameters and the anodic microbiome of a two-chambered continuous-flow MFC was studied. For each inoculum, three different HRTs were tested (1 day, 3 days, and 6 days). The inoculum from the fish canning industry significantly increased voltage production (with a maximum value of 802 mV), power density (with a maximum value of 78 mW m-2), coulombic efficiency (with a maximum value of 19.3%), and organic removal rate (ORR) compared to the inocula from domestic WWTPs. This effect was linked to greater absolute and relative abundances of electroactive microorganisms (e.g., Geobacter, Desulfovibrio, and Rhodobacter) and predicted electron transfer genes in the anode microbiome likely due to better adaption to salinity conditions. The ORR and current production were also enhanced at shorter HRTs (1 day vs. 3 and 6 days) across all inocula. This effect was related to a greater abundance and diversity of bacterial communities at HRT of 1 day compared to longer HRTs. Our findings have important bioengineering implications and can help improve the performance of MFCs treating saline effluents such as those from the seafood industry. KEY POINTS: • Inoculum type and HRT impact organic matter removal and current production. • Changes in bioenergy generation were linked to the electroactive anodic microbiome. • Shorter HRT favored increases in the performance of the MFC.

Deciphering the Role of WWTPs in Cold Environments as Hotspots for the Dissemination of Antibiotic Resistance Genes

Cold environments are the most widespread extreme habitats in the world. However, the role of wastewater treatment plants (WWTPs) in the cryosphere as hotspots in antibiotic resistance dissemination has not been well established. Hence, a snapshot of the resistomes of WWTPs in cold environments, below 5 °C, was provided to elucidate their role in disseminating antibiotic resistance genes (ARGs) to the receiving waterbodies. The resistomes of two natural environments from the cold biosphere were also determined. Quantitative PCR analysis of the aadA, aadB, ampC, blaSHV, blaTEM, dfrA1, ermB, fosA, mecA, qnrS, and tetA(A) genes indicated strong prevalences of these genetic determinants in the selected environments, except for the mecA gene, which was not found in any of the samples. Notably, high abundances of the aadA, ermB, and tetA(A) genes were found in the influents and activated sludge, highlighting that WWTPs of the cryosphere are critical hotspots for disseminating ARGs, potentially worsening the resistance of bacteria to some of the most commonly prescribed antibiotics. Besides, the samples from non-disturbed cold environments had large quantities of ARGs, although their ARG profiles were highly dissimilar. Hence, the high prevalences of ARGs lend support to the fact that antibiotic resistance is a common issue worldwide, including environmentally fragile cold ecosystems.

Structure of fungal communities in sequencing batch reactors operated at different salinities for the selection of triacylglyceride-producers from a fish-canning lipid-rich waste stream

Oleaginous fungi natively accumulate large amounts of triacylglycerides (TAG), widely used as precursors for sustainable biodiesel production. However, little attention has been paid to the diversity and roles of fungal mixed microbial cultures (MMCs) in sequencing batch reactors (SBR). In this study, a lipid-rich stream produced in the fish-canning industry was used as a substrate in two laboratory-scale SBRs operated under the feast/famine (F/F) regime to enrich microorganisms with high TAG-storage ability, under two different concentrations of NaCl (SBR-N: 0.5g/L; SBR-S: 10g/L). The size of the fungal community in the enriched activated sludge (EAS) was analyzed using 18S rRNA-based qPCR, and the fungal community structure was determined by Illumina sequencing. The different selective pressures (feeding strategy and control of pH) implemented in the enrichment SBRs throughout operation increased the abundance of total fungi. In general, there was an enrichment of genera previously identified as TAG-accumulating fungi (Apiotrichum, Candida, Cutaneotrichosporon, Geotrichum, Haglerozyma, Metarhizium, Mortierella, Saccharomycopsis, and Yarrowia) in both SBRs. However, the observed increase of their relative abundances throughout operation was not significantly linked to a higher TAG accumulation.

Effects of sulphur amino acids on the size and structure of microbial communities of aerobic granular sludge bioreactors

Granular activated sludge has been described as a promising tool in treating wastewater. However, the effect of high concentrations of sulphur amino acids, cysteine and methionine, in the evolution, development and stability of AGS-SBRs (aerobic granular sludge in sequential batch reactors) and their microbial communities is not well-established. Therefore, this study aimed to evaluate microbial communities' size, structure and dynamics in two AGS-SBRs fed with two different concentrations of amino acids (50 and 100 mg L⁻¹ of both amino acids). In addition, the impact of the higher level of amino acids was also determined under an acclimatization or shock strategy. While N removal efficiency decreased with amino acids, the removal of the organic matter was generally satisfactory. Moreover, the abrupt presence of both amino acids reduced even further the removal performance of N, whereas under progressive adaptation, the removal yield was higher. Besides, excellent removal rates of cysteine and methionine elimination were found, in all stages below 80% of the influent values. Generally considered, the addition of amino acids weakly impacts the microbial communities' total abundances. On the contrary, the presence of amino acids sharply modulated the dominant bacterial structures. Furthermore, the highest amino acid concentration under the shock strategy resulted in a severe change in the structure of the microbial community. Acidovorax, Flavobacterium, Methylophilus, Stenotrophomonas and Thauera stood out as the prominent bacteria to cope with the high presence of cysteine and methionine. Hence, the AGS-SBR technology is valuable for treating influents enriched in sulphur Aa inclusively when a shock strategy was used.

Dynamics of PHA-Accumulating Bacterial Communities Fed with Lipid-Rich Liquid Effluents from Fish-Canning Industries

The biosynthesis of polyhydroxyalkanoates (PHAs) from industrial wastes by mixed microbial cultures (MMCs) enriched in PHA-accumulating bacteria is a promising technology to replace petroleum-based plastics. However, the populations' dynamics in the PHA-accumulating MMCs are not well known. Therefore, the main objective of this study was to address the shifts in the size and structure of the bacterial communities in two lab-scale sequencing batch reactors (SBRs) fed with fish-canning effluents and operated under non-saline (SBR-N, 0.5 g NaCl/L) or saline (SBR-S, 10 g NaCl/L) conditions, by using a combination of quantitative PCR and Illumina sequencing of bacterial 16S rRNA genes. A double growth limitation (DGL) strategy, in which nitrogen availability was limited and uncoupled to carbon addition, strongly modulated the relative abundances of the PHA-accumulating bacteria, leading to an increase in the accumulation of PHAs, independently of the saline conditions (average 9.04 wt% and 11.69 wt%, maximum yields 22.03 wt% and 26.33% SBR-N and SBR-S, respectively). On the other hand, no correlations were found among the PHAs accumulation yields and the absolute abundances of total Bacteria, which decreased through time in the SBR-N and did not present statistical differences in the SBR-S. Acinetobacter, Calothrix, Dyella, Flavobacterium, Novosphingobium, Qipengyuania, and Tsukamurella were key PHA-accumulating genera in both SBRs under the DGL strategy, which was revealed as a successful tool to obtain a PHA-enriched MMC using fish-canning effluents.