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Article

Insights into Wastewater Nitrogen Conversion to Protein via Photosynthetic Bacteria

by
Wei Zhao
1,
Chenghao Wu
1,
Sijia Zheng
2 and
Guangming Zhang
3,*
1
School of Heilongjiang River and Lake Management, Heilongjiang University, 36 Xuefu 3rd Street, Harbin 150080, China
2
Chongqing Dazu District Development and Reform Commission, Chongqing Dazu District People’s Government, No. 101, East Section of 1st Ring North Road, Tangxiang Street, Chongqing 400000, China
3
School of Energy & Environmental Engineering, Hebei University of Technology, Xiping Road No. 5340, Beichen District, Tianjin 300130, China
*
Author to whom correspondence should be addressed.
Water 2025, 17(6), 826; https://doi.org/10.3390/w17060826
Submission received: 26 January 2025 / Revised: 7 March 2025 / Accepted: 11 March 2025 / Published: 13 March 2025
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Abstract

:
The global shortage of protein resources has highlighted microbial processes as a promising solution for protein production. Photosynthetic bacteria (PSB) offer advantages in protein synthesis, yet the mechanisms underlying nitrogen conversion to protein remain insufficiently understood. To clarify these mechanisms, nitrogen metabolism-related genes and networks were analyzed using high-throughput sequencing. Synthetic sugar wastewater served as the initial substrate. The results showed that at a nitrogen concentration of 200 mg/L with a combined NH4-N + NO3-N supply, the nitrogen conversion rate reached 3.3, and protein production peaked at 130.35 mg/(L·d). Under these conditions, 68.4% of the utilized nitrogen originated from NH4-N, and 31.6% from NO3-N, leading to an increase in pro-N to 12.46 mg. Transcriptome analysis revealed high expression of nirK, norB, and nosZ, confirming significant denitrification, while the absence of nitrate reductase, GLDH, GDH, and GltS in Rp. palustris corresponded to a lower protein yield of 53.28 mg/(L·d). Additionally, genes related to nitrogen transport (amtB, nrtABC), ammonium assimilation (glnA, gltB, gltD), and nitrate reduction (nasA, narB) were upregulated, facilitating nitrogen utilization. These findings provide insights into optimizing nitrogen utilization for improved protein synthesis in PSB-based wastewater treatment.

1. Introduction

With the increase in population and the abundant use of feed, the worldwide demand for protein has become more prominent [1]. Single-cell protein (SCP), known as microbial protein, has high nutritional value due to its high content of protein, vitamins, essential amino acids, and lipids and can be used as a protein supplement for human food or animal feed [2]. Photosynthetic bacteria (PSB) are rich in various biological resources and have been proven to be an effective pathway that can be used for the production of SCP with a high protein content (generally more than 40%). The protein from PSB has a wide range of uses and can be used not only as feed or fertilizer, but also as food or a food additive directly.
As early as the 1970s, some scholars proposed that PSB could be used to produce protein [3,4]. In recent years, domestic and foreign researchers began to study the production of protein by PSB from wastewater. Meng et al. [5] obtained 420.9 mg/g protein from brewery wastewater treatment by PSB. Hülsen et al. [6] found that the wastewater from poultry farms, slaughterhouses, and sugar factories could be used as raw materials for protein production by PSB and could result in high protein production (>96 g/L) in a biofilm photobioreactor [7]. It has been found that PSB can treat a variety of wastewaters such as municipal wastewater, food processing wastewater, and livestock wastewater to achieve high protein production [8,9].
Nitrogen is an important component of protein, and PSB can convert nitrogen in the substrate to organic nitrogen (organic-N) in the biomass. Few studies have been conducted on the effect of nitrogen conversion on protein yield, and the existing studies on nitrogen have basically focused on ammonia nitrogen. Ammonia nitrogen is closely related to protein yield, as a high concentration of NH4+-N can improve protein production, and NH4+-N removal was positively related to the content of protein. Although recent studies have advanced experimental research and model-based parameter optimization, such as using machine learning to assess multifactorial influences on PSB protein synthesis and identifying a direct causal relationship between COD/N ratio and PSB protein content [10], the underlying mechanisms of nitrogen conversion remain unclear, particularly regarding the effects of different nitrogen sources on nitrogen transformation and protein synthesis.
Therefore, this paper discusses the effects of different nitrogen on the protein production from PSB, including different concentrations and types of nitrogen. Based on the study of nitrogen balance and nitrogen metabolism during protein recovery by PSB, the metabolic mechanisms of nitrogen conversion are revealed, and the effective concentration and type of nitrogen for protein production are determined. The findings are used to contribute to the improvement of protein yield, reveal the industrialization potential of protein, help to realize the popularization and practical application of PSB, and provide possible clean energy.

2. Materials and Methods

2.1. Materials

The initial wastewater used in the experiment was synthetic sugar wastewater as described before [11]. The PSB used in this study included a PSB mixture with the dominant strain of Rp. palustris from the company of South Ranch, Yunnan, China, and Rp. palustris from Beinachuanglian Biotechnology Co. (Suzhou, China). The cells were cultured in a thermostat shaker (120 r/min, 26–30 °C) in an improved RCVBN medium with a light intensity of 2000 lux [5]. For each group of experiments, the biomass of PSB was cultured to 2000 mg/L to treat wastewater.

2.2. The Operation

Each test was conducted in a 300 mL conical flask, which was filled with 240 mL wastewater (inoculated with 20% (v/v) of PSB). The 20% (v/v) PSB inoculation ratio was determined based on preliminary experiments assessing OD593 at different inoculation levels to ensure stable biomass growth and efficient nitrogen conversion. In order to obtain good protein yield, the experiments were carried out under light–anaerobic conditions with a cultivation temperature of 26–30 °C [12,13]. Light–anaerobic conditions were set as follows: the headspace was flushed with argon for 5 min before the bottles were sealed with a rubber septum, and a light intensity of 2000 lux was provided by an incandescent lamp. Based on the previous tests in this study, the C/N of the wastewater was determined to be 15, and the test period for each group of experiments was 3 d.
The nitrogen source concentration experimental groups were set to use NH4-N in synthetic sugar wastewater as the nitrogen source with nitrogen source concentrations of 50, 200, 500, 1000, 3000, and 5000 mg/L. For the nitrogen source type experimental groups, the type of nitrogen source, (NH4)2SO4, NaNO2, NaNO3, and urea, was changed to represent NH4-N, NO2-N, NO3-N, and organic-N, respectively, setting specific experimental groups as NH4-N, NO2-N, NO3-N, NH4-N + NO2-N, NH4-N + NO3-N, urea, and NH4-N + urea. Based on the appropriate concentration and type of nitrogen source determined from the above experiments, a group was set up to determine the balance of the nitrogen element under this condition. The organisms used in these three experiments were all PSB mixtures. The nitrogen metabolism experiments were the same as the nitrogen balance setup; the only difference was that the strain used was Rp. palustris. A sterile negative control group without PSB inoculation was included to evaluate the impact of abiotic processes on nitrogen metabolism. The negative control group without PSB inoculation followed the same conditions as the experimental group, isolating the effect of biotic processes on nitrogen conversion (no significant abiotic influence on nitrogen conversion was observed in the negative control group).

2.3. Analytical Methods

Samples were collected from bioreactors and centrifuged at 11,000 rpm for 10 min to obtain the supernatant for testing TN, NH4-N, NO2-N, and NO3-N, which were determined according to the APHA method [14]. The concentration of organic-N was obtained by using TN subtract to the NH4-N, NO2-N, and NO3-N concentrations in wastewater. The collected PSB were used to measure biomass and protein content. The biomass was measured under 660 nm with a TU 1900 spectrophotometer (Beijing Purkinje General Instrument Co., Beijing, China) [15]. Protein was detected by a determination kit (Beijing Regan Biotechnology Co., Beijing, China) according to the improved Lowry method [16]. Nitrogen in cells (bio-N) was determined with an elemental analyzer (Elemantar Vario EL cube, Elemantar, Langenselbold, Germany), and the concentration of nitrogen in protein (pro-N) was equal to the protein concentration in the biomass divided by the nitrogen-to-protein conversion factor of 6 [17,18].

2.4. Molecular Analysis

Samples for molecular analysis were taken from experimental sets of nitrogen sources treated with Rp. palustris of appropriate concentration and type. Total ribonucleic acid (RNA) was extracted using the TRIzol reagent following the manufacturer’s protocol, and RNA integrity and purity were assessed using an Agilent 2100 Bioanalyzer (Agilent Technologies, Inc., Santa Clara, CA, USA). Complementary deoxyribonucleic acid (cDNA) libraries were constructed using the New England Biolabs Next Ultra RNA Library Preparation Kit (New England Biolabs, Inc., Ipswich, MA, USA). The genomes of the samples were determined by Shanghai Majorbio Bio-pharm Technology Co., Ltd. (Shanghai, China) using the Illumina HiSeq high-throughput sequencing method, followed by bioinformatics analysis of the transcriptome data. Raw sequencing reads were quality-checked using FastQC and trimmed with Trimmomatic to remove low-quality bases and adapter sequences. Clean reads were then aligned to the reference genome using Hierarchical Indexing for Spliced Alignment of Transcripts 2 (HISAT2 (v2.2.1)), and gene expression levels were quantified with FeatureCounts. Differential gene expression analysis was conducted using Differential Expression Sequencing 2 (DESeq2 (v3.20)), with significantly differentially expressed genes identified based on an adjusted p-value threshold (false discovery rate < 0.05). Functional annotation and pathway enrichment analysis were performed using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database to classify expressed genes according to their associated pathways and functions, constructing a nitrogen metabolism pathway map.

3. Results and Discussion

3.1. The Effect of Nitrogen Source Concentration on Protein Production

Although PSB can tolerate a wide range of nitrogen sources, both too high and too low concentrations can be detrimental to the growth and protein production of PSB. Therefore, this study first addresses the optimal nitrogen source concentration for protein production by PSB.
The treatment of sugar wastewater with PSB performed well at removing NH4-N and SCP production according to Figure 1. The results showed that PSB effectively removed NH4-N from food wastewater, with a removal rate of 93.56–96.89%. When the concentration of NH4-N was 200 mg/L, it was best for protein production, with a protein content of 48.52% and productivity of 58.01 mg/(L·d). Atasoglu and Wallace [19] found the concentration of ammonia has an important effect on protein production. In this study, when the concentration exceeded 200 mg/L, the protein production decreased with the increase in ammonia nitrogen concentration, which may be due to the high concentration of ammonia nitrogen being toxic to microorganisms. For example, when the concentration was 1000 mg/L, methanogens were severely inhibited [20,21].
To ensure environmental relevance, the selection of nitrogen concentrations should align with typical wastewater compositions. Industrial and municipal wastewaters often contain varying NH4⁺-N levels, influencing microbial activity and metabolic pathways. Understanding the concentration threshold beyond which ammonia toxicity occurs is crucial for optimizing PSB-based protein production in practical applications.

3.2. The Effect of Nitrogen Source Type on Protein Production

Inorganic nitrogen (NH4-N, NO2-N, NO3-N) and organic-N sources serve as important nitrogen sources for PSB, which could have a removal effect of 99.75%, 94.9%, 98.0%, and 79.2%, respectively [22]. However, the choice of nitrogen source not only affects nitrogen removal efficiency but also influences microbial growth and protein production. As shown in Figure 2, urea was the most effective single nitrogen source for protein production, indicating its high bioavailability to PSB. However, when multiple nitrogen sources were combined, both PSB growth and protein synthesis were further enhanced. This suggests that a mixed nitrogen supply may provide a more balanced nutrient environment, promoting more efficient metabolic activity and protein biosynthesis.

3.2.1. Single Source of Nitrogen

Urea, as an effective organic nitrogen source for photoautotrophic organisms, had promising applications in microalgae cultivation [23,24]; however, it has been less studied for PSB. In general, PSB can metabolize and synthesize organisms directly using organic-N [25,26]. In this study, urea achieved a nitrogen conversion rate of 3.35 (concentration of protein converted/concentration of nitrogen source consumed), and the protein concentration obtained reached 565.4 mg/L, indicating that urea was a conducive nitrogen source for PSB protein production. This result was close to the study of Wang et al. [27], who found that organic-N sources are more conducive to the growth and production of PSB than inorganic nitrogen sources; for example, the effect of an organic-N source on biomass and hydrogen production is better than that of an inorganic nitrogen source. Therefore, urea was the most efficient choice of nitrogen source when the single nitrogen source was converted to protein production from PSB wastewater treatment.
Most of the existing studies on PSB protein production used NH4-N as the nitrogen source, and all obtained good protein yields, which were as high as 713 ± 13 mg/g [28,29]. There was also a good protein yield of 611 ± 13 mg/g and a high nitrogen conversion rate of 3.71 when NH4-N was used in this study. Most of the NH4-N in wastewater might be transformed into PSB biomass production to form protein, in which Yang [30] found that the removal rate of NH4-N and the content of SCP fitted the Boltzmann function, while some NH4-N might combine with NO2-N through the annamox effect to form pro-N in biomass.
From Figure 2, it can be seen that NO2-N and NO3-N were not conducive to PSB growth and protein production when used as nitrogen sources compared to other nitrogen sources, and both nitrogen conversion rates were lower than 1.0. Previous studies have found that PSB can use NO2-N and NO3-N with good removal effects compared to the present study, probably because the concentrations discussed in previous studies were low (<20 mg/L), while the concentration in the present study was a high concentration (200 mg/L) [28,29]. The pathway involved in nitrite is not clear from previous studies, while high concentrations of nitrite may inhibit PSB growth and protein production by increasing oxidative stress, disrupting cell membranes, and reducing photosynthesis [31,32].
Shapleigh [33] found that the metabolic pathways of NO3-N in PSB are dissimulation and assimilation, and the nitrogen produced by assimilation can be converted into biomass by nitrogen fixation. As shown in Figure 2, NO3-N was the nitrogen source most detrimental to protein production when the nitrogen source concentration was 200 mg/L. Some studies [34,35] showed that with the increase in NO3− concentration, PSII reaction center excitation pressure gradually increased, electron transmission was blocked, and nitrogen accumulated (NH4-N and organic-N content increased), causing a series of nitrogen-containing compound metabolic disorders, affecting the conversion and utilization of nitrogen. At the same time, with the strengthening of stress, the content of protein nitrogen in cells decreased, possibly due to a series of hydrolyzed enzyme activities, such as a protease increase, accelerated decomposition, and a protein nitrogen content decrease. In addition, compared with NH4-N or organic-N as a nutrient source, with the use of nitrate, more energy was needed for protein synthesis, which resulted in a lower yield of protein [36].

3.2.2. Combined Nitrogen Sources

As shown in Figure 2, the combined nitrogen sources all effectively improved the growth of PSB as well as protein production, with a nitrogen conversion rate of about 3.3 (except for the NH4-N + NO2-N group with a conversion rate of 2.15). The best inorganic combined nitrogen source was NH4-N + NO3-N with protein productivity up to 130.35 mg/(L·d). Wan et al. [36] found the use of ammonia and nitrate can be more conducive to the growth of bacteria and can have a more profound impact on bacteria communities. In addition, PSB may use NH4+ as the electron donor [37] by denitrification in combination with NO3− to form N2, which can be released or form pro-N in biomass. The combination of urea and NH4-N was also very beneficial for protein production. Previous studies showed that the use of organic–inorganic compound nitrogen sources can improve the richness, diversity, and evenness of bacteria [38], and the number of microorganisms with the use of NH4-N + organic-N combined nitrogen sources is the highest [39]. This indicated that the NH4-N + urea combined nitrogen sources may be more conducive to increasing the number and diversity of PSB, may stabilize the bacterial community structure, and may be more conducive to the growth of biomass and protein production. Thus, NH4-N + NO3-N may have increased protein production directly by promoting the protein conversion pathway, while NH4-N + urea may have increased total protein production indirectly by increasing the biomass of PSB. Although NH4-N + NO2-N also enhanced protein production, the formation of organic nitrogen in organisms from denitrification and nitrogen fixation by nitrite may have limited gene expression or key enzymes due to high nitrite nitrogen concentrations, thus limiting protein production.

3.3. Nitrogen Balance of PSB Protein Production

A nitrogen source concentration of 200 mg/L and a combination of NH4-N + NO3-N were selected for wastewater treatment to investigate nitrogen conversion following the experiment. The nitrogen content in the wastewater plus the Bio-N, inorganic nitrogen, and organic nitrogen contained in the inoculated PSB solution were measured; thus, the total initial nitrogen content was 71.07 mg. Since the conditions were light–anaerobic, the gas N was calculated using an elemental balance based on the difference between the initial total nitrogen and all other forms of nitrogen at the end. As can be seen in Figure 3, the NH4-N content decreased from a starting percentage of 47% to 5%, and the NO3-N changed from 38% to 17%. Sixty percent of the consumed nitrogen source was bio-transformed by PSB to form 25.76 mg bio-N. A large amount of pro-N was converted in the bio-N, with up to 12.46 mg in the organism; the overall percentage of pro-N increased by 14%, and the overall protein yield increased by 2.4 times. The other 7% remaining bio-N aside from pro-N (non-pro-N) may be present in the PSB biomass in other forms of elemental nitrogen. In addition, through PSB wastewater treatment, part of the consumed nitrogen source was converted to form gas N, probably mainly N2 [40,41], with the percentage of gas N reaching 27% and the percentage of organic-N increasing by 15% at the end of the experiment, while the content of NO2-N in this process was only 0.03 mg.
The assumed production of N2 could prove the existence of a denitrification pathway of the PSB mixture, which could promote the conversion of NO3-N into N2 and then into biomass through nitrogen fixation. It was consistent with the metabolic pathway of the dominant strain of the PSB, Rp. palustris, and NO3-N could also be directly reduced to NH4-N through assimilation [33,42]. Comparing the conversion rates of NH4-N and NO3-N (Figure 3), it could be found that in this combined nitrogen source system, 68.4% of the converted nitrogen source comes from NH4-N, and 31.6% from NO3-N. Microorganisms were still mainly using NH4-N conversion to achieve protein production. Therefore, future research on protein production from PSB wastewater treatment could be focused on how to promote better conversion of NH4-N to protein.

3.4. Nitrogen Metabolism

The samples were obtained for transcriptome sequencing after the experiments using Rp. palustris treated under light–anaerobic conditions with the previously selected nitrogen source concentration of 200 mg/L and nitrogen source type of NH4-N + NO3-N. Genes related to nitrogen metabolism in annotation based on sequencing results were first examined by comparing gene expression with the known complete sequence of Rp. palustris TIE-1 (GenBank: CP001096.1) from the National Center for Biotechnology Information (NCBI) (Table 1), which was the main strain used among the Rp. palustris strains for which complete genomes could be found in the NCBI. Then, the nitrogen metabolic pathway was mapped in combination with the nitrogen conversion pathways that these genes may be involved in under the conditions of this experiment in Figure 4.
As can be seen from Table 1, the expression of the nitrogen metabolism genes involved in Rp. palustris in the study under the conditions was generally consistent with that of Rp. palustris TIE-1. The large counts of transcripts of nitrite reductase (nirK), nitric oxide reductase (norB), and nitric oxide synthase (nosZ) proved the presence of significant denitrification in the nitrogen conversion pathway of the experiment. In addition, the significant counts of glnA and gltB regarding the formation of glutamate could explain the protein yield of 437.4 mg/g under the condition.
The nitrogen metabolic network of this study is shown in Figure 4. The key genes expressed in this study were different from those usually involved in the reduction of nitrate to nitrite by denitrification. The common key enzyme genes used include narBGHI of nitrate reductase (Nar), nirBDKS of nitrite reductase (NR), nrfAH of nitrite reductase (cytochrome c-552) (Nrf), and napAB of nitrate reductase (cytochrome) (Nap) [33,43,44]. However, the key enzyme gene used in this study was nasS of assimilatory nitrate reductase (Nas), which was considered as a putative nitrate transport protein, and little research has been conducted on it. Combined with the overall expression of nitrate reductase, it can be speculated that the low nitrate conversion of 3.3 when using NH4-N + NO3-N may be due to the low overall nitrate reductase activity in this combined nitrogen source system, and the specific key enzyme genes involved were not well suited for use. Glutamate, an important constituent amino acid of proteins, usually has two pathways for the assimilation of ammonia to glutamate; one is the direct conversion of ammonia to glutamate by glutamate dehydrogenase (GLDH or GDH) and glutamate synthase (GltS), and the other is through the conversion of ammonia to glutamine and then to glutamate [45,46]. In the present study, the key enzyme genes involved in that metabolic pathway of glutamate dehydrogenase were not detected, and only one metabolic pathway, glutamine, was available, thus possibly explaining the low protein yield (53.28 mg/(L·d)). A critical factor for the assimilation of nitrogen sources such as NH4-N and NO3-N was the presence of key enzymes Nas, GDH, and GltS [47]. The absence of these enzymes can significantly hinder the ability of Rp. palustris to utilize specific nitrogen sources efficiently [48,49]. For example, the lack of Nas may prevent Rp. palustris from efficiently utilizing NO3⁻ as a nitrogen source, thereby limiting protein production. Similarly, the absence of GDH or GltS could restrict the efficient conversion of ammonia to glutamate, a key amino acid in proteins, potentially leading to lower protein yields. This explains the relatively low protein yield of 53.28 mg/(L·d) observed in this study. From Figure 4, it is known that there could be other nitrogen metabolic pathways that may affect protein production, such as the conversion of nitroalkanes to nitrite and formamide, cyanate, and nitrile to ammonia, which may affect the conversion of nitrogen sources. This suggested that later, when treating wastewater containing the above compounds, moderate concentrations may not only not cause toxic effects on PSB, but also promote protein production.

4. Conclusions

PSB efficiently convert nitrogen sources into protein during wastewater treatment. At a nitrogen concentration of 200 mg/L with a combined NH4-N + NO3-N supply, the nitrogen conversion rate reached 3.3, and protein production peaked at 130.35 mg/(L·d). Under these conditions, 68.4% of the utilized nitrogen originated from NH4-N, and 31.6% from NO3-N, increasing pro-N to 12.46 mg. In contrast, Rp. palustris exhibited a lower protein yield of 53.28 mg/(L·d), likely due to the absence of Nas, GLDH, GDH, and GltS, as revealed by nitrogen metabolic network analysis. Additionally, the upregulation of genes involved in nitrogen transport (amtB, nrtABC), ammonium assimilation (glnA, gltB, gltD), and nitrate reduction (nasA, narB) enhanced nitrogen utilization. These findings provide valuable insights for optimizing nitrogen conversion to improve protein synthesis in PSB-based wastewater treatment.

Author Contributions

W.Z.: project administration; W.Z.: roles/writing—original draft; C.W. and S.Z.: writing—review and editing; G.Z.: investigation and methodology. All authors listed have made a substantial, direct, and intellectual contribution to the work. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Water Pollution Control and Treatment Science and Technology Major Project grant number 2018ZX07110003, Nature Scientific Foundation of Heilongjiang Province grant numbers LH2022C098, 2022 Open Fund of National Key Laboratory of Urban Water Resources and Water Environment grant number ES202217, and Basic Research Business Fees for Provincial Higher Education Institutions in Heilongjiang Province grant number 2023-KYYWF-1495.

Data Availability Statement

The datasets generated and/or analyzed during the current study are available from the corresponding author on request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Water 17 00826 g001
Figure 1. Protein production under different nitrogen source concentrations.
Figure 1. Protein production under different nitrogen source concentrations.
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Figure 2. Protein production under different nitrogen source types.
Figure 2. Protein production under different nitrogen source types.
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Figure 3. The nitrogen composition at the start and the end of the experiment.
Figure 3. The nitrogen composition at the start and the end of the experiment.
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Figure 4. The nitrogen metabolism network based on this experimental condition.
Figure 4. The nitrogen metabolism network based on this experimental condition.
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Table 1. The comparison of transcript counts between the samples (SPL) and Rp. palustris TIE-1 (REF) in the nitrogen metabolism.
Table 1. The comparison of transcript counts between the samples (SPL) and Rp. palustris TIE-1 (REF) in the nitrogen metabolism.
Gene NameSPLREFEnzyme NameSPLREF
nrtA1313Carbonic anhydrase393393
nrtB33Formamidase4242
nrtC1414Nitrilase2525
nasS4646
ncd2677677
npdA580580
nirK46074607
norB14791479
nosZ48774877
nifD2525
nirA1515
cynS2222
glnA17441744
gltB12,15812,158
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Zhao, W.; Wu, C.; Zheng, S.; Zhang, G. Insights into Wastewater Nitrogen Conversion to Protein via Photosynthetic Bacteria. Water 2025, 17, 826. https://doi.org/10.3390/w17060826

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Zhao W, Wu C, Zheng S, Zhang G. Insights into Wastewater Nitrogen Conversion to Protein via Photosynthetic Bacteria. Water. 2025; 17(6):826. https://doi.org/10.3390/w17060826

Chicago/Turabian Style

Zhao, Wei, Chenghao Wu, Sijia Zheng, and Guangming Zhang. 2025. "Insights into Wastewater Nitrogen Conversion to Protein via Photosynthetic Bacteria" Water 17, no. 6: 826. https://doi.org/10.3390/w17060826

APA Style

Zhao, W., Wu, C., Zheng, S., & Zhang, G. (2025). Insights into Wastewater Nitrogen Conversion to Protein via Photosynthetic Bacteria. Water, 17(6), 826. https://doi.org/10.3390/w17060826

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