Composition diversity and nutrition conditions for accumulation of polyhydroxyalkanoate (PHA) in a bacterial community from activated sludge

Optimization of activated sludge polyhydroxyalkanoates(PHAs) synthesis system by performing sludge activity recovery experiments and varying the initial sludge concentration

Polyhydroxyalkanoates(PHAs) are considered a good alternative to petroleum-based plastics because of their good biodegradability and biocompatibility. The synthesis of PHAs using activated sludge can not only solve the problem of the high cost of pure cultures but also improve the utilization value of activated sludge. In this study, sludge activity recovery experiments were firstly conducted and the effects of different initial sludge concentrations on the activated sludge PHAs synthesis system were further investigated. the initial sludge concentrations were 1#SBR (2800 ± 50) mg/L, 2#SBR (4200 ± 50) mg/L, and 3#SBR (5500 ± 50) mg/L. The results showed that the activity, sedimentation performance and PHAs synthesis capacity of activated sludge were enhanced after the sludge activity recovery experiment. At the initial sludge concentration of 4200 mg/L, the activated sludge PHAs synthesis system was operated stably and the synthesis efficiency of PHAs was enhanced. In contrast, at the initial sludge concentration of 2800 and 5500 mg/L, the steady state of the activated sludge PHAs synthesis system was damaged to different degrees at different times, and the synthesis efficiency of PHAs was greatly reduced.

Genome-centric metagenomics provides new insights into metabolic pathways of polyhydroxyalkanoates biosynthesis and functional microorganisms subsisting on municipal organic wastes

The microbial community of a sequencing batch reactor operated under feast and famine conditions for production of polyhydroxyalkanoates (PHAs) was characterized through high-throughput sequencing and metagenomic analysis. The fermented food waste and chemically-enhanced primary sludge was fed in this bioreactor. After acclimation, the PHA yield achieved as high as 0.60-0.69 g CODPHA/g CODS. The complete changes of microbial community structure were found during shifts of feedstock. A synthesis of SCL/MCL-PHAs pathway was established for PHA-producing bioreactor in this mixed-culture system. The structure-performance relationship of PHA-producing microbial community and feedstock composition was investigated. The results showed that microbial community tends to be decentralized and prefer team work for PHA synthesis to consume the multiple substrates and digest inevitable non-VFA contents in fermented liquor. This study also discovered unreported potential PHA producers (e.g., genera Tabrizicola, Nannocystis, Ga0077539, Ga0077559, JOSHI-001, SNC69-320 and UBA2334) subsisting on municipal organic wastes and expands the current knowledge about mixed-culture system that the PHA synthesis pathway is widely existed in activated sludge.

Valorization of lipid-rich wastewaters: A theoretical analysis to tackle the competition between polyhydroxyalkanoate and triacylglyceride-storing populations

The lipid fraction of the effluents generated in several food-processing activities can be transformed into polyhydroxyalkanoates (PHAs) and triacylglycerides (TAGs), through open culture biotechnologies. Although competition between storing and non-storing populations in mixed microbial cultures (MMCs) has been widely studied, the right selective environment allowing for the robust enrichment of a community when different types of accumulators coexist is still not clear. In this research, comprehensive metabolic analyses of PHA and TAG synthesis and degradation, and concomitant respiration of external carbon, were used to understand and explain the changes observed in a laboratory-scale bioreactor fed with the lipid-rich fraction (mainly oleic acid) of a wastewater stream produced in the fish-canning industry. It was concluded that the mode of oxygen, carbon, and nitrogen supply determines the enrichment of the culture in specific populations, and hence the type of intracellular compounds preferentially accumulated. Coupled carbon and nitrogen feeding regime mainly selects for TAG producers whereas uncoupled feeding leads to PHA or TAG production function of the rate of carbon supply under specific aeration rates and feast and famine phases lengths.

Optimization of a Two-Species Microbial Consortium for Improved Mcl-PHA Production From Glucose-Xylose Mixtures

Polyhydroxyalkanoates (PHAs) have attracted much attention as a good substitute for petroleum-based plastics, especially mcl-PHA due to their superior physical and mechanical properties with broader applications. Artificial microbial consortia can solve the problems of low metabolic capacity of single engineered strains and low conversion efficiency of natural consortia while expanding the scope of substrate utilization. Therefore, the use of artificial microbial consortia is considered a promising method for the production of mcl-PHA. In this work, we designed and constructed a microbial consortium composed of engineered Escherichia coli MG1655 and Pseudomonas putida KT2440 based on the "nutrition supply-detoxification" concept, which improved mcl-PHA production from glucose-xylose mixtures. An engineered E. coli that preferentially uses xylose was engineered with an enhanced ability to secrete acetic acid and free fatty acids (FFAs), producing 6.44 g/L acetic acid and 2.51 g/L FFAs with 20 g/L xylose as substrate. The mcl-PHA producing strain of P. putida in the microbial consortium has been engineered to enhance its ability to convert acetic acid and FFAs into mcl-PHA, producing 0.75 g/L mcl-PHA with mixed substrates consisting of glucose, acetic acid, and octanoate, while also reducing the growth inhibition of E. coli by acetic acid. The further developed artificial microbial consortium finally produced 1.32 g/L of mcl-PHA from 20 g/L of a glucose-xylose mixture (1:1) after substrate competition control and process optimization. The substrate utilization and product synthesis functions were successfully divided into the two strains in the constructed artificial microbial consortium, and a mutually beneficial symbiosis of "nutrition supply-detoxification" with a relatively high mcl-PHA titer was achieved, enabling the efficient accumulation of mcl-PHA. The consortium developed in this study is a potential platform for mcl-PHA production from lignocellulosic biomass.

Biodegradable polyhydroxyalkanoates production from wheat straw by recombinant Halomonas elongata A1

Waste straw bio-transformation of high value-added macromolecule polyhydroxyalkanoates (PHAs) was significance to environmental sustainable development. As a member of the PHA family, poly-β-hydroxybutyrate (PHB) could be synthesized by Halomonas elongata A1 with maximal yields of 22.8% and 11.8% of bacterial weights using glucose and carboxymethyl cellulose as carbon sources, respectively. To improve PHB production, we generated three recombinant strains, the H. elongata P2 with highest PHB biosynthesis ability. When wheat straw, mixed substrate and oleic acid were individually used as single carbon source, the maximal PHA polymer accumulation in the H. elongata P2 reached 5.2%, 16.5% and 27.5%, respectively, after 84 h of cultivation. This hardness, toughness and crystallization properties of the PHA macromolecule altered dependent on starting substrates, when analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). In terms of the hardness and roughness, the PHA produced from mixed substrates was much softer than that from wheat straw but harder than that from oleic acid. The long-chain carbon improved the softness and strength of the produced PHA. Our data indicate that economical substrates, such as straw and waste oil, can be used in the synthesis of multi-functional plastic products with biodegradable properties.

Poly(3-hydroxypropionate): Biosynthesis Pathways and Malonyl-CoA Biosensor Material Properties

Many single-use non-degradable plastics are a threat to life today, and several polyhydroxyalkanoates (PHAs) biopolymers have been developed in the bioplastic industry to place petrochemical-based plastics. One of such is the novel biomaterial poly(3-hydroxypropionate) [poly(3HP)] because of its biocompatibility, biodegradability, and high yield synthesis using engineered strains. To date, many bio-polymer-based functional composites have been developed to increase the value of raw microbial-biopolymers obtained from cheap sources. This review article broadly covers poly(3HP), a comprehensive summary of critical biosynthetic production pathways comparing the yields and titers achieved in different Microbial cell Factories. This article also provides extensive knowledge and highlights recent progress on biosensors' use to optimize poly(3HP) production, some bacteria host adopted for production, chemical and physical properties, life cycle assessment for poly(3HP) production using corn oil as carbon source, and some essential medical applications of poly(3HP).

Nutrient removal and microbial community structure variation in the two-sludge system treating low carbon/nitrogen domestic wastewater

A two-sludge system with separated phosphorus removal unit and nitrification unit was used to treat the actual municipal sewage deficient in organic carbon sources, with the carbon/nitrogen (C/N) ratio of 4.39. The system was first operated as anaerobic/oxic-nitrification (A/O-N) mode for 60 days (phase I), and then transformed into anaerobic/anoxic/oxic-nitrification (A/A/O-N) mode for the next following 80 days (phase II). Noteworthy, oxygen and nitrate acted as electronic acceptors for phosphorus removal in chronological order. Results indicated that deep phosphorus removal and complete nitrification were achieved at both phase I and phase II, and the system exhibited a higher microbial diversity. Microbial community abundance on genus level analysis indicated that Dechloromonas and Accumulibacter were respectively accumulated with 11.6 and 2.42% abundance (A/A/O sludge); and 9.31 and 1.29% Nitrospira and Nitrosomonas occupied the biofilm, and they performed denitrifying phosphorus removal (DNPR) and nitrification, respectively.

Shifts in microbial community structure and diversity in a novel waterfall biofilm reactor combined with MBBR under light and dark conditions

In this study, a novel, low-cost, easy-maintenance and effective waterfall aeration biofilm reactor (WFBR) was designed to treat wastewater with MBBR. The chemical oxygen demand (COD), nitrogen removal efficiency, and the microbial community structure in this novel system were evaluated for 70 days under light and dark conditions. The COD and ammonium nitrogen (NH₃–N) removal efficiency remained at approximately 90% and 100% respectively after 25 days, even if the influent substrate concentration and illumination condition changes. High-throughput sequencing was used to investigate the composition and function of the microbial community in different fillers in the treatment system. Dark padding, illuminate carrier and fabric play the good performance in nitrogen nitrification, denitrification and fixation respectively. The major classes present were Betaproteobacteria (30.2% on average), Cytophagia (19.8%), Gammaproteobacteria (11.7%), Alphaproteobacteria (11.2%), Sphingobacteriia (5.1%), Flavobacteriia (2.6%), Deltaproteobacteria (2.4%), Verrucomicrobiae (0.7%), Chloroplast (0.6%) and Clostridia (0.5%). These results could provide important guidance for the improvement of MBBR or other tradition wastewater treatment process, and could also enrich our theoretical understanding of microbial ecology.

In this study, a novel, low-cost, easy-maintenance and effective waterfall aeration biofilm reactor (WFBR) was designed to treat wastewater with MBBR.

Highly complex substrates lead to dynamic bacterial community for polyhydroxyalkanoates production

Mixed microbial cultures (MMC) and waste/surplus substrates, as hardwood spent sulfite liquor, are being used to decrease polyhydroxyalkanoates’ (PHA) production costs. The process involves two or three steps, being the selection step a crucial one. For the industrial implementation of this strategy, reactor stability in terms of both performance and microbial community presence has to be considered. A long-term operation of a sequencing batch reactor under feast/famine conditions was performed along with microbial community identification/quantification using FISH and DGGE. The community was found to be extremely dynamic, dominated by Alphaproteobacteria, with Paracoccus and Rhodobacter present, both PHA-storing microorganisms. 16S rRNA gene clone library further revealed that side populations’ non-PHA accumulators were able to strive (Agrobacterium, Flavobacteria, and Brachymonas). Nevertheless, reactor performance in terms of PHA storage was stable during operation time. The monitoring of the MMC population evolution provided information on the relation between community structure and process operation.

Evaluation of short-chain-length polyhydroxyalkanoate accumulation in Bacillus aryabhattai

This study was focused on the polyhydroxybutyrate (PHB) accumulation property of Bacillus aryabhattai isolated from environment. Twenty-four polyhydroxyalkanoate (PHA) producers were screened out from sixty-two environmental bacterial isolates based on Sudan Black B colony staining. Based on their PHA accumulation property, six promising isolates were further screened out. The most productive isolate PHB10 was identified as B. aryabhattai PHB10. The polymer production maxima were 3.264 g/L, 2.181 g/L, 1.47 g/L, 1.742 g/L and 1.786 g/L in glucose, fructose, maltose, starch and glycerol respectively. The bacterial culture reached its stationary and declining phases at 18 h and 21 h respectively and indicated growth-associated PHB production. Nuclear Magnetic Resonance (NMR) spectra confirmed the material as PHB. The material has thermal stability between 30 and 140 °C, melting point at 170 °C and maximum thermal degradation at 287 °C. The molecular weight and poly dispersion index of the polymer were found as 199.7 kDa and 2.67 respectively. The bacterium B. aryabhattai accumulating PHB up to 75% of cell dry mass utilizing various carbon sources is a potential candidate for large scale production of bacterial polyhydroxybutyrate.

Metagenomic insight into the bioaugmentation mechanism of Phanerochaete chrysosporium in an activated sludge system treating coking wastewater

Phanerochaete chrysosporium was seeded to a sequencing batch reactor treating phenol wastewater. Compared to the contrast reactor (R1), the bioaugmented reactor (R2) exhibits better performance in sludge settling ability, as well as biomass and phenol removal, even though the added fungus is not persistently surviving in the reactor. Bioaugmentation improved bacterial population, growing up to 10,000 times higher than that of eukaryotes. Metagenomic sequencing results show the bioaugmentation finally increases bacterial and eukaryotic richness, but reduces their community diversity. In contrast to R1, bacterial distribution in R2 is more concentrated in Proteobacteria. The relative abundances of filamentous fungi, yeast and microalgae in R2 are all higher than those in R1 at different treatment phases, and two reactors are finally dominated by different protozoan and metazoan. In conclusion, P. chrysosporium improves reactor performances by influencing microbial community structure, and this phenomenon might be attributed to the ecological competition in sludge and toxicity reduction of phenol wastewater. The novelty of this study emphasizes why a species which is not persistently active in bioreactor still plays a crucial role in enhancing reactor performance. Results obtained here impact the conventional criteria for selection of bioaugmentation microbes used in activated sludge systems.

The effect of anaerobic-aerobic and feast-famine cultivation pattern on bacterial diversity during poly-β-hydroxybutyrate production from domestic sewage sludge

The main objective of this work was to investigate the influence of different oxygen supply patterns on poly-β-hydroxybutyrate (PHB) yield and bacterial community diversity. The anaerobic-aerobic (A/O) sequencing batch reactors (SBR1) and feast-famine (F/F) SBR2 were used to cultivate activated sludge to produce PHB. The mixed microbial communities were collected and analyzed after 3 months cultivation. The PHB maximum yield was 64 wt% in SBR1 and 53 wt% in SBR2. Pyrosequencing analysis 16S rRNA gene of two microbial communities indicated there were nine and four bacterial phyla in SBR1 and SBR2, respectively. Specifically, Proteobacteria (36.4 % of the total bacterial community), Actinobacteria (19.7 %), Acidobacteria (14.1 %), Firmicutes (4.4 %), Bacteroidetes (1.7 %), Cyanobacteria/Chloroplast (1.5 %), TM7 (0.8 %), Gemmatimonadetes (0.2 %), and Nitrospirae (0.1 %) were present in SBR1. Proteobacteria (94.2 %), Bacteroidetes (2.9 %), Firmicutes (1.9 %), and Actinobacteria (0.7 %) were present in SBR2. Our results indicated the SBR1 fermentation system was more stable than that of SBR2 for PHB accumulation.

Effects of oxygen and carbon content on nitrogen removal capacities in landfill bioreactors and response of microbial dynamics

In this study, landfill bioreactors were tested to treat the recalcitrant leachate-nitrogen and the impacts of relevant operational parameters on its conversion were comprehensively investigated. We found that the highly diverse microbial community in landfill bioreactors could be substantially affected by increasing biodegradable carbon and oxygen content, which led to the whole system's intrinsic nitrogen removal capacity increasing from 50 to 70 %, and meanwhile, the contribution of anammox was detected less than 20 %. The sequencing and q-PCR results showed that microbial community in bioreactor was dominated by Proteobacteria (∼35 %) and Acidobacteria (~20 %) during the whole experiment. The abundance of anammox functioning bacteria (Amx) kept at a stable level (-2.5 to -2.2 log (copies/16S rRNA)) and was not statistically correlated to the abundance of anammox bacteria. However, significant linear correlation (p < 0.05) was determined between the abundance of nirS and Proteobacteria; amoA and AOB. Redundancy analysis (RDA) suggested that although oxygen and biodegradable carbon can both impose effects on microbial community structure, only biodegradable carbon content is the determinant in the total nitrogen removal.

Role of aeration intensity on performance and microbial community profiles in a sequencing batch reaction kettle (SBRK) for wastewater nutrients rapid removal

A lab-scale SBRK was operated to investigate the effects of aeration intensity on the system performance and microbial community dynamics within it. Results showed that the sewage nutrients was removed rapidly (just about 3-6h) with the aeration intensity increasing from 0 to 0.6MPa. Average effluent parameters were: COD below 50mg/L, NH4(+)-N less than 1mg/L, 1.5-4.5mg/L for nitrate and TP below 0.5mg/L. The highest community similarity and diversity emerged simultaneously with the aeration pressure rising from 0.2 to 0.4MPa, which was regarded as the optimal aeration intensity range. Microbial community shifted obviously and the function species of Comamonadaceae, Dechloromonas, Flavobacterium and Nitrospira dominated in the corresponding communities. RDA indicated that aeration intensity was the main factor for regulating system communities to optimize the system performance. It inferred that high aeration pressure played a key role on sewage nutrients rapid removal.

Extraction of polyhydroxyalkanoates from mixed microbial cultures: Impact on polymer quality and recovery

Polyhydroxyalkanoates (PHAs) can be extracted from mixed microbial cultures (MMCs) by means of dimethyl carbonate (DMC) or combination of DMC and sodium hypochlorite (NaClO). The protocol based on DMC, a green solvent never used before for the extraction of PHAs from MMC, allows an overall polymer recovery of 63%; also the purity and the molecular weight of the recovered polymers are good (98% and 1.2 MDa, respectively). The use of NaClO pretreatment before DMC extraction increases the overall PHA recovery (82%) but lowers the mean molecular weight to 0.6-0.2 MDa. A double extraction with DMC results to be the method of choice for the recovery of high quality PHAs from attractive but challenging MMCs.

Influence of organic loading rate and solid retention time on polyhydroxybutyrate production from hybrid poplar hydrolysates using mixed microbial cultures

The aim of this study was to investigate the potential of using wood hydrolysates (enzymatically hydrolyzed from hybrid poplar) as substrate to produce polyhydroxybutyrate (PHB) using mixed microbial cultures. The optimal operational conditions for fed-batch bioreactors were 4d solid retention time with an organic loading rate of 2.5g/Ld. The maximum PHB accumulated was 27% of cell dry weight with a yield of 0.32g/g (g PHB produced per g sugars consumed). Microbial community analysis was done at the genus level by 16S rRNA sequencing on an Illumina system and community evolution was observed among different samples and initial seed. Actinobacteria, Alpha- and Beta-proteobacteria were found to be the dominant groups in all the bioreactors. Several PHB-storing microorganisms were characterized belonging to Alpha- and Beta-proteobacteria.