Link between microbial composition and carbon substrate-uptake preferences in a PHA-storing community

Enrichment performance and salt tolerance of polyhydroxyalkanoates (PHAs) producing mixed cultures under different saline environments

The key to the resource recycling of saline wastes in form of polyhydroxyalkanoates (PHA) is to enrich mixed cultures with salt tolerance and PHA synthesis ability. However, the comparison of saline sludge from different sources and the salt tolerance mechanisms of salt-tolerant PHA producers need to be clarified. In this study, three kinds of activated sludge from different salinity environments were selected as the inoculum to enrich salt-tolerant PHA producers under aerobic dynamic feeding (ADF) mode with butyric acid dominated mixed volatile fatty acid as the substrate. The maximum PHA content (PHAm) reached 0.62 ± 0.01, 0.62 ± 0.02, and 0.55 ± 0.03 g PHA/g VSS at salinity of 0.5%, 0.8%, and 1.8%, respectively. Microbial community analysis indicated that Thauera, Paracoccus, and Prosthecobacter were dominant salt-tolerant PHA producers at low salinity, Thauera, NS9_marine, and SM1A02 were dominant salt-tolerant PHA producers at high salinity. High salinity and ADF mode had synergistic effects on selection and enrichment of salt-tolerant PHA producers. Combined correlation network with redundancy analysis indicated that trehalose synthesis genes and betaine related genes had positive correlation with PHAm, while extracellular polymeric substances (EPS) content had negative correlation with PHAm. The compatible solutes accumulation and EPS secretion were the main salt tolerance mechanisms of the PHA producers. Therefore, adding compatible solutes is an effective strategy to improve PHA synthesis in saline environment.

Evaluation of the production and extraction of polyhydroxybutyrate from volatile fatty acids by means of mixed cultures and B. cepacia

The global consumption of plastics generates accelerated environmental pollution in landfills and marine ecosystems. Biopolymers are the materials with the greatest potential to replace synthetic polymers in the market due to their good biodegradability, however, there are still several disadvantages, mainly related to their production cost. Considering the above, the generation of biodegradable and biocompatible bioplastics stands out as an alternative solution, some of which are made from renewable raw materials, including polyhydroxyalkanoates PHAs. Although much research has been done on bacteria with the capacity for intracellular accumulation of PHAs, among others, it is also possible to produce PHAs using mixed microbial cultures instead of a single microorganism, using natural microbial consortia that have the capacity to store high amounts of PHAs. In this contribution, three methods for the extraction and purification of PHAs produced by fermentation using volatile fatty acids as a carbon source at different concentrations were evaluated, using the pure strain Burkholderia cepacia 2G-57 and the mixed cultures of the activated sludge from the El Salitre WWTP, in order to select the best method from the point of view of environmental sustainability as this will contribute to the scalability of the process. The mixed cultures were identified by sequencing of the 16S gene. A yield of 89% was obtained from the extraction and purification of PHA using acetic acid as a solvent, which according to its properties is "greener" than chloroform. The polymer obtained was identified as polyhydroxybutylated PHB.

Arsenic stress on soil microbial nutrient metabolism interpreted by microbial utilization of dissolved organic carbon

In a 120-day microcosm incubation experiment, we investigated the impact of arsenic contamination on soil microbial nutrient metabolism, focusing on carbon cycling processes. Our study encompassed soil basal respiration, key enzyme activities (particularly, β-1,4-N-acetylglucosaminidase and phosphatases), microbial biomass, and community structure. Results revealed a substantial increase (1.21-2.81 times) in β-1,4-N-acetylglucosaminidase activities under arsenic stress, accompanied by a significant decrease (9.86%-45.20%) in phosphatase activities (sum of acid and alkaline phosphatases). Enzymatic stoichiometry analysis demonstrated the mitigation of microbial C and P requirements in response to arsenic stress. The addition of C-sources alleviated microbial C requirements but exacerbated P requirements, with the interference amplitude increasing with the complexity of the C-source. Network analysis unveiled altered microbial nutrient requirements and an increased resistance process of microbes under arsenic stress. Microbial carbon use efficiency (CUE) and basal respiration significantly increased (1.17-1.59 and 1.18-3.56 times, respectively) under heavy arsenic stress (500 mg kg-1). Arsenic stress influenced the relative abundances of microbial taxa, with Gemmatimonadota increasing (5.5-50.5%) and Bacteroidota/ Nitrospirota decreasing (31.4-47.9% and 31.2-63.7%). Application of C-sources enhanced microbial resistance to arsenic, promoting cohesion among microorganisms. These findings deepen our understanding of microbial nutrient dynamics in arsenic-contaminated areas, which is crucial for developing enzyme-based toxicity assessment systems for soil arsenic contamination.

A novel GH3-β-glucosidase from soda lake metagenomic libraries with desirable properties for biomass degradation

Beta-glucosidases catalyze the hydrolysis of the glycosidic bonds of cellobiose, producing glucose, which is a rate-limiting step in cellulose biomass degradation. In industrial processes, β-glucosidases that are tolerant to glucose and stable under harsh industrial reaction conditions are required for efficient cellulose hydrolysis. In this study, we report the molecular cloning, Escherichia coli expression, and functional characterization of a β-glucosidase from the gene, CelGH3_f17, identified from metagenomics libraries of an Ethiopian soda lake. The CelGH3_f17 gene sequence contains a glycoside hydrolase family 3 catalytic domain (GH3). The heterologous expressed and purified enzyme exhibited optimal activity at 50 °C and pH 8.5. In addition, supplementation of 1 M salt and 300 mM glucose enhanced the β-glucosidase activity. Most of the metal ions and organic solvents tested did not affect the β-glucosidase activity. However, Cu2+ and Mn2+ ions, Mercaptoethanol and Triton X-100 reduce the activity of the enzyme. The studied β-glucosidase enzyme has multiple industrially desirable properties including thermostability, and alkaline, salt, and glucose tolerance.

Aerobic digestibility of waste aerobic granular sludge (AGS) assessed by respirometry, physical-chemical analyses, modeling and 16S rRNA gene sequencing

Research has evolved on aerobic granular sludge (AGS) process, but still there are very few studies on the treatment of excess AGS sludge, with almost none considering its aerobic digestion. Here therefore, the aerobic digestibility of typical AGS sludge was assessed. Granules were produced from acetate-based synthetic wastewater (WW) and were subjected to aerobic digestion for 64 d. The stabilization process was monitored over time through physical-chemical parameters, oxygen uptake rates (OUR) and 16S rRNA gene sequencing. The microbial analyses revealed that the cultivated granules were dominated by slow-growing bacteria, mainly ordinary heterotrophic organisms with potential for polyhydroxyalkanoates (PHA) aerobic storage (PHA-OHOs), polyphosphate and glycogen accumulating organisms (PAOs and GAOs), fermentative anaerobes and nitrifiers (AOB and NOB). Differential abundance analysis of the bacterial data (before versus after digestion) discriminated between the most vulnerable microbiome genera and those most resistant to aerobic digestion. Furthermore, modeling of the stabilization process determined that the endogenous decay rate constant (bH) for the heterotrophs present in the granules was notably low; bH = 0.05 d-1 (average), four times less than for common activated sludge (AS), which is rated at 0.2 d-1. For first time, the research reveals another important feature of AGS sludge, i.e. the slow-decaying character of its bacteria (along with their known slow-growing character). This results in slower stabilization, need of bigger digesters and reconsideration of the specific OUR limits in biosolids regulations (SOUR limit of 1.5 mg/gTSS.h), for waste AGS compared to conventional waste AS. The study suggests that aerobic digestion of waste AGS (fully-granulated) could differ from that of conventional AS. Future work is needed on aerobic digestibility of real AGS sludges from municipal and industrial WWs, compared to synthetic WWs.

Bioaugmentation of Thauera mechernichensis TL1 for enhanced polyhydroxyalkanoate production in mixed microbial consortia for wastewater treatment

Polyhydroxyalkanoate (PHA) is a fully biodegradable bioplastic. To foster a circular economy, the integration of PHA production into wastewater treatment facilities can be accomplished using mixed microbial consortia. The effectiveness of this approach relies greatly on the enrichment of PHA-accumulating microorganisms. Hence, our study focused on bioaugmenting Thauera mechernichensis TL1 into mixed microbial consortia with the aim of enriching PHA-accumulating microorganisms and enhancing PHA production. Three sequencing batch reactors-SBRctrl, SBR2.5%, and SBR25%-were operated under feast/famine conditions. SBR2.5% and SBR25% were bioaugmented with T. mechernichensis TL1 at 2.5%w/w of mixed liquor volatile suspended solids (MLVSS) and 25%w/w MLVSS, respectively, while SBRctrl was not bioaugmented. SBR2.5% and SBR25% achieved maximum PHA accumulation capacities of 56.3 %gPHA/g mixed liquor suspended solids (MLSS) and 50.2 %gPHA/gMLSS, respectively, which were higher than the 25.4 %gPHA/gMLSS achieved by SBRctrl. The results of quantitative polymerase chain reaction targeting the 16S rRNA gene specific to T. mechernichensis showed higher abundances of T. mechernichensis in SBR2.5% and SBR25% compared with SBRctrl in the 3rd, 17th, and 31st cycles. Fluorescence in situ hybridization, together with fluorescent staining of PHA with Nile blue A, confirmed PHA accumulation in Thauera spp. The study demonstrated that bioaugmentation of T. mechernichensis TL1 at 2.5%w/w MLVSS is an effective strategy to enhance PHA accumulation and facilitate the enrichment of PHA-accumulating microorganisms in mixed microbial consortia. The findings could contribute to the advancement of PHA production from wastewater, enabling the transformation of wastewater treatment plants into water and resource recovery facilities.

Ecological succession and community assembly of mixed microbial culture polyhydroxyalkanoate production systems: Drivers of polyhydroxyalkanoate synthesis and Bdellovibrio predation

The production of polyhydroxyalkanoate (PHA) by mixed microbial culture (MMC) can reduce the pollution of plastics. Ecophysiological study of the microbial community assembly and succession is helpful for comprehensive understanding the MMC PHA production process. The operation mode of sequential aerobic dynamic discharge - aerobic dynamic feeding (ADD-ADF) was applied and the operation can be divided into acclimation phase and maturation phase. Deterministic process caused by selective pressure dominated the community assembly throughout the operation. In the acclimation phase, the physical selective pressure recovered the settling capacity of the system, and settling ability of the MMC was closely related to function of PHA synthesis. However, in the maturation phase, stochastic process caused sludge bulking, making the settling ability and PHA synthesis function of the MMC independent on each other. Stochastic process led to the succession of the dominant PHA-producing bacteria, for example, the predation of Paracoccus and Thauera by Bdellovibrio.

Effect of biodegradable PBAT microplastics on the C and N accumulation of functional organic pools in tropical latosol

Microplastics (MPs) pollution is becoming an emerging global stressor for soil ecosystems. However, studies on the impacts of biodegradable MPs on soil C sequestration have been mainly based on bulk C quantity, without considering the storage form of C, its persistency and N demand. To address this issue, the common poly (butylene adipate-co-terephthalate) (PBAT) was used as the model, and its effects on soil functional organic pools, including mineral-associated (MAOM), particulate (POM) and dissolved organic matter (DOM), were investigated from the novel coupled perspective of C and N stocks. After adding PBAT-MPs, the contents of soil POM-C, DOM-C, and MAOM-C were increased by 546.9 %-697.8 %, 54.2 %-90.3 %, and 13.7 %-18.9 %, respectively. Accordingly, the total C increased by 116.0 %-191.1 %. Structural equation modeling showed that soil C pools were regulated by PBAT input and microbial metabolism associated with C and N enzymes. Specifically, PBAT debris could be disguised as soil C to promote POM formation, which was the main pathway for C accumulation. Inversely, the MAOM-C and DOM-C formation was attributed to the PBAT microbial product and the selective consumption in DOM-N. Random forest model confirmed that N-activated (e.g., Nitrospirae) and PBAT-degrading bacteria (e.g., Gemmatinadetes) were important taxa for soil C accumulation, and the key enzymes were rhizopus oryzae lipas, invertase, and ammonia monooxygenase. The soil N accumulation was mainly related to the oligotrophic taxa (e.g., Chloroflexi and Ascomycota) associated with aggregate formation, decreasing the DOM-N by 46.9 %-84.3 %, but did not significantly change the total N storage and other N pools. Collectively, the findings highlight the urgency to control the nutrient imbalance risk of labile N loss and recalcitrant C enrichment in POM to avoid the depressed turnover rate of organic matter in MPs-polluted soil.

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.

Cellular RNA levels define heterotrophic substrate-uptake rate sub-guilds in activated sludge microbial communities

A heterotrophic-specialist model was proposed previously to divide wastewater treatment plant (WWTP) heterotrophs into sub-guilds of consumers of readily or slowly degradable substrates (RDS or SDS, respectively). The substrate degradation rate model coupled to metabolic considerations predicted that RNA and polyhydroxyalkanoate (PHA) levels would be positively correlated in the activated sludge communities with high RNA and PHA occurring in RDS-consumers, and low RNA with no PHA accumulation occurring in SDS-consumers because their external substrates are always present. This prediction was verified in previous studies and in the current one. Thus, RNA and PHA levels were used as biomarkers of the RDS- and SDS-consumer sub-guilds for cell sorting using flow cytometry of samples from three WWTPs. Subsequently, 16S rRNA gene amplicon sequencing revealed that the sorted groups were highly similar over time and among WWTPs, and demonstrated a clear segregation by RNA levels. Predicted ecophysiological traits based on 16S rRNA phylogeny suggested that the high-RNA population showed RDS-consumer traits such as higher rrn copy numbers per genome. Using a mass-flow immigration model, it appeared that the high-RNA populations exhibited high immigration rates more frequently than low-RNA populations, but the differences in frequencies were less with increasing solids residence times.

Effect of composition of volatile fatty acids on yield of polyhydroxyalkanoates and mechanisms of bioconversion from activated sludge

Polyhydroxyalkanoates (PHA) is green biodegradable natural polymer. Here PHA production from volatile fatty acids (VFAs) was investigated in sequential batch reactors inoculated with activated sludge. Single or mixed VFAs ranging from acetate to valerate were evaluated, and the dominant VFA concentration was 2 times of that of the others in the tests. Results showed that mixed substrates achieved about 1.6 times higher yield of PHA production than single substrate. The butyrate-dominated substrates maximized PHA content at 72.08% of VSS, and the valerate-dominated substrates were followed with PHA content at 61.57%. Metabolic flux analysis showed the presence of valerate in the substrates caused a more robust PHA production. There was at least 20% of 3-hydroxyvalerate in the polymer. Hydrogenophaga and Comamonas were the main PHA producers. As VFAs could be produced in anaerobic digestion of organic wastes, the methods and data here could be referred for efficient green bioconversion of PHA.

Influence of feedstock source on the development of polyhydroxyalkanoates-producing mixed microbial cultures in continuously stirred tank reactors

Polyhydroxyalkanoates (PHAs) are the new frontier of bioplastic production; however, research is needed to develop and characterise efficient mixed microbial communities (MMCs) for their application with a multi-feedstock approach. Here, the performance and composition of six MMCs developed from the same inoculum on different feedstocks were investigated through Illumina sequencing to understand community development and identify possible redundancies in terms of genera and PHA metabolism. High PHA production efficiencies (>80% mg COD_PHA mg^-1 COD_OA-consumed) were seen across all samples, but differences in the organic acids (OAs) composition led to different ratios of the monomers poly(3-hydroxybutyrate) (3HB) to poly(3-hydroxyvalerate) (3HV). Communities differed across all feedstocks, with enrichments in specific PHA-producing genera, but analysis of potential enzymatic activity identified a certain degree of functional redundancy, possibly leading to the general high efficiency seen in PHA production from all feedstocks. Leading PHAs producers across all feedstocks were identified in genera such as Thauera, Leadbetterella, Neomegalonema and Amaricoccus.

Polyhydroxyalkanoates (PHAs) synthesis and degradation by microbes and applications towards a circular economy

Overusing non-degradable plastics causes a series of environmental issues, inferring a switch to biodegradable plastics. Polyhydroxyalkanoates (PHAs) are promising biodegradable plastics that can be produced by many microbes using various substrates from waste feedstock. However, the cost of PHAs production is higher compared to fossil-based plastics, impeding further industrial production and applications. To provide a guideline for reducing costs, the potential cheap waste feedstock for PHAs production have been summarized in this work. Besides, to increase the competitiveness of PHAs in the mainstream plastics economy, the influencing parameters of PHAs production have been discussed. The PHAs degradation has been reviewed related to the type of bacteria, their metabolic pathways/enzymes, and environmental conditions. Finally, the applications of PHAs in different fields have been presented and discussed to induce comprehension on the practical potentials of PHAs.

Production of polyhydroxyalkanoate by mixed cultivation of Brevundimonas diminuta R79 and Pseudomonas balearica R90

The microflora in the activated sludge of propylene oxide saponification wastewater is characterized by a clear succession after enrichment and domestication, and the specifically enriched strains can significantly increase the yield of polyhydroxyalkanoate. In this study, Pseudomonas balearica R90 and Brevundimonas diminuta R79, which are dominant strain after domestication, were selected as models to examine the interactive mechanisms associated with the synthesis of polyhydroxyalkanoate by co-cultured strains. RNA-Seq analysis revealed the up-regulated expression of the acs and phaA genes of strains R79 and R90 in the co-culture group, which enhanced their utilization of acetic acid and synthesis of poly-β-hydroxybutyrate. Cell dry weight and the yield of poly-β-hydroxybutyrate in the co-culture group were accordingly considerably higher than those in the respective pure culture groups. In addition, two-component system, quorum-sensing, flagellar synthesis-related, and chemotaxis-related genes were enriched in strain R90, thereby indicating that compared with the R79 strain, R90 can adapt more rapidly to a domesticated environment. Expression of the acs gene was higher in R79 than in R90, and consequently, strain R79 could more efficiently assimilate acetate in the domesticated environment, and thus predominated in the culture population at the end of the fermentation period.

Single CSTR can be as effective as an SBR in selecting PHA-storing biomass from municipal wastewater-derived feedstock

A key step for the production of polyhydroxyalkanoates (PHAs) from organic waste streams is the selection of a biomass with a high PHA-storage capacity (selection-step), which is usually performed in sequencing batch reactors (SBR). A major advancement would be to perform such selection in continuous reactors to facilitate the full-scale implementation of PHA production from municipal wastewater (MWW)-derived feedstock. The present study therefore investigates to what extent a simple continuous-flow stirred-tank reactor (CSTR) represents a relevant alternative to anSBR. To this end, we operated two selection reactors (CSTR vs. SBR) on filtered primary sludge fermentate while performing a detailed analysis of the microbial communities, and monitoring PHA-storage over long-term (∼150 days) and during accumulation batches. Our study demonstrates that a simple CSTR is as effective as an SBR in selecting biomass with high PHA-storage capacity (up to 0.65 gPHA gVSS^-1) while being 50% more efficient in terms of substrate to biomass conversion yields. We also show that such selection can occur on VFA-rich feedstock containing nitrogen (N) and phosphorus (P) in excess, whereas previously, selection of PHA-storing organisms in a single CSTR has only been studied under P limitation. We further found that microbial competition was mostly affected by nutrient availability (N and P) rather than by the reactor operation mode (CSTR vs. SBR). Similar microbial communities therefore developed in both selection reactors, while microbial communities were very different depending on N availability. Rhodobacteraceae gen. were most abundant when growth conditions were stable and N-limited, whereas dynamic N- (and P-) excess conditions favoured the selection of the known PHA-storer Comamonas, and led to the highest observed PHA-storage capacity. Overall, we demonstrate that biomass with high storage capacity can be selected in a simple CSTR on a wider range of feedstock than just P-limited ones.

Responses of various carbon to nitrogen ratios to microbial communities, kinetics, and nitrogen metabolic pathways in aerobic granular sludge reactor

The role of different ammonia concentrations (mg N/L) (of 100 (carbon to nitrogen ratio (C/N) = 12; Stage I), 200 (C/N = 6; Stage II), 400 (C/N = 3; Stage III) and 200 (C/N = 6; Stage IV)) in nitrogen metabolic pathways, microbial community, and specific microbial activity were investigated in an aerobic granular sludge reactor. Heterotrophic ammonia oxidizing bacteria (HAOB) showed higher ammonia oxidation rates (AORs) than autotrophic ammonia oxidizing bacteria (AAOB) at higher C/N conditions (Stages I and II). Paracoccus was the dominant HAOB. AAOB, with only 0.2-0.3 % in relative abundance, showed 2.7-fold higher AORs than HAOB at elevated ammonia and free ammonia (FA) concentrations with C/N at 3. Nitrosomonas and a genus in Nitrosomondaceae family were the major AAOB. This study proposed that FA inhibition on heterotrophic bacteria might be the mechanism that contributes to the development of the autotrophic ammonia oxidation pathway and enrichment of AAOB.

Thauera sp. Sel9, a new bacterial strain for polyhydroxyalkanoates production from volatile fatty acids

Thauera is one of the main genera involved in polyhydroxyalkanoate (PHA) production in microbial mixed cultures (MMCs) from volatile fatty acids (VFAs). However, no Thauera strains involved in PHA accumulation have been obtained in pure culture so far. This study is the first report of the isolation and characterization of a Thauera sp. strain, namely Sel9, obtained from a sequencing batch reactor (S-SBR) set up for the selection of PHA storing biomass. The 16S rRNA gene evidenced a high sequence similarity with T. butanivorans species. Genome sequencing identified all genes involved in PHA synthesis, regulation and degradation. The strain Sel9 was able to grow with an optimum of chemical oxygen demand-to-nitrogen (COD:N) ratio ranging from 4.7 to 18.9. Acetate, propionate, butyrate and valerate were used as sole carbon and energy sources: a lag phase of 72 h was observed in presence of propionate. Final production of PHAs, achieved with a COD:N ratio of 75.5, was 60.12 ± 2.60 %, 49.31 ± 0.7 %, 37.31 ± 0.43 % and 18.06 ± 3.81 % (w/w) by using butyrate, acetate, valerate and propionate as substrates, respectively. Also, the 3-hydroxybutyrate/3-hydroxyvalerate ratio reflected the type of carbon sources used: 12.30 ± 0.82 for butyrate, 3.56 ± 0.02 for acetate, 0.93 ± 0.03 for valerate and 0.76 ± 0.02 for propionate. The results allow a better elucidation of the role of Thauera in MMCs and strongly suggest a possible exploitation of Thauera sp. Sel9 for a cost-effective and environmentally friendly synthesis of PHAs using VFAs as substrate.

Consistency between the metabolic performance of two aerobic granular sludge systems and the functional groups of bacteria detected by amplicon sequencing

Two sequential batch reactors (R1 and R2) of aerobic granular sludge (AGS) were inoculated with activated sludge of different origins. The objective was to investigate the granulation and the consistency between the structure of the microbial communities (16S rRNA amplicon sequencing) in each reactor and their metabolic performance (removal of C, N, and P). Both reactors were fed with acetate-based synthetic wastewater, targeting an anaerobic-aerobic cycle reputed to favor the phosphorus- and glycogen-accumulating organisms (PAO and GAO). Stable granulation was achieved in both reactors, where, instead of PAO, the dominant genera were ordinary heterotrophic organisms (OHO) such as Thauera, Paracoccus, and Flavobacterium known for their high capacity of aerobic storage of polyhydroxyalkanoates (PHA). Generally, there was good consistency between the metabolic behavior of each reactor and the bacterial genera detected. Both reactors showed high removals of C and complete nitrification (Nitrosomonas and Nitrospira detected) but a low level of simultaneous nitrification-denitrification (SND) during the aerated phase. The latter causes that nitrates were recycled to the initial phase, in detriment of PAO selection. Meanwhile, the study showed that selecting slow-growing OHOs (with aerobic storage capacity) favors stable granulation, revealing an alternative AGS technology for C and N removal.

Leads and hurdles to sustainable microbial bioplastic production

Indiscriminate usage, disposal and recalcitrance of petroleum-based plastics have led to its accumulation leaving a negative impact on the environment. Bioplastics, particularly microbial bioplastics serve as an ecologically sustainable solution to nullify the negative impacts of plastics. Microbial production of biopolymers like Polyhydroxyalkanoates, Polyhydroxybutyrates and Polylactic acid using renewable feedstocks as well as industrial wastes have gained momentum in the recent years. The current study outlays types of bioplastics, their microbial sources and applications in various fields. Scientific evidence on bioplastics has suggested a unique range of applications such as industrial, agricultural and medical applications. Though diverse microorganisms such as Alcaligenes latus, Burkholderia sacchari, Micrococcus species, Lactobacillus pentosus, Bacillus sp., Pseudomonas sp., Klebsiella sp., Rhizobium sp., Enterobacter sp., Escherichia sp., Azototobacter sp., Protomonas sp., Cupriavidus sp., Halomonas sp., Saccharomyces sp., Kluyveromyces sp., and Ralstonia sp. are known to produce bioplastics, the industrial production of bioplastics is still challenging. Thus this paper also provides deep insights on the advancements made to maximise production of bioplastics using different approaches such as metabolic engineering, rDNA technologies and multitude of cultivation strategies. Finally, the constraints to microbial bioplastic production and the future directions of research are briefed. Hence the present review emphasizes on the importance of using bioplastics as a sustainable alternative to petroleum based plastic products to diminish environmental pollution.

Valorization of Brewery Waste through Polyhydroxyalkanoates Production Supported by a Metabolic Specialized Microbiome

Simple Summary

Raw brewers’ spent grain, a by-product of beer production, is produced at a large scale and is usually used as animal feed or is landfilled. However, its composition shows that this feedstock has the potential for other applications, such as bioplastics production (e.g., polyhydroxyalkanoates). In this way, the aim of this work was to assess the use of raw brewers’ spent grain for polyhydroxyalkanoates production, adding new value to this feedstock. The results confirm the potential of raw brewers’ spent grain to produce polyhydroxyalkanoates, as the population was enriched in the microorganisms able to accumulate these biopolymers. These results will contribute to society’s knowledge and competence via the development of a treatment process for brewery waste of both environmental (productive waste treatment) and economic interest (production of biopolymers), which will certainly attract its application to the brewery industry worldwide.

Abstract

Raw brewers’ spent grain (BSG), a by-product of beer production and produced at a large scale, presents a composition that has been shown to have potential as feedstock for several biological processes, such as polyhydroxyalkanoates (PHAs) production. Although the high interest in the PHA production from waste, the bioconversion of BSG into PHA using microbial mixed cultures (MMC) has not yet been explored. This study explored the feasibility to produce PHA from BSG through the enrichment of a mixed microbial culture in PHA-storing organisms. The increase in organic loading rate (OLR) was shown to have only a slight influence on the process performance, although a high selectivity in PHA-storing microorganisms accumulation was reached. The culture was enriched on various PHA-storing microorganisms, such as bacteria belonging to the Meganema, Carnobacterium, Leucobacter, and Paracocccus genera. The enrichment process led to specialization of the microbiome, but the high diversity in PHA-storing microorganisms could have contributed to the process stability and efficiency, allowing for achieving a maximum PHA content of 35.2 ± 5.5 wt.% (VSS basis) and a yield of 0.61 ± 0.09 Cmmol_PHA/Cmmol_VFA in the accumulation assays. Overall, the production of PHA from fermented BSG is a feasible process confirming the valorization potential of the feedstock through the production of added-value products.

Influent carbon to phosphorus ratio drives the selection of PHA-storing organisms in a single CSTR

Enriching a biomass with a high fraction of polyhydroxyalkanoate-storing organisms (PHA-storers) represents an essential step in the production of PHAs (bioplastics) from municipal wastewater using mixed microbial cultures. A major challenge is however to create selective growth conditions that are favourable to PHA-storers. Our study thus investigates to what extent the influent COD to phosphorus (COD:P) ratio can be used as a tool for the robust selection of PHA-storers in a single continuous-flow stirred-tank reactor (CSTR). Therefore, we operated five CSTRs in parallel, fed with synthetic wastewater (50% acetate - 50% propionate) with different COD:P ratios (200-1000 gCOD gP^-1), and performed a detailed analysis of the microbial communities over long-term (30-70 solid retention times). Our study demonstrates that efficient and robust selection of PHA-storers can be achieved in a single CSTR at high influent COD:P ratios. The selective advantage for PHA-storers increases with the influent COD:P ratio, but only if growth conditions remain limited by both C-substrate and P. In contrast, selection performance deteriorates when COD:P ratios are too high and growth conditions are limited by P only. At an optimal COD:P ratio of 800 gCOD gP^-1, a stable microbial community consisting of >90% PHA-storers and dominated by Pannonibacter sp. was selected in the long-term. Finally, our results suggest that high COD:P ratios provide a selective advantage to microorganisms with low cellular P requirements, explaining why different PHA-storers (i.e., Xanthobacter sp. vs. Pannonibacter sp.) were selected depending on the influent COD:P ratio (i.e., 200 vs. 800 gCOD gP^-1). Overall, our results provide relevant insights for the development of a new approach for selecting PHA-storers, based on the use of a single CSTR and control of the influent COD:P ratio.

Effect of the organic loading rate on the PHA-storing microbiome in sequencing batch reactors operated with uncoupled carbon and nitrogen feeding

Over the last years, in a search for sustainable and biodegradable alternatives to petrol-based plastics, biotechnological applications turned to the potentialities of mixed microbial cultures (MMC) for producing polyhydroxyalkanoates (PHAs). Under a feast and famine regime, an uncoupled carbon (C) and nitrogen (N)-feeding strategy may be adopted by dosing the C-source at the beginning of the feast and the N-source at the beginning of the famine in order to stimulate a PHA storage response and microbial growth. Even though this strategy has been already successfully applied for the PHA production, very few information is to date available regarding the MMC operating in these systems and the influence of Organic Loading Rate (OLR) on their selection and enrichment. To fill the gap, this study investigated the effect of the OLR on the selection of PHA-accumulating microorganisms in a sequencing batch reactor (SBR) operated with an uncoupled C and N feeding strategy. The SBR cycle length was set at 12 h and four OLRs values (4.25, 8.50, 12.75 and 18 gCOD L^-1 d^-1) were tested by changing the concentration of the feeding solution, made of a synthetic mixture of acetic (85% of the overall COD) and propionic (15%) acids. The PHA-storage yield increased by increasing the OLR (up to 0.69 COD/COD at 12.75 gCOD L^-1 d^-1) but significantly decreased (0.27 COD/COD) at 18 gCOD L^-1 d^-1 concomitantly with a longer feast phase and a lower PHA content in the biomass at the end of the feast phase. The selective pressure induced by the applied OLRs strongly influenced the microbiome composition revealing a high content of putative PHA-storing bacteria, such as Rhodobacter, Thauera and Paracoccus, in the SBR operated at OLRs 4.25, 8.50 and 12.75 g COD L^-1 d^-1 (up to 97.4% of total reads) and a low content (5.4%) in the SBR at 18 g COD L^-1 d^-1where the predominance of genus Nitrinicola was instead observed.

Ordinary heterotrophic organisms with aerobic storage capacity provide stable aerobic granular sludge for C and N removal

The study investigated the mechanisms and microbial communities underlying the long-term stability and removal performances shown by aerobic granular sludge (AGS) reactor involving polyhydroxyalkanoates (PHA) aerobic-storing bacteria. The characteristics of the sludge, removal performances and bacterial community structure were determined. The prevailing metabolic phenotype was similar in the parent conventional activated sludge (CAS) reactor and its upgraded AGS version, showing high COD and NH₄ uptake, versus low P and N reduction. Polyphosphate and glycogen accumulating organisms, PAO and GAO, were not enriched in the reactors despite initial targeting of anaerobic-aerobic cycle. Instead, PHA-aerobic storing bacteria (Thauera and Paracoccus) were dominant, but revealing a stable AGS system for BOD and N removal. The PAO/GAO failed selection and Thauera overgrowth were analyzed for beneficial use in developing alternative AGS technology for BOD and N removal applications.

Rapid recovery of mixed culture polyhydroxyalkanoate production system from EPS bulking using azithromycin

The long-term stable operation of the mixed culture polyhydroxyalkanoate (PHA) enrichment stage is the guarantee for the continuous synthesis of PHA, however extracellular polymeric substances (EPS) sludge bulking occurred from time to time may cause the operation fail. In order to solve this problem, as a quencher of signal molecules and antibiotic, azithromycin (AZM) was used in the two systems with different modes to recover the sedimentation capacity of the sludge. The results showed that AZM addition resulted in the reduction of polysaccharide /protein (PS/PN) ratio in EPS and significant improvement of the sedimentation capacity of the sludge. Quorum quenching of AZM or aiiA gene maintained the sedimentation ability of the sludge in a relay mode. By adding AZM, the growth of Thauera and Flavobacterium, which caused sludge bulking, was inhibited. Paracoccus, a strong PHA producer, has been enriched to ensure that the maximum PHA synthesis of the system.

Production and Characterization of Polyhydroxyalkanoates from Wastewater via Mixed Microbial Cultures and Microalgae

In the context of circular economy and sustainable production of materials, this project investigated the feasibility of producing sustainable polyhydroxyalkanoates (PHA) from microalgae and sludge used in the treatment of municipal wastewater. The overall process was studied looking at the main steps: microalgae production, fermentation of the biomass, production and characterization of the PHAs. It was possible to obtain blends of hydroxybutyrate-hydroxyvalerate copolymers with high molecular weights and different compositions depending on the nature of the feedstock (mixed volatile fatty acids). In some cases, almost completely amorphous PHA materials were obtained, suggesting a potential diversification of uses and applications.

The impact of carbon to nitrogen ratios and pH on the microbial prevalence and polyhydroxybutyrate production levels using a mixed microbial starter culture

Growth conditions have been frequently studied in optimizing polyhydroxybutyrate (PHB) production, while few studies were performed to unravel the dynamic mixed microbial consortia (MMCs) in the process. In this study, the relationship between growth conditions (C/N ratios and pH) and the corresponding key-microbes were identified and monitored during PHB accumulation. The highest PHB level (70 wt% of dry cell mass) was obtained at pH 9, C/N 40, and acetic acid 10 g/L. Linking the dominant genera with the highest point of PHB accumulation, Thauera was the most prevalent species in all MMCs of pH 9, except when a C/N ratio of 1 was applied. Notably, dominant bacteria shifted at pH 7 (C/N 10) from Thauera (0 h) to Paracoccus, and subsequently to Alcaligenes following the process of PHB accumulation and consumption. Further understanding of the relationship between the structure of the microbial community and the performance will be beneficial for regulating and obtaining high PHB accumulation within an MMC. Our study illustrates the impact of C/N ratios and pH on microbial prevalence and PHB production levels using a mixed microbial starter culture. This knowledge will broaden industrial perspectives for regulating high PHB production and timely harvesting.

Ecological insight into incompatibility between polymer storage and floc settling in polyhydroxyalkanoate producer selection using complex carbon sources

Polyhydroxyalkanoate (PHA) producer selection is a key step in mixed culture (MC) production. This study focused on incompatibility between PHA storage and floc settling of MCs in the selection process. In a selector using fermented waste activated sludge as substrate under varying organic loading, average maximum PHA content obtained in batch assays increased by ∼ 22 wt% and biomass concentration increased by ∼ 34% with the increasing of organic loading. However, poor floc settling occurred, causing decreased batch PHA production and costly downstream process. A flank community which can corporately use non-VFA organics existed in the selector. When organic loading increased, PHA producers had stronger negative interactions, but not cooperation with the flank community members. Thus, high PHA storage of MCs was bounded to the domination of core PHA producer. But the domination of Thauera bacteria under high organic loading indirectly induced a bloom of filamentous bacteria.

Insightful Advancement and Opportunities for Microbial Bioplastic Production

Impetuous urbanization and population growth are driving increased demand for plastics to formulate impeccable industrial and biomedical commodities. The everlasting nature and excruciating waste management of petroleum-based plastics have catered to numerous challenges for the environment. However, just implementing various end-of-life management techniques for assimilation and recycling plastics is not a comprehensive remedy; instead, the extensive reliance on finite resources needs to be reduced for sustainable production and plastic product utilization. Microorganisms, such as bacteria and algae, are explored substantially for their bioplastic production repertoire, thus replacing fossil-based plastics sooner or later. Nevertheless, the utilization of pure microbial cultures has led to various operational and economical complications, opening the ventures for the usage of mixed microbial cultures (MMCs) consisting of bacteria and algae for sustainable production of bioplastic. The current review is primarily focuses on elaborating the bioplastic production capabilities of different bacterial and algal strains, followed by discussing the quintessence of MMCs. The present state-of-the-art of bioplastic, different types of bacterial bioplastic, microalgal biocomposites, operational factors influencing the quality and quantity of bioplastic precursors, embracing the potential of bacteria-algae consortia, and the current global status quo of bioplastic production has been summarized extensively.

Effects of the Sludge Retention Time and Carbon Source on Polyhydroxyalkanoate-Storing Biomass Selection under Aerobic-Feast and Anoxic-Famine Conditions

Polyhydroxyalkanoates (PHAs) are versatile biodegradable polymers produced by bacteria and are suitable for many downstream applications. They can be produced inexpensively from mixed microbial cultures under feast and famine conditions in the presence of biobased volatile fatty acids (VFAs). Here, we investigated the effect of changing the sludge retention time (SRT) and the addition of fermented cellulosic primary sludge (CPS) as a carbon source on the selection of PHA-storing biomass when applying the feast and famine strategy under aerobic and anoxic conditions, respectively. Increasing the SRT from 5 to 7-10 days enhanced PHA yields under feast conditions from 0.18 gCOD_PHA/gCOD_VFA (period 1) to 0.40 gCOD_PHA/gCOD_VFA (period 2). The use of fermented CPS as a carbon source (period 3) increased PHA yields to 0.62 gCOD_PHA/gCOD_VFA despite the presence of biodegradable non-VFA fractions. Microbial characterization by denaturing gradient gel electrophoresis and fluorescence in situ hybridization revealed high microbial speciation during the three experimental periods. In period 3, the dominant genera were Thauera, Paracoccus, and Azoarcus, which accounted for ∼95% of the total microbial biomass.

Waste to bioplastics: How close are we to sustainable polyhydroxyalkanoates production?

Increased awareness of environmental sustainability with associated strict environmental regulations has incentivized the pursuit of novel materials to replace conventional petroleum-derived plastics. Polyhydroxyalkanoates (PHAs) are appealing intracellular biopolymers and have drawn significant attention as a viable alternative to petrochemical based plastics not only due to their comparable physiochemical properties but also, their outstanding characteristics such as biodegradability and biocompatibility. This review provides a comprehensive overview of the recent developments on the involved PHA producer microorganisms, production process from different waste streams by both pure and mixed microbial cultures (MMCs). Bio-based PHA production, particularly using cheap carbon sources with MMCs, is getting more attention. The main bottlenecks are the low production yield and the inconsistency of the biopolymers. Bioaugmentation and metabolic engineering together with cost effective downstream processing are promising approaches to overcome the hurdles of commercial PHA production from waste streams.

Optimization of an enriched mixed culture to increase PHA accumulation using industrial saline complex wastewater as a substrate

Polyhydroxyalkanoates (PHA) appear as good candidates to substitute conventional petroleum-based plastics since they have similar properties but with the advantage of being biodegradable. Wastewater streams with high organic content are feasible substrates for PHA production resulting in an opportunity for waste recovery. One of the main challenges is the optimization of the selection of microorganisms with high PHA storage capacity. This microbial selection is performed in sequencing batch reactors (SBR) operated under an aerobic feast/famine (F/F) regime. In the present study, a settling stage was added at the end of the feast phase of the enrichment cycle of a SBR fed with pre-acidified cooked mussel processing wastewater (containing up to 12 g NaCl/L). Settling and subsequent supernatant discharge favoured the wash-out of non-accumulating microorganisms as well as the removal of substances that enhanced their undesired development (proteins and carbohydrates). Microbial analysis performed by fluorescence in situ hybridization (FISH) technique showed shifts in the microbial community; the presence of genus Paracoccus increased whereas genera Comamonas decreased. Moreover, the process efficiency was improved with the increase of the PHA production yield (Y_PHA) and the maximum PHA storage capacity (max. PHA) from 0.48 to 0.72 Cmmol_PHA/Cmmol_VFA and from 40 to 60 wt%, respectively. The polymer composition also changed, its HB:HV ratio varied from 83:17 to 70:30. Results obtained in the present study showed that settling after the feast phase promoted the removal of carbon sources that did not contribute to PHA production and the washout of non-storing bacteria, which favoured the culture enrichment.

Toward flexible regulation of polyhydroxyalkanoate composition based on substrate feeding strategy: Insights into microbial community and metabolic features

The suitable feeding strategy considering both substrate preference (enrichment stage) and flexible regulation (PHA accumulation stage) were investigated, respectively, based on intracellular polymers synthesis peculiarities of the three types of cultures (M-Ac, M-Pr and M-Bu), which were enriched correspondingly using acetic type, propionic type and butyric type substrate. Compared to M-Ac and M-Bu cultures, maximum PHA content (PHA_m) of M-Pr exhibited the most stable responses to varying fractions of propionic acid (f_Pr) of the substrate. The substrate composed of acetic acid and propionic acid (Mix-AP) demonstrated higher efficiency in regulation of polymer composition than that composed of butyric acid and propionic acid (Mix-BP). For the whole process of three-stage MC PHA production, propionic acid-dominated acidification products should be used for the long-term enrichment of PHA producers, and acidification products mainly composed of propionic and acetic acid are preferred considering the regulation of polymer composition in PHA accumulation stage.

Biobased technologies for the efficient extraction of biopolymers from waste biomass

Regardless of considerable progress in synthetic plastic or polymer-based industry, its low biodegradability is a critical issue. Nevertheless, natural "biopolymers" are gradually replacing them for being inherently biodegradable, eco-friendly with other unique properties. This article aims to present a review regarding different extraction techniques of biopolymers [natural (cellulose, chitin, lignin, pectin, starch, xylan), synthetic (polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyvinyl alcohol (PVA), polymethayl methacrylate (PMMA)] from waste using bio-based methods. The role of bio-based techniques in terms of conventional/ecologically stable strategies for biomass pre-treatment was investigated for proper utilization of waste. The review summarizes strong interplay between technological and future challenges of biopolymer extraction from waste and paints a discussion of how conventional resources could be replaced with more environmentally friendly materials. Therefore, we advocate the implementation of biomass waste from food, organic, and other bio-based industries that revolutionizes the stance of biopolymer in various emerging fields.

Mixed culture polyhydroxyalkanoate (PHA) synthesis from nutrient rich wet oxidation liquors

Organic waste residues can be hydrothermally treated to produce organic acid rich liquors. These hydrothermal liquors are a potential feedstock for polyhydroxyalkanoate (PHA) production. We investigated the effect of dissolved oxygen concentration and substrate feeding regimes on PHA accumulation and yield using two hydrothermal liquors derived from a mixture of primary and secondary municipal wastewater treatment sludge and food waste. The enriched culture accumulated a maximum of 41% PHA of cell dry weight within 7 h; which is among the highest reported for N and P rich hydrothermal liquors. Recovered PHA was 77% polyhydroxybutyrate and 23% polyhydroxyvalerate by mass. The families Rhodocyclaceae (84%) and Saprospiraceae (20.5%) were the dominant Proteobacteria (73%) in the enriched culture. The third most abundant bacterial genus, Bdellovibrio, includes species of known predators of PHA producers which may lead to suboptimal PHA accumulation. The PHA yield was directly proportional to DO concentration for ammonia stripped liquor (ASL) and inversely proportional to DO concentration for low strength liquor (LSL). The highest yield of 0.50 Cmol PHA/Cmol substrate was obtained for ASL at 25% DO saturation. A progressively increasing substrate feeding regime resulted in increased PHA yields. These findings demonstrate that substrate feeding regime and oxygen concentration can be used to control the PHA yield and accumulation rate thereby enhancing PHA production viability from nutrient rich biomass streams.

Impact of Organic Acids Supplementation to Hardwood Spent Sulfite Liquor as Substrate for the Selection of Polyhydroxyalkanoates-Producing Organisms

The effectiveness of polyhydroxyalkanoates (PHAs) production process from a waste stream is determined by the selection of a suitable mixed microbial culture (MMC). In this work, a feedstock from the paper industry, hardwood spent sulfite liquor (HSSL), supplemented with short-chain organic acids (SCOAs) to simulate a fermented effluent, was used as substrate to enrich a MMC in PHA-storing microorganisms. A stable culture was quickly established, and during the accumulation step the selected MMC reached a maximum PHA content of 34.6% (3HB:3HV-76:24). The bacterial community was analyzed through FISH analysis. Bacteria belonging to the four main classes were identified: Betaproteobacteria (44.7 ± 2.7%), Alphaproteobacteria (13.6 ± 1.3%) and Gammaproteobacteria (2.40 ± 1.1%) and Bacteroidetes (9.20 ± 3.8%). Inside the Betaproteobacteria class, Acidovorax (71%) was the dominant genus.

Improving PHA production in a SBR of coupling PHA-storing microorganism enrichment and PHA accumulation by feed-on-demand control

With volatile fatty acids as substrates, the typical polyhydroxyalkanoates (PHAs) production by mixed culture always includes two steps: PHA-storing culture enrichment via aerobic dynamic feeding strategy and PHA accumulation under nutrient-limited condition. To simplify the PHA-production steps, the enrichment and accumulation step were coupled in a SBR. At start-up period, to investigate the effect of settling selection, one acetate-fed SBR was operated by settling selection-double growth limitation (SS-DGL) strategy, while the other was operated by DGL strategy. The results showed that the stable operation in SBR1 was obtained at about 21, 12 days faster than SBR2, implying the settling selection accelerated the start-up process. After omitting the settling selection under the stable operation, the SBR1 was run above 15 days. The results showed that the performance was not substantial altered. Therefore, the settling selection affected the start-up process but not the stable operation. At operational period, based on the sharp decreasing of oxygen uptake rate (OUR), the poly-β-hydroxybutyrate (PHB) content was improved 13%, from 70 to 83% by feed-on-demand control-double growth limitation (FD-DGL). And the harvested volumetric productivity was 5.0 gPHB/L/day, almost 1-folder improvement. That was to say, the PHB production in a SBR of coupling the enrichment and accumulation step was improved by feed-on-demand control. Meanwhile, the FD experiment can keep steady running for 10 SRTs. Therefore, the SS-DGL/FD-DGL strategy was a promising method for PHA production.

Combined polyhydroxyalkanoates (PHA) and 1,3-propanediol production from crude glycerol: Selective conversion of volatile fatty acids into PHA by mixed microbial consortia

Crude glycerol is an important by-product of the biodiesel industry, which can be converted into volatile fatty acids (VFA) and/or 1,3-propanediol (1,3-PDO) by fermentation. In this study, a selective conversion of VFA to polyhydroxyalkanoates (PHA) was attained while leaving 1,3-PDO in the supernatant by means of mixed microbial consortia selection strategies. The process showed highly reproducible results in terms of PHA yield, 0.99 ± 0.07 C_mol PHA/C_mol S (0.84 g COD PHA/g COD S), PHA content (76 ± 3.1 g PHA/100 g TSS) and 1,3-PDO recovery (99 ± 2.1%). The combined process had an ultimate yield from crude glycerol of 0.19 g COD PHA and 0.42 g COD 1,3-PDO per g of input COD. The novel enrichment strategy applied for selectively transforming fermentation by-products into a high value product (PHA) demonstrates the significance of the enrichment process for targeting specific bio-transformations and could potentially prove valuable for other biotechnological applications as well.

Analysis of Medium-Chain-Length Polyhydroxyalkanoate-Producing Bacteria in Activated Sludge Samples Enriched by Aerobic Periodic Feeding

Analysis of mixed microbial populations responsible for the production of medium-chain-length polyhydroxyalkanoates (MCL-PHAs) under periodic substrate feeding in a sequencing batch reactor (SBR) was conducted. Regardless of activated sludge samples and the different MCL alkanoic acids used as the sole external carbon substrate, denaturing gradient gel electrophoresis analysis indicated that Pseudomonas aeruginosa was the dominant bacterium enriched during the SBR process. Several P. aeruginosa strains were isolated from the enriched activated sludge samples. The isolates were subdivided into two groups, one that produced only MCL-PHAs and another that produced both MCL- and short-chain-length PHAs. The SBR periodic feeding experiments with five representative MCL-PHA-producing Pseudomonas species revealed that P. aeruginosa has an advantage over other species that enables it to become dominant in the bacterial community.

Insights into Feast-Famine polyhydroxyalkanoate (PHA)-producer selection: Microbial community succession, relationships with system function and underlying driving forces

The Feast-Famine (FF) process has been frequently used to select polyhydroxyalkanoate (PHA)-accumulating mixed cultures (MCs), but there has been little insight into the ecophysiology of the microbial community during the selection process. In three FF systems with well-defined conditions, synchronized variations in higher-order properties of MCs and complicate microbial community succession mainly including enrichment and elimination of non-top competitors and unexpected turnover of top competitors, were observed. Quantification of PHA-accumulating function genes (phaC) revealed that the top competitors maintained the PHA synthesis by playing consecutive roles when the highly dynamic turnover occurred. Due to its specific physiological characteristics during the PHA-accumulating process, Thauera strain OTU 7 was found to be responsible for the fluctuating SVI, which threatened the robustness of the FF system. This trait was also responsible for its later competitive exclusion by the other PHA-producer, Paracoccus strain OTU 1. Deterministic processes dominated the entire FF system, resulting in the inevitable microbial community succession in the acclimation phase and maintenance of the stable PHA-accumulating function in the maturation phase. However, neutral processes, likely caused by predation from bacterial phages, also occurred, which led to the unpredictable temporal dynamics of the top competitors.

Modeling marine oily wastewater treatment by a probabilistic agent-based approach

This study developed a novel probabilistic agent-based approach for modeling of marine oily wastewater treatment processes. It begins first by constructing a probability-based agent simulation model, followed by a global sensitivity analysis and a genetic algorithm-based calibration. The proposed modeling approach was tested through a case study of the removal of naphthalene from marine oily wastewater using UV irradiation. The removal of naphthalene was described by an agent-based simulation model using 8 types of agents and 11 reactions. Each reaction was governed by a probability parameter to determine its occurrence. The modeling results showed that the root mean square errors between modeled and observed removal rates were 8.73 and 11.03% for calibration and validation runs, respectively. Reaction competition was analyzed by comparing agent-based reaction probabilities, while agents' heterogeneity was visualized by plotting their real-time spatial distribution, showing a strong potential for reactor design and process optimization.

Polyhydroxyalkanoates (PHA) production from fermented crude glycerol: Study on the conversion of 1,3-propanediol to PHA in mixed microbial consortia

Crude glycerol, a by-product from the biodiesel industry, can be converted by mixed microbial consortia into 1,3-propanediol (1,3-PDO) and volatile fatty acids. In this study, further conversion of these main products into polyhydroxyalkanoates (PHA) was investigated with the focus on 1,3-PDO. Two different approaches for the enrichment of PHA accumulating microbial consortia using an aerobic dynamic feeding strategy were applied. With the first approach, where nitrogen was present during the whole cycle, no net production of PHA from 1,3-PDO was observed in the fermented effluent, not even in a nitrogen-limited PHA accumulation assay. Nevertheless, experiments in synthetic substrates revealed that the conversion of 1,3-PDO to PHA was possible under nitrogen limiting conditions. Thus, a different enrichment strategy was formulated where nitrogen was limited during the feast phase to stimulate the storage response. Nitrogen was still supplied during the famine phase. With the latter strategy, a net production of PHA from 1,3-PDO was observed at a yield of 0.24 C_mol PHA/C_mol 1,3-PDO. The overall yield from the fermented effluent was 0.42 C_mol PHA/C_mol substrate. Overall, the PHA yield from 1,3-PDO seemed to be limited, similarly to when using glycerol as a substrate, by a decarboxylation step and accumulation of other storage polymers such as glycogen, and possibly, lipid inclusions.