Aerobic Heterotrophs Research Articles

Wintertime Simulations Induce Changes in the Structure, Diversity and Function of Antarctic Sea Ice-Associated Microbial Communities

Antarctic sea-ice is exposed to a wide range of environmental conditions during its annual existence; however, there is very little information describing the change in sea-ice-associated microbial communities (SIMCOs) during the changing seasons. It is well known that during the solar seasons, SIMCOs play an important role in the polar carbon-cycle, by increasing the total photosynthetic primary production of the South Ocean and participating in the remineralization of phosphates and nitrogen. What remains poorly understood is the dynamic of SIMCO populations and their ecological contribution to carbon and nutrient cycling throughout the entire annual life of Antarctic sea-ice, especially in winter. Sea ice at this time of the year is an extreme environment, characterized by complete darkness (which stops photosynthesis), extremely low temperatures in its upper horizons (down to −45 °C) and high salinity (up to 150–250 psu) in its brine inclusions, where SIMCOs thrive. Without a permanent station, wintering expeditions in Antarctica are technically difficult; therefore, in this study, the process of autumn freezing was modelled under laboratory conditions, and the resulting ‘young ice’ was further incubated in cold and darkness for one month. The ice formation experiment was primarily designed to reproduce two critical conditions: (i) total darkness, causing the photosynthesis to cease, and (ii) the presence of a large amount of algae-derived organic matter. As expected, in the absence of photosynthesis, the activity of aerobic heterotrophs quickly created micro-oxic conditions, which caused the emergence of new players, namely facultative anaerobic and anaerobic microorganisms. Following this finding, we can state that Antarctic pack-ice and its surrounding ambient (under-ice seawater and platelet ice) are likely to be very dynamic and can quickly respond to environmental changes caused by the seasonal fluctuations. Given the size of Antarctic pack-ice, even in complete darkness and cessation of photosynthesis, its ecosystem appears to remain active, continuing to participate in global carbon-and-sulfur cycling under harsh conditions.

Purposely Development of the Adaptive Potential of Activated Sludge from Municipal Wastewater Treatment Plant Focused on the Treatment of Landfill Leachate

Biological treatment is a key technology in landfill leachate treatment However, often its efficiency is not high enough due to the pollutants in concentrations above the critical ones. The present study aimed to investigate the adaptive responses that occur in activated sludge (AS) during landfill leachate purification. A model process with AS from a municipal wastewater treatment plant and landfill leachate in increasing concentrations was constructed. The data showed that when dilutions 25 and 50 times had been applied the structure of the AS was preserved, but the COD cannot be reduced below 209 mg O2/L. The feed of undiluted leachate destroyed the AS structure as SVI was reduced to 1 mL/g, biotic index to 1, floc size was greatly reduced and COD remained high (2526 mg O2/L). The dominant group of protozoa was changed from attached to free-swimming ciliates. An increase of the bacterial groups responsible for the xenobiotics elimination (aerobic heterotrophs, genera Pseudomonas, Acinetobacter, Azoarcus, Thauera, Alcaligenes) was registered. This was accompanied by a significant increase in free bacteria. The obtained data showed that for optimal treatment of this type of water it is necessary to include a combination of biological treatment with another non-biological method (membrane filtration, reverse osmosis, etc.).

Model-based design and operation of biotrickling filters for foul air H2S removal at wastewater networks

Biotrickling filters (BTFs) are odour control technologies that utilise the action of sulfur oxidising bacteria to treat foul air contaminated with H2S. BTFs are complex systems where an immobilised biofilm is allowed to grow on a supportive solid media, while the foul air flows counter-currently with a stream of trickling liquid. In this work, a mechanistic model is developed, based on first principles where applicable, that describes the interphase mass transfer and biological oxidation kinetics. The model also focuses on the spatial discretisation of a BTF bed and describes the competition between sulfur oxidising bacteria (SOB) and aerobic heterotrophs growing within different niches of the bed. The model successfully produced concentration profiles over time and space of all relevant chemical and biological species within the bed. The model was then used to theoretically investigate the effect of design and operating parameters on the bed performance. It was found that the optimum liquid rate could vary significantly based on other factors such as bed size and inlet H2S concentrations but a typical value lies between 0.3 and 1.3 m/hr, with a larger bed and/or higher H2S loads requiring higher loading rates to achieve the same treatment levels. The model also predicted that bed shape has no significant impact on H2S removal, provided all other conditions are the same. The model successfully allowed for more detailed design of industrial BTF units in terms of both sizing and tuning of operational parameters.

Performance of second-generation microbial protein used as aquaculture feed in relation to planetary boundaries

Carbon and nitrogen present in residual water streams can be converted into microbial protein and used as animal feed in aquaculture. While microbial protein is thought to be more environmentally sustainable when compared to proteins made from fish residues or plants, nothing is known about how it performs in an absolute sustainability perspective, relative to planetary boundaries. Here, a systems-oriented analysis using life cycle assessment (LCA) linked to the planetary boundaries framework was conducted to assess environmental performance of a pilot-scale microbial protein production from starch-rich process water using aerobic heterotrophs. Results showed that while this microbial-protein indeed performed significantly better than just fishmeal or soybean meal for impacts related to nitrogen (N) and phosphorus (P) flows, none of the three feeds were found sustainable in relation to all planetary boundaries. This constitutes an opportunity for technology developers when the microbial protein production is scaled up and matures.

Peat-Inhabiting Verrucomicrobia of the Order Methylacidiphilales Do Not Possess Methanotrophic Capabilities.

Methanotrophic verrucomicrobia of the order Methylacidiphilales are known as extremely acidophilic, thermophilic or mesophilic bacteria that inhabit acidic geothermal ecosystems. The occurrence of verrucomicrobial methanotrophs in other types of acidic environments remains an open question. Notably, Methylacidiphilales-affiliated 16S rRNA gene sequences are commonly retrieved from acidic (pH 3.5–5.5) peatlands. In this study, we compared the patterns of verrucomicrobial diversity in four acidic raised bogs and six neutral fens located in European North Russia. Methylacidiphilales-like 16S rRNA gene reads displaying 83–86% similarity to 16S rRNA gene sequences of currently described verrucomicrobial methanotrophs were recovered exclusively from raised bogs. Laboratory incubation of peat samples with 10% methane for 3 weeks resulted in the pronounced increase of a relative abundance of alphaproteobacterial methanotrophs, while no response was detected for Methylacidiphilales-affiliated bacteria. Three metagenome-assembled genomes (MAGs) of peat-inhabiting Methylacidiphilales bacteria were reconstructed and examined for the presence of genes encoding methane monooxygenase enzymes and autotrophic carbon fixation pathways. None of these genomic determinants were detected in assembled MAGs. Metabolic reconstructions predicted a heterotrophic metabolism, with a potential to hydrolyze several plant-derived polysaccharides. As suggested by our analysis, peat-inhabiting representatives of the Methylacidiphilales are acidophilic aerobic heterotrophs, which comprise a sister family of the methanotrophic Methylacidiphilaceae.

Fifteen shades of clay: distinct microbial community profiles obtained from bentonite samples by cultivation and direct nucleic acid extraction

Characterizing the microbiology of swelling bentonite clays can help predict the long-term behaviour of deep geological repositories (DGRs), which are proposed as a solution for the management of used nuclear fuel worldwide. Such swelling clays represent an important component of several proposed engineered barrier system designs and, although cultivation-based assessments of bentonite clay are routinely conducted, direct nucleic acid detection from these materials has been difficult due to technical challenges. In this study, we generated direct comparisons of microbial abundance and diversity captured by cultivation and direct nucleic acid analyses using 15 reference bentonite clay samples. Regardless of clay starting material, the corresponding profiles from cultivation-based approaches were consistently associated with phylogenetically similar sulfate-reducing bacteria, denitrifiers, aerobic heterotrophs, and fermenters, demonstrating that any DGR-associated growth may be consistent, regardless of the specific bentonite clay starting material selected for its construction. Furthermore, dominant nucleic acid sequences in the as-received clay microbial profiles did not correspond with the bacteria that were enriched or isolated in culture. Few core taxa were shared among cultivation and direct nucleic acid analysis profiles, yet those in common were primarily affiliated with Streptomyces, Micrococcaceae, Bacillus, and Desulfosporosinus genera. These putative desiccation-resistant bacteria associated with diverse bentonite clay samples can serve as targets for experiments that evaluate microbial viability and growth within DGR-relevant conditions. Our data will be important for global nuclear waste management organizations, demonstrating that identifying appropriate design conditions with suitable clay swelling properties will prevent growth of the same subset of clay-associated bacteria, regardless of clay origin or processing conditions.

Microbiology of barrier component analogues of a deep geological repository.

Canada is currently implementing a site selection process to identify a location for a deep geological repository (DGR) for the long-term storage of Canada's used nuclear fuel, wherein used nuclear fuel bundles will be sealed inside copper-coated carbon steel containers, encased in highly compacted bentonite clay buffer boxes, and sealed deep underground in a stable geosphere. Because a DGR must remain functional for a million years, it is important to examine ancient natural systems that serve as analogues for planned DGR components. Specifically, studying the microbiology of natural analogue components of a DGR is important for developing an understanding of the types of microorganisms that may be able to grow and influence the long-term stability of a DGR. This study explored the abundance, viability, and composition of microorganisms in several ancient natural analogues using a combination of cultivation and cultivation-independent approaches. Samples were obtained from the Tsukinuno bentonite deposit (Japan) that formed ∼10 mya, the Opalinus Clay formation (Switzerland) that formed ∼174 mya, and Canadian shield crystalline rock from Northern Ontario that formed ∼2.7 bya. Analysis of 16S rRNA gene amplicons revealed that three of the ten Tsukinuno bentonite samples analyzed were dominated by putative aerobic heterotrophs and fermenting bacteria from the phylum Actinobacteria, whereas five of the Tsukinuno bentonite samples were dominated by sequences associated with putative acidophilic chemolithoautotrophs capable of sulfur reduction. The remaining Tsukinuno bentonite samples, the Northern Ontario rock samples, and the Opalinus Clay samples generated inconsistent replicate 16S rRNA gene profiles and were associated primarily with contaminant sequences, suggesting that the microbial profiles detected were not sample-specific but spurious. Culturable aerobic heterotroph abundances were relatively low for all Tsukinuno bentonite samples, culturable anaerobic heterotrophs were only detected in half of the Tsukinuno samples, and sulfate-reducing bacteria (SRB) were only detected in one Tsukinuno sample by cultivation. Culture-specific 16S rRNA gene profiles from Tsukinuno clay samples demonstrated the presence of phyla Bacteroidetes, Proteobacteria, Actinobacteria, and Firmicutes among aerobic heterotroph cultures and additional bacteria from the phyla Actinobacteria and Firmicutes from anaerobic heterotroph plate incubations. Only one nucleic acid sequence detected from a culture was also associated with its corresponding clay sample profile, suggesting that nucleic acids from culturable bacteria were relatively rare within the clay samples. Sequencing of DNA extracted from the SRB culture revealed that the taxon present in the culture was affiliated with the genus Desulfosporosinus, which has been found in related bentonite clay analyses. Although the crystalline rock and Opalinus Clay samples were associated with inconsistent, likely spurious 16S rRNA gene profiles, we show evidence for viable and detectable microorganisms within several Tsukinuno natural analogue bentonite samples.

Pontibacillus sp. ALD_SL1 and Psychroflexus sp. ALD_RP9, two novel moderately halophilic bacteria isolated from sediment and water from the Aldabra Atoll, Seychelles.

Pontibacillus sp. ALD_SL1 and Psychroflexus sp. ALD_RP9 are two novel bacterial isolates from mangrove sediment and a moderately hypersaline pool on the Aldabra Atoll, Seychelles. The isolates represent two novel species were characterised physiologically and genomically. Pontibacillus sp. ALD_SL1 is a facultatively anaerobic yellow, motile, rod-shaped Gram-positive, which grows optimally at a NaCl concentration of 11%, pH 7 and 28°C. It is the third facultatively anaerobic member of the genus Pontibacillus. The organism gains energy through the fermentation of pyruvate to acetate and ethanol under anaerobic conditions. The genome is the first among Pontibacillus that harbours a megaplasmid. Psychroflexus sp. ALD_RP9 is an aerobic heterotroph, which can generate energy by employing bacteriorhodopsins. It forms Gram-negative, orange, non-motile rods. The strain grows optimally at NaCl concentrations of 10%, pH 6.5–8 and 20°C. The Psychroflexus isolate tolerated pH conditions up to 10.5, which is the highest pH tolerance currently recorded for the genus. Psychroflexus sp. ALD_RP9 taxonomically belongs to the clade with the smallest genomes. Both isolates show extensive adaptations to their saline environments yet utilise different mechanisms to ensure survival.

Metagenomic Insights Into Ecosystem Function in the Microbial Mats of a Large Hypersaline Coastal Lagoon System

The hypersaline lagoon system of Araruama (HLSA) is one of the largest in the world and one of the most important sources of evaporative salt in Brazil. The biogeochemical characteristics of this lagoon system led it to be considered a Precambrian relic. The HLSA also harbors extensive microbial mats, but the taxonomic and metabolic attributes of these mats are poorly understood. Our high-throughput metagenomics analyses demonstrated that the HLSA microbial mats are dominated by Proteobacteria, Cyanobacteria, and Bacteroidetes. Among Proteobacteria, Deltaproteobacteria comprises approximately 40% of the total population and it includes sulfate-reducing bacteria such as Desulfobacterales, Desulfuromonadales, and Desulfovibrionales. Differing in composition and function of their reaction centers, other phylogenetic diverse anoxygenic phototrophic bacteria were detected in the HLSA microbial mats metagenomes. The presence of photolithoautotrophs, sulfate reducers, sulfide oxidizers, and aerobic heterotrophs suggests the existence of numerous cooperative niches that are coupled and regulated by microbial interactions. We suggest that the HLSA microbial mats hold microorganisms and the necessary machinery (genomic repertoire to sustain metabolic pathways) to promote favorable conditions (i.e., create an alkaline pH microenvironment) for microbially mediated calcium carbonate precipitation process. Metagenome-assembled genomes (Ca. Thiohalocapsa araruaensisHLSAbin6 sp. nov. andCa. Araruabacter turfaeHLSAbin9 gen. nov. sp. nov.) obtained support the relevance of Sulfur metabolism and they are enriched with genes involved in the osmoadaptive networks, hinting at possible strategies to withstand osmotic stress. Metabolically versatile bacteria populations, able to use multiple nutrient sources and osmolytes, seem to be a relevant attribute to survive under such stressful conditions.

Advanced nitrogen and phosphorus removal by combining endogenous denitrification and denitrifying dephosphatation in constructed wetlands

To achieve high-efficiency nutrient removal in constructed wetlands (CWs), a novel simultaneous nitrogen and phosphorus removal (SNPR) process was developed by combining nitrification, endogenous denitrification, and denitrifying phosphorus removal. In SNPR process, denitrifying glycogen-accumulating organisms (DGAOs) and denitrifying polyphosphate-accumulating organisms (DPAOs) utilized NOx--N(NO3--N or NO2--N) as electron acceptor and poly-beta-hydroxy-alkanoates (PHAs) as carbon sources for endogenous denitrification and denitrifying phosphorus removal processes. Results from 217 days of operation showed that a high-level of nitrogen removal efficiency of 83.73% was achieved with influent COD/N of 4. The success was attributed to the fact that most of influent carbon sources could be transformed into PHAs before nitrification via enriching DGAOs and DPAOs in CW, which simultaneously improved nitrification and denitrification due to reducing oxygen and carbon sources consumption by aerobic heterotrophs. Phosphorus was mainly removed via denitrifying phosphorus removal, and PO43--P removal efficiency reached up to 87.84% with even common gravel used as substrate. Stoichiometry analysis revealed that DGAOs were the main organisms providing nitrite to DPAOs, suggesting that the effective PO43--P removal under high DGAO abundance condition might be attributed to the coordination of DGAOs and DPAOs in SNRP processes.

Thermophilic Chloroflexi Dominate in the Microbial Community Associated with Coal-Fire Gas Vents in the Kuznetsk Coal Basin, Russia.

Thermal ecosystems associated with areas of underground burning coal seams are rare and poorly understood in comparison with geothermal objects. We studied the microbial communities associated with gas vents from the coal-fire in the mining wastes in the Kemerovo region of the Russian Federation. The temperature of the ground heated by the hot coal gases and steam coming out to the surface was 58 °C. Analysis of the composition of microbial communities revealed the dominance of Ktedonobacteria (the phylum Chloroflexi), known to be capable of oxidizing hydrogen and carbon monoxide. Thermophilic hydrogenotrophic Firmicutes constituted a minor part of the community. Among the well-known thermophiles, members of the phyla Aquificae, Deinococcus-Thermus and Bacteroidetes were also found. In the upper ground layer, Acidobacteria, Verrucomicrobia, Actinobacteria, Planctomycetes, as well as Proteobacteria of the alpha and gamma classes, typical of soils, were detected; their relative abundancies decreased with depth. The phylum Verrucomicrobia was dominated by Candidatus Udaeobacter, aerobic heterotrophs capable of generating energy through the oxidation of hydrogen present in the atmosphere in trace amounts. Archaea made up a small part of the communities and were represented by thermophilic ammonium-oxidizers. Overall, the community was dominated by bacteria, whose cultivated relatives are able to obtain energy through the oxidation of the main components of coal gases, hydrogen and carbon monoxide, under aerobic conditions.

Differential effects of redox conditions on the decomposition of litter and soil organic matter

Soil redox conditions exert substantial influence on biogeochemical processes in terrestrial ecosystems. Humid tropical forest soils are often characterized by fluctuating redox, yet how these dynamics affect patterns of organic matter decomposition and associated CO2 fluxes remains poorly understood. We used a 13C-label incubation experiment in a humid tropical forest soil to follow the decomposition of plant litter and soil organic matter (SOM) in response to four redox regimes—static oxic or anoxic, and two oscillating treatments. We used high-resolution mass spectrometry to characterize the relative composition of organic compound classes in the water extractable OM. CO2 production from litter and SOM showed different responses to redox treatments. While cumulative production of SOM-derived CO2 was positively correlated with the length of oxic exposure (r = 0.89, n = 20), cumulative 13C-litter-derived CO2 production was not linked to oxygen availability. Litter-derived CO2 production was highest under static anoxic conditions in the first half of the experiment, and later dropped to the lowest rate amongst the treatments. In anoxic soils, we observed depletion of more oxidized water-extractable OM (especially amino sugar-, carbohydrate-, and protein-like compounds) over the second half of the experiment, which likely served as substrates for anaerobic CO2 production. Results from two-pool kinetic modeling showed that more frequent anoxic exposure limited decomposition of a slow-cycling C pool, but not a fast-cycling pool. These results suggest that aerobic and anaerobic heterotrophs were equally effective at degrading labile substrates released from fresh plant litter in this humid tropical forest soil, while aerobic decomposers were more effective in breaking down the potentially refractory compounds found in SOM.

Heterotrophic enzymatic biotransformations of organic micropollutants in activated sludge.

While heterotrophic microorganisms constitute the major fraction of activated sludge biomass, the role of heterotrophs in the biotransformation of organic micropollutants (OMPs) has not been fully elucidated. Yet, such knowledge is essential, particularly when conceiving novel wastewater treatment plants based on a two-stage process including an A-stage under heterotrophic conditions and a B-stage based on anammox activity. Biotransformation of OMPs in activated sludge is thought to mostly occur cometabolically thanks to the action of low specificity enzymes involved in the metabolism of the primary substrates. For a better understanding of the process, it is important to determine such enzymatic activities and the underlying mechanisms involved in OMPs biotransformation. This task has proven to be difficult due to the lack of information about the enzymatic processes and the complexity of the biological systems present in activated sludge. In this paper, a continuous aerobic heterotrophic reactor following 20 OMPs at environmental concentrations was operated to (i) assess the potential of heterotrophs during the cometabolic biotransformation of OMPs, (ii) identify biotransformation reactions catalyzed by aerobic heterotrophs and (iii) predict possible heterotrophic enzymatic activities responsible for such biotransformations. Contradicting previous reports on the dominant role of nitrifiers in OMPs removal during activated sludge treatment, the heterotrophic population proved its capacity to biotransform the OMPs to extents equivalent to reported values in nitrifying activated sludge plants. Besides, 12 transformation products potentially formed through the activity of several enzymes present in heterotrophs, including monooxygenases, dioxygenases, hydrolases and transferases, were identified.

Transport of dissolved oxygen at the sediment-water interface in the spanwise oscillating flow

The distribution and concentration of dissolved oxygen (DO) play important roles in aerobic heterotroph activities and some slow chemical reactions, and can affect the water quality, biological communities, and ecosystem functions of rivers and lakes. In this work, the transport of high Schmidt number DO at the sediment-water interface of spanwise oscillating flow is investigated. The volume-averaged Navier-Stokes (VANS) equations and Monod equation are used to describe the flow in the sediment layer and the sediment oxygen demand of microorganisms. The phase-averaged velocities and concentrations of different amplitudes and periods are studied. The dependence of DO transfer on the amplitude and period is analyzed by means of phase-average statistical quantities. It is shown that the concentration in the sediment layer is positively correlated with the turbulence intensity, and the DO concentration and penetration depth in the sediment layer increases when the period and amplitude of the oscillating flow increase. Moreover, in the presence of oscillating flow, a specific scaling relationship exists between the Sherwood number/oxygen consumption of aerobic heterotrophs and the Reynolds number.

Microbial succession and dynamics in meromictic Mono Lake, California.

Mono Lake is a closed‐basin, hypersaline, alkaline lake located in Eastern Sierra Nevada, California, that is dominated by microbial life. This unique ecosystem offers a natural laboratory for probing microbial community responses to environmental change. In 2017, a heavy snowpack and subsequent runoff led Mono Lake to transition from annually mixed (monomictic) to indefinitely stratified (meromictic). We followed microbial succession during this limnological shift, establishing a two‐year (2017–2018) water‐column time series of geochemical and microbiological data. Following meromictic conditions, anoxia persisted below the chemocline and reduced compounds such as sulfide and ammonium increased in concentration from near 0 to ~400 and ~150 µM, respectively, throughout 2018. We observed significant microbial succession, with trends varying by water depth. In the epilimnion (above the chemocline), aerobic heterotrophs were displaced by phototrophic genera when a large bloom of cyanobacteria appeared in fall 2018. Bacteria in the hypolimnion (below the chemocline) had a delayed, but systematic, response reflecting colonization by sediment “seed bank” communities. Phototrophic sulfide‐oxidizing bacteria appeared first in summer 2017, followed by microbes associated with anaerobic fermentation in spring 2018, and eventually sulfate‐reducing taxa by fall 2018. This slow shift indicated that multi‐year meromixis was required to establish a sulfate‐reducing community in Mono Lake, although sulfide oxidizers thrive throughout mixing regimes. The abundant green alga Picocystis remained the dominant primary producer during the meromixis event, abundant throughout the water column including in the hypolimnion despite the absence of light and prevalence of sulfide. Our study adds to the growing literature describing microbial resistance and resilience during lake mixing events related to climatic events and environmental change.

Purple phototrophic bacteria are outcompeted by aerobic heterotrophs in the presence of oxygen

There is an ongoing debate around the effect of microaerobic/aerobic conditions on the wastewater treatment performance and stability of enriched purple phototrophic bacteria (PPB) cultures. It is well known that oxygen-induced oxidative conditions inhibit the synthesis of light harvesting complexes, required for photoheterotrophy. However, in applied research, several publications have reported efficient wastewater treatment at high dissolved oxygen (DO) levels. This study evaluated the impact of different DO concentrations (0-0.25 mg·L−1, 0-0.5 mg·L−1 and 0-4.5 mg·L−1) on the COD, nitrogen and phosphorus removal performances, the biomass yields, and the final microbial communities of PPB-enriched cultures, treating real wastewaters (domestic and poultry processing wastewater). The results show that the presence of oxygen suppressed photoheterotrophic growth, which led to a complete pigment and colour loss in a matter of 20-30 h after starting the batch. Under aerobic conditions, chemoheterotrophy was the dominant catabolic pathway, with wastewater treatment performances similar to those achieved in common aerobic reactors, rather than those corresponding to phototrophic systems (i.e. considerable total COD decrease (45-57% aerobically vs. ± 10% anaerobically). This includes faster consumption of COD and nutrients, lower nutrient removal efficiencies (50-58% vs. 72-99% for NH4+-N), lower COD:N:P substrate ratios (100:4.5-5.0:0.4-0.8 vs. 100:6.7-12:0.9-1.2), and lower apparent biomass yields (0.15-0.31 vs. 0.8-1.2 g CODbiomass·g CODremoved−1)). The suppression of photoheterotrophy inevitably resulted in a reduction of the relative PPB abundances in all the aerated tests (below 20% at the end of the tests), as PPB lost their main competitive advantage against competing aerobic heterotrophic microbes. This was explained by the lower aerobic PPB growth rates (2.4 d−1 at 35 °C) when compared to common growth rates for aerobic heterotrophs (6.0 d−1 at 20 °C). Therefore, PPB effectively outcompete other microbes under illuminated-anaerobic conditions, but not under aerobic or even micro-aerobic conditions, as shown by continuously aerated tests controlled at undetectable DO levels. While their aerobic heterotrophic capabilities provide some resilience, at non-sterile conditions PPB cannot dominate when growing chemoheterotrophically, and will be outcompeted.

Determination of design loading rates for simultaneous anaerobic oxidation/partial nitrification–denitrification process and application in treating dairy industry effluent

Organic carbon and nitrogen removal from highly polluted streams by using a simultaneous anaerobic oxidation/partial nitrification–denitrification (SAO/PND) system are investigated. Design loading rates of the chemical oxygen demand (COD) and total inorganic nitrogen (TIN) in this new developed process are recommended as 11.80 g COD L-1 d-1 and 0.63 g TIN L-1 d-1. The results showed 97% COD and 92% TIN removal efficiencies. High performance of the system was achieved in treating real dairy wastewater as well, and the effluent complied with international discharge standards into inland surface waters. Organic carbon was removed through anaerobic oxidation, assimilation, P–uptake by polyphosphate accumulating organisms (PAOs) and denitrifying PAOs (DPAOs), aerobic heterotrophs, and denitrification by DPAOs and denitrifying ordinary heterotrophic organisms (OHOs). Nitrogen removal mechanisms were assimilation, partial nitrification–denitrification, anaerobic ammonium oxidation (anammox), and small portion uncharacterized processes. The SAO/PND system is found as an efficient, innovative, cost–effective, energy efficient, and small footprint process with less intensive operation and maintenance requirements. This system has been verified as a robust treatment method, and will yield new insights into the design of treating highly polluted streams in the future.

Ammonium and organic carbon co-removal under feammox-coupled-with-heterotrophy condition as an efficient approach for nitrogen treatment

Nitrification is the rate limiting step in the nitrogen removal processes since nitrifiers have high oxygen demand, but poorly compete with aerobic heterotrophs. In a laboratory-scaled system, we investigated a process of ammonium oxidation under ferric-iron reducing condition (feammox) in the presence of organic carbon using influents with high NH4+ and COD contents, and ferrihydrite as the only electron acceptor. Batch incubations testing influents with different NH4+ and COD concentrations revealed that the [COD]/[NH4+] ratio of 1.4 and the influent redox potential ranging from − 20 to + 20 mV led to the highest removal efficiencies, i.e. 98.3% for NH4+ and 58.8% for COD. N2 was detected as the only product of NH4+ conversion, whereas NO2− and NO3− were not detected. While operating continuously with influent having a [COD]/[NH4+] ratio of 1.4, the system efficiently removed NH4+ (> 91%) and COD (> 54%) within 6 day retention time. Fluorescence in situ hybridization analyses using Cy3-labeled 16S rRNA oligonucleotide probes revealed that gamma-proteobacteria dominated in the microbial community attaching to the matrix bed of the system. The iron-reduction dependent NH4+ and COD co-removal with a thorough conversion of NH4+ to N2 demonstrated in this study would be a novel approach for nitrogen treatment.

Uklanjanje patogenih mikroorganizama u biološkom sistemu sa plutajućim ostrvima

Pathogenic microorganisms in water pose a great risk to human health. Therefore, it is necessary to find an efficient, environmentally friendly, and economically acceptable solution for their removal from polluted and wastewater. This paper presents the efficiency of a biological system with floating islands in the removal of pathogenic microorganisms from the water of a polluted urban river. The modified floating treatment wetland consisted of a collection tank, 4 calls with floating islands and 1 cell with algae, which enabled additional water polishing. The results of the research showed that the biological system constructed on the bank of this river had a high efficiency in reducing the number of various groups of pathogenic microorganisms. Within the cells with the floating islands, 100% efficiency in the removal of coliform bacteria of faecal origin was achieved, and the reduction of pathogens was continued within the cell with algae. The realised efficiency of removal of total coliform bacteria was 100% in all cells, except in the cell 4 with decorative aquatic macrophytes, in which the efficiency was 97%. The number of intestinal enterococci was reduced in the range of 92 to 97% in cells with plants, and up to 98% in the cells with algae. The floating islands and algae also enabled a high reduction in the number of aerobic heterotrophs and facultative oligotrophs. In addition, the ratio of these microorganisms had a value above 1 during the entire period of water treatment, which indicated that natural processes of self-purification of polluted water ran smoothly in the floating treatment wetland. Due to the reduction of pathogenic microorganisms, water that belonged to class V, i.e., III, after the discharge from the biological system, had the characteristics of water with excellent ecological status (class I).

Ecophysiological Study of Paraburkholderia sp. Strain 1N under Soil Solution Conditions: Dynamic Substrate Preferences and Characterization of Carbon Use Efficiency.

We used time-resolved metabolic footprinting, an important technical approach used to monitor changes in extracellular compound concentrations during microbial growth, to study the order of substrate utilization (i.e., substrate preferences) and kinetics of a fast-growing soil isolate, Paraburkholderia sp. strain 1N. The growth of Paraburkholderia sp. 1N was monitored under aerobic conditions in a soil-extracted solubilized organic matter medium, representing a realistic diversity of available substrates and gradient of initial concentrations. We combined multiple analytical approaches to track over 150 compounds in the medium and complemented this with bulk carbon and nitrogen measurements, allowing estimates of carbon use efficiency throughout the growth curve. Targeted methods allowed the quantification of common low-molecular-weight substrates: glucose, 20 amino acids, and 9 organic acids. All targeted compounds were depleted from the medium, and depletion followed a sigmoidal curve where sufficient data were available. Substrates were utilized in at least three distinct temporal clusters as Paraburkholderia sp. 1N produced biomass at a cumulative carbon use efficiency of 0.43. The two substrates with highest initial concentrations, glucose and valine, exhibited longer usage windows, at higher biomass-normalized rates, and later in the growth curve. Contrary to hypotheses based on previous studies, we found no clear relationship between substrate nominal oxidation state of carbon (NOSC) or maximal growth rate and the order of substrate depletion. Under soil solution conditions, the growth of Paraburkholderia sp. 1N induced multiauxic substrate depletion patterns that could not be explained by the traditional paradigm of catabolite repression.IMPORTANCE Exometabolomic footprinting methods have the capability to provide time-resolved observations of the uptake and release of hundreds of compounds during microbial growth. Of particular interest is microbial phenotyping under environmentally relevant soil conditions, consisting of relatively low concentrations and modeling pulse input events. Here, we show that growth of a bacterial soil isolate, Paraburkholderia sp. 1N, on a dilute soil extract resulted in a multiauxic metabolic response, characterized by discrete temporal clusters of substrate depletion and metabolite production. Our data did not support the hypothesis that compounds with lower energy content are used preferentially, as each cluster contained compounds with a range of nominal oxidation states of carbon. These new findings with Paraburkholderia sp. 1N, which belongs to a metabolically diverse genus, provide insights on ecological strategies employed by aerobic heterotrophs competing for low-molecular-weight substrates in soil solution.