Phenology and ecological role of aerobic anoxygenic phototrophs in freshwaters.

BACKGROUND: Aerobic anoxygenic phototrophic (AAP) bacteria are heterotrophic bacteria that supply their metabolism with light energy harvested by bacteriochlorophyll-a-containing reaction centers. Despite their substantial contribution to bacterial biomass, microbial food webs, and carbon cycle, their phenology in freshwater lakes remains unknown. Hence, we investigated seasonal variations of AAP abundance and community composition biweekly across 3 years in a temperate, meso-oligotrophic freshwater lake. RESULTS: AAP bacteria displayed a clear seasonal trend with a spring maximum following the bloom of phytoplankton and a secondary maximum in autumn. As the AAP bacteria represent a highly diverse assemblage of species, we followed their seasonal succession using the amplicon sequencing of the pufM marker gene. To enhance the accuracy of the taxonomic assignment, we developed new pufM primers that generate longer amplicons and compiled the currently largest database of pufM genes, comprising 3633 reference sequences spanning all phyla known to contain AAP species. With this novel resource, we demonstrated that the majority of the species appeared during specific phases of the seasonal cycle, with less than 2% of AAP species detected during the whole year. AAP community presented an indigenous freshwater nature characterized by high resilience and heterogenic adaptations to varying conditions of the freshwater environment. CONCLUSIONS: Our findings highlight the substantial contribution of AAP bacteria to the carbon flow and ecological dynamics of lakes and unveil a recurrent and dynamic seasonal succession of the AAP community. By integrating this information with the indicator of primary production (Chlorophyll-a) and existing ecological models, we show that AAP bacteria play a pivotal role in the recycling of dissolved organic matter released during spring phytoplankton bloom. We suggest a potential role of AAP bacteria within the context of the PEG model and their consideration in further ecological models.

Enhanced nitrate removal efficiency and microbial response of immobilized mixed aerobic denitrifying bacteria through biochar coupled with inorganic electron donors in oligotrophic water.

The nitrogen removal characteristics and microbial response of biochar-immobilized mixed aerobic denitrifying bacteria (BIADB) were investigated at 25 °C and 10 °C. BIADB removed 53.51 ± 1.72 % (25 °C) and 39.90 ± 4.28 % (10 °C) nitrate in synthetic oligotrophic water. Even with practical oligotrophic water, BIADB still effectively removed 47.66-53.21 % (25 °C), and 39.26-45.63 % (10 °C) nitrate. The addition of inorganic electron donors increased nitrate removal by approximately 20 % for synthetic and practical water. Bacterial and functional communities exhibited significant temperature and stage differences (P < 0.05), with temperature and total dissolved nitrogen being the main environmental factors. The dominant genera and keystone taxa exhibited significant differences at the two temperatures. Structural equation model analysis showed that dissolved organic matter had the highest direct and indirect effects on diversity and function, respectively. This study provides an innovative pathway for utilizing biochar and inorganic electron donors for nitrate removal from oligotrophic waters.

Comparison of moving bed biofilm reactor and bio-contact oxidation reactor start-up with heterotrophic nitrification-aerobic denitrification bacteria and activated sludge inoculation under high ammonia nitrogen conditions.

To overcome poor ammonia tolerance and removal performance of bio-contact oxidation (BCO) reactor inoculated with activated sludge for high-ammonia nitrogen (NH4+-N) chemical wastewater treatment, this study compared inoculating heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria in moving bed biofilm reactor (MBBR) with activated sludge inoculation in BCO reactor under simulated high NH4+-N conditions. Results revealed that MBBR achieved faster biofilm formation (20 days vs. 100 days for BCO) with notable advantages: 27.6 % higher total nitrogen (TN) and 29.9 % higher NH4+-N removal efficiency than BCO. Microbial analysis indicated optimal enrichment of the key nitrogen removal (NR) bacterium Alcaligenes, leading to increased expression of NR enzymes hydroxylamine reductase, ensuring the superior NR efficiency of the MBBR. Additionally, functional enzymes and genes analysis speculated that the NR pathway in MBBR was: NH4+-N â†’ NH2OH â†’ NO3--N â†’ NO2--N â†’ NO â†’ N2O â†’ N2. This research offers a practical and theoretical foundation for extending HN-AD bacteria-inoculated MBBR processes.

Screening and diversity of culturable HNAD bacteria in the MBR sewage treatment system.

The activated sludge was collected from the Membrane BioReactor (MBR) pool of the sewage treatment system of Sanxing Town, Jintang County, Chengdu, to obtain a good population of heterotrophic nitrifying/aerobic denitrifying (HNAD) bacteria. After undergoing enrichment, isolation, and purification, the HNAD bacteria were selected using the pure culture method. The 16S rDNA molecular technology was used to determine the taxonomy of bacteria. The heterophic nitrifying ability and denitrification capacity of HNAD strains was ascertained through their growth characteristics in heterotrophic nitrification and denitrification media. The results showed that 53 HNAD strains selected from the MBR pool belonged to 2 phyla, 3 classes, 6 orders, 6 families, and 7 genera, with 26 species. Acinetobacter was the largest and dominant genus. Among these, strains numbered (bacterial strain) SW21HD14, SW21HD17, and SW21HD18 were potentially new species in the Acinetobacter genus. Each HNAD strain showed a significant heterotrophic nitrifying and aerobic denitrifying efficiency compared with the control strain (P < 0.05). Specifically, 10 strains demonstrated ammonia nitrogen degradation of greater than 70 mg·L-1 and 9 strains demonstrated nitrate nitrogen degradation above 150 mg·L-1. The HNAD bacteria, which were selected from the MBR pool of sewage treatment system of the Sanxing Town sewage treatment plant, exhibited rich diversity and strong nitrogen removal ability. These findings offered an effective strain source and theoretical basis for implementing biological denitrification technology that involves synchronous nitrification and denitrification.

Aerobic bacteria produce nitric oxide via denitrification and promote algal population collapse.

Microbial interactions govern marine biogeochemistry. These interactions are generally considered to rely on exchange of organic molecules. Here we report on a novel inorganic route of microbial communication, showing that algal-bacterial interactions between Phaeobacter inhibens bacteria and Gephyrocapsa huxleyi algae are mediated through inorganic nitrogen exchange. Under oxygen-rich conditions, aerobic bacteria reduce algal-secreted nitrite to nitric oxide (NO) through denitrification, a well-studied anaerobic respiratory mechanism. The bacterial NO is involved in triggering a cascade in algae akin to programmed cell death. During death, algae further generate NO, thereby propagating the signal in the algal population. Eventually, the algal population collapses, similar to the sudden demise of oceanic algal blooms. Our study suggests that the exchange of inorganic nitrogen species in oxygenated environments is a potentially significant route of microbial communication within and across kingdoms.

Enhanced efficiency and mechanism of low-temperature biochar on simultaneous removal of nitrogen and phosphorus by combined heterotrophic nitrification-aerobic denitrification bacteria.

In this study, three strains of heterotrophic nitrification-aerobic denitrification (HN-AD) capable of simultaneously removing phosphorus were isolated from activated sludge, and low-temperature coconut shell biochar was prepared. The metabolic effects of combined HN-AD bacteria on the total nitrogen (TN) and total phosphorus (TP) were investigated, and the enhanced efficiency and mechanism of low-temperature biochar on the combined bacteria were also explored. The results indicated that the combined bacteria could adapt to environmental impacts and multiple nitrogen sources. The low-temperature biochar containing more aliphatic carbon and oxygen-containing functional groups enhanced the metabolic activity of combined HN-AD bacteria and accelerated the electron transfer process during nitrogen and phosphorus degradation. The removal efficiencies of TN and TP increased by 68% and 88%, respectively, in the treatment of actual sewage by biochar attached with combined bacteria. The findings form a basis for the engineering utilization of HN-AD and are of great practical significance.

Congener-specificity, dioxygenation dependency and association with enzyme binding for biodegradation of polybrominated diphenyl ethers by typical aerobic bacteria: Experimental and theoretical studies.

Polybrominated diphenyl ethers (PBDEs) are a group of organic pollutants that have attracted much concerns of scientific community over the ubiquitous distribution, chemical persistence and toxicological risks in the environment. Though a great number of aerobic bacteria have been isolated for the rapid removal of PBDEs, the knowledge about biodegradation characteristics and mechanism is less provided yet. Herein, the congener-specificity of aerobic biodegradation of PBDEs by typical bacteria, i.e. B. xenovorans LB400 was identified with the different biodegradation kinetics, of which the changes were largely hinged on the bromination pattern. The more bromination isomerically at ortho-sites other than meta-sites or the single bromination at one of aromatic rings might always exert the positive effect. The biodegradation of PBDEs should be thermodynamically constrained to some extent because the calculated Gibbs free energy changes of initial dioxygenation by quantum chemical method increased with the increase of bromination. Within the transition state theory, the high correlativity between the apparent biodegradation rates and Gibbs free energy changes implied the predominance and rate-limiting character of initial dioxygenation, while the regioselectivity of dioxygenation at the ortho/meta-sites was also manifested for the more negative charge population. The molecular binding with the active domain of dioxygenase BphA1 in aerobe was firstly investigated using docking approach. As significantly illustrated with the positive relationship, the higher binding affinity with BphA1 should probably signify the more rapid biodegradation. Besides the edge-on π-π stacking of PBDEs with F227 or Y277 and π-cation formulation with histidines (H233, H239) in BphA1, the reticular hydrophobic contacts appeared as the major force to underpin the high binding affinity and rapid biodegradation of PBDEs. Overall, the experimental and theoretical results would not only help understand the aerobic biodegradation mechanism, but facilitate enhancing applicability or strategy development of engineering bacteria for bioremediation of PBDEs in the environment.

Distribution of the new functional marker gene (pahE) of aerobic polycyclic aromatic hydrocarbon (PAHs) degrading bacteria in different ecosystems.

Understanding the degradation potentials in PAHs-contaminated sites is significant for formulating effective bioremediation strategies. pahE encoding PAHs hydratase-aldolase has been proven as a better new functional marker gene of aerobic PAHs-degrading bacteria to assess the biodegradation potential of indigenous PAHs-degrading bacterial population. However, the distribution of pahE and its relationship with environmental factors remain unknown. The present study observed spatial variations in the diversity and abundance of pahE across oilfield soils, mangrove sediments, and urban roadside soils. nahE from Pseudomonas, bphE from Hyphomonas oceanitis, nagE from Comamonas testosterone, and novel pahE genes were widely present in these PAHs-polluted ecosystems. The abundance of pahE in PAHs-contaminated sites was in the range of 105-106 copies·g-1 (dry weight). Redundancy analysis and Pearson's correlation analysis implied that the distribution of pahE in the PAHs-contaminated environment was mainly shaped by environmental factors such as PAHs pollution level, nutrient level, salinity, and water content. This work was the first to explore the distribution of the new functional marker gene (pahE) and its links with environmental parameters, which provided new insights into the ecophysiology and distribution of indigenous aerobic PAHs-degrading bacteria in contaminated sites.

Nitrogen removal intensification of aerobic granular sludge through bioaugmentation with "heterotrophic nitrification-aerobic denitrification" consortium during petroleum wastewater treatment.

The bioaugmentation potential of aerobic granular sludge (AGS) was investigated using heterotrophic nitrification-aerobic denitrification (HN-AD) bacterial consortium to improve nitrogen removal during petroleum wastewater treatment. An efficient HN-AD consortium was constructed by mixing Pseudomonas mendocina K0, Brucella sp. K1, Pseudomonas putida T4 and Paracoccus sp. T9. AGS bioaugmented by immobilized HN-AD consortium enhanced nitrogen removal, which showed NH4+-N and TN removal efficiency of 92.4% and 79.8%, respectively. The immobilized consortium addition facilitated larger AGS formation, while granules > 2.0 mm accounted for 16.7% higher than that of control (6.7%). Further, the abundance of napA gene was 4-times higher in the bioaugmented AGS as compared to the control, which demonstrated the long-term stability of HN-AD consortium in the bioreactor. The bioaugmented AGS also showed a higher abundance of xenobiotics biodegradation and nitrogen metabolism. These results highlight that bioaugmentation of AGS technology could be effectively used for enhanced denitrification of petroleum wastewater.

Biofilm formation during wastewater treatment: Motility and physiological response of aerobic denitrifying bacteria under ammonia stress based on surface plasmon resonance imaging.

A bacterial image analysis system based on surface plasmon resonance imaging was established to investigate the effect of bacterial motility on biofilm formation under high ammonia nitrogen at the single-cell level. The results showed that the bacterial mean rotation speed and vertical motility distance decreased with the increasing concentration of ammonia nitrogen. Ammonia nitrogen inhibited the metabolic activity of the bacteria, decreasing bacterial motility. Bacterial motility was negatively correlated with the biofilm-formation ability. The biofilm formation ability of Enterobacter cloacae strain HNR exposed to ammonia nitrogen was enhanced by reducing its movement and promoting EPS secretion. Genes related to the tricarboxylic acid cycle and oxidative phosphorylation were down-regulated, indicating inhibition of microbial energy metabolism. Genes related to bacterial secretion and lipopolysaccharide synthesis were up-regulated, facilitating the formation of biofilms and enabling the bacteria to resist ammonia nitrogen stress. This study provides new insights into the biofilm formation under ammonia stress.

A mechanistic review on aerobic denitrification for nitrogen removal in water treatment.

The traditional biological nitrogen removal technology consists of two steps: nitrification by autotrophs in aerobic circumstances and denitrification by heterotrophs in anaerobic situations; however, this technology requires a huge area and stringent environmental conditions. Researchers reached the conclusion that the denitrification process could also be carried out in aerobic circumstances with the discovery of aerobic denitrification. The aerobic denitrification process is carried out by aerobic denitrifying bacteria (ADB), most of which are heterotrophic bacteria that can metabolize various forms of nitrogen compounds under aerobic conditions and directly convert ammonia nitrogen to N2 for discharge from the system. Despite the fact that there is no universal agreement on the mechanism of aerobic denitrification, this article reviewed four current explanations for the denitrification mechanism of ADB, including the microenvironment theory, theory of enzyme, electron transport bottlenecks theory, and omics study, and summarized the parameters affecting the denitrification efficiency of ADB in terms of carbon source, temperature, dissolved oxygen (DO), and pH. It also discussed the current status of the application of aerobic denitrification in practical processes. Following the review, the difficulties of present aerobic denitrification technology are outlined and future research options are highlighted. This review may help to improve the design of current wastewater treatment facilities by utilizing ADB for effective nitrogen removal and provide the engineers with relevant references.

The influence of anaerobic dechlorination on the aerobic degradation of PCBs in e-waste-contaminated soils in an anaerobic-aerobic two-stage treatment.

The combination of microbial reductive dechlorination and aerobic oxidation (RD-AO) process was proposed to be a promising strategy for extensive bioremediation of highly chlorinated polychlorinated biphenyls (PCBs). Nonetheless, experimental evidence on the impact of the RD on subsequent AO in anaerobic-aerobic two-stage treatment remains scarce. The present study applied stable-isotope probing (SIP) to explore the RD-AO mediated degradation of PCBs in an e-waste-contaminated soil. The RD-AO treatment resulted in 37.1 % and 48.2 % degradation of PCB180 and PCB9, respectively, while the PCB9 degradation efficiency decreased compared to the sole AO (81.2 %). The inhibition of PCB aerobic degradation might be caused by the alteration of aerobic bacterial community, which was proved by a higher abundance of anaerobic bacteria and a lower abundance of aerobic bacteria being observed in the aerobic stage of RD-AO. Further evidence was obtained using DNA-SIP that the anaerobic stage altered the PCB degraders' community structures and changed three of the five degraders. There were four lineages (Arenimonas, Steroidobacter, Sulfurifustis, and Thermoanaerobacterales) identified as PCB degraders for the first time. Interestingly, three of them were found in RD-AO microcosm, suggesting that anaerobic-aerobic two-stage treatment can recruit novel bacteria involved in PCBs aerobic degradation. The present study provided novel insight into the synergistic integration of anaerobic and aerobic processes for extensive degradation of highly chlorinated PCBs.

Response of the aerobic denitrifying phosphorus accumulating bacteria Pseudomonas psychrophila HA-2 to low temperature and zinc oxide nanoparticles stress.

Performance and molecular changes of an aerobic denitrifying phosphorus accumulating bacteria Pseudomonas psychrophila HA-2 have been investigated under different temperatures and ZnO nanoparticles (NPs) exposures. Strain HA-2 removed 95.7% of total nitrogen (TN) and 24.6% of phosphorus at 10 °C, which was attributed to the joint up-regulation of intracellular energy metabolism and ribosome. Moreover, with the increase of ZnO NPs from 0 to 100 mg/L, TN and phosphurs removal efficiencies decreased from 95.7% to 44.5% and 24.6% to 6.8% at 10 °C, respectively, whereas phosphorus removal rate increased from 10.5% to 24.5% at 20 °C. Further transcriptomics and proteomics revealed that significant down-regulation of purine and amino acid metabolisms was the main reason for the inhibitory effect at 10 °C, while the up-regulation of antioxidant pathways and functional genes expressions was responsible for the promoted phosphorus accumulation at 20 °C. This study provides a potential solution for improving biological nutrients removal processes in winter months.

Iron-Activated Carbon Systems to Enhance Aboriginal Aerobic Denitrifying Bacterial Consortium for Improved Treatment of Micro-Polluted Reservoir Water: Performances, Mechanisms, and Implications.

Although many source waterbodies face nitrogen pollution problems, the lack of organic electron donors causes difficulties when aerobic denitrifying bacteria are used to treat micro-polluted water. Different forms of iron with granular activated carbon (AC) as carriers were used to stimulate aboriginal microorganisms for the purification of micro-polluted source water. Compared with the iron-absent AC system, targeted pollutants were significantly removed (75.76% for nitrate nitrogen, 95.90% for total phosphorus, and 80.59% for chemical oxygen demand) in the sponge-iron-modified AC system, which indicated that iron promoted the physical and chemical removal of pollutants. In addition, high-throughput sequencing showed that bacterial distribution and interaction were changed by ion dosage, which was beneficial for pollutant transformation and reduction. Microbial functions, such as pollutant removal and expression of functional enzymes that were responsible for the transformation of nitrate nitrogen to ammonia, were highly efficient in iron-applied systems. This study provides an innovative strategy to strengthen in situ remediation of micro-pollution in waterbodies.

Aerobes and phototrophs as microbial organic fertilizers: Exploring mineralization, fertilization and plant protection features.

Organic fertilizers and especially microbial biomass, also known as microbial fertilizer, can enable a paradigm shift to the conventional fertilizer-to-food chain, particularly when produced on secondary resources. Microbial fertilizers are already common practice (e.g. Bloom® and Synagro); yet microbial fertilizer blends to align the nutrient release profile to the plant's needs are, thus far, unexplored. Moreover, most research only focuses on direct fertilization effects without considering added value properties, such as disease prevention. This study has explored three promising types of microbial fertilizers, namely dried biomass from a consortium of aerobic heterotrophic bacteria, a microalga (Arthrospira platensis) and a purple non-sulfur bacterium (Rhodobacter sphaeroides). Mineralization and nitrification experiments showed that the nitrogen mineralization profile can be tuned to the plant's needs by blending microbial fertilizers, without having toxic ammonium peaks. In a pot trial with perennial ryegrass (Lolium perenne L.), the performance of microbial fertilizers was similar to the reference organic fertilizer, with cumulative dry matter yields of 5.6-6.7 g per pot. This was confirmed in a pot trial with tomato (Solanum lycopersicum L.), showing an average total plant length of 90-99 cm after a growing period of 62 days for the reference organic fertilizer and the microbial fertilizers. Moreover, tomato plants artificially infected with powdery mildew (Oidium neolycopersici), a devastating disease for the horticultural industry, showed reduced disease symptoms when A. platensis was present in the growing medium. These findings strengthen the application potential of this novel class of organic fertilizers in the bioeconomy, with a promising match between nutrient mineralization and plant requirements as well as added value in crop protection.

Evaluating the aerobic xylene-degrading potential of the intrinsic microbial community of a legacy BTEX-contaminated aquifer by enrichment culturing coupled with multi-omics analysis: uncovering the role of Hydrogenophaga strains in xylene degradation.

To develop effective bioremediation strategies, it is always important to explore autochthonous microbial community diversity using substrate-specific enrichment. The primary objective of this present study was to reveal the diversity of aerobic xylene-degrading bacteria at a legacy BTEX-contaminated site where xylene is the predominant contaminant, as well as to identify potential indigenous strains that could effectively degrade xylenes, in order to better understand the underlying facts about xylene degradation using a multi-omics approach. Henceforward, parallel aerobic microcosms were set up using different xylene isomers as the sole carbon source to investigate evolved bacterial communities using both culture-dependent and independent methods. Research outcome showed that the autochthonous community of this legacy BTEX-contaminated site has the capability to remove all of the xylene isomers from the environment aerobically employing different bacterial groups for different xylene isomers. Interestingly, polyphasic analysis of the enrichments disclose that the community composition of the o-xylene-degrading enrichment community was utterly distinct from that of the m- and p-xylene-degrading enrichments. Although in each of the enrichments Pseudomonas and Acidovorax were the dominant genera, in the case of o-xylene-degrading enrichment Rhodococcus was the main player. Among the isolates, two Hydogenophaga strains, belonging to the same genomic species, were obtained from p-xylene-degrading enrichment, substantially able to degrade aromatic hydrocarbons including xylene isomers aerobically. Comparative whole-genome analysis of the strains revealed different genomic adaptations to aromatic hydrocarbon degradation, providing an explanation on their different xylene isomer-degrading abilities.

Aerobic polychlorinated biphenyl-degrading bacteria isolated from the Tohoku region of Japan are not regionally endemic.

In the Tohoku region of Japan, 72% of the land comprises mountain forest zones. During winter, severe climatic conditions include heavy snowfall. In such an environment, which is considered high in biodiversity, we assumed that aerobic bacteria would be diverse and would possess the ability to degrade polychlorinated biphenyls (PCBs). In this study, 78 environmental samples were collected from the Tohoku region and 56 aerobic PCB-degrading bacterial strains were isolated. They belonged to the genera Achromobacter, Rhodococcus, Pseudomonas, Stenotrophomonas, Comamonas, Pigmentiphaga, Xenophilus, Acinetobacter, and Pandoraea. Previously reported aerobic PCB-degrading bacterial strains isolated in Japan belonged to the same genera, except that the genera Acidovorax and Bacillus were not identified in the present study. In particular, the isolated Comamonas testosteroni strains YAZ2 and YU14-111 had high PCB-degrading abilities. Analysis of the sequences of the YAZ2 and YU14-111 strains showed that the gene structures of the bph operon, which encode enzymes associated with PCB degradation, were the same as those of the Acidovorax sp. KKS102 strain. Moreover, 2,3-biphenyl dioxygenase activity was responsible for the degradation characteristics of all the isolated strains. Overall, this study suggests that aerobic PCB-degrading bacteria are not specifically endemic to the Tohoku region but distributed across Japan.

The Pathway of Sulfide Oxidation to Octasulfur Globules in the Cytoplasm of Aerobic Bacteria.

Sulfur-oxidizing bacteria can oxidize hydrogen sulfide (H2S) to produce sulfur globules. Although the process is common, the pathway is unclear. In recombinant Escherichia coli and wild-type Corynebacterium vitaeruminis DSM 20294 with sulfide:quinone oxidoreductase (SQR) but no enzymes to oxidize zero valence sulfur, SQR oxidized H2S into short-chain inorganic polysulfide (H2Sn, n ≥ 2) and organic polysulfide (RSnH, n ≥ 2), which reacted with each other to form long-chain GSnH (n ≥ 2) and H2Sn before producing octasulfur (S8), the main component of elemental sulfur. GSnH also reacted with glutathione (GSH) to form GSnG (n ≥ 2) and H2S; H2S was again oxidized by SQR. After GSH was depleted, SQR simply oxidized H2S to H2Sn, which spontaneously generated S8. S8 aggregated into sulfur globules in the cytoplasm. The results highlight the process of sulfide oxidation to S8 globules in the bacterial cytoplasm and demonstrate the potential of using heterotrophic bacteria with SQR to convert toxic H2S into relatively benign S8 globules. IMPORTANCE Our results provide evidence of H2S oxidation producing octasulfur globules via sulfide:quinone oxidoreductase (SQR) catalysis and spontaneous reactions in the bacterial cytoplasm. Since the process is an important event in geochemical cycling, a better understanding facilitates further studies and provides theoretical support for using heterotrophic bacteria with SQR to oxidize toxic H2S into sulfur globules for recovery.

Photoheterotrophy by aerobic anoxygenic bacteria modulates carbon fluxes in a freshwater lake.

Lakes are a significant component of the global carbon cycle. Respiration exceeds net primary production in most freshwater lakes, making them a source of CO2 to the atmosphere. Driven by heterotrophic microorganisms, respiration is assumed to be unaffected by light, thus it is measured in the dark. However, photoheterotrophs, such as aerobic anoxygenic photoheterotrophic (AAP) bacteria that produce ATP via photochemical reactions, substantially reduce respiration in the light. They are an abundant and active component of bacterioplankton, but their photoheterotrophic contribution to microbial community metabolism remains unquantified. We showed that the community respiration rate in a freshwater lake was reduced by 15.2% (95% confidence interval (CI): 6.6-23.8%) in infrared light that is usable by AAP bacteria but not by primary producers. Moreover, significantly higher assimilation rates of glucose (18.1%; 7.8-28.4%), pyruvate (9.5%; 4.2-14.8%), and leucine (5.9%; 0.1-11.6%) were measured in infrared light. At the ecosystem scale, the amount of CO2 from respiration unbalanced by net primary production was by 3.69 × 109 g CO2 lower over these two sampling seasons when measured in the infrared light. Our results demonstrate that dark measurements of microbial activity significantly bias the carbon fluxes, providing a new paradigm for their quantification in aquatic environments.

Selective pressure of biphenyl/polychlorinated biphenyls on the formation of aerobic bacterial associations and their biodegradative potential.

Unique bacterial associations were formed in the polluted soils from territory of the industrial factories Open Joint Stock Company "The Middle Volga Chemical Plant," Chapaevsk, Russia and Open Joint Stock Company "Lubricant Producing Plant," Perm, Russia. This study evaluates the influence of the biphenyl/polychlorinated biphenyls (PCB) on the formation of aerobic bacterial associations and their biodegradative potential. Enrichment cultivation of the soil samples from the territories of these industrial factories with PCB (commercial mixture Sovol) was lead for forming aerobic bacterial enrichment cultures showing a unique composition. The dominating in these bacterial cultures was the phylum Proteobacteria (Beta- and Gammaproteobacteria). Using biphenyl as a carbon source led to decrease of biodiversity in the final stable bacterial associations. Periodic cultivation experiments demonstrated that the association PN2-B has a high degradative potential among the six studied bacterial associations. PN2-B degraded 100% mono-chlorobiphenyls (94.5 mg/L), 86.2% di-chlorobiphenyls (22.3 mg/L), 50.9% Sovol, and 38.4% Delor 103 (13.8 mg/L). Qualitative analysis of metabolites showed that association performed transformation of chlorobenzoic acids (PCB degradation intermediates) into metabolites of citrate cycle. Twelve individual strain-destructors were isolated. The strains were found to degrade 17.7-100% PCB1, 36.2-100% PCB2, 18.8-100% PCB3 (94.5 mg/L), and 15.7-78.2% PCB8 (22.3 mg/L). The strains were shown to metabolize chlorobenzoic acids formed during degradation of chlorobiphenyls. A unique ability of strains Micrococcus sp. PNS1 and Stenotrophomonas sp. PNS6 to degrade ortho-, meta-, and para-monosubstituted chlorobenzoic acids was revealed. Our results suggest that PN2-B and individual bacterial strains will be perspective for cleaning of the environment from polychlorinated biphenyls.