Multiplexed Workplace Measurements in Biogas Plants Reveal Compositional Changes in Aerosol Properties

Anaerobic digestion is an emerging technology producing energy from renewable resources or food waste. Exposure screenings, comprising hazardous substances and biological agents, at different workplaces are necessary for a comprehensive overview of potential hazards in order to assess the risk of employees in biogas plants. In order to analyse these parameters, workplace measurements were conducted in seven full-scale anaerobic digesters. Personal and stationary sampling was performed for inhalable and respirable particles, volatile organic compounds, ammonia, hydrogen sulphide, carbon monoxide, and carbon dioxide. Furthermore, concentrations of the total cell count, endotoxins, and fungi—down to species level—were determined in comparison to windward air. Sequencing of the 16S rRNA genes was utilized for the determination of the bacterial composition inside the biogas plants. Measurements of hazardous substances show hardly values reaching the specific occupational exposure limit value, except ammonia. An approximate 5-fold increase in the median of the total cell count, 15-fold in endotoxins, and 4-fold in fungi was monitored in the biogas plants compared with windward air. Specifying the comparison to selected workplaces showed the highest concentrations of these parameters for workplaces related to delivery and cleaning. Strikingly, the fungal composition drastically changed between windward air and burdened workplaces with an increase of Aspergillus species up to 250-fold and Penicillium species up to 400-fold. Sequence analyses of 16S rRNA genes revealed that many workplaces are dominated by the order of Bacillales or Lactobacillales, but many sequences were not assignable to known bacteria. Although significant changes inside the biogas plant compared with windward air were identified, that increase does not suggest stricter occupational safety measures at least when applying German policies. However, exposure to biological agents revealed wide ranges and specific workplace measurements should be conducted for risk assessment.

Eggshells as a source for occupational exposure to airborne bacteria in hatcheries

Occupational exposure to high concentrations of airborne bacteria in poultry production is related to an increased risk of respiratory disorders. However, potential sources and formation of hatchery bioaerosols are rarely characterized. In this study, bacterial multiplication on fresh shell fragments from turkey hatching eggs under conditions present in a hatcher incubator was investigated. A 10⁵-fold amplification was observed both by colony count and total cell count gaining 4 × 10⁷ cfu/cells per gram eggshell within 30 hr of incubation. Furthermore, the bacterial community present on eggshells was analyzed by generation of 16S rRNA gene clone libraries and identification of eight isolates. RFLP analysis revealed no shift in community composition during incubation and Enterococcus faecalis and Enterococcus gallinarum were found as the predominant species on turkey eggshells, both have been classified as risk group 2 microorganisms (German TRBA 466). Since Enterococcus spp. were found as predominant species on turkey eggshells, contribution of this genus to bioaerosol formation was demonstrated. During different work activities with poult and eggshell handling concentrations of airborne enterococci up to 1.3 × 10⁴ cfu m^-3 were detected. In contrast, no enterococci were identified at a day without poult or eggshell processing. In conclusion, turkey hatching eggs carry a viable specific microflora from breeder flocks to hatcheries. After hatching of turkey poults, hatcher incubators and eggshell fragments provide appropriate conditions for excessive bacterial growth. Thus, high bacterial loads on eggshell fragments are a source of potential harmful bioaersols caused by air flows, poult activity, and handling of equipment.

Concentration of bioaerosols in composting plants using different quantification methods

BACKGROUND

Bioaerosols (organic dusts) containing viable and non-viable microorganisms and their metabolic products can lead to adverse health effects in exposed workers. Standard quantification methods of airborne microorganisms are mainly based on cultivation, which often underestimates the microbial burden. The aim of the study was to determine the microbial load in German composting plants with different, mainly cultivation-independent, methods. Second purpose was to evaluate which working areas are associated with higher or lower bioaerosol concentrations.

METHODS

A total of 124 inhalable dust samples were collected at different workplaces in 31 composting plants. Besides the determination of inhalable dust, particles, and total cell numbers, antigen quantification for moulds (Aspergillus fumigatus, Aspergillus versicolor, Penicillium chrysogenum, and Cladosporium spp.) and mites was performed. Concentrations of β-glucans as well as endotoxin and pyrogenic activities were also measured. The number of colony forming units (cfu) was determined by cultivation of moulds and actinomycetes in 36 additional dust samples.

RESULTS

With the exception of particle numbers, concentrations of all determined parameters showed significant correlations (P < 0.0001; r Spearman: 0.40-0.80), indicating a close association between these exposure markers. Colony numbers of mesophilic moulds and actinomycetes correlated also significantly with data of cultivation-independent methods. Exposure levels showed generally large variations. However, all parameters were measured highest in dusty working areas like next to the shredder and during processing with the exception of Cladosporium antigens that were found in the highest concentrations in the delivery area. The lowest concentrations of dust, particles, antigens, and pyrogenic activity were determined in wheel loader cabins (WLCs), which were equipped with an air filtration system.

CONCLUSION

It was possible to assess the microbial load of air in composting plants with different quantification methods. Since allergic and toxic reactions may be also caused by nonliving microorganisms, cultivation-independent methods may provide additional information about bioaerosol composition. In general, air filtration reduced the bioaerosol exposure shown in WLCs. Due to the fact that the mechanical processing of compost material, e.g. by shredding or sieving is associated with the generation of high bioaerosol concentrations, there is still a need of improved risk assessment and state-of-the-art protective measures in composting plants.

Quantification of Saccharopolyspora rectivirgula in composting plants: assessment of the relevance of S. rectivirgula

Exposure to bioaerosols in composting plants can lead to negative health effects on compost workers. Health complaints vary between cough, irritation of the eyes and the skin, sinusitis, or dyspnea among others. It is fact that compost materials harbor high concentrations of microorganisms, which were aerosolized during handling compost. Within the present study, total cell numbers between 3.4 × 10(4) and 1.6 × 10(8) cell counts per m(3) air were determined after 4',6-Diamidin-2-phenylindol DAPI staining in 124 samples from German composting plants. Special attention should be paid to some specific microorganisms, which are able to cause health complaints. Saccharopolyspora rectivirgula, known to be one of the major causes of extrinsic allergic alveolitis (EAA, also called hypersensitivity pneumonitis, HP), was often found in environments of agricultural production, where the classical form of EAA ('farmer's lung disease') is common, but also in composting plants. In Germany, cases are known where workers had to terminate their work due to this disease. However, up to now, the relevance of S. rectivirgula at composting plants is unexplained. This study showed that high concentrations of airborne S. rectivirgula were found in composting plants similar to that found in agricultural production. Altogether, in 86.7% of the 124 analyzed samples, S. rectivirgula was detected using quantitative real-time polymerase chain reaction (PCR). Estimated concentrations ranged between 1.24 × 10(2) cell counts of S. rectivirgula per cubic meter air next to the rotted residues and 1.5 × 10(7) cell counts next to a converter. Furthermore, our methodical proceedings were verified. To analyze DNA extraction limits through the amount of cells within one sample, the DNA concentration was compared with total cell counts (TCCs). Altogether, when TCC was <1.4 × 10(5) cells per DNA extraction assay, no DNA was measurable; when TCC reached 3.5 × 10(6) cells, DNA was always detectable by fluorometric method. To overcome limitation of DNA measurement using fluorometric method, samples without measurable DNA were inserted in a PCR assay with universal primers. Results showed that a gain of 37% was possible, when samples were additionally analyzed by universal PCR. Hence, cell counts >2.0 × 10(6) cells were necessary to measure DNA concentrations in 90% of the analyzed samples, whereas cell counts <3.0 × 10(5) are sufficient to detect PCR products. Therefore, sampling of bioaerosols should be done in consideration of the expected cell count per cubic meter air. Note, to get measurable DNA using a fluorometer, >3.5 × 10(6) cells must be sampled for one DNA extraction assay. With this study, the real-time PCR approach for the detection of S. rectivirgula at workplaces in compost plants was revised, and the results revealed that this method is suitable for occupational exposure measurements.

Detection of airborne bacteria in a German turkey house by cultivation-based and molecular methods

Today's large-scale poultry production with densely stocked and enclosed production buildings is often accompanied by very high concentrations of airborne microorganisms leading to a clear health hazard for employees working in such environments. Depending on the expected exposure to microorganisms, work has to be performed under occupational safety conditions. In this study, turkey houses bioaerosols were investigated by cultivation-based and molecular methods in parallel to determine the concentrations and the composition of bacterial community. Results obtained with the molecular approach showed clearly its applicability for qualitative exposure measurements. With both, cultivation-based and molecular methods species of microorganism with a potential health risk for employees (Acinetobacter johnsonii, Aerococcus viridans, Pantoea agglomerans, and Shigella flexneri) were identified. These results underline the necessity of adequate protection measures, including the recommendation to wear breathing masks during work in poultry houses.

Jeotgalicoccus coquinae sp. nov. and Jeotgalicoccus aerolatus sp. nov., isolated from poultry houses

Two Gram-stain-positive, non-motile, non-spore-forming cocci (strains MK-7(T) and MPA-33(T)) were isolated from poultry houses. Strain MK-7(T) was isolated on marine broth agar from coquina, a food supplement for female ducks used in a duck-fattening farm. Strain MPA-33(T) was isolated from the air of a turkey house on TSA after filter sampling. On the basis of 16S rRNA gene sequence similarity studies, both strains were shown to belong to the genus Jeotgalicoccus; MK-7(T) was most closely related to Jeotgalicoccus psychrophilus YKJ-115(T) (99.3 % similarity) and MPA-33(T) was most closely related to Jeotgalicoccus halotolerans YKJ-101(T) (98.8 %). The quinone system of MK-7(T) was composed of equal amounts of menaquinones MK-7 and MK-6 and that of MPA-33(T) contained 76 % MK-7 and 24 % MK-6. The polar lipid profile of strain MK-7(T) consisted of the major compounds diphosphatidylglycerol and phosphatidylglycerol and six unidentified lipids present in minor to moderate amounts. In strain MPA-33(T), diphosphatidylglycerol was the single predominant lipid, whereas phosphatidylglycerol was detected in moderate amounts. In addition, one unidentified phospholipid and four unidentified lipids were detected. Fatty acid profiles with iso-15 : 0 and anteiso-15 : 0 as major fatty acids supported the affiliation of the strains to the genus Jeotgalicoccus. The results of physiological and biochemical tests as well as DNA-DNA hybridizations allowed clear phenotypic differentiation of strains MK-7(T) and MPA-33(T) from the most closely related species. Strains MK-7(T) and MPA-33(T) therefore represent novel species, for which the names Jeotgalicoccus coquinae sp. nov. (type strain MK-7(T) =DSM 22419(T) =CCM 7682(T) =CCUG 57956(T)) and Jeotgalicoccus aerolatus sp. nov. (type strain MPA-33(T) =DSM 22420(T) =CCM 7679(T) =CCUG 57953(T)) are proposed.

Complex encounters at the macrophage-mycobacterium interface: studies on the role of the mannose receptor and CD14 in experimental infection models with Mycobacterium avium

The initial interactions between mycobacterial cell wall components and receptor structures on the surface of macrophages may be critical in determining the outcome of infection. They may trigger the ingestion and digestion of microorganisms, but they may also promote the intracellular persistence and growth of mycobacteria. Using Mycobacterium avium as a model system, three approaches of different complexities were used to analyse some structural features and some functional consequences of M. avium interacting with the macrophage mannose receptor or CD14, a pattern recognition receptor. Binding specificities of a recombinant, truncated extracellular portion of the mannose receptor were assayed in a novel ELISA-formatted system using viable M. avium cells as ligands. Infection with M. avium strains differing in their virulence were performed in murine bone marrow-derived macrophages and in mice with a targeted deletion of the CD14 gene. These parallel and converging approaches not only help define the molecular basis for understanding early events in the pathogenesis of mycobacterial infections, but are also necessary to ultimately determine the relevance of in vitro findings in the context of actual manifestations of disease in vivo.

A new approach to measure gross CO2 fluxes in leaves. Gross CO2 assimilation, photorespiration, and mitochondrial respiration in the light in tomato under drought stress

We developed a new method using 13CO2 and mass spectrometry to elucidate the role of photorespiration as an alternative electron dissipating pathway under drought stress. This was achieved by experimentally distinguishing between the CO2 fluxes into and out of the leaf. The method allows us to determine the rates of gross CO2 assimilation and gross CO2 evolution in addition to net CO2 uptake by attached leaves during steady-state photosynthesis. Furthermore, a comparison between measurements under photorespiratory and non-photorespiratory conditions may give information about the contribution of photorespiration and mitochondrial respiration to the rate of gross CO2 evolution at photosynthetic steady state. In tomato (Lycopersicon esculentum Mill. cv Moneymaker) leaves, drought stress decreases the rates of net and gross CO2 uptake as well as CO2 release from photorespiration and mitochondrial respiration in the light. However, the ratio of photorespiratory CO2 evolution to gross CO2 assimilation rises with water deficit. Also the contribution of re-assimilation of (photo) respiratory CO2 to gross CO2 assimilation increases under drought.

Ammonia assimilation by Aspergillus nidulans: [15N]ammonia study

15N kinetic labelling studies were done on liquid cultures of wild-type Aspergillus nidulans. The labelling pattern of major amino acids under 'steady state' conditions suggests that glutamate and glutamine-amide are the early products of ammonia assimilation in A. nidulans. In the presence of phosphinothricin, an inhibitor or glutamine synthetase, 15N labelling of glutamate, alanine and aspartate was maintained whereas the labelling of glutamine was low. This pattern of labelling is consistent with ammonia assimilation into glutamate via the glutamate dehydrogenase pathway. In the presence of azaserine, an inhibitor of glutamate synthase, glutamate was initially more highly labelled than any other amino acid, whereas its concentration declined. Isotope also accumulated in glutamine. Observations with these two inhibitors suggest that ammonia assimilation can occur concurrently via the glutamine synthetase/glutamate synthase and the glutamate dehydrogenase pathways in low-ammonia-grown A. nidulans. From a simple model it was estimated that about half of the glutamate was synthesized via the glutamate dehydrogenase pathway; the other half was formed from glutamine via the glutamate synthase pathway. The transfer coefficients of nine other amino acids were also determined.

Effect of dissolved inorganic carbon on oxygen evolution and uptake by Chlamydomonas reinhardtii suspensions adapted to ambient and CO2-enriched air

Mass spectrometric measurements of (16)O2 and (18)O2 isotopes were used to compare the rates of gross O2 evolution (E0), O2 uptake (U0) and net O2 evolution (NET) in relation to different concentrations of dissolved inorganic carbon (DIC) by Chlamydomonas reinhardtii cells grown in air (air-grown), in air enriched with 5% CO2 (CO2-grown) and by cells grown in 5% CO2 and then adapted to air for 6h (air-adapted).At a photon fluence rate (PFR) saturating for photosynthesis (700 μmol photons m(-2) s(-1)), pH=7.0 and 28°C, U0 equalled E0 at the DIC compensation point which was 10μM DIC for CO2-grown and zero for air-grown cells. Both E0 and U0 were strongly dependent on DIC and reached DIC saturation at 480 μM and 70 μM for CO2-grown and air-grown algae respectively. U0 increased from DIC compensation to DIC saturation. The U0 values were about 40 (CO2-grown), 165 (air-adapted) and 60 μmol O2 mg Chl(-1) h(-1) (air-grown). Above DIC compensation the U0/E0 ratios of air-adapted and air-grown algae were always higher than those of CO2-grown cells. These differences in O2 exchange between CO2- and air-grown algae seem to be inducable since air-adapted algae respond similarly to air-grown cells.For all algae, the rates of dark respiratory O2 uptake measured 5 min after darkening were considerably lower than the rates of O2 uptake just before darkening. The contribution of dark respiration, photorespiration and the Mehler reaction to U0 is discussed and the energy requirement of the inducable CO2/HCO3 (-) concentrating mechanism present in air-adapted and air-grown C. reinhardtii cells is considered.

Effect of Photon Fluence Rate on Oxygen Evolution and Uptake by Chlamydomonas reinhardtii Suspensions Grown in Ambient and CO(2)-Enriched Air

A closed system consisting of an assimilation chamber furnished with a membrane inlet from the liquid phase connected to a mass spectrometer was used to measure O(2) evolution and uptake by Chlamydomonas reinhardtii cells grown in ambient (0.034% CO(2)) or CO(2)-enriched (5% CO(2)) air. At pH = 6.9, 28 degrees C and concentrations of dissolved inorganic carbon (DIC) saturating for photosynthesis, O(2) uptake in the light (U(o)) equaled O(2) production (E(o)) at the light compensation point (15 micromoles photons per square meter per second). E(o) and U(o) increased with increasing photon fluence rate (PFR) but were not rate saturated at 600 micromoles photons per square meter per second, while net O(2) exchange reached a saturation level near 500 micromoles photons per square meter per second which was nearly the same for both, CO(2)-grown and air-grown cells. Comparison of the U(o)/E(o) ratios between air-grown and CO(2)-grown C. reinhardtii showed higher values for air-grown cells at light intensities higher than light compensation. For both, air-grown and CO(2)-grown algae the rates of mitochondrial O(2) uptake in the dark measured immediately before and 5 minutes after illumination were much lower than U(o) at PFR saturating for net photosynthesis. We conclude that noncyclic electron flow from water to NADP(+) and pseudocyclic electron flow via photosystem I to O(2) both significantly contribute to O(2) exchange in the light. In contrast, mitochondrial respiration and photosynthetic carbon oxidation cycle are regarded as minor O(2) consuming reactions in the light in both, air-grown and CO(2)-grown cells. It is suggested that the "extra" O(2) uptake by air-grown algae provides ATP required for the energy dependent CO(2)/HCO(3) (-) concentrating mechanism known to be present in these cells.

Effect of carbon dioxide and temperature on photosynthetic CO2 uptake and photorespiratory CO 2 evolution in sunflower leaves

Using an open gas-exchange system, apparent photosynthesis, true photosynthesis (TPS), photorespiration (PR) and dark respiration of sunflower (Helianthus annuus L.) leaves were determined at three temperatures and between 50 and 400 μl/l external CO2. The ratio of PR/TPS and the solubility ratio of O2/CO2 in the intercellular spaces both decreased with increasing CO2. The rate of PR was not affected by the CO2 concentration in the leaves and was independent of the solubility ratio of oxygen and CO2 in the leaf cell. At photosynthesis-limiting concentrations of CO2, the ratio of PR/TPS significantly increased from 18 to 30°C and the rate of PR increased from 4.3 mg CO2 dm(-2) h(-1) at 18°C to 8.6 mg CO2 dm(-2) h(-1) at 30°C. The specific activity of photorespired CO2 was CO2-dependent but temperature-independent, and the carbon traversing the glycolate pathway appeared to be derived both from recently fixed assimilate and from older reserve materials. It is concluded that PR as a percentage of TPS is affected by the concentrations of O2 and CO2 around the photosynthesizing cells, but the rate of PR may also be controlled by other factors.