The effect of polychlorinated biphenyls (PCBs) on the membrane lipids of Pseudomonas stutzeri

In this study we examined the effect of polychlorinated biphenyls (PCBs) on biomass production of a PCB-degrading Pseudomonas stutzeri, and on the fatty acid profile of its major membrane lipids. Growth based on biomass weight was stimulated when PCBs were added at the time of inoculation, but PCB addition three days after inoculation led to a significant decrease in biomass. Simultaneous addition of PCBs plus biphenyl or PCBs plus carvone negatively affected P. stutzeri biomass (addition of biphenyl or carvone at the time of inoculation and PCBs to three-day-old culture). In the presence of PCBs alone the amount of the prevalent fatty acids C16:0 and C17-cyclopropyl fatty acid (C17-CP) of P. stutzeri in total and neutral lipids was significantly reduced. When PCBs were added together with carvone (carvone at the time of inoculation and PCBs after three days) a significant reduction of these fatty acids was obtained, but, in addition, oleic, cis-vaccenic, and cyclononadecanic (C19-CP) acids were increased. When PCBs were combined to biphenyl the prevalent fatty acids were reduced and oleic, cis-vaccenic, and cyclononadecanic acids were increased in total and neutral lipids. Addition of 3-chlorobenzoic acid led to a significant growth inhibition and to the production of oleic and cis-vaccenic acids in the membrane fraction phosphatidylcholine.     

Influence of PCBs on the predator-prey relation between bacteria and protozoa in soil

Abstract This work deals with the impact of a possible accidental pollutant, pyralene (Prodelec, France; PCBs in trichlorobenzene), intoduced into the soil. Its influence on the predator-prey relation between bacteria and amoebae was studied by comparing the population dynamics of (i) an inoculated bacterial population ( A. lipoferum ) chosen as a biological tracer, (ii) the indigenous bacterial microflora, (iii) the infigenous amoebae. In the absence of pyralene the inoculated bacterial population decreased from 10⁷ to 10⁴ bacteria g⁻¹ soil (dw), grazed by the infigenous amoebae whose numbers increased 3-fold. In contrast, in presence of 2500 ppm of pyralene the introduced bacteria survived at a higher level (3·10⁶ bacteria g⁻¹ soil (dw)) while the number of amoebae diminished slightly. No predation occurred with PCB contamination. The indigenous bacterial microflora was not affected quantitatively by pyralene. In pure liquid culture with 500 ppm of pyralene added, bacterial growth was inhibited and an amoebal strain isolated from an inoculated uncontaminated soil was killed. We conclude that the active form of the amoebae were killed, and encystement was inhibited by pyralene in the soil. Hence the protozoa were unable to regulate the introduced A. lipoferum strain as they did in the absence of the pollutant.     

Molecular diagnostics and chemical analysis for assessing biodegradation of polychlorinated biphenyls in contaminated soils

Summary The microbial populations in PCB-contaminated electric power substation capacitor bank soil (TVA soil) and from another PCB-contaminated site (New England soil) were compared to determine their potential to degrade PCB. Known biphenyl operon genes were used as gene probes in colony hybridizations and in dot blots of DNA extracted from the soil to monitor the presence of PCB-degrading organisms in the soils. The microbial populations in the two soils differed in that the population in New England soil was enriched by the addition of 1000 p.p.m. 2-chlorobiphenyl (2-CB) whereas the population in the TVA capacitor bank soil was not affected. PCB degradative activity in the New England soil was indicated by a 50% PCB disappearance (gas chromatography), accumulation of chlorobenzoates (HPLC), and¹⁴CO₂ evolution from¹⁴C-2CB. The PCB-degrading bacteria in the New England soil could be identified by their positive hybridization to thebph gene probes, their ability to produce the yellowmeta-cleavage product from 2,3-dihydroxybiphenyl (2,3-DHB), and the degradation of specific PCB congeners by individual isolates in resting cell assays. Although the TVA capacitor bank soil lacked effective PCB-degrading populations, addition of a PCB-degrading organism and 10 000 p.p.m. biphenyl resulted in a >50% reduction of PCB levels. Molecular characterization of soil microbial populations in laboratory scale treatments is expected to be valuable in the design of process monitoring and performance verification approaches for full scale bioremediation.     

Seasonal-spatial distributions,congener profile,and risk assessment of polychlorinated biphenyls (PCBS) in the surficial sediments from the coastal area of Bangladesh

A comprehensive congener specific assessment of polychlorinated biphenyls (PCBs) was conducted for the first time in Bangladesh. All 209 PCB congeners in the surficial coastal sediments from the coastal areas of Bangladesh were analyzed by GC-MS/MS. The total concentrations of PCBs (∑PCBs) varied from 5.27 to 92.21 and 4.61 to 105.3 ng/g dw in winter and summer, respectively, and the ranges were comparable to or higher than those recorded in the sediments from the coastal areas of India, Korea, China, and Taiwan. The seasonal difference in the levels of PCBs was not statistically significant (p > 0.05). The spatial distribution revealed that the areas with recent urbanization and industrialization (Chittagong, Cox’s Bazar and Sundarbans) were more contaminated with PCBs than the unindustrialized area (Meghna Estuary). Moderately chlorinated (4–6 Cl) homologs dominated PCB profiles. A set of congeners based on their detection frequencies and abundance were identified and categorized as potential environmental marker PCBs, which can be used for the future selective monitoring studies where there would be limitations on whole congener assessment. Ecotoxicologically, the sedimentary PCB concentrations exceeded some of the existing environmental quality standards, suggesting a potential threat to the aquatic organisms in the Bangladeshi coastal areas.     

Ecotoxicological Risk Assessment of Polychlorinated Biphenyls (PCBs) in Bank Sediments from along the Yamuna River in Delhi,India

The River Yamuna originates from the Yamunotri glacier of the Himalayas and travels 22 km in the Delhi region. The river is used for various purposes in Delhi including drinking water supply. Twenty-eight polychlorinated biphenyls (PCBs) congeners were measured in bank sediments along the river, and their ecotoxicological risk was evaluated. Concentrations of ∑28PCBs varied from 0.20–21.16 ng g^?1 (dry wt.) with mean and median values of 6.63 ng g^?1 and 5.84 ng g^?1 (±0.69 ng g^?1), respectively. The concentration of 12 dl-PCBs concentrations varied from 0.04–2.86 ng g^?1 with a mean of 1.04 ± 0.11 ng g^?1, and their toxic equivalency ranged between <0.01–28.67 pg WHO-TEQ g^?1 with a mean of 10.77 ± 1.06 pg WHO-TEQ g^?1. CB-37, CB-44, CB-114, and CB-118 congeners were dominant among all PCBs congeners. The tri-PCBs (49%) were the main contributors to the PCB homolog followed by tetra-PCBs (35%), and penta-PCB (14%). Because there are no environmental guidelines in India for PCBs in river and marine sediments, concentrations of PCBs and their toxic equivalents were compared in a screening-level assessment with established freshwater sediment quality guidelines and found lower than those guideline values, which suggests no adverse ecotoxicological effect.     

Degradation and Detoxification of Nicosulfuron by a Pseudomonas Strain Isolated from a Contaminated Cornfield Soil

ABSTRACT

The dissipation and detoxification of nicosulfuron (NS) by Pseudomonas aeruginosa B9 isolated from a cornfield soil was investigated. The fastest decline of NS occurred at 40 µg ml^?1 in liquid media with 0.25% glucose plus 0.05% yeast extract (DT₅₀ = 4 days) with a notable pH reduction (pH ? 5). Bioassay tests showed considerable phytotoxicity of NS for Cress (Lepidium sativum L.) with 50% shoot growth inhibition (SGI) at 40 µg ml^?1. The dissipation of NS (40 µg ml^?1) by the B9 isolate reduced the SGI significantly (SGI: up to 45 ± 3%) compared to the non-inoculated media (SGI: up to 58 ± 4%). In soils with the B9 isolate, NS dissipation, especially at 0.3 µg g^?1, was faster with a more significant SGI reduction (k = 0.08 ± 0.00 day^?1; SGI = 2 ± 1%) compared to non-inoculated samples (k = 0.03 ± 0.00 day^?1; SGI = 8 ± 1%). NS initially inhibited soil respiration, microbial biomass carbon, and dehydrogenase activity. The effect was however transient, and these parameters recovered within 10 days, especially in the presence of the isolate. Overall, this study proves Pseudomonas aeruginosa B9 as a suitable candidate for bioremediation of NS in contaminated sites.     

Molecular assessment of the potential for in situ bioremediation of PCBs from aquatic sediments

Polychlorinated biphenyls (PCBs) are a family of xenobiotic compounds that are ubiquitous and oftentimes persistent environmental pollutants. As such, PCBs are a common target of sediment remediation efforts. Microbial degradation of sediment pollutants such as PCBs offers an environmentally sound and economically favorable alternative to conventional means of remediation such as dredging. This project describes the development of a PCR-based assay to determine the potential for PCB bioremediation by the resident microbial consortium in contaminated sediments. Using PCR and RT-PCR of DNA and RNA, respectively, extracted from aquatic sediments collected from the western basin of Lake Erie and one of its tributaries, we were able to amplify the bphA1 gene that encodes the large subunit of biphenyl dioxygenase. Since other studies have determined that the BphA1 gene product dictates PCB congener specificity, this assay may prove to be a useful screen for endemic catabolic activities for PCB mixtures in aquatic sediments.     

多氯联苯降解菌Burkholderia xenovorans LB400研究进展

Burkholderia xenovorans LB400是一株多氯联苯(polychlorinated biphenyls,PCBs)降解菌,可以氧化含有1?6个氯取代基的多氯联苯。近年来,由于其广泛的底物谱和优异的降解性能,菌株LB400已成为研究原核生物降解多氯联苯的生物化学和分子生物学方面的模式生物。目前关于PCBs的微生物降解研究已不再局限于对微生物资源的挖掘,而是更多地聚焦在LB400等降解菌的PCBs降解基因、降解酶的酶学特性以及酶的人工分子进化等方面。同时,LB400作为早期发现的降解菌,其对多氯联苯的降解途径、底物范围及相关机制也被广泛探讨;但是对于PCBs降解相关基因的调控研究较少。因此,本文以Burkholderia xenovorans LB400对多氯联苯降解为核心,通过综述其代谢途径、代谢相关基因和酶系以及降解应用等方面的研究进展,以期为深入探讨Burkholderia xenovorans LB400的应用以及进一步在遗传、分子和生化水平研究其他多氯联苯降解菌株提供借鉴。     

Using SPMDs to Assess Natural Recovery of PCB-contaminated Sediments in Lake Hartwell,SC: I. A Field Test of New In-Situ Deployment Methods

Results from the field testing of some innovative sampling methods developed to evaluate risk management strategies for polychlorinated biphenyl (PCB) contaminated sediments are presented. Semipermeable membrane devices (SPMDs) were combined with novel deployment methods to quantify the availability of PCBs at the Sangamo-Weston Lake Hartwell Superfund Site in SC. Three locations in Lake Hartwell were examined: a background site (BKG) with little detectable contamination and two contaminated sites (T-M/N and T-O). PCB availability was quantified using sediment surface samplers designed to hold SPMDs in contact with surface sediments, benthic dome samplers designed to enclose and suspend SPMDs at the sediment-water interface, and commercially obtained SPMD cages suspended in the water column. A two-way analysis of variance showed significant effects by sampler type (P < 0.0001) and site (P < 0.0001) for mean time-weighted average (TWA) total PCBs (t-PCBs). Regardless of the SPMD sampler used, mean TWA t-PCBs were directly proportional to the level of contamination present (BKG < T-M/N < T-O). Water column and surface sediment sampler t-PCB uptake patterns were described by a significant linear fit of the data (r² = 0.9625, p < 0.0001, and r² = 0.8188, p < 0.0001, respectively). Dome and sediment surface SPMD samples had a higher percentage of higher chlorinated PCBs compared to water column samples.     

Determinants of Serum PCBs in Adolescents and Adults: Regression Tree Analysis and Linear Regression Analysis

Regression tree analysis, a non-parametric method, was undertaken to identify predictors of the serum concentration of polychlorinated biphenyls (sum of marker PCB ¹ ABBREVIATIONS: BMI: body-mass index, CV: cross validation, ln: natural logarithm, ns: not significant, PCAHs: polychlorinated aromatic hydrocarbons, PCBs: polychlorinated biphenyls, R² _a: adjusted coefficient of determination, VIF: variance inflation factor. View all notes 138, 153, and 180) in humans. This method was applied on biomonitoring data of the Flemish Environment and Health study (2002–2006) and included 1679 adolescents and 1583 adults. Potential predictor variables were collected via a self-administered questionnaire, assessing information on lifestyle, food intake, use of tobacco and alcohol, residence history, health, education, hobbies, and occupation. Relevant predictors of human PCB exposure were identified with regression tree analysis using ln-transformed sum of PCBs, separately in adolescents and adults. The obtained results were compared with those from a standard linear regression approach. The results of the non-parametric analysis confirm the selection of the covariates in the multiple regression models. In both analyses, blood fat, gender, age, body-mass index (BMI) or change in bodyweight, former breast-feeding, and a number of nutritional factors were identified as statistically significant predictors in the serum PCB concentration, either in adolescents, in adults or in both. Regression trees can be used as an explorative analysis in combination with multiple linear regression models, where relationships between the determinants and the biomarkers can be quantified.     

Polychlorinated biphenyls in vegetable soils from Changchun,Northeast China: Concentrations,distribution, sources and human health risks

To investigate the occurrences of polychlorinated biphenyls (PCBs) in suburban vegetable soils of Changchun area, Northeast China, 106 urban vegetable soil samples were collected from Changchun City, Nongan County, Dehui City, Yushu City, Jiutai City, Shuangyang District. We analyzed the concentrations, compositions and sources of 7 PCBs in top soils of Changchun area, and evaluated the non-carcinogenic and carcinogenic risk of PCBs pollution to exposed population. The total concentrations of 7 PCBs ranged from 1.31 to 148 ng/g dry weight (dw) with a mean value of 42.0 ng/g and dominated by Hepta-CBs and Penta-CBs. Principal component analysis (PCA) revealed that PCB pollution in soils of Changchun area mainly related to transportation, vehicle emissions, paints and other industries. Human health risk assessment showed that the cumulative non-carcinogenic and the cumulative carcinogenic risk in children and adults in the industrial land and residential land were acceptable, considering only 7 PCBs homologues were analyzed in this study, the actual risk could be higher.     

Monitoring of level of mean concentration and toxicity equivalence (TEQ) of polychlorinated biphenyls (PCBs) in selected vegetables,beans and grains in khanewal and multan,Pakistan

Contamination of food chain by Polychlorinated biphenyls through use of pesticides, electric and industrial waste poses human health risk. In previous studies, PCB species were stated as endocrine disrupting pollutants and showed toxic health effects like cancerous and noncancerous in animals. The aim of this study was to investigate the levels of PCBs and its toxicity equivalence in food item from plant source to evaluate the health risk in Khanewal and Multan, Pakistan. Samples were collected and processed for further analysis of PCB species through GC/MS after extraction and clean up. The mean concentrations of PCBs ranged as 2.71–151.67 ng/g in beans and grains and 2.30–97.00 ng/g dry weight in vegetables and were lower than 200–3000 ng/g PCBs recommended by FDA tolerance level for all foods. The mean concentrations of two NDL-PCB species detected in all vegetables, beans and grains except S.indicum and T.aestivum were lower than maximum allowable concentration of non-dioxin like PCBs i.e. 40ngg^?1 reported by European Commission. Mean TEQ of sum of 14 PCB species ranged as 1.52–5.91 ng-WHO-TEQg^?1 in vegetables and 1.46–10.04 ng-WHO-TEQg^?1 in beans and grains. The present study concluded that the mean concentrations and mean TEQs of PCB species in most of the vegetables, beans and grains were found safe but due to higher consumption rate of some vegetables and grains, posed the moderate level of risk for human health. This study emphasizes on an implement of the strict rules regarding the use of restricted chemicals to diminish the effluence in food chains. Current research will be useful in up gradation of effective measures to reduce the poisonous contribution of PCB sources and the sustainability of terrestrial ecosystem in the country.     

Metabolism of Atrazine in Liquid Cultures and Soil Microcosms by Nocardioides Strains Isolated from a Contaminated Nigerian Agricultural Soil

Atrazine-degrading microorganisms designated EAA-3 and EAA-4, belonging to the genus Nocardioides, were obtained from an agricultural soil in Nigeria. The degradation kinetics of the two strains revealed total disappearance of 25 mg l^?1 of atrazine in less than 72 h of incubation at the rate of 0.42 mg l^?1 h^?1 and 0.35 mg l^?1 h^?1, respectively. Screening for atrazine catabolic genes in these organisms revealed the presence of trzN, atzB, and atzC. Other genes, specifically atzA, atzD, and trzD, were not detected. Potential intermediates of atrazine catabolic route such as hydroxyatrazine, desethylatrazine, and desisopropylatrazine were utilized as sources of carbon and energy, while desisopropyl desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine were attacked but in the presence of glucose. A soil microcosm study showed that degradation was faster in microcosms contaminated with 13 mg of atrazine per g^?1 of soil compared with 480 mg g^?1 of soil. In the former, degradation was 10% higher in the inoculated soil than the non-inoculated control (natural attenuation) over the 28-day study period. Corresponding value obtained for the latter was nearly 70% higher. This study has demonstrated that the bacterial strains isolated enhanced atrazine degradation and the catabolic activities of these strains were not affected with increasing soil atrazine concentration.     

The Removal of Pb and Cd from Heavily Contaminated Soil in Kayseri,Turkey by a Combined Process of Soil Washing and Electrodeposition

In this study, a combined system of soil washing and electrodeposition was designed to remove Pb (16381±643 mg/kg) and Cd (34347±1310 mg/kg) from contaminated soil. 0.05 M Na₂EDTA was used as a chelating agent for the remediation of soil, taken from the nearby city Kayseri, Turkey. As a result of the batch extraction tests, maximum removals were determined as; at the 20:1 liquid: soil ratio for Pb is 60.7%, for Cd at the 30:1 liquid: soil ratio is 67.4%. An electrochemical treatment was applied to the waste washing solution which appeared to be the second pollutant after the Na₂EDTA extraction from the soil. With extraction tests of Pb and Cd, being transformed from the solid phase to the liquid phase. The electrochemical treatment (electrodeposition), performed in three different potential (6 V, 8 V and 10 V) and maximum removal efficiencies, were found 99.7% and 80.3% at 10 V for Pb and Cd, respectively.

Speciation tests (BCR) were carried out, both before and after the soil washing process, to evaluate the redistribution of metal fraction in the soil. The fraction, associated with the organic substance, was found as 10.67% for Pb and 1.81% for Cd. The metal bioavailability factor increased after soil washing, which indicates that EDTA could enhance the mobility of Pb and Cd.     

食用调和油中花生油含量的近红外光谱分析

采用偏最小二乘法(PLS)等方法建立了食用调和油中花生油含量定量分析的近红外光谱定标模型。采集食用调和油样品在4 000 cm-1~10 000 cm-1范围内的近红外漫反射光谱,光谱经一阶导数处理后,采用偏最小二乘法建立样品中花生油含量的定标模型,并用Leave-one-out内部交叉验证法对模型进行验证。模型相关系数为0.99961,校正均方根RMSEC为0.830%。比较不同光谱预处理方法对定标模型的影响,结果表明一阶导数Corr.coeff最好。采用不同的化学计量学方法建立的定标模型中以偏最小二乘回归法最理想。     

Absolute Configuration of (+)-1-Acetoxy-p-menth-3-one Isolated from Essential Oil of Mentha gentilis (L.)

The most effective electro-energizing fermentation (E-E F) conditions for l-glutamate (l-Glu) production by Brevibacterium flavum No. 2247 were determined. The adding of 0.01 mm neutral red at the beginning of cultivation was found most effective. A 1.5 V direct current was applied to the culture broth at 6~8 hr after inoculation in the cathode compartment, l-Glu was produced at 51.0 mg per ml, and this is about a 15 % increase in yield compared to the yield of the not electro-energizing (E-E) control (44.3 mg/ml).     

Comparison of EDTA- and Citric Acid-Enhanced Phytoextraction of Heavy Metals in Artificially Metal Contaminated Soil by Typha Angustifolia

A pot experiment was conducted to study the performance of EDTA and citric acid (CA) addition in improving phytoextraction of Cd, Cu, Pb, and Cr from artificially contaminated soil by T. angustifolia. T. angustifolia showed the remarkable resistance to heavy metal toxicity with no visual toxic symptom including chlorosis and necrosis when exposed to metal stress. EDTA-addition significantly reduced plant height and biomass, compared with the control, and stunted plant growth, while 2.5 and 5 mM CA addition induced significant increases in root dry weight. EDTA, and 5 and 10 mM CA significantly increased shoot Cd, Pb, and Cr concentrations compared with the control, with EDTA being more effective. At final harvest, the highest shoot Cd, Cr, and Pb concentrations were recorded in the treatment of 5 mM EDTA addition, while maximal root Pb concentration was found at the 2.5 mM CA treatment. However, shoot Cd accumulation in the 10 mM CA treatment was 36.9% higher than that in 2.5 mM EDTA, and similar with that in 10 mM EDTA. Shoot Pb accumulation was lower in 10 mM CA than that in EDTA treatments. Further, root Cd, Cu, and Pb accumulation of CA treatments and shoot Cr accumulation in 5 or 10 mM CA treatments were markedly higher than that of control and EDTA treatments. The results also showed that EDTA dramatically increased the dissolution of Cu, Cr, Pb, and Cd in soil, while CA addition had less effect on water-soluble Cu, Cr, and Cd, and no effect on Pb levels. It is suggested that CA can be a good chelator candidate for T. angustifolia used for environmentally safe phytoextraction of Cd and Cr in soils.     

Bioremediation of Soil Contaminated with Diesel Using Inorganic Nitrogen Sources: Incorporating nth-Order Algorithm in the Evaluation of Process Kinetics

In the present study, we investigated the effects of inorganic nitrogen sources—(NPK fertilizer, 15:15:15), (urea fertilizer, 46:0:0), (NH₄)₂SO₄ as well as monitored natural attenuation on the bioremediation of diesel-polluted soil. At the end of the 6-week study, the highest degradation was recorded in soil amended with NPK fertilizer (95 ± 2.77%) while the least total petroleum hydrocarbon removal was observed in monitored natural attenuation (89 ± 2.91%). Nth-order kinetics effectively described three of the treatments out of the four treatment plans. These include urea amendment (r² = 0.9925, average relative error (ARE) = 1.45%, root mean square error (RMSE) = 0.038, k_n = (3.57 ± 0.61) × 10^?2, n = 1.33), NPK fertilizer amendment (r² = 0.9751, ARE = 3.241%, RMSE = 0.086, k_n = (8.04 ± 0.23) × 10^?1, n = 0.74), and monitored natural attenuation (r² = 0.9697, ARE = 2.77%, RMSE = 0.073, k_n = (1.57 ± 0.50) × 10^?2, n = 1.16). The values of n from the nth-order kinetics parameter estimation indicated that all the treatments resulted in diesel degradation that followed a first-order kinetics path. Thus, the outcome of kinetic modeling showed that nth-order can be used as validating tool when many kinetic orders are under consideration. The phytotoxicity assay with Zea mays showed that the treatments plans resulted in germination indices of 17–55%.     

Degradation of Phycobilisomes in Synechocystis sp. PCC6803: EVIDENCE FOR ESSENTIAL FORMATION OF AN NblA1/NblA2 HETERODIMER AND ITS CODEGRADATION BY A Clp PROTEASE COMPLEX

When cyanobacteria acclimate to nitrogen deficiency, they degrade their large (3–5-MDa), light-harvesting complexes, the phycobilisomes. This massive, yet specific, intracellular degradation of the pigmented phycobiliproteins causes a color change of cyanobacterial cultures from blue-green to yellow-green, a process referred to as chlorosis or bleaching. Phycobilisome degradation is induced by expression of the nblA gene, which encodes a protein of ∼7 kDa. NblA most likely acts as an adaptor protein that guides a Clp protease to the phycobiliproteins, thereby initiating the degradation process. Most cyanobacteria and red algae possess just one nblA-homologous gene. As an exception, the widely used “model organism” Synechocystis sp. PCC6803 expresses two such genes, nblA1₆₈₀₃ and nblA2₆₈₀₃, both of whose products are required for phycobilisome degradation. Here, we demonstrate that the two NblA proteins heterodimerize in vitro and in vivo using pull-down assays and a Förster energy-transfer approach, respectively. We further show that the NblA proteins form a ternary complex with ClpC (the HSP100 chaperone partner of Clp proteases) and phycobiliproteins in vitro. This complex is susceptible to ATP-dependent degradation by a Clp protease, a finding that supports a proposed mechanism of the degradation process. Expression of the single nblA gene encoded by the genome of the N₂-fixing, filamentous cyanobacterium Nostoc sp. PCC7120 in the nblA1/nblA2 mutant of Synechocystis sp. PCC6803 induced phycobilisome degradation, suggesting that the function of the NblA heterodimer of Synechocystis sp. PCC6803 is combined in the homodimeric protein of Nostoc sp. PCC7120.