Chloroplast Pigments Research Articles

Distribution of bathyal meiofauna in the region of the Subtropical Front, Chatham Rise, south-west Pacific

Metazoan meiofauna was sampled along a temperate latitude transect (41–47°S 178°30′E) across the Chatham Rise, south-west Pacific, from water depths of 350–2600 m on three occasions (austral autumn 1997, spring 1997, summer 2000). Samples were collected using a multicorer and extracted on a 63-μm mesh. Meiofaunal density and biomass were negatively correlated with water depth, median grain-size and sediment calcium carbonate content, and positively correlated with sediment chlorophyll a. There were no significant relationships between meiofaunal abundance and biomass and measures of sediment organic matter and bacterial productivity and biomass, except in summer when bacterial and meiofaunal biomass were positively correlated. Vertical penetration of meiofauna into the sediment was related to sediment organic matter and sediment chloroplastic pigments. Variation in meiofaunal abundance at different spatial scales was examined at two sites: at 450 and 2300 m on the northern slope of the rise. At both sites, variation between subcores of a multicore (< 10-cm scale) was lower than that of multicores within a deployment (< 1-m scale). However, whilst the highest variance component at the shallow site was for multicores within a deployment, it was between multicore deployments (< 1-km scale) for the deep site. Meiofaunal density and biomass were generally higher on the southern slope of the rise than on the northern slope, a trend probably attributable to high productivity of the overlying Subtropical Front and the flux of more nutritious organic material to the sea floor.

Understanding the Mechanisms Employed by Trichoderma virens to Effect Biological Control of Cotton Diseases

Understanding the Mechanisms Employed by <i>Trichoderma virens</i> to Effect Biological Control of Cotton Diseases

Signs of oxidative stress in the chlorotic leaves of iron starved plants

Studies were made to relate signs of oxidative stress in chlorotic and non-chlorotic leaves of plants receiving deficient supply, either nil (chlorotic leaves) or 10 μM (non-chlorotic leaves) of Fe, with thiobarbituric acid reactive substance (TBARS) and Fe status of leaf tissues. Total Fe concentration in the young leaves of mulberry, maize and cauliflower plants supplied deficient Fe did not show any significant change. Deficient supply of Fe caused decreases in the activities of catalase, peroxidase and ascorbate peroxidase and increases in the activity and number of isoforms of superoxide dismutase (SOD), accumulation of superoxide anion radical (O 2 −) and concentration of H 2O 2 in the young leaves of each mulberry, maize or cauliflower plants. While the chlorotic leaves of Fe-starved mulberry, maize and cauliflower plants had significantly lower TBARS compared to green leaves of the controls or non-chlorotic leaves of cauliflower plants supplied low Fe (10 μM). While TBARS concentration in the young leaves of these plants was well correlated with the concentrations of chloroplastic pigments, and activities of catalase and ascorbate peroxidase, its relationship with leaf tissue Fe or H 2O 2 concentration was rather poor. Progressive increase in the activity and induction of new isoforms of SOD and higher accumulation H 2O 2 and O 2 − may be considered as signs of oxidative stress, whereas, increased ascorbate content along with lower mole fraction of ascorbic acid/total ascorbate are indicative of disturbed cellular redox environment in Fe-starved plants. It is concluded that chlorotic leaves of Fe-starved plants though have elevated titre of reactive oxygen species they are less susceptible to oxidative damage probably due to lower chloroplastic pigments/or low functional Fe in the tissue.

Dynamic chloroplast pigments concentration in leaves of soybean ( Glycine max [L.] Merr.) under reduced tillage

The objectives of this experiment were to determine the chloroplast pigments dynamics of soybean leaves during the growth stages under different tillage systems, which can be a major factor limiting yield of soybean. The greatest differences between the photosynthetic productivity parameters of the investigated soybean were determined from reproductive stages (R2 and R3 – 4). The chlorophyll a, chlorophyll a/b and carotenoids content under CT, DH and NT were greater in the reproductive stages (R2 and R3 – 4) than in the early stages (V3 – 4 and R1). The concentration dynamics of chlorophyll b and chlorophyll a/b was very similar in all growth stages and under all tillage systems in the 2-yr average. The increased drought stress in 2003 was likely critical in the observed lower seed yields in 2003. The yield of soybean was significantly lower under NT than CT and DH treatments in both years. The relationship between the soybean yield and chloroplast pigments concentration is strongly influenced by external factors. In the 2-yr average the soybean yield was considerably affected by the years and tillage systems. Statistical analysis showed a very significant relationship between chlorophyll pigments content, but photosynthetic parameters investigated did not correlate with soybean yield.

Distribution of sediment chloroplastic pigments in the Southern Yellow Sea, China

The distribution of sediment chloroplastic pigments (Chl-a, i.e. chlorophyll a and Pha-a, i.e. phaeophorbide a) in the Southern Yellow Sea of China was studied. Samples were collected from four cruises in January and June 2003, and January and June 2004. The results show that the vertical distribution of Chl-a and Pha-a in the sediment layers 0–2cm, 2–5cm and 5–8cm, follows a stable ratio, 5:3:2. The average ratio of Pha-a to Chl-a in sediment is 2.83. Spearman 2-tailed rank correlation analysis shows that Chl-a and Pha-a contents in each sediment layer have a highly significant correlation. The average contents of Chl-a and Pha-a in the sediment of the 0–8cm layer in the investigated area are 0.31–0.47µgg−1 and 1.28–1.40 µgg−1 sediment (dry weight), respectively. The average Chl-a and Pha-a contents in sediment are higher in summer than in winter. ANOVA analysis shows that there is a highly significant variation among the Chl-a contents (P=0.002>0.01) of the four cruies, but this is not true for the case of Pha-a content (P=0.766>0.05). The average Chl-a and Pha-a contents in the 2 sediment layers (0–2cm and 2–5cm) have significant or highly significant correlations with organic matter (OM), median diameter (Mdo), silt plus clay percentage in the January 2003 cruise. In the June 2003 cruise, the average Chl-a content in the 3 sediment layers (0–2cm, 2–5cm, and 5–8cm) has a significant correlation with meiofauna biomass, and Pha-a content has highly significant correlations with water depth, bottom water temperature, OM and Mdo. The contents of Chl-a and Pha-a are lower than those in estuaries and intertidal areas, but close to those in the same area studied previously.

Macrobenthic animal assemblages of the continental margin off Chile (22° to 42°S)

A quantitative study of macrobenthos was carried out on three transects on the shelf and continental slope off Chile (22° to 42°S; from 100 to 2000 m water depth) within and beneath the oxygen minimum zone (OMZ). Macrobenthos mean densities ranged from 104 to 13 808 ind m−2, with highest values off Concepción (∼36°S), where highest chloroplastic pigment equivalents were also measured. Polychaetes were the numerically dominant group in all transects and depths, followed by peracarid crustaceans. Species richness and diversity correlated with observed changes in bottom-water oxygen concentrations and sediment-bound pigments. Our results show that the shelf macrobenthic communities were negatively affected by low oxygen. The non-metric multidimensional scaling (nMDS) analysis evidenced depth-related station groups which may be related to the different environments provided by the water masses involved. Indeed, the depth ranges of stations groups with their specific species inventories coincide quite well with the boundaries of the three important water masses in the region, the Equatorial Subsurface Water (∼50 m to ∼400 m depth), the Antarctic Intermediate Water (∼400 to ∼1200 m depth), and the Pacific Deep Water (&gt;1200 m depth).

Functioning of the photosynthetic apparatus under low and high light conditions in chlorotic spruce needles as evaluated by in vivo chlorophyll fluorescence

The photosynthetic apparatus rapidly responds to the environmental influences. In vivo chlorophyll fluorescence was applied for the evaluation of photosystem II (PSII) and electron-transport chain functioning and for determination of photochemical and nonphotochemical quenching in chlorotic spruce needles exposed to urban pollution. More injured needles had lower content of chloroplast pigments and changed chloroplast ultrastructure, in comparison with less injured needles. The maximum PSII efficiency was measured in dark-adapted samples, whereas other parameters were measured under low and high light conditions (125 and 1400 µmol photons/(m2s), respectively). The PSII efficiency and relative electron transport rate (rel. ETR) were lowered at both irradiance levels while the photochemical quenching was significantly lower only in high light. Nonphotochemical quenching coefficients (qN) values were higher at both light levels in more injured needles, however, the difference was insignificant. High nonphotochemical quenching in both needle groups probably made possible the photosynthetic apparatus to function at the high light level. Our results suggested that the lowering of the chlorophyll content could be considered as a protecting event rather than just the consequence of the stress.

Arsenic as a factor affecting virus infection in tomato plants: changes in plant growth, peroxidase activity and chloroplast pigments

The influence of arsenic and Cucumber mosaic virus (CMV), applied separately and simultaneously on young tomato plants was studied. The plants were cultivated in containers under glasshouse conditions. Four main variants were arranged. The first one was without additional As pollution of soil, named as a control, and the other three variants, with As added at 25, 50 and 100 mg kg −1 to dry soil respectively. Half of the plants in each experimental container were inoculated with CMV and the rest uninoculated. A clear response in plant behavior under the conditions of biotic and abiotic stress was estimated. Both arsenic and virus infection had a negative effect on tomato plants by limiting the growth of their roots and above growth parts. The changes in roots were more significant than of stems. Virus infection was a stronger stress factor than arsenic applied at levels of 25 and 50 mg kg −1. The effect of each stress factor applied separately was enhanced in cases of their simultaneous application. The strongest negative effect was manifested in the infected plants, treated with excess arsenic of 100 mg kg −1. It was established that the infection, caused by CMV in tomatoes, was affected by the presence of arsenic in the soil and concentration of the latter. Doses of 25 and 50 mg kg −1 were favorable for infection development, while the dose of 100 mg kg −1 was an inhibitor. Virus infection induced stronger specific peroxidase activity (SPOA) than As treatment. The combination of both stress factors reduced the positive peroxidase response caused by virus infection. Arsenic at rate 50 and 100 mg kg −1, virus infection and the combination of both stress factors at 25 mg kg −1 reduced chlorophyll a, chlorophyll b and carotenoid content The virus infection in cases of the higher arsenic doses reduced the As effect. There was an interaction between the two effects of biotic and abiotic stress. When arsenic and virus infection were applied simultaneously, they caused modification of the effect of each stress on the plants, when applied separately.

Distribution of meiobenthos at bathyal depths in the Mediterranean Sea. A comparison between sites of contrasting productivity

In order to study the distribution of meiobenthos (Metazoa and Foraminifera) at bathyal depths along a west-east productivity gradient in the Mediterranean Sea, stations along the continental slopes of the Balearic Sea, west Ionian and east Ionian Seas were sampled during the DESEAS Trans-Mediterranean Cruise in June-July 2001. Standing stock of total meiobenthos differed considerably among the sampling stations, with marked differences occurring between sampling depths and sites. At 600 m depth, meiobenthic abundances were slightly higher over the Balearic continental slope, whereas at the deeper stations (800 m and 1500-1700 m), abundances were significantly higher in the west Ionian Sea. Significant relationships were found between the abundances of major groups and the chloroplastic pigments, indicating that food availability is a major factor controlling the distribution of meiobenthos. Apart from the overall differences in productivity between the western and eastern Mediterranean Sea, local hydrographic features and topographic differences greatly influence the spatial variability of the environmental parameters within each sub-basin and thus the distribution of meiobenthos in the bathyal zone.

Leaf orientation, photorespiration and xanthophyll cycle protect young soybean leaves against high irradiance in field

In order to fully understand the adaptive strategies of young leaves in performing photosynthesis under high irradiance, leaf orientation, chloroplast pigments, gas exchange, as well as chlorophyll a fluorescence kinetics were explored in soybean plants. The chlorophyll content and photosynthesis in young leaves were much lower than that in fully expanded leaves. Both young and fully expanded leaves exhibited down-regulation of the maximum quantum yield ( F V/ F M) at noon in their natural position, no more serious down-regulation being observed in young leaves. However, when restraining leaf movement and vertically exposing the leaves to 1200 μmol m −2 s −1 irradiance, more pronounced down-regulation of F V/ F M was observed in young leaves; and the actual photosystem II (PS II) efficiency ( Ф PSII) drastically decreased with the significant enhancement of non-photochemical quenching (NPQ) and ‘High energy’ quenching ( q E) in young leaves. Under irradiance of 1200 μmol m −2 s −1, photorespiration ( P r) in young leaves measured by gas exchange were obviously lower, whereas the ratio of photorespiration/gross photosynthetic rate ( P r/ P g) were higher than that in fully expanded leaves. Compared with fully expanded leaves, young leaves exhibited higher xanthophyll pool and a much higher level of de-epoxidation components when exposure to high irradiance. During leaf development, the petiole angle gradually increased all the way. Especially, the midrib angle decreased with the increasing of irradiance in young leaves; however, no distinct changes were observed in mature leaves. The changes of leaf orientation greatly reduced the irradiance on young leaf surface under natural positions. In this study, we suggested that the co-operation of leaf angle, photorespiration and thermal dissipation depending on xanthophyll cycle could successfully prevent young leaves against high irradiance in field.

Enhanced photoprotection at the early stages of leaf expansion in field-grown soybean plants

Gas exchange, chlorophyll a fluorescence kinetics, chloroplast pigments and antioxidant enzymes were investigated to explore the development of photoprotective mechanisms in soybean leaves from emergence to full expansion under field conditions. During leaf development, photosynthesis ( P n) gradually increased. Although the maximum quantum yield of PSII photochemistry ( F v/ F m) was quite high at the initial stages of leaf development, it was appreciably lower than that in fully expanded leaves. During daily courses, reversible decrease in F v/ F m was noted at various stages, implying that no photodamage occurred. When exposed to irradiance, a substantial elevation in the actual PSII efficiency ( Φ PSII) together with a remarkable decrease in non-photochemical quenching (NPQ) was observed with the process of leaf development. In this study, we observed that newly initiating leaves possessed relative larger xanthophyll pool size (V + A + Z)/Chl, but it began to decrease with leaf expanding until fully expanded. Further experiments revealed that the decline of relative xanthophyll cycle pool size during leaf expanding was owing to the fact that the chlorophyll contents per area increased faster than that of the xanthophyll cycle pigments. In addition, activities of the antioxidative enzymes, such as SOD, APX, CAT, POD and GR, were also enhanced at the early stages of leaf expansion. We suggested that photoprotective mechanisms, including xanthophyll cycle and antioxidant enzymic system, have developed firstly as soon as leaf emerged. It was the timely development of the mechanisms in young leaves that dissipate excess excitation energy protecting leaves against photodamage at the early stages of leaf development. The relative leaf water content increased with the process of leaf development and exhibited significant negative linear correlation with NPQ, xanthophyll cycle pigments and antioxidant enzyme activities in soybean leaves. We proposed that the changes in leaf turgor might be involved in triggering the activation of photoprotective mechanisms together with high irradiance at the initiating stages of leaf expanding.

The small-sized benthic biota of the Håkon Mosby Mud Volcano (SW Barents Sea slope)

R/V POLARSTERN expedition ARK XVIII/1 in summer 2002 provided the opportunity to carry out a sampling programme to assess the activity, biomass and composition of the small-sized benthic biota (size range: bacteria to meiofauna) around the active mud-oozing and methane-seeping Håkon Mosby Mud Volcano (HMMV) on the SW Barents Sea slope, Northern North-Atlantic. A total of 11 stations, covering different areas (e.g., bacterial mat sites, and pogonophoran fields) within the crater, and sites outside the caldera were sampled using a multiple corer. Subsamples were analyzed for various biogenic compounds to estimate the flux of organic matter to the seafloor (sediment-bound chloroplastic pigments indicating phytodetritus), activities (bacterial exo-enzymatic turnover rates) and the total biomass [from bulk parameters, like phospholipid (PL) concentrations in the sediments] of the smallest sediment-inhabiting organisms (range: bacteria to meiofauna). Direct investigations of bacterial numbers and biomasses as well as on meiofauna densities and composition completed our investigations at HMMV. As expected for a comparable small deep-sea area with only minor disparity in water depth between sampling sites, our investigations revealed generally no significant differences in organic matter input from phytodetritus sedimentation between sampling sites inside and outside HMMV. Bacterial exo-enzymatic activities as well as total microbial biomass (TMB) and meiofauna densities, however, exhibited generally higher values at HMMV, compared to sites outside the mud volcano. Enhanced benthic life at HMMV is based on chemosynthetic processes, making the mud volcano a “chemosynthetic oasis” in an otherwise oligotrophic deep-sea environment. As we did not find any indication for bacterial symbioses in the meiofauna, comparably rich meiofaunal assemblages at HMMV are presumably indirectly related to a general enhanced biological production.

Biology and systematics of heterokont and haptophyte algae

In this paper, I review what is currently known of phylogenetic relationships of heterokont and haptophyte algae. Heterokont algae are a monophyletic group that is classified into 17 classes and represents a diverse group of marine, freshwater, and terrestrial algae. Classes are distinguished by morphology, chloroplast pigments, ultrastructural features, and gene sequence data. Electron microscopy and molecular biology have contributed significantly to our understanding of their evolutionary relationships, but even today class relationships are poorly understood. Haptophyte algae are a second monophyletic group that consists of two classes of predominately marine phytoplankton. The closest relatives of the haptophytes are currently unknown, but recent evidence indicates they may be part of a large assemblage (chromalveolates) that includes heterokont algae and other stramenopiles, alveolates, and cryptophytes. Heterokont and haptophyte algae are important primary producers in aquatic habitats, and they are probably the primary carbon source for petroleum products (crude oil, natural gas).

Off-line separation and determination of rare earth elements associated with chloroplast pigments of hyperaccumulator Dicranopteris dichotoma by normal-phase liquid chromatography and ICP-MS.

An off-line normal-phase liquid chromatography-ICP-MS method has been used for separation and determination of the rare earth elements (REE) associated with chloroplast pigments of Dicranopteris dichotoma. The stability of REE-bound pigments was tested, and almost no destruction of REE-bound pigments occurred during the so-called normal-phase liquid chromatography. The accumulated free REE ions on the microcrystalline cellulose column were cleaned by elution with 5 mmol L(-1) 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (P507), to avoid exchange of these free ions with metals from the pigments. When these precautions were taken, the method was applied to the study of REE-bound pigments in D. dichotoma. ICP-MS results showed REE were present in chlorophylls and lutein, although REE concentrations in carotene and pheophytin were both below procedural blank levels. By careful analysis of the eluate fractions containing chlorophyll a it was found that REE-bound chlorophyll a in D. dichotoma was slightly enriched in the fractions with relatively short retention time. Results indicated that the retention time of REE-bound chlorophyll a might be slightly less than that of magnesium chlorophyll a, and REE-bound chlorophylls might be of relatively low polarity in comparison with magnesium bound chlorophylls. This phenomenon could be explained by the special double-decker sandwich-structure of REE-bound chlorophylls, as was reported by us and other authors. On the basis of these results we preferred to consider that REE can replace magnesium in chlorophyll a of D. dichotoma, and that the role of REE-bound chlorophylls in photosynthesis cannot be neglected. These data might be useful for understanding of both the properties of REE-bound pigments and the effect of REE on plant photosynthesis.

Separation and determination of chloroplast pigments from spinach by thin-layer chromatography: A student laboratory experiment

Separation and determination of chloroplast pigments from spinach by thin-layer chromatography: A student laboratory experiment

Chlorophyll and carotenoid degradation mediated by thylakoid-associated peroxidative activity in olives ( Olea europaea) cv. Hojiblanca

A peroxidative activity was found in solubilized thylakoid membranes of olives (Olea europaea) cv. hojiblanca that catalyses degradation of chloroplast pigments in the presence of H2O2 and 2,4-dichlorophenol (DCP). The intermediate products of this degradation were analyzed using HPLC with diode array detection and the results indicated that 13(2)-OH-chlorophyll a and 13(2)-OH-chlorophyll b were the primary catabolites. The peroxidative activity assosiated with the thylakoid membranes affected, not only chlorophyll a and chlorophyll b, but also other accessory pigments in the photosynthetic process, such as the carotenoids. Quantitatively, the progressive decrease of the ratios Chl a/b and total Chls a+b/carotenoids indicated a more rapid disappearance of Chl a than of Chl b and a faster degradation of Chls a+b than of carotenoids.

Evidence for the involvement of lipoxygenase in the oxidative processes associated with the appearance of green staining alteration in the Gordal olive

AbstractLipoxygenase (LOX) activity and chloroplast pigment content were monitored during fruit growth in Gordal and Manzanilla olive varieties (Olea europaea regalis and Olea europaea pomiformis respectively). At all growth stages, LOX activity was greater in Gordal than in Manzanilla, and in both varieties, enzymatic activity peaks coincided with the maximum presence of oxidised chlorophyll pigments in the fruits. The higher lipid peroxidation potential measured directly in vitro and indirectly in vivo in the Gordal variety and its correspondence with higher contents of oxidised catabolites of chlorophyll suggested a greater tendency and sensitivity of this variety to oxidative processes. This could also explain the high organelle disorganisation levels reached during industrial processing of the fruit, allowing the formation of copper–chlorophyll complexes associated with the green staining alteration that affects Gordal olives. Copyright © 2003 Society of Chemical Industry

Measuring antioxidants in tree species in the natural environment: from sampling to data evaluation.

Biochemical measurements of antioxidants and protective pigments have been successfully introduced as markers of environmental stress in field studies (mainly forest studies). A guideline for field sampling and analysis methods is required to allow better comparison of data from different studies. The present review paper recommends HPLC methods for the analysis of ascorbate and glutathione (in oxidized and reduced form), tocopherols, and chloroplast pigments. Methodological variations are substantially lower (coefficients of variance of repeated extractions typically 4-9%) than biological variations of field samples (typical variation coefficients 8-36%), hence special emphasis is put on considerations of sampling standardization in the field with respect to sample time (seasonal and diurnal) and representative sampling of individuals and tissues. Following the suggestions in this paper would enable researchers to produce results that could be compared with those of several forest studies on conifers published in recent years. A larger data-set available for multivariate statistical evaluations (e.g. principal component analysis and cluster analysis) will enhance the diagnostic value of such investigations.

Recombinant Lhca2 and Lhca3 subunits of the photosystem I antenna system.

In this study, two gene products (Lhca2 and Lhca3), encoding higher plants (Arabidopsis thaliana) Photosystem I antenna complexes, were overexpressed in bacteria and reconstituted in vitro with purified chloroplast pigments. The chlorophyll-xanthophyll proteins thus obtained were characterized by biochemical and spectroscopic methods. Both complexes were shown to bind 10 chlorophyll (a and b) molecules per polypeptide, Lhca2 having higher chlorophyll b content as compared to Lhca3. The two proteins differed for the number of carotenoid binding sites: two and three for Lhca2 and Lhca3, respectively. beta-carotene was specifically bound to Lhca3 in addition to the xanthophylls violaxanthin and lutein, indicating a peculiar structure of carotenoid binding sites in this protein since it is the only one so far identified with the ability of binding beta-carotene. Analysis of the spectroscopic properties of the two pigment proteins showed the presence of low energy absorption forms (red forms) in both complexes, albeit with different energies and amplitudes. The fluorescence emission maximum at 77 K of Lhca2 was found at 701 nm, while in Lhca3 the major emission was at 725 nm. Reconstitution of Lhca3 without Chl b reveals that Chl b is not involved in originating the low energy absorption forms of this complex. The present data are discussed in comparison to the properties of the recombinant Lhca1 and Lhca4 complexes and of the native LHCI preparation, previously analyzed, thus showing a comprehensive description of the gene products composing the Photosystem I light harvesting system of A. thaliana.

Aquaculture impact on benthic microbes and organic matter cycling in coastal mediterranean sediments: A synthesis

Microbial assemblages and organic matter composition as well as their response to the disturbance induced by mussel and fish-farm biodeposition were compared in several areas of the Mediterranean: La Spezia (Ligurian Sea), Gaeta (Tyrrhenian Sea), Cattolica (Adriatic Sea) and Cyprus (Levantine Sea), on both unvegetated and Posidonia bed sediments. In all systems investigated, organic matter (as biopolymeric carbon) accumulated in aquaculture impacted sediments. Among the main biochemical classes, lipids appeared to be a good tracer of aquaculture impact, especially in fish-farm sediments. Exoenzymatic activities displayed higher values in sediment beneath the cages, indicating faster organic matter cycling. A significant accumulation of chloroplastic pigments was observed under mussel farms (related to the deposition of faeces and pseudo faeces), but also on fish-farm sediments. The presence of newly deployed cages induced rapid changes in the benthic compartment, and sediments reached rapidly (6 weeks) reducing conditions. Bacterial and total microbial density increased significantly in impacted sediments. Although the contribution of prokaryotic auto-fluorescent cells was very low, this component displayed a clear response to organic biodeposition, increasing significantly beneath the cages. Conversely, eukaryotic auto-fluorescent cells decreased. The ratio of benthic auto-fluorescent cells to total bacterial number proved to be a new, sensitive descriptor of biodeposition impact. Heterotrophic bacteria (CFU, and particularly the number of gram-negative bacteria: Cytophaga / Flexibacter -like bacteria) increased significantly in sediments beneath the farm. The similarities and differences observed among sites, latitudes, microbial components and typology of impact (mussel vs. fish farm) are analysed and discussed.