Assessing the contribution of diazotrophs to microbial Fe uptake using a group specific approach in the Western Tropical South Pacific Ocean.

Diazotrophs are often limited by iron (Fe) availability in the oligotrophic ocean. The Western Tropical South Pacific (WTSP) ocean has been suggested as an intense N2 fixation area due to Fe fertilizations through shallow hydrothermal activity. Yet, the Fe demand of diazotrophs in their natural habitat, where they cohabit with other microbial organisms also requiring Fe, remains unknown. Here we develop and apply a method consisting of coupling 55Fe uptake experiments with cell-sorting by flow cytometry, and provide group-specific rates of in situ Fe uptake by the microbial community in the WTSP, in addition to bulk and size fractionation rates. We reveal that the diazotrophs Crocosphaera watsonii and Trichodesmium contribute substantially to the bulk in situ Fe uptake (~33% on average over the studied area), despite being numerically less abundant compared to the rest of the planktonic community. Trichodesmium had the highest cell-specific Fe uptake rates, followed by C. watsonii, picoeukaryotes, Prochlorococcus, Synechococcus and finally heterotrophic bacteria. Calculated Fe:C quotas were higher (by 2 to 52-fold) for both studied diazotrophs compared to those of the non-diazotrophic plankton, reflecting their high intrinsic Fe demand. This translates into a diazotroph biogeographical distribution that appears to be influenced by ambient dissolved Fe concentrations in the WTSP. Despite having low cell-specific uptake rates, Prochlorococcus and heterotrophic bacteria were largely the main contributors to the bulk Fe uptake (~23% and ~12%, respectively). Overall, this group-specific approach increases our ability to examine the ecophysiological role of functional groups, including those of less abundant and/or less active microbes.

An annual survey of bacterial production, respiration and ectoenzyme activity in coastal NW Mediterranean waters: temperature and resource controls.

We simultaneously measured bacterial production (BP), bacterial respiration (BR), alkaline phosphatase activity (phos) and ectoaminopeptidase activity (prot) in relation to biogeochemical parameters, nutritive resources and in situ temperature over a 1-year survey at the long-term observatory the SOLEMIO station (Marseille bay, NW Mediterranean Sea). Despite its proximity to the coast, oligotrophic conditions prevailed at this station (yearly mean of Chl a = 0.43 µg dm(-3), NO3 = 0.55 µmol dm(-3) and PO4 = 0.04 µmol dm(-3)). Episodic meteorological events (dominant winds, inputs from the Rhone River) induced rapid oscillations (within 15 days) in temperature and sometimes salinity that resulted in rapid changes in phytoplankton succession and a high variability in C/P ratios within the particulate and dissolved organic matter. Throughout the year, BP ranged from 0.01 to 0.82 µg C dm-(3) h-(1) and bacterial growth efficiency varied from 1 to 39%, with higher values in summer. Enrichment experiments showed that BP was limited most of the year by phosphorus availability (except in winter). A significant positive correlation was found between in situ temperature, BP, BR and phos. Finally, we found that temperature and phosphate availability were the main factors driving heterotrophic bacterial activity and thus play a fundamental role in carbon fluxes within the marine ecosystem.

Longitudinal and vertical trends of bacterial limitation by phosphorus and carbon in the Mediterranean Sea.

The effect of phosphate (P), nitrate (N), and organic carbon (C, glucose) enrichment on heterotrophic bacterial production was examined along two longitudinal transects covering the whole Mediterranean Sea during June and September 1999. During these cruises, integrated bacterial production ranged from 11 to 349 mgC m(-2) d(-1) for the 0-150 m layer. P was found to stimulate bacterial production (BP) in 13 out of 18 experiments, in the eastern and in the western Mediterranean Sea. Organic carbon stimulation of bacterial production was observed at two stations in the Alboran Sea, where the highest bacterial production was recorded (216 and 349 mg C m(-2) d(-1)) and in the Sicily Strait. Maximum rates of alkaline phosphatase (AP) increased from the Alboran to the Levantine Sea whereas AP turnover time decreased. Moreover, alkaline phosphatase activity was not systematically reduced following additions of P. In cases of P limitation, however, the alkaline phosphatase activity to bacterial production ratio was severely reduced in the P and NPC enrichments. Generally, the addition of the limiting factor--whether P or C--had a synchronous stimulating effect on bacterial production and ectoaminopeptidase activity and induced a decline in the amino acid respiration percentage. At two selected stations in the eastern and northwestern Mediterranean, response to enrichment was tested on vertical profiles. Bacteria shifted from P to C limitation at a depth where soluble reactive phosphorus was still undetectable, but corresponding to a strong increase in alkaline phosphatase turnover time. Our results showed that values of AP turnover time lower than 100 h corresponded to situations of P limitation of bacterial production.

Validation of HPLC method of analysis of tetracycline residues in eggs and broiler meat and its application to a feeding trial.

HPLC with ion-pairing chromatography and diodearray detection at 355 nm was used to determine tetracycline antibiotics in eggs and broiler meat. The analytical methods were optimized and validated. The mean recovery values for oxytetracycline for eggs and for tetracycline for breast meat were 76%. The within-day precision ranged from 8.0 to 11.8% for oxytetracycline in eggs and from 6.1 to 15.5% for tetracycline in breast meat. The between-day precision was 4.8% and 5.0% respectively for oxytetracycline in eggs and tetracycline in breast meat. The limit of detection and the limit of quantitation for oxytetracycline in eggs were 2.2 and 13.0 ng/g respectively. These limits for tetracycline in breast meat were 10.5 and 20.9 ng/g respectively. Residue values of tetracycline antibiotics in eggs and broiler meat were determined after oral administration of medicated feed. Medicated feed with 840 mg/kg oxytetracycline was provided to laying hens for seven successive days. Two days after the administration was stopped, the mean oxytetracycline residue value in the eggs was already lower than the Maximum Residue Limit (MRL)-level and reached 118 ng/g. Broilers were supplied with medicated feed containing 480 mg/kg tetracycline for seven successive days. Four days after the administration was stopped, the mean tetracycline residue value in breast meat decreased below the MRL and was 86 ng/g.

Influence of phytoplankton lysis or grazing on bacterial metabolism and trophic relationships.

Experimental microcosms were used to study the dynamics of heterotrophic bacterial populations with respect to phytoplankton loss. In a two-stage linked culture system, we artificially separated production and loss processes of a diatom Phaeodactylum tricornutum. In the first (productive) stage, the algae developed axenically and continuously. The outflow was fluxed in two degradation stages, where phytoplankton-derived detritus resulted respectively from: (1) excretion and by-products of phagotrophic organisms (protozoans), and (2) bacterial degradation through bacterial attachment and lysis. According to the phytoplankton decay mode, i.e., lysis or grazing, bacterial adaptations were different. The study of bacterial productivity and aminopeptidase activity showed specific bacterial evolution during the succession of different prey-predator relationships. The occurrence of aggregates allowed nanoflagellates to develop an alternative diet; they fed not only on bacteria, but also on partially degraded phytoplankton detritus, inducing a strong short-cut in the food chain. Sources and controls of extracellular proteolytic activity are discussed. Such experimental approaches are interesting because they separate bacterial lysis and protozoan grazing of phytoplankton, as well as the fates of their corresponding phytoplankton detritus in the microbial food web.

Current role of semen storage and artificial insemination in the turkey industry.

The turkey industry is moving towards the development of stud farms, but an essential condition is the existence of efficient methods to store semen. Much research has been done recently to determine the number of viable spermatozoa in an insemination dose needed for maintaining optimum fertility. Practical methods to determine the number of intact spermatozoa in semen, both before and after storage, are under development. It is now possible to store turkey semen for 6 to 24 h without appreciable loss in fertility and hatchability. Ideal experimental conditions for 48 h storage have not yet been fully determined. Development of new storage media, allowing the insemination of very low numbers of spermatozoa, may provide interesting possibilities regarding the use of elite sires.

[Enumeration and size of planktonic bacteria determined by image analysis coupled with epifluorescence]. / Numération et taille des bactéries planctoniques au moyen de l'analyse d'images couplée à l'épifluorescence.

The interest of the image analysis procedure is the time-saving in automated planktonic bacterial counting and sizing, with the possibility of manual visual field control at all times. Bacterial biomass (in number and volume) and bacterial projected area histograms were determined with a microcomputer. Performance limits of image-analysed epifluorescence microscopy were: camera sensitivity, considering the very low fluorescence levels on stained bacteria; pixel-micron conversion factor, and the impossibility of the apparatus distinguishing between bacteria and fluorescent small particles. This method is not of interest for counting sediment bacteria.

Effect of semen storage time and number of spermatozoa inseminated on the fertility and hatchability of eggs from dwarf broiler breeder hens.

Semen from commercial breeder males was diluted two-fold and stored for 6 and 24 h at 2 to 3 degrees C. For each storage period, groups of caged dwarf broiler breeder hens from the same strain were inseminated with 300, 200 or 100 x 10(6) spermatozoa. Three replicates of 15 birds were inseminated per treatment. Control hens were inseminated with 150 x 10(6) fresh, undiluted spermatozoa. Inseminations were performed for 5 consecutive weeks during a first (32 to 36 weeks of age) and for 6 consecutive weeks during a second experimental period (42 to 47 weeks). During weeks 33 to 36 of the first period, only 24 h storage and 100 x 10(6) spermatozoa produced lower (P less than 0.05) hatchability of all eggs set than the control (84.4 compared to 88.6%). During weeks 43 to 47 of the second period, no significant differences between treatments were observed. Embryonic mortality, measured at different periods during incubation, was not affected by the storage time or the number of spermatozoa inseminated.

A comparison of the reproductive and growth performances of offspring from broiler breeder males selected for early growth rate using artificial insemination and unselected males kept on deep litter.

Broiler breeder males were selected for early growth rate at 5 weeks of age (average weight + 0.5 SD). The reproductive and growth performances of the offspring of these males using artificial insemination with stored semen was compared with those from non-selected males kept on deep litter under conditions of natural mating. On three different occasions (31, 41 and 51 weeks of age), the eggs of the two treatments were incubated and, although the reproductive performances showed little difference over the entire period, hatchability of eggs set was significantly (p less than 0.01) higher for the field hens on the first occasion. The opposite was true after 50 weeks of age due to a serious decline in fertility in natural mating. At all periods, the selected males produced significantly (p less than 0.01) heavier offspring at six weeks of age.

Early body-weight selection of broiler breeder males in relation to reproductive and growth performance of their offspring.

1. The effectiveness of selection of broiler breeder males for body weight at 3 weeks of age on later growth, semen quality and performance of progeny has been tested. 2. Correlation between 3- and 20-week body weights in the breeders was poor but significant. 3. On the basis of 3-week body weight males were divided into heavy birds (mean + 0.5 standard deviation) and all birds. 4. Semen quality was not different between the two groups, but some selection for semen quality was practised within groups. 5. There were no differences in fertility and hatchability of eggs produced from hens artificially inseminated with diluted, stored semen from both groups. 6. There was a small, positive, but non-significant, effect of selection of breeder males on body weight of progeny at 6 weeks of age.

The effect of tonicity of storage media for fowl semen on the occurrence of neck-bending spermatozoa, fertility and hatchability.

1. Semen of White Leghorn and Rhode Island Red males was stored for 24 h in diluents hypertonic (460 mOsm/kg H2O) and isotonic (340 mOsm/kg H2O) to cock seminal plasma. 2. Compared with the fertility results with semen that had been stored in the hypertonic diluent or was fresh, the fertility of the White Leghorns was not affected after storage in the isotonic diluent; a decrease (P less than 0-05) was observed, however, using Rhode Island Red semen and isotonic diluent. 3. Fresh RIR semen contained 2-3% "neck-bent spermatozoa" (NBS) which was increased to 4-23% and 5-76% after dilution in hypertonic and isotonic diluents respectively and stored for 24 h. It is doubtful whether this increase (P less than 0-05) is the sole reason for the lowered fertility obtained with this breed after storage in the isotonic diluent.