Use of reporter-gene based bacteria to quantify phenanthrene biodegradation and toxicity in soil

A phenanthrene-degrading bacterium, Sphingomonas paucimobilis EPA505 was used to construct two fluorescence-based reporter strains. Strain D harboring gfp gene was constructed to generate green fluorescence when the strain started to biodegrade phenanthrene. Strain S possessing gef gene was designed to die once phenanthrene biodegradation was initiated and thus to lose green fluorescence when visualized by a live/dead cell staining. Confocal laser scanning microscopic observation followed by image analysis demonstrates that the fluorescence intensity generated by strain D increased and the intensity by strain S decreased linearly at the phenanthrene concentration of up to 200 mg/L. Such quantitative increase and decrease of fluorescence intensity in strain D (i.e., from 1 to 11.90 ± 0.72) and strain S (from 1 to 0.40 ± 0.07) were also evident in the presence of Ottawa sand spiked with the phenanthrene up to 1000 mg/kg. The potential use of the reporter strains in quantitatively determining biodegradable or toxic phenanthrene was discussed.     

Sorption and mobility of pharmaceutical compounds in soil irrigated with reclaimed wastewater

Use of reclaimed wastewater for irrigation is an important route for the introduction of pharmaceutical compounds (PCs) into the environment. In this study, the mobility and sorption-desorption behavior of carbamazepine, naproxen and diclofenac were studied in soil layers sampled from a plot irrigated with secondary-treated wastewater (STWW). Carbamazepine and diclofenac were significantly retarded in the 0-5 cm soil sample rich in soil organic matter (SOM): carbamazepine was not affected by the water quality (freshwater versus STWW), whereas diclofenac exhibited a higher retardation factor (RF) in the freshwater system. Naproxen exhibited significantly lower RFs than diclofenac but with a similar trend - higher retardation in the freshwater versus STWW system. In the 5-15 cm soil sample containing low SOM, naproxen was highly mobile while carbamazepine and diclofenac were still retarded. In the 15-25 cm sample, all compounds exhibited their lowest RFs. Sorption data suggested that SOM governs the studied PCs' interactions with the soil samples. However, higher carbon-normalized sorption coefficients were measured for the PCs in the 15-25 cm sample, suggesting that both quantity and the physicochemical nature of SOM affect sorption interactions. While both naproxen and carbamazepine exhibited reversible sorption isotherms, diclofenac exhibited pronounced sorption-desorption hysteresis. This study suggests that carbamazepine and diclofenac can be classified as slow-mobile compounds in SOM-rich soil layers. When these compounds pass this layer and/or introduced into SOM-poor soils, their mobility increases significantly. This emphasizes the potential transport of PCs to groundwater in semiarid zones due to intensive irrigation with reclaimed wastewater in SOM-poor soils.     

In-nest environment modulates nestmate recognition in the ant<Emphasis Type="Italic"> Camponotus fellah</Emphasis>

Multiple behavioral and chemical studies indicate that ant nestmate recognition cues are low-volatile substances, in particular hydrocarbons (HCs) located on the cuticular surface. We tested the hypothesis that in the ant Camponotus fellah, nest environment, in particular nest volatile odors, can modulate nestmate-recognition-mediated aggression. Workers were individually confined within their own nest in small cages having either a single mesh (SM = limited physical contact permitted) or a double mesh (DM = exposed to nest volatiles only) screen. Individual workers completely isolated outside their nest (CI) served as control. When reintroduced into a group of 50 nestmates, the CI workers were attacked as alien ants after only 2 weeks of separation, whereas the SM workers were treated as nestmates even after 2 months of separation. Aggression towards DM ants depended on the period of isolation. Only DM workers isolated for over 2 months were aggressed by their nestmates, which did not significantly differ from the CI nestmates. Cuticular HC analyses revealed that the profile of the non-isolated ants (NI) was clearly distinct from that of CI, SM and DM ants. Profile differences matched the aggressive response in the case of CI ants but were uncorrelated in the case of SM or DM ants. This suggests that keeping the ants within the nest environment affected nestmate recognition in additional ways than merely altering their HC profile. Nest environment thus appears to affect label–template mismatch by modulating aggressive behavior, as well as the direction at which cuticular HCs diverged during the separation period.     

Dufour's gland secretion of the queen honeybee (Apis mellifera): an egg discriminator pheromone or a queen signal?

The role of Dufour's gland secretion as an egg discriminator pheromone was reevaluated by simultaneously exposing workers to two combs, one containing queen- or worker-laid eggs and the second containing treated or untreated worker-laid eggs. Treatments included extracts of Dufour's gland secretion as well as the synthetic esters that were identified in the secretion. Policing was clearly detected both in queenright and queenless colonies by the swift removal of worker, but not of queen eggs. However, neither the glandular secretion nor its synthetic ester constituents were able to protect worker-born eggs from policing. Treated worker eggs were removed significantly faster than queen eggs, and at the same rate as non-treated worker eggs. These results are not consistent with the hypothesis that the secretion serves as an egg-marking pheromone. Chemical analyses of the queen abdominal tips revealed the presence of Dufour's esters, indicating that the glandular secretion oozes out and spreads over the cuticle around the genital chamber. However, contamination while ovipositing may also explain the minute amounts of these esters that were detected on the egg surface. Dufour's gland caste-specific composition suggests that in queens it may constitute a signal that plays a role in queen-worker interactions. Attraction bioassays revealed that the queen secretion, but not that of workers, is very attractive to workers. When applied either on a glass slide or on another worker, a retinue formed around the "surrogate queen". We conclude that Dufour's gland secretion constitutes part of a complex queen signal that is the basis for the social integrity of the honeybee colony.     

Dufour’s gland pheromone as a reliable fertility signal among honeybee (Apis mellifera) workers

When a colony becomes queenless and without the possibility of requeening, honeybee workers initiate reproduction and lay male eggs about a week later. Assays in which two bees were confined in a small arena revealed that they establish a reproductive dominance hierarchy, i.e., one worker demonstrates greater ovarian development than her paired bee. Reproductive dominance is independent of relatedness, and can be established between full sisters, cousins, or random nestmates. A social environment, however, is obligatory, as singly housed bees fail to develop ovaries on the same time scale. Allowing varying degrees of social interactions between the paired bees revealed that olfaction of volatile bee compounds, as well as tactile communication, seem to provide the necessary social environment. Ovarian development was accompanied by the production of queen-like Dufours gland secretion in these workers. Especially notable was the increase in the queen-like esters. This increase was tightly linked to ovarian development and not necessarily to the dominance status of the bees in the pair. Thus, the occurrence of queen-like esters can serve as a reliable fertility signal. Advertising ovarian status may recruit helper workers with less developed ovaries (and which are less likely to successfully reproduce before colony breakdown) to assist their nestmates and thereby gain inclusive fitness. Revealing the role of Dufours gland secretion as a fertility signal adds another dimension to our understanding of how queen pheromones operate. The mandibular-gland secretion is a good predictor of dominance hierarchy, being correlated with false-queen characteristics but not fertility, whereas Dufours gland secretion is a good predictor of fertility but not dominance hierarchy.Communicated by R.F.A. Moritz