Biochemical and nutritional characterization of the medfly gut symbiont Enterobacter sp. AA26 for its use as probiotics in sterile insect technique applications

Background

Symbiotic bacteria contribute to a multitude of important biological functions such as nutrition and reproduction and affect multiple physiological factors like fitness and longevity in their insect hosts. The melon fly, Zeugodacus cucurbitae (Coquillett), is an important agricultural pest that affects a variety of cultivated plants belonging mostly to the Cucurbitaceae family. It is considered invasive and widespread in many parts of the world. Several approaches are currently being considered for the management of its populations including the environmentally friendly and effective sterile insect technique (SIT), as a component of an integrated pest management (IPM) strategy. In the present study, we examined the effect of diet and radiation on the bacterial symbiome of Z. cucurbitae flies with the use of Next Generation Sequencing technologies.

Results

Melon flies were reared on two diets at the larval stage, an artificial bran-based diet and on sweet gourd, which affected significantly the development of the bacterial profiles. Significant differentiation was also observed based on gender. The effect of radiation was mostly diet dependent, with irradiated melon flies reared on the bran diet exhibiting a significant reduction in species diversity and richness compared to their non-irradiated controls. Changes in the bacterial symbiome of the irradiated melon flies included a drastic reduction in the number of sequences affiliated with members of Citrobacter, Raoultella, and Enterobacteriaceae. At the same time, an increase was observed for members of Enterobacter, Providencia and Morganella. Interestingly, the irradiated male melon flies reared on sweet gourd showed a clear differentiation compared to their non-irradiated controls, namely a significant reduction in species richness and minor differences in the relative abundance for members of Enterobacter and Providencia.

Conclusions

The two diets in conjunction with the irradiation affected significantly the formation of the bacterial symbiome. Melon flies reared on the bran-based artificial diet displayed significant changes in the bacterial symbiome upon irradiation, in all aspects, including species richness, diversity and composition. When reared on sweet gourd, significant changes occurred to male samples due to radiation, only in terms of species richness.

     

High aeration rate enhances flow stratification in full-scale oxidation ditch

Aerated channel reactors with a uniform field of aeration may display flow stratification and short-circuit phenomena in wastewater treatment systems. In this study, we present data suggesting that flow stratification is closely related to the aeration rate and the arrangement of aerators. A full-scale oxidation ditch, with a total volume of 6,500 m³ and a membrane-diffused aerated zone of 60 × 7 × 5 m (length–width–depth), was selected for water velocity measurements. Two profiles of the oxidation ditch were studied in detail: the first one was at the end of the aerated zone and the second one at the end of the anoxic zone. The results of this work demonstrate that the horizontal water velocity at the end of the aerated zone displayed significant stratification, with maximum velocity near the water surface (0.5–0.7 m/s) and almost zero velocity at a depth of 2.5 m. At the end of the anoxic zone, water velocity was uniform and equal to 0.27–0.31 m/s. Increasing the aeration rate from 1,800 to 4,300 m³/h, almost 90% of the water flow was found to discharge through the upper-half of the channel reactor profile. Different options to mitigate flow stratification of the oxidation ditch are discussed in this paper.     

On-line load monitoring of wastewaters with a respirographic microbial sensor

This paper demonstrates the functionality, laboratory testing and field application of a microbial sensor that is capable of monitoring the organic pollution extent of wastewaters both off-line in a laboratory and on-line in a wastewater treatment plant. The biosensor was first developed in the laboratory using synthetic wastewater and then applied to monitor the effluent of the unit. The basic working principle of the biosensor is based on the on-line measurement of CO2 concentration in the off gas produced during carbon compound degradation by microbial respiration activities. CO2 concentration under operation conditions (constant oxygen flow rate, residence time and pH) is closely related to the extent of organic pollution (biochemical oxygen demand, chemical oxygen demand). CO2 monitoring is carried out by an infrared spectrometer, whereas current organic pollution is determined off-line according to the conventional 5-day lasting BOD analysis. Off gas analysis of CO2 concentration strongly correlates with off-line biochemical oxygen demand measurements allowing continuous on-line monitoring of the organic load within a wastewater treatment plant. Thus, real time process control and operation become feasible.     

Use of a microbial sensor: a new approach to the measurement of inhibitory effects on the microbial activity of activated sludge

This paper presents a new method for the measurement of inhibitory effects in wastewater treatment plants on the basis of a continuous measurement of the microbial respiration product (CO(2)). The microbial sensor developed for this purpose consists of a small conical fluidized bed reactor connected to a cylindrical chamber that comprises part of the sample recirculation system. Activated sludge microbes are immobilized on spherical (diameter=1-2 mm) reticulated sinter glass carriers. Pure oxygen is supplied via the cylindrical chamber in order to sustain a highly dense population of microbial mass. The mean hydraulic retention time in the microbial sensor ranges between 30 and 40 min, while temperature is maintained at 30 degrees C, and pH 6.4. Carbon dioxide in the off-gas, which reflects the microbial activity, is continuously analyzed by means of an infrared analyzer. Inhibition of microbial activity (toxicity) can be determined as the mean percent reduction in carbon dioxide concentration. Several substances were tested and proved toxic to the microbes. With this microbial sensor, early detection of toxic substances becomes feasible, preventing them from entering an activated sludge unit operation.     

Development and implementation of microbial sensors for efficient process control in wastewater treatment plants

This paper demonstrates the functionality, laboratory testing and field application of a microbial sensor, which can be modified to monitor organic pollution extent, toxicity and over-(under)load of wastewaters both under anaerobic and aerobic conditions. Since nitrification is related to protons formation and the addition of alkaline is necessary for pH control, an aerobic biosensor monitoring Na₂CO₃ consumption was developed and practically implemented to control the nitrification process. As CO₂ is the respiration product from aerobic degradation which can be correlated to the organic pollution extent, the previous biosensor was modified to monitor and measure the online toxicity and BOD/COD. Under anaerobic conditions, the online measurement of NaOH consumption and biogas production allowed the detection of toxicity incidents and over-(under)load in the influent. Such toximeters get in contact with the wastewater the earliest possible, providing sufficient time for protection of sensitive biological wastewater treatment processes and for the implementation of control and management strategies.     

Use of a microbial sensor: inhibition effect of azo-reactive dyes on activated sludge

This paper summarizes the methodology utilized for measuring the toxic and inhibitory effects of azo-reactive dyes on the activity of activated sludge. The microbial sensor employed in this study consisted of a small-fluidized bed reactor in which the microbial mass was immobilized on spherical (diameter =1-2 mm) reticulated sinter glass carriers. To sustain a highly dense population of aerobic microbes, pure oxygen was supplied via a cylindrical chamber, which comprised part of the sample re-circulation system. The mean hydraulic retention time in the microbial sensor ranged between 30 and 40 min, while temperature was maintained at 30 degrees C and pH at 6.4. Inhibition of microbial activity (toxicity) was determined as the mean percent reduction in carbon dioxide production from microorganisms' respiration. Several azo-reactive dyes demonstrated toxicity when applied at a high concentration (2 g/l), however, a portion of the microbes showed tolerance to the dyes. Moreover, textile wastewater demonstrated very efficient biodegradation.