Abdennaceur Hassen

Microbial characterization during composting of municipal solid waste

This study investigates the prevailing physico-chemical conditions and microbial community; mesophilic bacteria, yeasts and filamentous fungi, bacterial spores, Salmonella and Shigella as well as faecal indicator bacteria: total coliforms, faecal coliforms and faecal Streptococci, present in a compost of municipal solid waste. Investigations were conducted in a semi-industrial pilot plant using a moderate aeration during the composting process. Our results showed that: (i) auto-sterilization induced by relatively high temperatures (60-55 degrees C) caused a significant change in bacterial communities. For instance, Escherichia coli and faecal Streptococci populations decreased, respectively, from 2 x 10(7) to 3.1 x 10(3) and 10(7) to 1.5 x 10(3) cells/g waste dry weight (WDW); yeasts and filamentous fungi decreased from 4.5 x 10(6) to 2.6 x 10(3) cells/g WDW and mesophilic bacteria were reduced from 5.8 x 10(9) to 1.8 x 10(7) bacteria/g WDW. On the other hand, the number of bacterial spores increased at the beginning of the composting process, but after the third week their number decreased notably; (ii) Salmonella disappeared completely from compost by the 25th day as soon as the temperature reached 60 degrees C; and (iii) the bacterial population increased gradually during the cooling phase. While Staphylococci seemed to be the dominant bacteria during the mesophilic phase and at the beginning of the thermophilic phase, bacilli predominated during the remainder of the composting cycle. The appearance of gram-negative rods (opportunistic pathogens) during the cooling phase may represent a serious risk for the sanitary quality of the finished product intended for agronomic reuse. Compost sonication for about 3 min induced the inactivation of delicate bacteria, in particular gram-negatives. By contrast, gram-positive bacteria, especially micrococcus, spores of bacilli, and fungal propagules survived, and reached high concentrations in the compost.

Resistance of environmental bacteria to heavy metals

Bacteria were isolated from different naturally polluted environments. Metal-resistant bacteria were selected and minimal inhibitory concentrations of heavy metals (MICs) for each isolate were determined. In addition, the mobility of the most important metallic cations (Cu, Zn, Cr, Cd, Co, Hg) was evaluated by comparing results obtained by two tests of toxicity in solid and liquid media. Results of the test of toxicity in solid media agreed with those in liquid, however, inhibitory concentrations in solid media were much higher than those in liquid. The range of metal concentrations tolerated in solid and liquid media yielded information on the capacity of adsorption and complexation of the metals. Mercury, and to a lesser degree copper, seemed to have a good capacity for adsorption and complexation and, consequently, had a limited diffusion in different naturally polluted environments. The presence of metals in the growth medium allowed us to maintain the tolerance of bacteria at a comparable level with that observed in naturally polluted environments. Cu and Cr were the best tolerated metals. Hg was the most toxic component for all bacteria, followed by Co and Cd. Pseudomonas aeruginosa (strain S6), with a relatively high MIC for metals and a large spectrum of antibiotic resistance appears to be a bacterial model for eco-toxicological studies.

Thuricin 7: a novel bacteriocin produced by Bacillus thuringiensis BMG1.7, a new strain isolated from soil

Aims: Detection and identification of new antagonistic activities towards Bacillus cereus and relatives.

UV disinfection of treated wastewater in a large-scale pilot plant and inactivation of selected bacteria in a laboratory UV device

Abstract Efficiency of UV disinfection of unfiltered and filtered secondary wastewater effluent, using a large-scale pilot system, and the inactivation of six bacterial species in a laboratory UV-device have been studied. Pilot plant studies revealed low levels of coliforms and streptococci (3 logarithmic units reduction) when a wastewater UV transmission of 45% and an average effective UV dose of 100 mW s cm−2 were used. By contrast, removal of Pseudomonas aeruginosa appeared insufficient (

Effects of heavy metals on Pseudomonas aeruginosa and Bacillus thuringiensis

Abstract The biosorption of the heavy metals most frequently found in polluted environments by Pseudomonas aeruginosa and Bacillus thuringiensis was studied. The effects of these metals on bacterial growth, quantity of dry cells, ammonium assimilation, pigment production, and protein synthesis were investigated. At lower concentrations than the minimal inhibitory concentration (MIC), the metals partially limited bacterial growth and caused an inhibition proportional to the metal concentration applied. The production of bacterial biomass varied according to the nature and concentration of the metals, and to the bacterial strain studied. The biosorption of metals by P. aeruginosa and B. thuringiensis was variable. Mercury and copper appeared to be the elements most adsorbed by bacteria. Citrate noticeably increased the biosorption of chromium by P. aeruginosa (0.07–45.9%) and copper by B. thuringiensis (18.7–33.8%). Metallic cations exerted variable effects on protein synthesis. Zinc stimulated protein synthesis in P. aeruginosa, and cadmium inhibited it significantly in B. thuringiensis. Mercury and cobalt, at concentrations below the MIC, always inhibited the synthesis of pigments in P. aeruginosa. The strong interactions of mercury and copper with organic matter suggest that these undesirable elements might be removed from the environment by bacterial trapping and sequestration. A better understanding of the different forms of metals actually existing in polluted environments (speciation) would be of great interest.

Microbial biomass in a soil amended with different types of organic wastes

Application of different types of organic wastes may have a marked effect on soil microbial biomass and its activity. The objective of this study was to quantify the amount of microbial biomass in a loamy-clayey soil, amended with different types of organic waste residues (composts of municipal solid waste of different ages, sewage sludge and farmyard manure) and incubated for 8 weeks at 25°C and two-thirds of field capacity, using the fumigation–extraction method. Both microbial biomass-C and -N (B C and B N, respectively) appeared to be dependent on the type of organic waste residues, on their degree of stability, and on their chemical characteristics. In general, organic wastes increased the microbial biomass-C content in the soil and the microbial B C was positively correlated with the organic C content, the C/N, neutral detergent fibre/N (NDF/N) and acid detergent fibre/N (ADF/N) ratios. The microbial biomass content decreased according to the period of incubation, especially when the compost used was immature. The microbial biomass-N was positively correlated with the total N and percentage of hemicellulose. The microbial biomass-C was linearly related with the microbial biomass-N and the ratio B C/B N was exponentially related with the B C.

Modeling of secondary treated wastewater disinfection by UV irradiation： Effects of suspended solids content

This work aimed to study UV-resistant strains of Pseudomonas aeruginosa, to propose a formulation of the kinetics of secondary treated wastewater disinfection and to underline the influence of suspended solids on the inactivation kinetics of these strains. Some investigations were carried out for the validation of some simulation models, from the simplest, the kinetics model of Chick-Watson reduced to first order, to rather complex models such as multi-kinetic and Collins-Selleck models. Results revealed that the involved processes of UV irradiation were too complex to be approached by a simplified formulation, even in the case of specific strains of microorganisms and the use of nearly constant UV radiation intensity. In fact, the application of Chick-Watson model in its original form is not representative of the kinetics of UV disinfection. Modification, taking into account the speed change during the disinfection process, has not significantly improved results. On the other hand, the application of Collins-Selleck model demonstrates that it was necessary to exceed a least dose of critical radiation to start the process of inactivation. To better explain the process of inactivation, we have assumed that the action of disinfectant on the survival of lonely microorganisms is faster than its action on suspended solids protected or agglomerated to each others. We can assume in this case the existence of two inactivation kinetics during the processes (parallel and independent) of the first-order. For this reason, the application of a new kinetic model by introducing a third factor reflecting the influence of suspended solids in water on disinfection kinetics appeared to be determinant for modeling UV inactivation of P. aeruginosa in secondary treated wastewater.

Detection of viable but non cultivable Escherichia coli after UV irradiation using a lytic Qβ phage

In order to qualify the germicidal efficacy of ultraviolet (UV) disinfection system, we generally determine the reduction of viable bacteria after UV-C irradiation. However, the simple count of viable and cultivable bacteria in usual media cannot reflect whether or not the UV dose applied to disinfect water is sufficient to inactivate bacteria. Indeed, there is a bacterial mix in the UV-treated water: dead bacteria, viable and cultivable bacteria and viable but noncultivable bacteria (VBNC). The third type of bacteria can constitute a potential risk for public health. In fact, VBNC bacteria can be active and cause diseases. Consequently, the combination of a conventional method used to measure colony-forming ability after UV disinfection and the determination of adsorption constants of a lytic Qβ phage in relation to irradiated host cells by an increased UV dose (Escherichia coli ATCC 13965) allows the detection of active bacteria, which lose their cultivability in usual growth media, but keep the phage susceptibility.

Mineralization of nitrogen in a clayey loamy soil amended with organic wastes enriched with Zn, Cu and Cd

Abstract This paper deals with the evaluation of the availability of mineral nitrogen in soil amended with different organic wastes (sewage sludges, farm manure, and compost of municipal solid wastes) and the impact of an additional amount of Cu, Zn and Cd on N-mineralization. Net rates of mineralization fluctuated in the soil amended with organic wastes between 11·67 and 33·61 mg kg −1 . The decreasing order of mineralization, expressing a decreasing order of microbiological activity, was: soil+sludges > soil+manure > soil+compost > soil. From the kinetic study, it was seen that the mineralization process could be divided into two main periods: the first was from soil moistening up to the fourth week and the second from week 8 to week 16. The first phase of incubation was a period of microbial adaptation to the new environment of soil amended with organic wastes and enriched with Cu, Zn and Cd. This phase was often marked by N consumption-immobilization. The second phase was characterized by active kinetics of mineralization and intense microbial activity. The influence of the organic amendments according to the value of N 0 (the N-mineralization potential) was: N 0 (soil) 0 (compost) 0 (manure) 0 (sludges) . The inhibitory effect of the added metals on N-mineralization was: Cd > Cu > Zn. For many reasons, the global effect of metals on N-mineralization was very variable. A sufficiently long latent time (i weeks) was needed for tolerant microorganisms to release or to start N-mineralization.

Diversity of auxin-producing bacteria associated to Pseudomonas savastanoi-induced olive knots

Forty three strains were isolated from knots induced by Pseudomonas savastanoi in different olive cultivars. All the selected bacteria were shown to produce variable amounts of the plant growth hormone indole‐3‐acetic acid (IAA). Amplification of the intergenic transcribed spacers (ITS) between 16S and 23S rDNA genes, allowed the clustering of the isolates into seven distinct groups. All isolates from ITS group 1 were positive to the Pseudomonas savastanoi pv. savastanoi specific iaa L gene as shown by PCR. Partial sequencing of 16S rDNA gene confirmed the identity of these isolates to Pseudomonas savastanoi strains and allowed to tentatively assign the other isolates from the remaining ITS groups to Pantoea oleae/agglomerans, Burkholderia cepacia, Pseudomonas putida, Stenotrophomonas maltophilia and Hafnia alvei. Identification of endophytic knot‐derived isolates revealed association of various saprophytic and putative human pathogenic bacteria with P. savastanoi pv. savastanoi in knot environment of olive infected trees. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)