Abdellatif Boudabous

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.

Detection and characterization of the novel bacteriocin entomocin 9, and safety evaluation of its producer, Bacillus thuringiensis ssp. entomocidus HD9

Aims: To identify and characterize new bacteriocins from a collection of 41 strains belonging to 27 subspecies of Bacillus thuringiensis, and to evaluate the safety of the producers.

Evidence for the involvement of galectin-3 in mesenchymal stem cell suppression of allogeneic T-cell proliferation

Human bone marrow‐derived mesenchymal stem cells (MSC) are multipotent non‐hematopoietic progenitors that have regulatory activity on immune cells. NOD‐ and Toll‐like receptors (NLR, TLR) have several roles in immunity, including those relevant to pathogen recognition and shaping the course of immune responses by controlling gene expression. We have shown that these innate immune receptors are expressed by hematopoietic CD34+ progenitors and MSC. To uncover genes critical in MSC function, first we have used microarray to screen for potential transcripts whose levels are altered in response to NOD‐1 and TLR‐2 activation, and second we validated some candidate genes using real‐time RT‐PCR, Western blots and cellular assays. Amongst the altered genes, galectin‐3 was upregulated at both mRNA and protein levels in response to TLR‐2 activation. Interestingly, MSC secreted galectin‐3, a protein known to modulate T‐cell proliferation, gene expression, cell adhesion and migration. Knockdown of galectin‐3 in MSC using small interfering RNA (siRNA) reduced the immunosuppressive effect of MSC on mixed lymphocyte cultures when compared to cells treated with an irrelevant siRNA (P < 0.05). Collectively, the data emphasize a new role of galectin‐3 in the immunomodulatory function of MSC and indicate that NOD signalling pathway is also functional in these cells.

Nature of Polymorphisms in 16S-23S rRNA Gene Intergenic Transcribed Spacer Fingerprinting of Bacillus and Related Genera

ABSTRACT The intergenic transcribed spacers (ITS) between the 16S and 23S rRNA genetic loci are frequently used in PCR fingerprinting to discriminate bacterial strains at the species and intraspecies levels. We investigated the molecular nature of polymorphisms in ITS-PCR fingerprinting of low-G+C-content spore-forming bacteria belonging to the genera Bacillus, Brevibacillus, Geobacillus, and Paenibacillus. We found that besides the polymorphisms in the homoduplex fragments amplified by PCR, heteroduplex products formed during PCR between amplicons from different ribosomal operons, with or without tRNA genes in the ITS, contribute to the interstrain variability in ITS-PCR fingerprinting patterns obtained in polyacrylamide-based gel matrices. The heteroduplex nature of the discriminating bands was demonstrated by fragment separation in denaturing polyacrylamide gels, by capillary electrophoresis, and by cloning, sequencing, and recombination of purified short and tRNA gene-containing long ITS. We also found that heteroduplex product formation is enhanced by increasing the number of PCR cycles. Homoduplex-heteroduplex polymorphisms (HHP) in a conserved region, such as the 16S and 23S rRNA gene ITS, allowed discrimination of closely related strains and species undistinguishable by other methods, indicating that ITS-HHP analysis is an easy and reproducible additional tool for strain typing.

Genetic relationship in the ‘Bacillus cereus group’ by rep‐PCR fingerprinting and sequencing of a Bacillus anthracis‐specific rep‐PCR fragment

Aims: To evaluate the genetic relationship in the Bacillus cereus group by rep‐PCR fingerprinting.

Mesenchymal stem cell-mediated T cell suppression occurs through secreted galectins

Human galectins are involved in a variety of biological and pathological processes including cell adhesion, apoptosis, differentiation, immune regulation and tumour evasion. Previously, we identified galectin-3 as the first human lectin involved in the modulation of the immunosuppressive potential of mesenchymal stem cells (MSCs). In this study, we report on the expression profiles and potential activities of other galectins expressed in these cells. The data show that MSCs constitutively express galectins-1, -3 and -8 at both the mRNA and protein levels. In contrast to galectin-8, galectins-1 and -3 are secreted and found on the cell surface. MSC-mediated T cell suppression was inhibited by galectin-1-specific siRNAs but not by galectin-8-specific siRNAs. The double knockdown of galectins-1 and -3 almost abolished the immunosuppressive capacity of MSCs. The use of a competitive inhibitor for galectin binding, ß lactose, restored alloresponsiveness, implying an extracellular mechanism of action of galectins. Collectively, the data highlight the involvement of secreted galectins-1 and -3 in MSC-mediated T cell suppression. The immunosuppression by MSC-secreted galectins should facilitate the use of recombinant galectin-1 and/or -3 as a novel therapy to alleviate inflammatory reactions such as those seen in graft versus host disease (GvHD) and autoimmune disorders.