Fungal feeding preferences and molecular gut content analysis of two abundant oribatid mite species (Acari: Oribatida) under the canopy of Prosopis laevigata (Fabaceae) in a semi-arid land.

Prosopis laevigata (mesquite; Fabaceae) forms fertility islands in soils of semi-arid lands where microbial diversity concentrates in response to the accumulation of resources in the soil beneath individual plants, promoting organic matter decomposition and nutrient cycling. This phenomenon provides suitable conditions for the proliferation of key edaphic elements such as fungi and mites. Mite-fungal interactions are central for our understanding of nutrient cycling processes in resource-limited arid food webs; yet, no information is available about fertility islands in semi-arid lands. Thus, we aimed to determine in vitro fungal-based feeding preferences and molecular gut content of the oribatid mite species Zygoribatula cf. floridana and Scheloribates cf. laevigatus, which are abundant under the canopy of P. laevigata in an intertropical semi-arid zone in Central Mexico. Our results on the gut content analysis of these oribatid species resulted in the ITS-based identification of the following fungi: Aspergillus homomorphus, Beauveria bassiana, Filobasidium sp., Mortierella sp., Roussoella sp., Saccharomyces cerevisiae, Sclerotiniaceae sp. and Triparticalcar sp. Furthermore, under laboratory conditions both oribatid mite species exhibited feeding preferences on melanized fungi, such as Cladosporium spp., whereas A. homomorphus and Fusarium penzigi were avoided. Our findings indicated that the analyzed oribatid mite species have similar feeding preferences for melanized fungi, which might suggest resource partitioning and a degree of preference, explaining the coexistence of both oribatid species.

Effect of Predation by Colpoda sp. in Nitrogen Fixation Rate of Two Free-Living Bacteria.

Biological nitrogen fixation is limited to several groups of prokaryotes, some of them reduce nitrogen as free-living nitrogen-fixing bacteria. Protozoa predation on these latter releases sequestered nitrogen that may enhance the formation of new bacterial biomass and possibly increase nitrogen fixation within soil microbial communities. We aim to evaluate the predation effect of Colpoda sp. on two nitrogen fixers: Azospirillum lipoferum and Stenotrophomonas sp. during their lag, early exponential, and exponential phases. The kinetics of bacterial population growth was determined in the predators' presence or absence and the effect of predation on the rate of N fixation was evaluated through the reduction of acetylene to ethylene technique. Colpoda sp. showed a non-significant difference in preferences between the two species offered as prey. Consequently, the abundance of A. lipoferum and Stenotrophomonas sp. decreased significantly due to predator's pressure and both species responded by increasing their specific growth rate. Likewise, predation promoted greater nitrogen fixation rate by CFU during the lag phase in A. lipoferum (0.20 nM/CFU with predation vs 0.09 nM/CFU without predation) and Stenotrophomonas sp. (0.22 nM/CFU vs 0.09 nM/CFU respectively). During early exponential phase (29 h), the rate diminished to 0.13 and 0.05 nM/CFU in A. lipoferum and to 0.09 nM/CFU and 0.05 nM/CFU in Stenotrophomonas sp. Finally, during the exponential phase (52 h), only A. lipoferum without predation produced 0.003 nM/CFU of ethylene. Thus, the nitrogenase activity was higher in the lag and the early exponential phases when predator activity was involved.

Effect of methyl parathion on nitrous oxide production: a laboratory study.

We investigated the diversity of a denitrifying gene (nirK) and the emission of CO(2) and N(2)O, in a "chinampa" soil contaminated with methyl parathion. Soil at 40% of water holding capacity was spiked with methyl parathion at four concentrations (i.e. 0, 0.7, 1.47 and 4.27 g kg(-1) dry soil), while emission of N(2)O and CO(2) and nirK diversity was determined after 0, 1, 14, 30, 60 and 90 days. The emission of N(2)O on a daily base and the cumulative emission of CO(2) was not affected by the different concentrations of methyl parathion applied to soil. The diversity of the nirK gene, determined by using temperature gradient gel electrophoresis (TGGE), decreased with increased methyl parathion application. It was found that methyl parathion had effect on the emissions of N(2)O and CO(2), and reduced the diversity of the nirK gene. Consequently, the reduced diversity of the nirK gene could affect the emission of N(2)O.

Honey compositional convergence and the parallel domestication of social bees.

Honey collection evolved from simple honey hunting to the parallel and independent domestication of different species of bees in various parts of the world. In this study, we investigate the extent to which the composition of Apis and stingless bee honeys has been a driver in the selection of different bee species for domestication in Mesoamerica (Mexico) and Asia (Thailand) using a sampling design that combines peak honey profiling by H1 NMR spectroscopy with the collection of honeys from domesticated and undomesticated bee species. Our results show that, independently of the region of the world considered, domesticated stingless bees produce honey whose compositional profiles differ from those of the non-domesticated species and exhibit more similarities towards honeys produced by the domesticated Apis species. Our results provide evidence for the first time that the search for natural sweeteners in the environment by our ancestors led to the parallel and independent domestication of social bees producing honeys with similar compositional profiles.

Effect of volatile fatty acids in anaerobic conditions on viability of helminth ova (Ascaris suum) in sanitization of municipal sludge.

The present work aimed at evaluating the effect of four different mixtures of diverse volatile fatty acids (VFAs) on the viability of helminth ova (Ascaris suum), under mesophilic (35°C) anaerobic conditions and at different incubation times, in order to reproduce the process of two-phase anaerobic digestion. The mixtures of VFAs contained acetic, propionic, butyric, valeric, and isovaleric acids, used at concentrations normally found in acidogenic anaerobic digesters. The four treatments all showed a reduction in Ascaris suum ova viability, among which Treatment III (4.2 g-acetic acid L-1 + 2.2 g-propionic acid L-1 + 0.6 g-valeric acid L-1 + 0.6 g-isovaleric acid L-1) resulted the most efficient. We found that the full effect of VFAs on the viability loss of Ascaris suum ova in mesophilic conditions requires a minimum incubation time of 3 days. The highest efficiency in the loss of viability was observed with Treatment III and 4-day incubation. Interestingly, the proportion of acetic acid was three times as much in this treatment than in the other ones and resulted in an effect in a minimum time of 3 days. The mesophilic condition, however, was not sufficient to induce a complete loss of viability.

Analysis of microbial communities developed on the fouling layers of a membrane-coupled anaerobic bioreactor applied to wastewater treatment.

The structure of the biofouling layers formed on a pilot-scale membrane-coupled upflow anaerobic sludge blanket bioreactor (UASB) used to treat urban wastewater was analyzed by scanning electron microscopy and electron-dispersive X-ray microanalysis. For comparison, control samples of the membranes were fed either UASB effluent or raw wastewater in a laboratory-scale experiment. Microbial diversity in the fouling materials was analyzed by temperature gradient gel electrophoresis (TGGE) combined with sequence analysis of partial 16S rRNA. Significant differences in structure of the Bacteria communities were observed amongst the different fouling layers analyzed in the UASB membranes, particularly following a chemical cleaning step (NaClO), while the Archaea communities retained more similarity in all samples. The main Bacteria populations identified were evolutively close to Firmicutes (42.3%) and Alphaproteobacteria (30.8%), while Archaea were mostly affiliated to the Methanosarcinales and Methanospirillaceae. Sphingomonadaceae-related bacteria and methanogenic Archaea were persistently found as components of biofouling, regardless of chemical cleaning.

Synthesis, characterization, biocide and toxicological activities of di-n-butyl- and diphenyl-tin(IV)-salicyliden-beta-amino alcohol derivatives.

The one pot reaction of salicylaldehyde 1, beta-amino alcohols 2a-2c, and di-n-butyltin(IV) oxide 3a or diphenyltin(IV) oxide 3b produced five diorganotin(IV) compounds, 4a-4c, 5a, and 5c, in good yields. All compounds were characterized by IR, (1)H, (13)C, and (119)Sn NMR spectroscopy, and elemental analysis; furthermore, compounds 4b, 4c, 5a, and 5c were characterized by X-ray diffraction analysis. After the structural characterization, all of the compounds were tested in vitro against Bacillus subtilis (Gram-positive, strain ATCC 6633), Escherichia coli (Gram-negative, strain DH5alpha), Pseudomonas aeruginosa (Gram-negative, strain BH3), Desulfovibrio longus (strain DSM 6739), and Desulfomicrobium aspheronum (strain DSM 5918) to assess their antimicrobial activity. Compounds 4 and 5 demonstrated a wide range of bactericidal activities against the tested aerobic (one Gram-positive and two Gram-negative subtypes) and anaerobic bacteria (two sulfate-reducing bacteria, SRB). Compound 5 had better bactericidal performances than compound 4. For all of the compounds, the acute toxicity was measured using luminescent bacteria toxicity (LBT-Microtox) tests to track their further environmental impact. According to these results and in order to fulfill environmental regulations, the toxicity of the compounds studied herein can be modulated through the proper selection of the disubstituted tin(IV) moiety.

Interaction between methanogenic and sulfate-reducing microorganisms during dechlorination of a high concentration of tetrachloroethylene.

A methanogenic and sulfate-reducing consortium, which was enriched on medium containing tetrachloroethylene (PCE), had the ability to dechlorinate high concentrations of PCE. Dehalogenation was due to the direct activity of methanogens. However, interactions between methanogenic and sulfate-reducing bacteria involved modification of the dechlorination process according to culture conditions. In the absence of sulfate, the relative percentage of electrons used in PCE dehalogenation increased after an addition of lactate in batch conditions. The sulfate reducers would produce further reductant from lactate catabolism. This reductant might be used by methanogenic bacteria in PCE dechlorination. A mutualistic interaction was observed in the absence of sulfate. However in the presence of sulfate, methanogenesis and dechlorination decreased because of interspecific competition, probably between the H(2)-oxydizing methanogenic and sulfate-reducing bacteria in batch conditions. In the semicontinuous fixed-bed reactor, the presence of sulfate did not affect dechlorination and methanogenesis. The sulfate-reducing bacteria may not be competitors of H(2)-consuming methanogens in the reactor because of the existence of microbial biofilm. The presence of the fixed film may be an advantage for bioremediation and industrial treatment of effluent charged in sulfate and PCE. This is the first report on the microbial ecology of a methanogenic and sulfate-reducing PCE-enrichment consortium.