Hemeroteca Cientifica Catalana
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Spatiotemporal distribution of the magnetotactic multicellular prokaryote Candidatus Magnetoglobus multicellularis in a Brazilian hypersaline lagoon and in microcosms
Full text linkCandidatus Magnetoglobus multicellularis is an unusual morphotype of magnetotactic prokaryotes. These microorganisms are composed of a spherical assemblage of gram-negative prokaryotic cells capable of swimming as a unitaligned along a magnetic field. While they occur in many aquatic habitats around the world, high numbers of Ca. M. multicellularishave been detected in Araruama Lagoon, a large hypersaline lagoon near the city of Rio de Janeiro, in Brazil. Here,we report on the spatiotemporal distribution of one such population in sediments of Araruama Lagoon, including its annualdistribution and its abundance compared with the total bacterial community. In microcosm experiments, Ca. M. multicellulariswas unable to survive for more than 45 days: the population density gradually decreased coinciding with a shift to theupper layers of the sediment. Nonetheless, Ca. M. multicellularis was detected throughout the year in all sites studied. Changes in the population density seemed to be related to the input of organic matter as well as to salinity. The populationdensity of Ca. M. multicellularis did not correlate with the total bacterial counts; instead, changes in the microbial communitystructure altered their counts in the environment. [Int Microbiol 2012; 15(3):141-149
Isolation and characterization of aerobic microorganisms with cellulolytic activity in the gut of endogeic earthworms
Full text linkThe ability of earthworms to decompose lignocellulose involves the assistance of microorganisms in their digestive system. While many studies have revealed a diverse microbiota in the earthworm gut, including aerobic and anaerobicmicroorganisms, it remains unclear which of these species contribute to lignocellulose digestion. In this study, aerobicmicroorganisms with cellulolytic activity isolated from the gut of two endogeic earthworms, Amynthas heteropoda (Megascolecidae) and Eisenia fetida (Lumbricidae) were isolated by solid culture of gut homogenates using filter paper as acarbon source. A total of 48 strains, including four bacterial and four fungal genera, were isolated from two earthworm species. Characterization of these strains using enzyme assays showed that the most representative ones had exocellulase andxylanase activities, while some had weak laccase activity. These findings suggest that earthworms digest lignocellulose byexploiting microbial exocellulase and xylanase besides their own endocellulase. Phylogenetic analysis showed that among thecellulolytic isolates in both earthworm species Burkholderia and Chaetomium were the dominant bacterial and fungal members.[Int Microbiol 2012; 15(3):121-130
Role of the denitrifying Haloarchaea in the treatment of nitrite-brines
Full text linkHaloferax mediterranei is a denitrifying halophilic archaeon able to reduce nitrate and nitrite under oxic and anoxic conditions. In the presence of oxygen, nitrate and nitrite are used as nitrogen sources for growth. Under oxygen scarcity,this haloarchaeon uses both ions as electron acceptors via a denitrification pathway. In the present work, the maximal nitriteconcentration tolerated by this organism was determined by studying the growth of H. mediterranei in minimal medium containing30, 40 and 50 mM nitrite as sole nitrogen source and under initial oxic conditions at 42 °C. The results showed theability of H. mediterranei to withstand nitrite concentrations up to 50 mM. At the beginning of the incubation, nitrate wasdetected in the medium, probably due to the spontaneous oxidation of nitrite under the initial oxic conditions. The completeremoval of nitrite and nitrate was accomplished in most of the tested conditions, except in culture medium containing 50 mMnitrite, suggesting that this concentration compromised the denitrification capacity of the cells. Nitrite and nitrate reductases activities were analyzed at different growth stages of H. mediterranei. In all cases, the activities of the respiratory enzymeswere higher than their assimilative counterparts; this was especially the case for NirK. The denitrifying and possibly detoxifyingrole of this enzyme might explain the high nitrite tolerance of H. mediterranei. This archaeon was also able to remove60 % of the nitrate and 75 % of the nitrite initially present in brine samples collected from a wastewater treatment facility.These results suggest that H. mediterranei, and probably other halophilic denitrifying Archaea, are suitable candidates for thebioremediation of brines with high nitrite and nitrate concentrations. [Int Microbiol 2012; 15(3):111-119
Metal and antibiotic resistance of bacteria isolated from the Baltic Sea
Full text linkThe resistance of 49 strains of bacteria isolated from surface Baltic Sea waters to 11 antibiotics was analyzedand the resistance of selected strains to three metal ions (Ni2+, Mn2+, Zn2+) was tested. Most isolates belonged to Gammaproteobacteria (78 %), while Alphaproteobacteria (8 %), Actinobacteria (10 %), and Bacteroidetes (4 %) were lessabundant. Even though previous reports suggested relationships between resistance and the presence of plasmids or the abilityto produce pigments, no compelling evidence for such relationships was obtained for the strains isolated in this work. In particular, strains resistant to multiple antibiotics did not carry plasmids more frequently than sensitive strains. A relationbetween resistance and the four aminoglycosides tested (gentamycin, kanamycin, neomycin, and streptomycin), but not tospectinomycin, was demonstrated. This observation is of interest given that spectinomycin is not always classified as anaminoglycoside because it lacks a traditional sugar moiety. Statistical analysis indicated relationships between resistance tosome antibiotics (ampicillin and erythromycin, chloramphenicol and erythromycin, chloramphenicol and tetracycline, erythromycinand tetracycline), suggesting the linkage of resistance genes for antibiotics belonging to different classes. The effectsof NiSO4, ZnCl2 and MnCl2 on various media suggested that the composition of Marine Broth might result in low concentrationsof Mn2+ due to chemical interactions that potentially lead to precipitation. [Int Microbiol 2012; 15(3):131-139