3 research outputs found
Enumeration and characterization of arsenic-tolerant diazotrophic bacteria in a long-term heavy-metal-contaminated soil
The abundance of arsenic-tolerant diazotrophic
bacteria was compared in a long-term contaminated
soil versus a non-contaminated one. In addition, the
characterization of tolerant diazotrophic bacteria was
carried out. Differences in the number of heterotrophic
N2 fixers were found between soils. Contaminated soil
showed a decrease in the microbial population size of
about 80%, confirming the great sensitivity of this
group of soil bacteria to metals. However, quantitative
analysis of the response to increased doses of arsenic
reveals that the proportion of the culturable diazotrophic
community tolerant to arsenic was identical for both
soils (contaminated and non-contaminated). Twentytwo
arsenic-tolerant diazotrophic isolates were obtained
and further characterized. 16S ribosomal DNA sequence
analysis revealed that these bacterial isolates
were distributed among four taxons (Actinobacteria,
Firmicutes, γ-Proteobacteria, and β-Proteobacteria).
Most genera recovered from the contaminated soil were
also found in the uncontaminated soi
Monitoring of biophysicochemical changes in a silty clay soil contaminated with LNAPLs
The interdependence between time domain induced polarization measurements at uncontaminated and
artificially contaminated soil samples with diesel and biophysicochemical alterations caused by diesel
degradation was investigated during 12 months. The research was performed on a slightly alkaline soil,
with high content of organic matter (148 g/kg) and silty clay texture. Soil clay mineralogy was mainly
composed of plagioclase, amphibole, biotite, interstratified mica-smectite, goethite and some vestigial
kaolinite. A decrease on resistivity and induced polarization (IP) in contaminated soil was observed during
the 12 months. This reduction on geoelectrical parameters was related to: 1) the increase on the electrolyte
conductivity; 2) the increase on interfacial surface area, as result of biotite transformation and weathering of
other ferromagnesian minerals and 3) a slight increase in soil aggregation, caused by diesel-degrading
microorganisms (a significant increase of the numbers of specific carbon degraders was observed). After
4 months, the IP response was lowest in the contaminated soil which was explained by inhibition of the
cation exchange capacity due to two possible processes: 1) clay particles coating by organic molecules and
2) attachment of microbial cells (biofilms) to clay particles and/or soil aggregates. The results suggest that
the content and mineralogy of the clay fraction as well as the aggregation state of the soils contaminated
with LNAPL's affect the IP response. This response is a diagnostic of the biophysicochemical alterations
occurring during diesel degradation as a result of biological activit
Prevalence and characterization of Listeria monocytogenes isolated from soft cheese
A survey was made in 1995–1996 for Listeria spp. in 63 soft cheeses, made from raw ewe’s milk using traditional methods, in the
Province of Beira Baixa (Portugal). Listeria spp. were isolated from 47 (75%) of the cheeses, L.monocytogenes was isolated from 29
(46%), and L.innocua but not L.monocytogenes from 18 (29%). Of 24 isolates of L.monocytogenes that were serotyped, 20 were
serotype 4b, three were serotype 1/2b and one was serotype 1/2a. Phage typing of isolates of L.monocytogenes and L.innocua showed
that in some cases a particular phage type was associated with cheese from a particular source. Twenty four strains of
L.monocytogenes tested were able to grow at 30 Cin culture medium adjusted with HCl to a pH in the range from 4.4 to 6.0 within 3
days; in the pH range 4.4–6.8 a representative strain grew most rapidly at pH 6.8. The pH range in the cheeses during maturation
was between about 5.2–6.4. Whether L.monocytogenes could multiply in the cheeses would depend on factors such as concentration
of organic acids and of salt, and storage temperature.info:eu-repo/semantics/publishedVersio