Forty-six Aeromonas spp. strains were isolated from fresh fish and investigated for their antimicrobial susceptibility, detection of Class 1 integrons by PCR, and arrangement of gene cassettes. Selected isolates were further characterized by enterobacterial repetitive intergenic consensus-PCR. Twenty isolates were found to carry Class 1 integrons. Amplification of the variable regions of the integrons revealed diverse bands ranging in size from 150 to 1,958 pb. Sequence analysis of the variable regions revealed the presence of several gene cassettes, such as adenylyl transferases (aadA2 and aadA5), dihydrofolate reductases (dfrA17 and dfrA1), chloramphenicol acetyl transferase (catB3), β-lactamase (oxa2), lincosamide nucleotidil transferase (linF), aminoglycoside-modifying enzyme (apha15), and oxacillinase (bla OXA-10). Two open reading frames with an unknown function were identified as orfC and orfD. The aadA2 cassette was the most common integron found in this study. Interestingly, five integrons were detected in the plasmids that might be involved in the transfer of resistance genes to other bacteria. This is a first report of cassette encoding for lincosamides (linF) resistance in Aeromonas spp. Implications on the incidence of integrons in isolates of Aeromonas spp. from fresh fish for human consumption, and its possible consequences to human health are discussed.

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Extreme alkalinity and salinity affects different processes involved in the N cycle, such as mineralization and nitrification, so it might affect the denitrification process and the N 2 O-to-N 2 ratio. An alkaline saline soil of the former lake Texcoco with electrolytic conductivity (EC) 12.6 dS m −1 and pH 10.0, and an 'extreme' alkaline saline soil with EC 56 dS m −1 and pH 10.4 were amended with 100 mg NO 3 − -N kg −1 , purged of all O 2 , shaken and incubated anaerobically for 72 h. A 'normal' agricultural soil of Acolman with EC 0.8 dS m −1 and pH 6.3 was used as control. Treatments were with or without acetylene (C 2 H 2 ) (found to inhibit reduction of N 2 O to N 2 ) and with or without chloramphenicol (found to inhibit de novo synthesis of reduction enzymes), while emission of CO 2 and N 2 O and concentrations of NO 3 − and NO 2 − were monitored. The NO 3 − reduction rate was not affected by C 2 H 2 or chloramphenicol in the Acolman soil, but decreased >3.5 times when chloramphenicol was added to the Texcoco soils. The concentration of NO 2 − increased 3 times when chloramphenicol was added to the Acolman soil after 72 h, was similar in the Texcoco soil with EC 12 dS m −1 , but chloramphenicol decreased it 14 times in the Texcoco soil with EC 56 dS m −1 . The emission of N 2 O in the unamended Acolman soil was 0.09 mg N kg −1 and N 2 6.5 mg N kg −1 soil after 72 h resulting in a N 2 O-to-N 2 ratio of 0.014, while N 2 O production was 0.05 mg N kg −1 in the Texcoco soil with EC 12.6 dS m −1 and N 2 1.6 mg N kg −1 resulting in a N 2 O-to-N 2 ratio of 0.031. The emission of N 2 O in the Texcoco soil with EC 56 dS m −1 was 1.3 mg N kg −1 soil after 72 h and that of N 2 was 2.0 mg N kg −1 resulting in a N 2 O-to-N 2 ratio of 0.65. It was found that the activity of NO 2 − and N 2 O reductase decreased with increased pH and EC, so that the concentrations of NO 2 − , N 2 O and the N 2 O-to-N 2 ratio increased with increased EC and pH, although that the effect of other soil characteristics can not be excluded.

The objective of this study was to investigate the changes in the chemical partitioning of Cu, Pb, Cr and Zn within a column of soil incubated with an anaerobic sewage sludge (ANSS) for 2.5 months. The soil was irrigated during the incubation period. A sequential extraction method was used to fractionate these metals into exchangeable, weakly adsorbed, organic, Al oxide, Fe-Mn oxide, and residual, respectively. ANSS was applied at a loading rate of 69 Mg ha −1 . The soil is a Dystric Cambisol with low pH (<3.8), low CEC [<10 cmol(+) kg −1 below the first 4 cm depth], and low base saturation (<7%). The addition of the ANSS caused a decrease in concentrations of Cu, Pb, and Cr in the A1 horizon, and an increase in the concentrations with depth. Below the A1 horizon, concentrations of Cu increased uniformly (~1 mg cm −1 ), and the greatest increases were observed in the residual, Fe-Mn oxides, and weakly adsorbed fractions. Maximum increases in Pb occurred at 4-9 cm of depth (1.6 mg cm −1 ), and mainly affected the weakly adsorbed fraction. Chromium essentially accumulated at the limit between the A2 and the Bw horizons (1.1-1.5 mg cm −1 ) as residual and organic bound forms, probably through particulate transport. Zinc mainly accumulated in the A1 horizon (2.9 mg cm −1 ) as exchangeable Zn. At depth, Zn increments were predominantly observed in the residual fraction. The results of this study thus demonstrate the redistribution of contaminants into different chemical pools and soil layers after sludge amendment.

A new haloalkaliphilic archaeon, strain B4(T), was isolated from the former lake Texcoco in Mexico. The cells were Gram-negative, pleomorphic-shaped, pink to red pigmented and aerobic. Strain B4(T) required at least 2.5 M NaCl for growth, with optimum growth at 3.4 M NaCl. It was able to grow over a pH range of 7.5-10.0 and temperature of 25-50 °C, with optimal growth at pH 9 and 37 °C. Cells are lysed in hypotonic treatment with less than 1.3 M NaCl. The major polar lipids of strain B4(T) were phosphatidylglycerol and methyl-phosphatidylglycerophosphate. Phospholipids were detected, but not glycolipids. The nucleotide sequence of the 16S rRNA gene revealed that the strain B4(T) was phylogenetically related to members of the genus Natronorubrum. Sequence similarity with Natronorubrum tibetense was 96.28 %, with Natronorubrum sulfidifaciens 95.06 % and Natronorubrum sediminis 94.98 %. The G+C content of the DNA was 63.3 mol%. The name of Natronorubrum texcoconense sp. nov. is proposed. The type strain is B4(T) (=CECT 8067(T) = JCM 17497(T)).