Optimization of <Emphasis Type="Italic">Renealmia mexicana</Emphasis> (Klotzsch ex. Petersen) cultivation <Emphasis Type="Italic">in vitro</Emphasis>

Renealmia mexicana (Klotzsch ex. Petersen) is a tropical plant found in southern México with an ornamental value and a potential source of curcuminoids. Its distribution in Chiapas has decreased because of deforestation and low propagation and germination rate, so a protocol for in vitro propagation was developed. An orthogonal experimental design of L₉ (3⁴) in triplicate was used to investigate the effect of 6-benzyl adenine (BA), indole butyric acid (IBA), silver nitrate (AgNO₃), and sucrose on shoot, root, and leaf development of plantlets grown in vitro. Plantlets with well-developed shoots and roots were transferred to pots containing a mixture of peat moss and agrolite for hardening before transfer to soil. The Murashige and Skoog (Physiol. Plant. 15:473–497, 1962) mineral medium (MS) supplemented with 4.4 μM BA, 2.5 μM IBA, 11.7 μM AgNO_3y and 5.5% (w/v) sucrose gave most shoots, 8.9 μM BA, 2.5 μM IBA, 17.7 μM AgNO₃ and 5.5% (w/v) sucrose most roots, and 8.9 μM BA, 4.9 μM IBA, 11.7 μM AgNO₃ and 3.0% (w/v) sucrose most leaves, although other combinations were statistically equivalent in each case. Sucrose was the factor that most explained the variation in the promotion of shoots, roots, and leaves. The protocol developed resulted in up to 100% survival when plantlets were transferred to soil using AgNO₃, confirming that hardening of plantlets in vitro using hormonal stimulation was a suitable strategy to improve acclimatization.     

Phylogenetic analysis of the archaeal community in an alkaline-saline soil of the former lake Texcoco (Mexico)

The soil of the former lake Texcoco is an extreme environment localized in the valley of Mexico City, Mexico. It is highly saline and alkaline, where Na⁺, Cl⁻, HCO₃⁻ and CO₃²⁻ are the predominant ions, with a pH ranging from 9.8 to 11.7 and electrolytic conductivities in saturation extracts from 22 to 150 dS m⁻¹. Metagenomic DNA from the archaeal community was extracted directly from soil and used as template to amplify 16S ribosomal gene by PCR. PCR products were used to construct gene libraries. The ribosomal library showed that the archaeal diversity included Natronococcus sp., Natronolimnobius sp., Natronobacterium sp., Natrinema sp., Natronomonas sp., Halovivax sp., “Halalkalicoccus jeotgali” and novel clades within the family of Halobacteriaceae. Four clones could not be classified. It was found that the archaeal diversity in an alkaline-saline soil of the former lake Texcoco, Mexico, was low, but showed yet uncharacterized and unclassified species. César Valenzuela-Encinas and Isabel Neria-González contributed equally to this publication.     

Short term changes in dynamics of C and N in soil when crops are cultivated on permanent raised beds

Densely populated, intensively cropped highland areas in the subtropics are prone to erosion and declining soil fertility, making agriculture unsustainable. Permanent raised bed planting systems, as a form of conservation agriculture, have been developed to reduce production costs while conserving resources and sustaining the environment. In 2004, a new experiment with long term focus was started under rain fed conditions at El Batán (Mexico; 2,240 m a.s.l.; 19.31N, 98.50W; Cumulic Phaeozem), which aims at understanding the effects of (1) tillage (conventionally tilled or permanent raised beds), (2) residue management (retention or removal) and (3) N fertilizer application (0 or 120 kg N/ha) on N availability in a yearly maize/wheat rotation system. Incubation experiments were conducted to establish how the different treatments affect C and N dynamics in the soil. Tillage increases the availability of soil organic matter by soil aggregate disruption, enhancing C and N mineralization. Conventionally tilled raised beds with incorporation of crop residues increased the CO₂ production rate. In both tillage systems, retention of maize or wheat residue without N fertilizer application led to N immobilization. In permanent raised beds, however, the immobilization due to residue retention could be compensated by application of N fertilizer, while conventionally tilled raised beds appeared to use the applied N fertilizer less efficiently.     

A comparative study of Taxol production in liquid and solid‐state fermentation with Nigrospora sp. a fungus isolated from Taxus globosa

Aims: To determine in liquid (LF) and solid‐state fermentation (SSF) the effect of medium concentration on growth and Taxol produced by Nigrospora sp., a fungus isolated from the Mexican yew. Methods and Results: Nigrospora sp. was grown at different concentrations of the base culture medium M1D, i.e. two (2×), four (4×), six (6×) and eight times (8×) the base concentration. The titres of Taxol determined by competitive inhibition enzyme immunoassay increased with increasing medium concentration in LF and SSF but were higher in SSF in every medium concentration. The Taxol produced in SSF and LF with 8× medium was 221 and 142 ng l^?1. The SSF gave also higher biomass, growth and sugar utilization than LF in every medium. The growth and sugar consumption were modelled by the logistic and the Pirt models, respectively. However, the Luedeking–Piret model was unsuitable for Taxol. Conclusions: The SSF surpassed LF in terms of Taxol, growth and sugar utilization; thus, it has significant advantages over LF. Significance and Impact of the Study: This is the first report on Taxol production by SSF and the first contribution to evaluate the influence of the medium on Taxol production in LF and SSF.     

Identification of Antibiotic Resistance Cassettes in Class 1 Integrons in Aeromonas spp. Strains Isolated From Fresh Fish (Cyprinus carpio L.)

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.     

Bacterial colonization of a fumigated alkaline saline soil

After chloroform fumigating an arable soil, the relative abundance of phylotypes belonging to only two phyla (Actinobacteria and Firmicutes) and two orders [Actinomycetales and Bacillales (mostly Bacillus)] increased in a subsequent aerobic incubation, while it decreased for a wide range of bacterial groups. It remained to be seen if similar bacterial groups were affected when an extreme alkaline saline soil was fumigated. Soil with electrolytic conductivity between 139 and 157 dS m^?1, and pH 10.0 and 10.3 was fumigated and the bacterial community structure determined after 0, 1, 5 and 10 days by analysis of the 16S rRNA gene, while an unfumigated soil served as control. The relative abundance of the Firmicutes increased in the fumigated soil (52.8 %) compared to the unfumigated soil (34.2 %), while that of the Bacteroidetes decreased from 16.2 % in the unfumigated soil to 8.8 % in the fumigated soil. Fumigation increased the relative abundance of the genus Bacillus from 14.7 % in the unfumigated soil to 25.7 %. It was found that phylotypes belonging to the Firmicutes, mostly of the genus Bacillus, were dominant in colonizing the fumigated alkaline saline as found in the arable soil, while the relative abundance of a wide range of bacterial groups decreased.     

A cooperative PNPase-Hfq-RNA carrier complex facilitates bacterial riboregulation

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Conservation agriculture, increased organic carbon in the top-soil macro-aggregates and reduced soil CO2 emissions

Background and aims

Conservation agriculture, the combination of minimal soil movement (zero or reduced tillage), crop residue retention and crop rotation, might have the potential to increase soil organic C content and reduce emissions of CO₂.

Methods

Three management factors were analyzed: (1) tillage (zero tillage (ZT) or conventional tillage (CT)), (2) crop rotation (wheat monoculture (W), maize monoculture (M) and maize-wheat rotation (R)), and (3) residue management (with (+r), or without (?r) crop residues). Samples were taken from the 0–5 and 5–10?cm soil layers and separated in micro-aggregates (< 0.25?mm), small macro-aggregates (0.25 to 1?mm) and large macro-aggregates (1 to 8?mm). The carbon content of each aggregate fraction was determined.

Results

Zero tillage combined with crop rotation and crop residues retention resulted in a higher proportion of macro-aggregates. In the 0–5?cm layer, plots with a crop rotation and monoculture of maize and wheat in ZT+r had the greatest proportion of large stable macro-aggregates (40%) and highest mean weighted diameter (MWD) (1.7?mm). The plots with CT had the largest proportion of micro-aggregates (27%). In the 5–10?cm layer, plots with residue retention in both CT and ZT (maize 1?mm and wheat 1.5?mm) or with monoculture of wheat in plots under ZT without residues (1.4?mm) had the greatest MWD. The 0–10?cm soil layer had a greater proportion of small macroaggregates compared to large macro-aggregates and micro-aggregates. In the 0–10?cm layer of soil with residues retention and maize or wheat, the greatest C content was found in the small and large macro-aggregates. The small macro-aggregates contributed most C to the organic C of the sample. For soil cultivated with maize, the CT treatments had significantly higher CO₂ emissions than the ZT treatments. For soil cultivated with wheat, CTR-r had significantly higher CO₂ emissions than all other treatments.

Conclusion

Reduction in soil disturbance combined with residue retention increased the C retained in the small and large macro-aggregates of the top soil due to greater aggregate stability and reduced the emissions of CO₂ compared with conventional tillage without residues retention and maize monoculture (a cultivation system normally used in the central highlands of Mexico).     

Composting of tannery effluent with cow manure and wheat straw

Wastewater from the leather industry in León (Guanajuato, México) is discharged into the Turbio river without treatment. Tannery wastewater contains utilizable nutrients, but also toxic organic compounds which might affect soil processes and plant growth, and pathogens, which might pose a threat to the local farming community. Tannery effluent was composted with cow manure and wheat straw for 90 days to reduce pathogens and toxic organic compounds and monitored. The compost was characterized by an electrolytic conductivity (EC) of 28.1 ms cm(-1), cation exchange capacity of 17.7 meq 100 g(-1), an absorbance at 645 nm of 0.0175, a respiration rate of 0.062 mg CO2-C kg(-1) compost-C day(-1), pH 8.5 and C:N ratio 7:1 with a germination index for cress (Lepidium sativum) of 48% after 90 days. Less than 10 faecal coliforms and no Salmonella sp., Shigella sp. or eggs of helminthes were detected in the compost while total coliforms decreased by log10 of 2. Total concentrations of lead (Pb) were 8.9 mgkg(-1) dry compost, chromium (Cr) 77 mg kg(-1) dry compost, cadmium (Cd) 0.4 mg kg(-1) dry compost, copper (Cu) 10.3 mg kg(-1) dry compost and sodium (Na) 14,377 mg kg(-1) dry compost. The compost characteristics indicated that it was mature, but the germination index for cress of less than 50% suggested possible remaining phytotoxic compounds. However, the large salt concentrations (especially Na), might have inhibited cress development and thus reduced the germination index. The large salt concentration might thus limit the use of this kind of compost.     

Natronorubrum texcoconense sp. nov., a haloalkaliphilic archaeon isolated from soil of the former lake Texcoco (Mexico)

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).