A strategy to obtain axenic cultures of Arthrospira spp. cyanobacteria.

A strategy to obtain axenic cultures of the cyanobacterium Arthrospira sp. ('platensis') Lefevre 1963/M-132-1 strain, consisting of a series of physical and chemical procedures, and the application of an optimized pool of antibiotics, is described in this paper. This strategy, which is an inexpensive and fast way to obtain axenic cultures, can be applied to Arthrospira spp. from culture collections or samples from their natural habitats to eliminate a wide spectrum of contaminants. A high alkaline treatment (pH 12, using KOH) of 72 h is a determinant initial procedure applied to eliminate protozoa and Microcystis sp. Bacteria were eliminated by an optimal antibiotic pool treatment, and Chroococcus sp. residuals were discarded by serial dilution. Optimal concentrations of the antibiotics composing the pool were obtained by a 2(4) factorial central composite rotatable design (CCRD) and Response Surface Methodology (RSM), resulting in: ampicillin 61.6 µg/ml, penicillin 85.8 µg/ml, cefoxitin 76.9 µg/ml, and meropenem 38.9 µg/ml. The results also indicate that cefoxitin was the most effective antibiotic of this pool. After obtaining the axenic culture, identification of Lefevre 1963/M-132-1 strain was performed using amplification and sequencing of the ITS region (including part of 16S rRNA, tRNA Ile, ITS, tRNA Ala and part of 23S rRNA region) and fatty acid composition data. Data base comparison revealed that Lefevre strain is closely related to A. platensis species (99% identity), while fatty acid composition data suggested A. maxima. These seemingly contradictory results are discussed.

Optimisation of a culture medium containing fish silage for L-lysine production by Corynebacterium glutamicum.

In a first step the effects of 10 components of a culture medium designed for L-lysine production were evaluated with a 2(10-6) factorial design. Among them, glucose, fish silage, and ammonium sulphate showed a significant effect. In a second step, an orthogonal-central composite experimental design and response surface methodology was performed with five from the 10 initial compounds. The determination coefficient (R2) of the fitted second-order model was 0.990. L-lysine production with the optimised medium increased 2.6 times as compared with the original medium.

Association of cyclopoid copepods with the habitat of the malaria vector Anopheles aquasalis in the peninsula of Paria, Venezuela.

The southern region of the Paria Peninsula shows a high malaria incidence. This work relates the abundances of cyclopoid species and the malaria vector Anopheles aquasalis to certain abiotic parameters and vegetation features. Samples were collected over a 4-month period in several habitats, including marsh, irrigation channel, lagoon, and mangrove swamp during the wet season and the wet-dry transition. Dominant plant species in the marsh were Typha dominguensis and Eleocharis mutata. Mesocyclops meridianus also was dominant in the marsh. Highest densities of An. aquasalis larvae, as well as lowest pH values and highest sulfate concentrations, were found in habitats containing E. mutata. Statistical correlation analysis showed that abundances of M. longisetus longisetus and An. aquasalis larvae were positively and significantly correlated in the irrigation channel, and abundances of M. meridianus and An. aquasalis larvae were negatively and significantly correlated in the E. mutata marsh.