Geographic homogeneity and non-equilibrium patterns of mtDNA sequences in Tuscany,Italy

The geographical distribution of 49 mtDNA sequences from 22 localities in Southern Tuscany, Italy, was studied by molecular analysis of variance, by a new spatial autocorrelation statistic specifically designed for sequence data and by reconstructing genealogies of haplotypes. All these methods indicated a high homogeneity of populations. Nevertheless, genetic variability showed significant departure from equilibrium expectations, in agreement with the predicted effects of a population expansion. We suggest that a past population expansion that was probably associated with a migrational wave and with local gene flow between localities prevented spatial structuring in Southern Tuscany. Received: 30 November 1995 / Revised: 5 March 1996     

A theoretical study of pentacyclo-undecane cage peptides of the type [Ac-X-Y-NHMe].

The conformational preferences of peptides of the type, Ac-X-Y-NHMe, where X and Y = Ala, cage and Pro, were studied by means of computational techniques within the framework of a molecular mechanics approach. For each of the eight peptide analogues, extensive conformational searches were carried out using molecular dynamics (MD) and simulated annealing (SA) protocols in an iterative fashion. Both results are in good agreement and complement each other. The conformational search indicates that the cage residue restricts the conformational freedom of the dipeptide considerably in comparison with the other model residues used. This study revealed that proline exhibits a greater tendency in promoting reverse-turn characteristics in comparison to the cage peptides, which show promising beta-turn characteristics. It was also found that 300-500 K is not sufficient to overcome rotational barriers for cage peptides. In all cases, the low-energy conformers have a tendency to form bent structures.     

Dynamics of long-term continuous culture of Limnospira indica in an air-lift photobioreactor

MELiSSA (Microecological Life Support System Alternative) is a developing technology for regenerative life support to enable long-term human missions in Space and has developed a demonstration Pilot Plant. One of the components of the MELiSSA Pilot Plant system is an 83L external loop air-lift photobioreactor (PBR) where Limnospira indica (previously named Arthrospira sp. PC8005) is axenically cultivated in a continuous operation mode for long-periods. Its mission is to provide O₂ and consume CO₂ while producing edible material. Biological and process characterization of this PBR is performed by analysing the effect of two main variables, dilution rate (D) and PFD (Photon Flux Density) illumination. A maximum oxygen productivity () of 1.35 mmol l⁻¹ h⁻¹ is obtained at a D of 0.025 h⁻¹ and PFD of 930 µmol m⁻² s⁻¹. Photoinhibition can occur when a 1 g l⁻¹ cell density culture is exposed to PFD higher than 1700 µmol m⁻² s⁻¹. This process is reversible if the illumination is returned to dim light (150 µmol m⁻² s⁻¹), proving the cell adaptability and capacity to respond at different illumination conditions. Influence of light intensity in cell composition is also described. Specific photon flux density (qPFD) has a direct effect on phycobiliproteins and chlorophyll content causing a decrease of 62.5% and 47.8%, respectively, when qPFD increases from 6.1 to 19.2 µmol g⁻¹ s⁻¹. The same trend is observed for proteins and the opposite for carbohydrate content. Morphological and spiral structural features of L. indica are studied by confocal microscopy, and size distribution parameters are quantified. A direct effect between trichome width and CDW/OD ratio is observed. Changes in size distribution are not correlated with environmental factors, further confirms the adaptation capacity of the cells. The systematic analysis performed provides valuable insights to understand the key performance criteria of continuous culture in air-lift PBRs.     

The effect of nuclease on transformation efficiency in Serratia marcescens

No differences in the efficiency of transformation were observed from both plasmid and chromosomal DNA in Serratia marcescens 2170 and an extracellular nuclease defective isogenic strain. The efficiency of transformation was the same for Escherichia coli 5K and E. coli containing a recombinant plasmid conferring the ability to synthesize a S. marcescens nuclease. From these results we conclude that the extracellular nuclease of S. marcescens 2170 is not the main cause of the low efficiency of transformation observed in this bacterium.