RESUMO
BACKGROUND: The use of cyanobacteria and microalgae as cell factories to produce biofuels and added-value bioproducts has received great attention during the last two decades. Important investments have been made by public and private sectors to develop this field. However, it has been a challenge to develop a viable and cost-effective platform for cultivation of cyanobacteria and microalgae under outdoor conditions. Dealing with contamination caused by bacteria, weedy algae/cyanobacteria and other organisms is a major constraint to establish effective cultivation processes. RESULTS: Here, we describe the implementation in the cyanobacterium Synechococcus elongatus PCC 7942 of a phosphorus selective nutrition system to control biological contamination during cultivation. The system is based on metabolic engineering of S. elongatus to metabolize phosphite, a phosphorus source not normally metabolized by most organisms, by expressing a bacterial phosphite oxidoreductase (PtxD). Engineered S. elongatus strains expressing PtxD grow at a similar rate on media supplemented with phosphite as the non-transformed control supplemented with phosphate. We show that when grown in media containing phosphite as the sole phosphorus source in glass flasks, the engineered strain was able to grow and outcompete biological contaminants even when the system was intentionally inoculated with natural competitors isolated from an irrigation canal. The PtxD/phosphite system was successfully used for outdoor cultivation of engineered S. elongatus in 100-L cylindrical reactors and 1000-L raceway ponds, under non-axenic conditions and without the need of sterilizing containers and media. Finally, we also show that the PtxD/phosphite system can be used as selectable marker for S. elongatus PCC 7942 transgenic strains selection, eliminating the need of antibiotic resistance genes. CONCLUSIONS: Our results suggest that the PtxD/phosphite system is a stable and sufficiently robust strategy to control biological contaminants without the need of sterilization or other complex aseptic procedures. Our data show that the PtxD/phosphite system can be used as selectable marker and allows production of the cyanobacterium S. elongatus PCC 7942 in non-axenic outdoor reactors at lower cost, which in principle should be applicable to other cyanobacteria and microalgae engineered to metabolize phosphite.
RESUMO
OBJECTIVE: Primary cardiac tumors are rare neoplasms in humans, of which the most common is the atrial Myxoma. The objective of this study was to find the incidence of these tumors at the Heart Center of Puerto Rico and the Caribbean. METHODS: This study was approved by the Institutional Review Board of the Medical Sciences Campus University of Puerto Rico to review the records at the Heart Center of patients with heart tumors in the last 14 years. RESULTS: The sample consists of 55 patients (78.9% were females and 24.1% were male) with a median age of 52 years. Sixty-five percent of patients lived in rural areas. Clinical presentations included shortness of breath (43.1%), chest pain (37.9%), asymptomatic (25%), palpitations (20.7%), neurologic symptoms (10.3%) and dizziness (6.9%). Electrocardiographic findings included normal sinus rhythm (53.4%), non-specific ST-T changes (32.8%), sinus tachycardia (20.7%), left atrial enlargement (10.3%) and atrial fibrillation (8.6%). A subgroup presenting with atrial fibrillation prior to diagnosis had left atrial myxoma. The tumors found, in descending order of frequency are: left atrial myxoma, right atrial myxoma, papillary fibroelastoma, hamartoma, lipoma and rhabdomyoma. We found a correlation between large left atrial myxoma and atrial fibrillation. CONCLUSION: The most frequent heart tumor was atrial myxoma. The larger myxomas were associated with atrial fibrillation.