From protoplasts to gene clusters

Microalgae protoplasts isolation and fusion for biotechnology research

Protoplasts are microbial or vegetable cells lacking a cell wall. These can be obtained from microalgae by an enzymatic hydrolysis process in the presence of an osmotic stabilizer. In general, protoplasts are experimentally useful in physiological, geneticand bio-chemical studies, so their acquisition and fusion will continue to be an active research area in modern biotechnology. The fusion of protoplasts in microalgae constitutes a tool for strain improvement because it allows both intra and interspecific genetic recombina-tion, resulting in organisms with new or improved characteristics of industrial interest. In this review we briefly describe themethod-ology for obtaining protoplasts, as well as fusion methods and the main applications of microalgal platforms.

Recombinant expression of four oxidoreductases in Phanerochaete chrysosporium improves degradation of phenolic and non-phenolic substrates

Phanerochaete chrysosporium belongs to a group of lignin-degrading fungi that secretes various oxidoreductive enzymes, including lignin peroxidase (LiP) and manganese peroxidase (MnP). Previously, we demonstrated that the heterologous expression of a versatile peroxidase (VP) in P. chrysosporium recombinant strains is possible. However, the production of laccases (Lac) in this fungus has not been completely demonstrated and remains controversial. In order to investigate if the co-expression of Lac and VP in P. chrysosporium would improve the degradation of phenolic and non-phenolic substrates, we tested the constitutive co-expression of the lacIIIb gene from Trametes versicolor and the vpl2 gene from Pleurotus eryngii, and also the endogenous genes mnp1 and lipH8 by shock wave mediated transformation. The co-overexpression of peroxidases and laccases was improved up to five-fold as compared with wild type species. Transformant strains showed a broad spectrum in phenolic/non-phenolic biotransformation and a high percentage in synthetic dye decolorization in comparison with the parental strain. Our results show that the four enzymes can be constitutively expressed in a single transformant of P. chrysosporium in minimal medium. These data offer new possibilities for an easy and efficient co-expression of laccases and peroxidases in suitable basidiomycete species.

Tandem shock waves to enhance genetic transformation of Aspergillus niger

Filamentous fungi are used in several industries and in academia to produce antibiotics, metabolites, proteins and pharmaceutical compounds. The development of valuable strains usually requires the insertion of recombinant deoxyribonucleic acid; however, the protocols to transfer DNA to fungal cells are highly inefficient. Recently, underwater shock waves were successfully used to genetically transform filamentous fungi. The purpose of this research was to demonstrate that the efficiency of transformation can be improved significantly by enhancing acoustic cavitation using tandem (dual-pulse) shock waves. Results revealed that tandem pressure pulses, generated at a delay of 300 μs, increased the transformation efficiency of Aspergillus niger up to 84% in comparison with conventional (single-pulse) shock waves. This methodology may also be useful to obtain new strains required in basic research and biotechnology.

Purification of a vesicle-vacuole fraction functionally linked to aflatoxin synthesis in Aspergillus parasiticus

Current studies in our laboratory demonstrate a functional link between vesicles, vacuoles and aflatoxin biosynthesis in the filamentous fungus, Aspergillus parasiticus. Under aflatoxin inducing conditions in liquid yeast-extract sucrose medium, A. parasiticus undergoes a shift from vacuole biogenesis to accumulation of an enhanced number of vesicles which exhibit significant heterogeneity in size and density. As a first step in conducting a detailed analysis of the role of these organelles in aflatoxin synthesis, we developed a novel method to purify the vesicle and vacuole fraction using protoplasts prepared from cells harvested during aflatoxin synthesis. The method includes the following steps: 1] preparation of protoplasts from mycelia grown for 36 h under aflatoxin inducing conditions; 2] release of vesicles and vacuoles from purified protoplasts in the presence of Triton X-100; and 3] fractionation of the vesicles and vacuoles using a "one-step high density cushion". The vesicle-vacuole fraction showed a 35 fold enrichment in alpha-mannosidase activity (vacuole marker) and non-detectable succinate dehydrogenase and lactate dehydrogenase activities (mitochondrial and cytoplasmic markers, respectively). Confocal laser scanning microscopy with the vacuole dyes MDY-64 and CMAC demonstrated that the fraction contained pure vesicles and vacuoles and was devoid of membranous debris. Transmission electron microscopy (TEM) confirmed that no mitochondria or unbroken protoplasts contaminated the purified fraction. The purified organelles exhibited significant size heterogeneity with a range of sizes similar to that observed in whole cells and protoplasts.