The biotechnology of microalgae has gained considerable importance in recent decades. Applications range from simple biomass production for food and feed to valuable products for ecological applications. For most of these applications, the market is still developing and the biotechnological use of microalgae will extend into new areas. Considering the enormous biodiversity of microalgae and recent developments in genetic engineering, this group of organisms represents one of the most promising sources for new products and applications. With the development of sophisticated culture and screening techniques, microalgal biotechnology can already meet the high demands of both the food and pharmaceutical industries.

Valuable products from biotechnology of microalgae.

Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control.

Biodiesel production from oleaginous microorganisms

Modulation of Chemical Composition and Other Parameters of the Cell by Growth Rate

Luria-Bertani broth supports Escherichia coli growth to an optical density at 600 nm (OD600) of 7. Surprisingly, however, steady-state growth ceases at an OD600 of 0.3, when the growth rate slows down and cell mass decreases. Growth stops for lack of a utilizable carbon source. The carbon sources for E. coli in Luria-Bertani broth are catabolizable amino acids, not sugars.

Escherichia coli Physiology in Luria-Bertani Broth

Several parameters of phage T4 adsorption to and growth in Escherichia coli B/r were determined. All changed monotonously with the bacterial growth rate (μ), which was modified by nutritional conditions. Adsorption rate was faster at higher μ values, positively correlated to cell size, and increased by pretreatment with low penicillin (Pn) concentrations; it was directly proportional to total cellular surface area, indicating a constant density of T4 receptors on cell envelopes irrespective of growth conditions. Parameters of phage development and cell lysis were μ-dependent. The rate of phage release and burst size increased, while the eclipse and latent periods decreased with increasing μ. Differentiation between the contribution of several physiological parameters to the development of T4 was performed by manipulating the host cells. A competitive inhibitor of glucose uptake, methyl α-D-glucoside, was exploited to reduce the growth rate in the same effective carbon source. Synchronous cells were obtained by the ‘baby-machine’ and large cells were obtained by pretreatment with low Pn concentrations. Lysis was delayed by superinfection, and DNA content and concentration were modified by growing a thy mutant in limiting thymine concentrations. The results indicate that burst size is not limited by cell size or DNA composition, nor directly by the rate of metabolism, but rather by the rates of synthesis and assembly of phage components and by lysis time. The rates of synthesis and assembly of phage components seem to depend on the content of the protein-synthesizing system and lysis time seems to depend on cellular dimensions.

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Bacteriophage T4 development depends on the physiology of its host Escherichia coli

An extended multiplex PCR method was established to rapidly identify and classify Bacillus thuringiensis strains containing cry (crystal protein) genes toxic to species of Lepidoptera, Coleoptera, and Diptera. The technique enriches current strategies and simplifies the initial stages of large-scale screening of cry genes by pinpointing isolates that contain specific genes or unique combinations of interest with potential insecticidal activities, thus facilitating subsequent toxicity assays. Five pairs of universal primers were designed to probe the highly conserved sequences and classify most (34 of about 60) genes known in the following groups: 20 cry1, 3 cry2, 4 cry3, 2 cry4, 2 cry7, and 3 cry8 genes. The DNA of each positive strain was probed with a set of specific primers designed for 20 of these genes and for cry11A. Twenty-two distinct cry-type profiles were identified from 126 field-collected B. thuringiensis strains. Several of them were found to be different from all published profiles. Some of the field-collected strains, but none of the 16 standard strains, were positive for cry2Ac. Three standard and 38 field-collected strains were positive by universal primers but negative by specific primers for all five known genes of cry7 and cry8. These field-collected strains seem to contain a new gene or genes that seem promising for biological control of insects and management of resistance.

/pdf/extended-screening-by-pcr-for-seven-cry-group-genes-from-2fru1yud6k.pdf

Extended Screening by PCR for Seven cry-Group Genes from Field-Collected Strains of Bacillus thuringiensis

The entire 127,923-bp sequence of the toxin-encoding plasmid pBtoxis from Bacillus thuringiensis subsp. israelensis is presented and analyzed. In addition to the four known Cry and two known Cyt toxins, a third Cyt-type sequence was found with an additional C-terminal domain previously unseen in such proteins. Many plasmid-encoded genes could be involved in several functions other than toxin production. The most striking of these are several genes potentially affecting host sporulation and germination and a set of genes for the production and export of a peptide antibiotic.

/pdf/complete-sequence-and-organization-of-pbtoxis-the-toxin-20wa8646wu.pdf

Complete sequence and organization of pBtoxis, the toxin-coding plasmid of Bacillus thuringiensis subsp. israelensis.

Changes in thymine concentration in the growth medium affect the chromosome replication time of thymineless cells. This alone may account for changes in cell composition and provide a demonstration of the absence of coupling between replication velocity and growth rate.

Arieh Zaritsky

Papers

Bacteriophage T4 development depends on the physiology of its host Escherichia coli

Extended Screening by PCR for Seven cry-Group Genes from Field-Collected Strains of Bacillus thuringiensis

Complete sequence and organization of pBtoxis, the toxin-coding plasmid of Bacillus thuringiensis subsp. israelensis.

Effect of Thymine Concentration on the Replication Velocity of DNA in a Thymineless Mutant of Escherichia coli

Role of the nucleoid in the toporegulation of division.