Rapid analytical methods for the microalgal and cyanobacterial biorefinery: Application on strains of industrial importance

Metabolic and Lipid Biomarkers for Pathogenic Algae, Fungi, Cyanobacteria, Mycobacteria, Gram-Positive Bacteria, and Gram-Negative Bacteria

The utilization of metabolomics and lipidomics analytical platforms in the study of pathogenic microbes is slowly expanding. These research approaches will significantly contribute to the establishment of microbial metabolite and lipid databases of significant value to all researchers in microbiology. In this review, we present a high-level overview of some examples of biomarkers that can be used to detect the presence of microbes, monitor the expansion/decline of a microbe population, and add to our understanding of microbe biofilms and pathogenicity. In addition, increased knowledge of the metabolic functions of pathogenic microbes can contribute to our understanding of microbes that are utilized in diverse industrial applications. Our review focuses on lipids, secondary metabolites, and non-ribosomal peptides that can be monitored using electrospray ionization high-resolution mass spectrometry (ESI-HRMS).

Temperature-induced zeaxanthin overproduction in Synechococcus elongatus PCC 7942

The exogenous crtZ gene from Brevundimonas sp. SD212, coding for a 3,3' β-car hydroxylase, was expressed in Synechococcus elongatus PCC 7942 under the control of a temperature-inducible promoter in an attempt to engineer the carotenoid metabolic pathway, to increase the content of zeaxanthin and its further hydroxylated derivatives caloxanthin and nostoxanthin. These molecules are of particular interest due to their renowned antioxidant properties. Cultivation of the engineered strain S7942Z-Ti at 35 °C, a temperature which is well tolerated by the wild-type strain and at which the inducible expression system is activated, led to a significant redistribution of the relative carotenoid content. β-Carotene decreased to about 10% of the pool that is an excess of a threefold decrease with respect to the control, and concomitantly, zeaxanthin became the dominant carotenoid accounting for about half of the pool. As a consequence, zeaxanthin and its derivatives caloxanthin and nostoxanthin collectively accounted for about 90% of the accumulated carotenoids. Yet, upon induction of CrtZ expression at 35 °C the S7942Z-Ti strain displayed a substantial growth impairment accompanied, initially, by a relative loss of carotenoids and successively by the appearance of chlorophyll degradation products which can be interpreted as markers of cellular stress. These observations suggest a limit to the exploitation of Synechococcus elongatus PCC 7942 for biotechnological purposes aimed at increasing the production of hydroxylated carotenoids.

Simultaneous purification of fucoxanthin isomers from brown seaweeds by open-column and high-performance liquid chromatography

Simultaneous purification of fucoxanthin isomers from brown seaweeds by two steps of open-column chromatography (OCC) and reversed-phase (RP)-high-performance liquid chromatography (HPLC) is described. Analysis and identification of fucoxanthin isomers were performed by chromatographic and spectrophotometric properties such as retention time (tR), spectral shape, maximal absorption wavelength (λmax), Q-ratio, and mass spectrometry (MS) data including the ratio of fragment ions. The optimal conditions for a simultaneous separation and purification were examined by changing several parameters of HPLC, i.e., mobile phase composition, equilibration time, and column oven temperature. The purification procedure consisted of the following two steps: first, highly purified fucoxanthin fraction was obtained by a silica-gel OCC. Then, four major fucoxanthin isomers, all-trans, 13'-cis, 13-cis, and 9'-cis, were simultaneously separated and purified by RP-HPLC with an analytical C30 column and gradient elution in a mixture of water, methanol, and methyl tert-butyl ether. The purity of fucoxanthin isomers purified was >95% for all-trans and 9'-cis, 85% for 13'-cis, and >80% for 13-cis. A large-scale purification by RP-HPLC using a preparative C18 column was effective for the purification of all-trans and 9'-cis with a yield of 95%. This developed technique was fully applicable to analyze the enhanced production of fucoxanthin isomers by iodine-catalyzed stereomutation which composed of 9 isomer species including 9-cis.

On-Line Monitoring of Biological Parameters in Microalgal Bioprocesses Using Optical Methods

Microalgae are promising sources of fuels and other chemicals. To operate microalgal cultivations efficiently, process control based on monitoring of process variables is needed. On-line sensing has important advantages over off-line and other analytical and sensing methods in minimizing the measurement delay. Consequently, on-line, in-situ sensors are preferred. In this respect, optical sensors occupy a central position since they are versatile and readily implemented in an on-line format. In biotechnological processes, measurements are performed in three phases (gaseous, liquid and solid (biomass)), and monitored process variables can be classified as physical, chemical and biological. On-line sensing technologies that rely on standard industrial sensors employed in chemical processes are already well-established for monitoring the physical and chemical environment of an algal cultivation. In contrast, on-line sensors for the process variables of the biological phase, whether biomass, intracellular or extracellular products, or the physiological state of living cells, are at an earlier developmental stage and are the focus of this review. On-line monitoring of biological process variables is much more difficult and sometimes impossible and must rely on indirect measurement and extensive data processing. In contrast to other recent reviews, this review concentrates on current methods and technologies for monitoring of biological parameters in microalgal cultivations that are suitable for the on-line and in-situ implementation. These parameters include cell concentration, chlorophyll content, irradiance, and lipid and pigment concentration and are measured using NMR, IR spectrophotometry, dielectric scattering, and multispectral methods. An important part of the review is the computer-aided monitoring of microalgal cultivations in the form of software sensors, the use of multi-parameter measurements in mathematical process models, fuzzy logic and artificial neural networks. In the future, software sensors will play an increasing role in the real-time estimation of biological variables because of their flexibility and extendibility.