Radically rethinking agriculture for the 21st century.

Population growth, arable land and fresh water limits, and climate change have profound implications for the ability of agriculture to meet this century's demands for food, feed, fiber, and fuel while reducing the environmental impact of their production. Success depends on the acceptance and use of contemporary molecular techniques, as well as the increasing development of farming systems that use saline water and integrate nutrient flows.

Screening South Indian medicinal plants for antifungal activity against cutaneous pathogens.

In this study, twenty-eight South Indian medicinal plants were screened for their anti-fungal activity against six species of fungi (Trichophyton mentagrophytes, T. rubrum, T. soudanense, Candida albicans, Torulopsis glabrata, and C. krusei). Three plant species extracts, Celastrus paniculatus, Eriodendron anfractuosum and Ficus glomerata showed inhibitory activity. An aqueous extract of galls of Terminalia chebula showed inhibitory effects on three dermatophytes (Trichophyton spp.) and three yeasts (Candida spp.). Seeds extract of T. chebula inhibited only the growth of T. glabrata. An aqueous extract of T. chebula showed inhibitory effects higher than those measured in ethanol extracts. It is therefore suggested that tannins are plausible candidates for the anti-dermatophytic effects of T. chebula. Chebulinic acid, a known tannin of T. chebula was tested and found not inhibitory, thus a search for the active compound is needed.

Physico-chemical parameters influencing DNase activity of the cyanobacterium Spirulina platensis.

The effects of temperature, Mg2+, EDTA concentration and rinsing on extra- and intra-cellular DNase activity of Spirulina platensis strain SSP-14, were investigated. The results indicate that the tested strain contains very high extra- and intracellular DNase activity, which actually hinders the transfer of foreign gene(s) to S. platensis, a cyanobacterium with multiple economic potentials. The extracellular DNase activity could easily be removed by rinsing the cells with Zarrouk medium more than once. The intracellular DNase activity could also be inhibited by (1) removal of Mg2+, (2) maintaining EDTA concentration above 1 mmol l(-1), and (3) manipulating below 0-4 degrees C, during all the incubation procedures. We suggest that, by using one or more of, or combining, all those experimental conditions, the chances of foreign DNA attempted to be introduced into S. platensis without being digested would be increased.

Does astaxanthin protect Haematococcus against light damage?

The photoprotective function of the ketocarotenoid astaxanthin in Haematococcus was questioned. When exposed to high irradiance and/or nutritional stress, green Haematococcus cells turned red due to accumulation of an immense quantity of the red pigment astaxanthin. Our results demonstrate that: 1) The addition of diphenylamine, an inhibitor of astaxanthin biosynthesis, causes cell death under high light intensity; 2) Red cells are susceptible to high light stress to the same extent or even higher then green ones upon exposure to a very high light intensity (4000 mumol photon m(-2)s(-1)); 3) Addition of 1O2 generators (methylene blue, rose bengal) under noninductive conditions (low light of 100 mumol photon m(-2)s(-1) induced astaxanthin accumulation. This can be reversed by an exogenous 1O2 quencher (histidine); 4) Histidine can prevent the accumulation of astaxanthin induced by phosphate starvation. We suggest that: 1) Astaxanthin is the result of the photoprotection process rather than the protective; 2) 1O2 is involved indirectly in astaxanthin accumulation process.

Photoacclimation in the Red Alga Porphyridium cruentum: Changes in Photosynthetic Enzymes, Electron Carriers, and Light-Saturated Rate of Photosynthesis as a Function of Irradiance and Spectral Quality.

Acclimation of the photosynthetic apparatus to changes in the light environment was studied in the unicellular red alga Porphyridium cruentum (American Type Culture Collection No. 50161). Absolute or relative amounts of four photosynthetic enzymes and electron carriers were measured, and the data were compared with earlier observations on light-harvesting components (F.X. Cunningham, Jr., R.J. Dennenberg, L. Mustárdy, P.A. Jursinic, E. Gantt [1989] Plant Physiol 91: 1179-1187; F.X. Cunningham, Jr., R.J. Dennenberg, P.A. Jursinic, E. Gantt [1990] Plant Physiol 93: 888-895) and with measurements of photosynthetic capacity. P(max), the light-saturated rate of photosynthesis on a chlorophyll (Chl) basis, increased more than 4-fold with increase in growth irradiance from 6 to 280 mueinsteins.m(-2).s(-1). Amounts of ferredoxin-NADP(+) reductase, ribulose-1,5-bisphosphate carboxylase, and cytochrome f increased in parallel with P(max), whereas numbers of the light-harvesting complexes (photosystem [PS] I, PSII, and phycobilisomes) changed little, and ATP synthase increased 7-fold relative to Chl. The calculated minimal turnover time for PSII under the highest irradiance, 5 ms, was thus about 4-fold faster than that calculated for cultures grown under the lowest irradiance (19 ms). A change in the spectral composition of the growth light (irradiance kept constant at 15 mueinsteins.m(-2).s(-1)) from green (absorbed predominantly by the phycobilisome antenna of PSII) to red (absorbed primarily by the Chl antenna of PSI) had little effect on the amounts of ribulose-1,5-bisphosphate carboxylase, ATP synthase, and phycobilisomes on a Chl, protein, or thylakoid area basis. However, the number of PSI centers declined by 40%, cytochrome f increased by 40%, and both PSII and ferredoxin-NADP(+) reductase increased approximately 3-fold on a thylakoid area basis. The substantial increase in ferredoxin-NADP(+) reductase under PSI light is inconsistent with a PSI-mediated reduction of NADP as the sole function of this enzyme. Our results demonstrate a high degree of plasticity in content and composition of thylakoid membranes of P. cruentum.

A macromodel for outdoor algal mass production.

A model describing growth of an outdoor algal (Spirulina platensis)culture was developed. The model can simulate biomass production, pH, growth rate, oxygen evolution, and CO(2) fixation rate. It was calibrated and validated against experimental data obtained by a novel automatic data logger/controller instrumentation which can number most vital parameters of the culture including on line estimation of oxygen production rate (OPR). The importance of understanding light distribution through the pond and its effects on the photosynthesis and respiration processes are emphasized. A maximum yield of about 38 g day(-1) m(-2) under optimal conditions is predicted. The present model can also be a useful tool for optimization of algal mass production sites.

Recent advances in microalgal biotechnology.

In the last ten years, several reviews (Benemann et al, 1987; Goldman, 1979a; Richmond, 1986b; Soeder, 1980) and books (Borowitzka and Borowitzka, 1988b; Richmond, 1986a; Lembi and Waaland, 1988) have been published on the historical background of mass cultivation of microalgal biomass, and its possible commercial applications. This review presents a brief description of the concept of microalgal biotechnology, and describes some of the recent developments, mainly in the application and commercial development of this relatively new biotechnology, Finally, an attempt is made to indicate those areas where current research and development are paving the way for future applications.

Automatic on-line growth estimation method for outdoor algal biomass production.

An on-line measuring procedure for estimating productivity in outdoor algal cultures was developed and tested experimentally. The procedure is based on a previously described method for on-line measuring net O(2) production rate (OPR). The data obtained by this method was found to correlate well with the conventional procedures for estimation productivity by measuring the changes in biomass concentration in the culture. The new procedure seems to be superior to the latter since it can be carried out in an almost continuous way and can give immediate indication on the productivity. OPR could be used to monitor on-line the photosynthetic and/or respiration activity in small research fermentors or in large-scale open systems outdoors.

An automatic method for on-line estimation of the photosynthetic rate in open algal ponds.

An analytical model for dissolved oxygen concentration in an algal minipond was used to develop a new method for estimating, on-line, the net O(2) production rate (OPR) of the biological process. The method was tested experimentally and was found to provide crucial information on the vitality of the biological process and to provide an early warning of a possible forthcoming collapse of the ecosystern. It is suggested that the newly developed model and measurement method could provide investigators with useful tools for optimization of algal cultivation in the laboratory and plant.

Construction of shuttle vectors capable of conjugative transfer from Escherichia coli to nitrogen-fixing filamentous cyanobacteria.

Wild-type cyanobacteria of the genus Anabaena are capable of oxygenic photosynthesis, differentiation of cells called heterocysts at semiregular intervals along the cyanobacterial filaments, and aerobic nitrogen fixation by the heterocysts. To foster analysis of the physiological processes characteristic of these cyanobacteria, we have constructed a family of shuttle vectors capable of replication and selection in Escherichia coli and, in unaltered form, in several strains of Anabaena. Highly efficient conjugative transfer of these vectors from E. coli to Anabaena is dependent upon the presence of broad host-range plasmid RP-4 and of helper plasmids. The shuttle vectors contain portions of plasmid pBR322 required for replication and mobilization, with sites for Anabaena restriction enzymes deleted; cyanobacterial replicon pDU1, which lacks such sites; and determinants for resistance to chloramphenicol, streptomycin, neomycin, and erythromycin.