Modeling of biomass productivity in tubular photobioreactors for microalgal cultures: effects of dilution rate, tube diameter, and solar irradiance

A macromodel is developed for estimating the year-long biomass productivity of outdoor cultures of microalga in tubular photobioreactors. The model evaluates the solar irradiance on the culture surface as a function of day of the year and the geographic location. In a second step, the geometry of the system is taken into account in estimating the average irradiance to which the cells are exposed. Finally, the growth rate is estimated as a function of irradiance, taking into account photoinhibition and photolimitation. The model interconnects solar irradiance (an environmental variable), tube diameter (a design variable), and dilution rate (an operating variable). Continuous cultures in two different tubular photobioreactors were analyzed using the macromodel. The biomass productivity ranged from 0.50 to 2.04 g L-1 d-1, and from 1.08 to 2. 76 g L-1 d-1, for the larger and the smaller tube diameter photobioreactors, respectively. The quantum yield ranged from 1.1 to 2.2 g E-1; the higher the incident solar radiation, the lower the quantum yield. Simultaneous photolimitation and photoinhibition of outdoor cultures was observed. The model reproduced the experimental results with less than 20% error. If photoinhibition was neglected, and a growth model that considered only photolimitation was used to fit the data, the error increased to 45%, thus reflecting the inadequacy of previous outdoor growth models that disregard photoinhibition. Copyright 1998 John Wiley & Sons, Inc.     

Molecular cloning, sequence and regulation of expression of the recA gene of the phototrophic bacterium Rhodobacter sphaeroides

The recA gene of Rhodobacter sphaeroides 2.4.1 has been isolated by complementation of a UV-sensitive RecA^– mutant of Pseudomonas aeruginosa. Its complete nucleotide sequence consists of 1032 bp, encoding a polypeptide of 343 amino acids. The deduced amino acid sequence displayed highest identity to the RecA proteins from Rhizobium mehloti, Rhizobium phaseoli, and Agrobacterium tumefaciens. An Escherichia coli-like SOS consensus region, which functions as a binding site for the LexA repressor molecule was not present in the 215 by upstream region of the R. sphaeroides recA gene. Nevertheless, by using a recA-lacZ fusion, we have shown that expression of the recA gene of R. sphaeroides is inducible by DNA damage. A recA-defective strain of R. sphaeroides was obtained by replacement of the active recA gene by a gene copy inactived in vitro. The resulting recA mutant exhibited increased sensitivity to UV irradiation, and was impaired in its ability to perform homologous recombination as well as to trigger DNA damage-mediated expression. This is the first recA gene from a Gram-negative bacterium that lacks an E. coli-like SOS box but whose expression has been shown to be DNA damage-inducible and auto-regulated.     

Isolation and characterization of a cDNA encoding the zebra finch myelin proteolipid protein

A cDNA was isolated from a zebra finch telencephalon cDNA library that encodes the myelin proteolipid protein. The clone was 2874 nucleotides long containing an open reading frame of 831 nucleotides that encoded a 277 amino acid myelin proteolipid protein. The 5-and 3 untranslated regions were 112 and 1931 nucleotides, respectively. In Northern blots the clone hybridized to 3 bands of 3.5, 2.4 and 1.5 Kb in mouse brain RNA, but to only a single band of 3.0 kb in zebra finch brain RNA, suggesting the lack of alternative polyadenylation sites within the 3 untranslated region of the zebra finch PLP mRNAs. There was a small degree of homology between the zebra finch and chicken PLP 5 untranslated regions, but relatively little homology of the 5 untranslated regions of the zebra finch PLP cDNA clone with the homologous regions of PLP cDNAs of many mammalian species. Except for a small stretch of considerable homology, there was little overall homology with the 3 untranslated regions of mammalian PLP mRNAs. Approximately 10% (i.e. 28) of the amino acids in the zebra finch PLP differed from mammalian PLP, with most of these changes located within exon 3. There were 16 amino acid changes between zebra finch and chicken, suggesting that greater sequence variation in PLP structure is tolerated among avian species than among mammalian species.Abbreviations DM20 25 kDa proteolipid protein in myelin - PLP classic 30 kDa myelin proteolipid protein Special issue dedicated to Dr. Marjorie B. Lees.     

Patch clamp studies of single intact secretory granules.

The membrane of secretory granules is involved in the molecular events that cause exocytotic fusion. Several of the proteins that have been purified from the membrane of secretory granules form ion channels when they are reconstituted in lipid bilayers and, therefore, have been thought to form part of the molecular structure of the exocytotic fusion pore. We have used the patch clamp technique to study ion conductances in single isolated secretory granules from beige mouse mast cells. We found that the membrane of the intact granule had a conductance of < 50 pS. No abrupt changes in current corresponding to the opening and closing of ion channels were observed, even under conditions where exocytotic fusion occurred. However, mechanical tension or a large voltage pulse caused the breakdown of the granule membrane resulting in the abrupt opening of a pore with an ion conductance of about 1 nS that fluctuated rapidly and could expand to an immeasurably large conductance or close completely. Surprisingly, the behavior of these pores resembled the pattern of conductance changes of exocytotic fusion pores observed in degranulating beige mast cells. This similarity supports the view that the earliest fusion pore is formed upon the breakdown of a bilayer such as that formed during hemifusion.     

Intermittent instability is widespread in plankton communities

Chaotic dynamics appear to be prevalent in short-lived organisms including plankton and may limit long-term predictability. However, few studies have explored how dynamical stability varies through time, across space and at different taxonomic resolutions. Using plankton time series data from 17 lakes and 4 marine sites, we found seasonal patterns of local instability in many species, that short-term predictability was related to local instability, and that local instability occurred most often in the spring, associated with periods of high growth. Taxonomic aggregates were more stable and more predictable than finer groupings. Across sites, higher latitude locations had higher Lyapunov exponents and greater seasonality in local instability, but only at coarser taxonomic resolution. Overall, these results suggest that prediction accuracy, sensitivity to change and management efficacy may be greater at certain times of year and that prediction will be more feasible for taxonomic aggregates.     

Aspects of the resistance of lactic acid bacteria to hop bitter acids

Resistance to trans -isohumulone is found only in those lactic acid bacteria which can grow in beer. The degree of resistance could not be altered by plasmid curing, or mutation induced by u.v. light. Organisms resistant to trans -isohumulone were resistant to the related hop acids(-)-humulone and colupulone. Equally, organisms sensitive to trans -isohumulone were also sensitive to related compounds. No other features correlated with hop resistance, including cell morphology, colony morphology, pH range for growth, sugar utilization profile, products of metabolism, manganese requirement and sensitivity to superoxide radicals, expression of cellular proteins, and resistance or sensitivity to selected antibacterial agents.     

Efficiency of utilization of high and low quality forage by three goat breeds

Alpine, Angora and Nubian kids, 6–8 months old and weighing 15–25 kg were grazed on high quality (wheat) or low quality pasture (dormant bermudagrass) for 54 d to evaluate breed differences and metabolic responses. Each kid on the bermudagrass pasture also received daily 200 g of a 24% CP supplement to stimulate intake.

Wheat pasture had an in vitro organic matter digestibility (IVOMD) of 78 vs. 35% for the Bermuda pasture. Goats gained 50 g/d on wheat pasture vs. 10 g/d on Bermuda pasture (P<0.02). Angora kids gained the least weight on Bermuda (−8 g/d; P<0.05) and most on wheat pasture (62 g/d; P<0.05). Mohair production was greater for Angora goats on wheat pasture compared to those on Bermuda pastures (9.9 vs. 6.2 g/100 cm²; P<0.05). Angora goats on Bermuda pastures had elevated levels of NEFA and plasma ammonia, and reduced levels of plasma urea N, consistent with catabolism of body tissue stores. Angora goats tended to have lower concentration of rumen VFA and ammonia. Angora goats appear to be more sensitive to inanition as compared to Alpine and Nubian goats. Presumably, their obligate nutrient requirements for hair production limits their ability to adapt, making them more vulnerable to nutritional stress.     

Light-dependent phagotrophy in the freshwater mixotrophic chrysophyte Dinobryon cylindricum

The mixotrophic (bacterivorous), freshwater chrysophyte Dinobryon cylindricum was cultured under a variety of light regimes and in bacterized and axenic cultures to investigate the role of phototrophy and phagotrophy for the growth of this alga. D. cylindricum was found to be an obligate phototroph. The alga was unable to survive in continuous darkness even when cultures were supplemented with high concentrations of bacteria, and bacterivory ceased in cultures placed in the dark for a period longer than one day. Axenic growth of the alga was poor even in an optimal light regime. Live bacteria were required for sustained, vigorous growth of the alga in the light. Carbon (C), nitrogen (N), and phosphorus (P) budgets determined for the alga during growth in bacterized cultures indicated that bacterial biomass ingested by the alga may have contributed up to 25% of the organic carbon budget of the alga. Photosynthesis was the source of most (75%) of the organic carbon of the alga. D. cylindricum populations survived but did not grow when cultured in a continuous low light intensity (30 E m^–2 sec^–1), or in a light intensity of 150 E m^–2 sec^–1 for only two hours each day. Net efficiency of incorporation of bacterial C, N, and P into algal biomass under these two conditions was zero (i.e., no net algal population growth). We conclude that the primary function of bacterivorous behavior in D. cylindricum may be to provide essential growth factor(s) or major nutrients for photosynthetic growth, or to allow for the survival of individuals during periods of very low light intensity or short photoperiod. Offprint requests to: David A. Caron     

The status ofColobus polykomos dollmani Schwarz

The two West African black-and-white colobus taxa,Colobus polykomos andC. vellerosus, are distinct species. A supposedly intermediate subspecies,C. polykomos dollmani, is actually a hybrid swarm, in whichC. vellerosus genes greatly predominate. We propose a hypothesis to explain this situation.