Phycobilisome-Deficient Strains of Synechocystis sp. PCC 6803 Have Reduced Size and Require Carbon-Limiting Conditions to Exhibit Enhanced Productivity.

Reducing excessive light harvesting in photosynthetic organisms may increase biomass yields by limiting photoinhibition and increasing light penetration in dense cultures. The cyanobacterium Synechocystis sp. PCC 6803 harvests light via the phycobilisome, which consists of an allophycocyanin core and six radiating rods, each with three phycocyanin (PC) discs. Via targeted gene disruption and alterations to the promoter region, three mutants with two (pcpcT→C) and one (ΔCpcC1C2:pcpcT→C) PC discs per rod or lacking PC (olive) were generated. Photoinhibition and chlorophyll levels decreased upon phycobilisome reduction, although greater penetration of white light was observed only in the PC-deficient mutant. In all strains cultured at high cell densities, most light was absorbed by the first 2 cm of the culture. Photosynthesis and respiration rates were also reduced in the ΔCpcC1C2:pcpcT→C and olive mutants. Cell size was smaller in the pcpcT→C and olive strains. Growth and biomass accumulation were similar between the wild-type and pcpcT→C under a variety of conditions. Growth and biomass accumulation of the olive mutant were poorer in carbon-saturated cultures but improved in carbon-limited cultures at higher light intensities, as they did in the ΔCpcC1C2:pcpcT→C mutant. This study shows that one PC disc per rod is sufficient for maximal light harvesting and biomass accumulation, except under conditions of high light and carbon limitation, and two or more are sufficient for maximal oxygen evolution. To our knowledge, this study is the first to measure light penetration in bulk cultures of cyanobacteria and offers important insights into photobioreactor design.

Distribution and morphology of two endemic gomphonemoid species, Gohphonema kaznakowi Mereschkowsky and G-yangtzensis Li nov sp in China

The morphology of Gomphonema kaznakowi Mereschkowsky was investigated using light microscopy. This species has two morphologically distinct areas near the headpole; an unornamented and an ornamented area. The two areas are distinguished from each other by the combination of size and striae number. A new species, Gomphonema yangtzensis Li nov. sp. is identified based on an ornamented area near the headpole. G. kaznakowi is reported from the upper and middle part of the Yangtze River, and was also found in the upper section of the Yellow River. G. yangtzensis was found in the upper area of the Yellow River and the middle of the Yangtze River. Their limited distribution may be due to certain environmental conditions or a different dispersal rate. Both species are illustrated.

Potamothrix scleropenis sp nov (Oligochaeta : Tubificidae) from Fuxian Lake, the deepest lake in southwest China

Potamothrix scleropenis sp. nov. (Tubificidae: Tubificinae) is described from the profundal zone (74 m) of Fuxian Lake, the deepest lake (up to 155 m) on the Yunnan-Guizhou Plateau in China. The new species is assigned to Potamothrix because of its short vasa deferentia. and its tubular atria without ejaculatory ducts and prostate glands. It differs from congeners by its cuticularized penis sheaths; bifurcated, strongly curved spermathecal chaetae; bifurcated lower prongs of bifids; and feathered hairs. P scleropenis appears closely related to P cekanovskajae Finogenova, 1972 and P tudoranceai porka, 1994, since all the three species have homogeneous atria without prostate glands.

A miniature insertion element transposable in Microcystis sp FACHB 854

A 186-bp sequence with imperfect terminal inverted repeats and target direct repeats but without any transposase-encoding capacity was found to be transposable in an isolate derived from Microcystis sp. FACHB 854. This miniature insertion element, designated as ISM854-1, and with its homologues present at least 10 copies in the genome of Microcystis FACHB 854, is inserted into the 8-bp long and AT-rich target sequences, but none or few in other Microcystis strains. A variant of ISM854-1, denoted ISM854-1A, has perfect inverted repeat sequences and may transpose in pairs in a structure like a composite transposon. This is the first report of non-autonomous transposition of a mini-IS in a cyanobacterium.

Response of growth and fatty acid compositions of Nannochloropsis sp to environmental factors under elevated CO2 concentration

Nannochloropsis sp. was grown with different levels of nitrate, phosphate, salinity and temperature with CO2 at 2,800 mu l l(-1). Increased levels of NaNO3 and KH2PO4 raised protein and polyunsaturated fatty acids (PUFAs) contents but decreased carbohydrate, total lipid and total fatty acids (TFA) contents. Nannochloropsis sp. grew well at salinities from 22 to 49 g l(-1), and lowering salinity enhanced TFA and PUFAs contents. TFA contents increased with the increasing temperature but PUFAs contents decreased. The highest eicosapentaenoic acid (EPA, 20:5 omega 3) content based on the dry mass was above 3% under low N (150 mu M NaNO3) or high N (3000 mu M NaNO3) condition. Excessive nitrate, low salinity and temperature are thus favorable factors for improving EPA yields in Nannochloropsis sp.

The functional divergence of two glgP homologues in Synechocystis sp PCC 6803

Glycogen phosphorylase (GlgP, EC 2.4.1.1) catalyzes the cleavage of glycogen into glucose-1-phosphate (Glc-1-P), the first step in glycogen catabolism. Two glgP homologues are found in the genome of Synechocystis sp. PCC 6803, a unicellular cyanobacterium: sll1356 and slr1367. We report on the different functions of these glgP homologues. sll1356, rather than slr1367, is essential for growth at high temperatures. On the other hand, when CO2-fixation and the supply of glucose are both limited, slr1367 is the key factor in glycogen metabolism. In cells growing autotrophically, sll1356 plays a more important role in glycogen digestion than slr1367. This functional divergence is also supported by a phylogenetic analysis of glgP homologues in cyanobacteria.

Regulation by hetC of genes required for heterocyst differentiation and cell division in Anabaena sp strain PCC 7120

Unlike those of the wild-type strain, proheterocysts of the Anabaena sp. strain PCC 7120 hetC strain keep dividing. ftsZ, the most critical cell division gene, is up-regulated in hetC proheterocysts. Heterocyst differentiation genes hglD, hglE, patB, nijB, and xisA are no longer expressed in the hetC mutant. hetC also regulates the expression of patA, a pattern formation gene.

Reactive oxygen species and antioxidant enzymes activity of Anabaena sp PCC 7120 (Cyanobacterium) under simulated microgravity

It was found that reactive oxygen species in Anabaena cells increased under simulated microgravity provided by clinostat. Activities of intracellular antioxidant enzymes, such as superoxide dismutase, catalase were higher than those in the controlled samples during the 7 days' experiment. However, the contents of gluathione, an intracellular antioxidant, decreased in comparison with the controlled samples. The results suggested that microgravity provided by clinostat might break the oxidative/antioxidative balance. It indicated a protective mechanism in algal cells, that the total antioxidant system activity increased, which might play an important role for algal cells to adapt the environmental stress of microgravity. (C) 2004 Elsevier Ltd. All rights reserved.

Endocrine disrupting effects on Chinese rare minnow (Gobiocypris rarus) fed with field collected Limnodrilus sp.

The potential endocrine disrupting effects and other toxicity effects on aquatic biota resulted from food uptake was simulated by feeding the laboratory cultured rare minnow(Gobiocypris rarus) with field collected Limnodrilus sp. The results indicated that the food chain processes affected significantly the growth, slightly reduced gonadosomatic indices, and elevated hepatosomatic indices. There was an obvious vitellogenin(VTG) induction, which generally only occurred in mature female, in the serum of juvenile rare minnow and mature male when fed with Limnodrilus sp. In addition, the rare minnow feeding on Limnodrilus sp. had significantly high renal indices, it meant obvious renal hyperplasia. The present work suggested that. Limnodrilus sp. from field water may contain toxic pollutants and could lead to endocrine disruption effects to the predators. It was concluded that endocrine disruptors may not only be assimilated through water, but also be bioconcentrated through food web. The results also suggested the importance of food selection in conducting the study of endocrine disruption effects using sensitive species.

alr0117, a two-component histidine kinase gene, is involved in heterocyst development in Anabaena sp PCC 7120

Anabaena sp. PCC; 7120 was mutagenized by transposon Tn5-1087b, generating a mutant whose heterocysts lack the envelope polysaccharide layer. The transposon was located between nucleotides 342 and 343 of alr0117, a 918 bp gene encoding a histidine kinase for a two-component regulatory system. Complementation of the mutant with a DNA fragment containing alr0117 and targeted inactivation of the gene confirmed that alr0117 is involved in heterocyst development. RT-PCR showed that alr0117 was constitutively expressed in the presence or absence of a combined-nitrogen source. hepA and patB, the two genes turned on during wild-type heterocyst development, were no longer activated in an alr0117-null mutant. The two-component signal transduction system involving alr0117 may control the formation of the envelope polysaccharide layer and certain late events essential to the function of heterocysts.

pkn22 (alr2502) encoding a putative Ser/Thr kinase in the cyanobacterium Anabaena sp PCC 7120 is induced by both iron starvation and oxidative stress and regulates the expression of isiA

In cyanobacteria, the isiA gene is required for cell adaptation to oxidative damage caused by the absence of iron. We show here that a putative Ser/Thr kinase gene, pkn22 (alr2052), is activated by iron deficiency and oxidative damage in Anabaena sp. PCC 7120. A pkn22 insertion mutant is unable to grow when iron is limiting. pkn22 regulates the expression of isiA (encoding CP43') but not of isiB (encoding flavodoxin) and psbC (CP43). Fluorescence measurement at 77 K reveals the absence of the typical signature of CP43' associated with photosystem I in the mutant under iron-limiting conditions. We propose that Pkn22 is required for the function of isiA/CP43' and constitutes a regulatory element necessary for stress response. (C) 2003 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

A TPR-family membrane protein gene is required for light-activated heterotrophic growth of the cyanobacterium Synechocystis sp PCC 6803

The unicellular cyanobacterium Synechocystis sp. PCC6803 can grow heterotrophically in complete darkness, given that a brief period of illumination is supplemented every day (light-activated heterotrophic growth, LAHG), or under very weak ( < 0.5 mumol m(-2) s(-1)) but continuous light. By random insertion of the genome with an antibiotic resistance cassette, mutants defective in LAHG were generated. In two identical mutants, sll0886, a tetratricopeptide repeat (TPR)-family membrane protein gene, was disrupted. Targeted insertion of sll0886 and three downstream genes showed that the phenotype was not due to a polar effect. The sll0886 mutant shows normal photoheterotrophic growth when the light intensity is at 2.5 mumol m(-2) s(-1) or above, but no growth at 0.5 mumol m(-2) s(-1). Homologs to sll0886 are also present in cyanobacteria that are not known of LAHG. sll0886 and homologs may be involved in controlling different physiological processes that respond to light of low fluence. (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Optimization of growth and fatty acid composition of a unicellular marine picoplankton, Nannochloropsis sp., with enriched carbon sources

A unicellular marine picoplankton, Nannochloropsis sp., was grown under CO2-enriched photoautotrophic or/and acetate-added mixotrophic conditions. Photoautotrophic conditions with enriched CO2 of 2800 mul CO2 l(-1) and aeration gave the highest biomass yield (634 mg dry wt l(-1)), the highest total lipid content (9% of dry wt), total fatty acids (64 mg g(-1) dry wt), polyunsaturated fatty acids (35% total fatty acids) and eicosapentaenoic acid (EPA, 20:5omega3) (16 mg g(-1) dry wt or 25% of total fatty acids). Mixotrophic cultures gave a greater protein content but less carbohydrates. Adding sodium acetate (2 mM) decreased the amounts of the total fatty acids and EPA. Elevation of CO2 in photoautotrophic culture thus enhances growth and raises the production of EPA in Nannochloropsis sp.

Description of a new species of the genus Tylopharynx (Nemata : Diplogasteroidea), T-clariamphida sp n., with a redescription of T-foetida (Butschli, 1874) Goffart, 1930

Tylopharynx clariamphida sp. n. is described from muddy sand collected in Anhui Province, China. It can be distinguished from T foetida (Butschli, 1874), the type and only species of the genus, by numerous characters: having 24 to 26 prominent and clearly separated longitudinal ridges, a higher lip region with no hint of a cephalic framework, more prominent amphidial foveae in lateral view, wider and more posteriorly located amphidial apertures, smaller basal knobs of stoma, longer metacorpus, more enlarged phasmids, shorter spicules with shorter digitate terminus, shorter reflexed part of testis, and thicker gubernaculum with more angular shape. For comparison, an expanded description is given for T foetida from Belgium, and SEM photographs of both species are provided.