Continuous Light Conditions Research Articles

The influence of day/night cycles on biomass yield and composition of Neochloris oleoabundans

BackgroundDay/night cycles regulate the circadian clock of organisms to program daily activities. Many species of microalgae have a synchronized cell division when grown under a day/night cycle, and synchronization might influence biomass yield and composition. Therefore, the aim of this study was to study the influence of day/night cycle on biomass yield and composition of the green microalgae Neochloris oleoabundans. Hence, we compared continuous turbidostat cultures grown under continuous light with cultures grown under simulated day/night cycles.ResultsUnder day/night cycles, cultures were synchronized as cell division was scheduled in the night, whereas under continuous light cell division occurred randomly synchronized cultures were able to use the light 10–15% more efficiently than non-synchronized cultures. Our results indicate that the efficiency of light use varies over the cell cycle and that synchronized cell division provides a fitness benefit to microalgae. Biomass composition under day/night cycles was similar to continuous light, with the exception of starch content. The starch content was higher in cultures under continuous light, most likely because the cells never had to respire starch to cover for maintenance during dark periods. Day/night cycles were provided in a ‘block’ (continuous light intensity during the light period) and in a ‘sine’ (using a sine function to simulate light intensities from sunrise to sunset). There were no differences in biomass yield or composition between these two ways of providing light (in a ‘block’ or in a ‘sine’).ConclusionsThe biomass yield and composition of N. oleoabundans were influenced by day/night cycles. These results are important to better understand the relations between research done under continuous light conditions and with day/night cycle conditions. Our findings also imply that more research should be done under day/night cycles.

Enhanced growth and total fatty acid production of microalgae under various lighting conditions induced by flashing light.

Microalgae are gaining importance as a source of high-value bioproducts. However, data regarding optimization of algal productivity via variation of environmental factors are lacking. Here, we evaluated a novel lighting method for the enhancement of biomass and total fatty acid (TFA) productivities during algal cultivation. We cultivated six different algal strains (Chlorella vulgaris KCTC AG10002, Acutodesmus obliquus KGE18, Uronema sp. KGE03, Micractinium reisseri KGE19, Fragilaria sp., and Spirogyra sp.) under various lighting conditions-continuous light (CL), light-dark cycle (LD), and continuous dark (CD)-with or without additional flashing light. We monitored dry cell weight (DCW) and TFA concentrations during cultivation. For each algal strain, the growth rate showed markedly different responses to the various lighting modes. The growth rates of C. vulgaris KCTC AG10002 (1.34-fold DCW increase, LD with flash), A. obliquus KGE18 (5.16-fold DCW increase, LD with flash), Uronema sp. KGE03 (2.77-fold DCW increase, CL with flash), and M. reisseri KGE19 (1.52-fold DCW increase, CL with flash) markedly increased in response to flashing light. Additionally, in some algal strains cultivated under the LD mode, the flashing light treatment induced increased TFA concentrations (C. vulgaris, 1.19-fold increase; A. obliquus, 2.59-fold increase; and M. reisseri, 3.31-fold increase). Phytohormone analysis of M. reisseri revealed increases in growth rate and TFA concentrations, associated with phytohormone induction via flashing light (e.g. 2.93-fold increase in gibberellic acid); hence, flashing light can promote substantial alterations in algal metabolism.

A new link between plant metabolism and circadian rhythms?

A new link between plant metabolism and circadian rhythms?

Interaction of melatonin and gonadotropin-inhibitory hormone on the zebrafish brain-pituitary-reproductive axis.

Circadian cycles and photoperiod are known to influence reproductive physiology in several animals. Neuropeptides, such as gonadotropin-inhibitory hormone (GNIH) and gonadotropin-releasing hormone (GNRH), are influenced by melatonin in birds and mammals. The present study demonstrates the role of melatonin in oocyte maturation in the zebrafish (Danio rerio), via the brain-pituitary-reproductive axis, under different photic conditions. Melatonin was significantly higher both in the whole brain and ovary under continuous dark (DD) compared to continuous light (LL) conditions. Transcription of gnih in the brain was high in LL, but low in DD; similarly, melatonin exogenous treatment reduced gnih in cultured brain in a dose-dependent manner. Expression of gnrh3, however, was high in both continuous photic conditions (DD and LL), whereas fshb and lhb were high only during DD. kiss2, another neuropeptide, was high in LL, but kiss1 remain unchanged among the conditions. At the gonad level, expression of fshr, lhcgr, mtnr1aa, and mtnr1ab tracked with the expression of their respective ligand in DD and LL. The expression of mprb is high in DD ovary, although intra-ovarian growth factors (tgfb1a and bmp15) were low. The measured increased percentages of germinal vesicle breakdown, expression of Cyclin B1, and reduced Cdc2p34 phosphorylation are consistent with increased maturation in the dark. Our study thus links melatonin to the inhibition of gnih in the brain-pituitary-reproductive axis of zebrafish in response to photic conditions.

Global metabolic rewiring for improved CO2 fixation and chemical production in cyanobacteria

Cyanobacteria have attracted much attention as hosts to recycle CO2 into valuable chemicals. Although cyanobacteria have been engineered to produce various compounds, production efficiencies are too low for commercialization. Here we engineer the carbon metabolism of Synechococcus elongatus PCC 7942 to improve glucose utilization, enhance CO2 fixation and increase chemical production. We introduce modifications in glycolytic pathways and the Calvin Benson cycle to increase carbon flux and redirect it towards carbon fixation. The engineered strain efficiently uses both CO2 and glucose, and produces 12.6 g l−1 of 2,3-butanediol with a rate of 1.1 g l−1 d−1 under continuous light conditions. Removal of native regulation enables carbon fixation and 2,3-butanediol production in the absence of light. This represents a significant step towards industrial viability and an excellent example of carbon metabolism plasticity.

Endosperm-derived triploid plant regeneration in diploid Actinidia kolomikta, a cold-hardy kiwifruit relative

Endosperm culture is a unique technique for producing a triploid plant from diploid plants. In the present study, endosperm of a diploid cold-hardy kiwifruit relative, Actinidia kolomikta (Maxim. & Rupr.) Maxim., was cultured to regenerate triploid plants and expand ploidy variation in this mostly diploid species. Endosperm derived from fruits harvested 6–10 weeks after flowering (WAF) was used for the initial explants to examine the effect of plant growth regulators on callus formation and organogenesis. The endosperm-derived calli induced in MS medium with above 1.0mgL−1 of 2,4-dichlorophenoxyacetic acid (2,4-D) were soft, small, and translucent, and no morphogenic response was observed. Conversely, the endosperm-derived yellow-green calli induced in the medium with 2,4-D (0.1mgL−1) plus kinetin (1.0, 2.0, and 5.0mgL−1) were hard, compact, fast growing, and showed adventitious shoot primordia. These primordia elongated into shoots when the calli were transferred to MS medium supplemented with zeatin (1.0, 2.0, and 4.0mgL−1) under continuous light conditions. The shoots developed roots on half-strength MS medium lacking plant growth regulators. In total, 14 plants were obtained. Flow cytometry and chromosomal analysis confirmed that the regenerated plants were triploid, suggesting that the plant tissue originated from the endosperm. This study reveals that the endosperm of A. kolomikta has plant regeneration abilities and that the regenerated plants have the same ploidy level as the endosperm (triploid). These results may be of use for ploidy manipulation or polyploidy breeding in other species in the genus Actinidia.

Structural basis of jasmonate-amido synthetase FIN219 in complex with glutathione S-transferase FIP1 during the JA signal regulation

Far-red (FR) light-coupled jasmonate (JA) signaling is necessary for plant defense and development. FR insensitive 219 (FIN219) is a member of the Gretchen Hagen 3 (GH3) family of proteins in Arabidopsis and belongs to the adenylate-forming family of enzymes. It directly controls biosynthesis of jasmonoyl-isoleucine in JA-mediated defense responses and interacts with FIN219-interacting protein 1 (FIP1) under FR light conditions. FIN219 and FIP1 are involved in FR light signaling and are regulators of the interplay between light and JA signaling. However, how their interactions affect plant physiological functions remains unclear. Here, we demonstrate the crystal structures of FIN219-FIP1 while binding with substrates at atomic resolution. Our results show an unexpected FIN219 conformation and demonstrate various differences between this protein and other members of the GH3 family. We show that the rotated C-terminal domain of FIN219 alters ATP binding and the core structure of the active site. We further demonstrate that this unique FIN219-FIP1 structure is crucial for increasing FIN219 activity and determines the priority of substrate binding. We suggest that the increased FIN219 activity resulting from the complex form, a conformation for domain switching, allows FIN219 to switch to its high-affinity mode and thereby enhances JA signaling under continuous FR light conditions.

Genetic and isotope ratio mass spectrometric evidence for the occurrence of starch degradation and cycling in illuminated Arabidopsis leaves

Although there is a great wealth of data supporting the occurrence of simultaneous synthesis and breakdown of storage carbohydrate in many organisms, previous 13CO2 pulse-chase based studies indicated that starch degradation does not operate in illuminated Arabidopsis leaves. Here we show that leaves of gwd, sex4, bam4, bam1/bam3 and amy3/isa3/lda starch breakdown mutants accumulate higher levels of starch than wild type (WT) leaves when cultured under continuous light (CL) conditions. We also show that leaves of CL grown dpe1 plants impaired in the plastidic disproportionating enzyme accumulate higher levels of maltotriose than WT leaves, the overall data providing evidence for the occurrence of extensive starch degradation in illuminated leaves. Moreover, we show that leaves of CL grown mex1/pglct plants impaired in the chloroplastic maltose and glucose transporters display a severe dwarf phenotype and accumulate high levels of maltose, strongly indicating that the MEX1 and pGlcT transporters are involved in the export of starch breakdown products to the cytosol to support growth during illumination. To investigate whether starch breakdown products can be recycled back to starch during illumination through a mechanism involving ADP-glucose pyrophosphorylase (AGP) we conducted kinetic analyses of the stable isotope carbon composition (δ13C) in starch of leaves of 13CO2 pulsed-chased WT and AGP lacking aps1 plants. Notably, the rate of increase of δ13C in starch of aps1 leaves during the pulse was exceedingly higher than that of WT leaves. Furthermore, δ13C decline in starch of aps1 leaves during the chase was much faster than that of WT leaves, which provides strong evidence for the occurrence of AGP-mediated cycling of starch breakdown products in illuminated Arabidopsis leaves.

An Algorithm to Predict the Biomechanical Stiffening Effect in Corneal Cross-linking.

To develop an algorithm to predict the stiffening effect of CXL and to verify the accuracy with results obtained from experimental measurements. The algorithm considers different variables: the reaction kinetics of riboflavin diffusion and riboflavin photodegradation to determine the effective riboflavin concentration in different stromal layers; the oxygen diffusion and ultraviolet (UV) absorption to determine the amount of reactive oxygen species as a function of time and stromal depth. For the experimental comparison, corneas were deepithelialized, followed by riboflavin instillation for 30 minutes and UV irradiation. Different pulsed and continuous-light conditions were analyzed with irradiances ranging from 3 to 100 mW/cm2 and irradiation times from 8 to 30 minutes. Stress-relaxation measurements were performed in fresh-enucleated porcine (n = 66) and rabbit (n = 2) eyes directly after treatment, using a load of 0.6 MPa. A clear linear relationship was observed between the concentration of newly induced cross-links and the experimentally observed stiffening factor (R2 = 0.9432). An additional 1 mol/m3 of cross-links increased the mechanical stress resistance of the cornea by 50.4%. The efficacy of standard CXL in murine, lapine, and porcine corneas was inversely related to corneal thickness. The stiffening effect after CXL decreased by 4.1% per 100 µm (R2 = 0.9961). The proposed model, supported by data in porcine, murine, and lapine corneas, suggests a possibility of also predicting the biomechanical CXL efficacy in human corneas. The biomechanical efficacy of CXL may be increased by prolonged UV irradiation at reduced irradiances or by a higher oxygen pressure in the environment. Pulsed CXL does not accelerate CXL or increase its efficacy when compared to standard CXL of the same irradiation duration. This model might be used to calculate customized irradiation settings for high-risk cases, but also topography-guided CXL treatments. [J Refract Surg. 2017;33(2):128-136.].

Effect of NaCl and Na2SO4 salinities and light conditions on seed germination of purslane (Portulaca oleracea Linn.)

<p><em>Portulaca oleracea </em>Linn., commonly known as purslane, is a C<sub>4</sub> succulent and salt tolerant weed. The present work was focused on the seed germination of purslane under different levels of NaCl and Na<sub>2</sub>SO<sub>4 </sub>(25, 50, 100 and 200 mM) salinity along with continuous dark and light conditions. Results indicated that both salinity treatments had negative impact on seed germination under both light conditions. Interestingly, seed germination percentage of purslane was high under both salinity treatments and continuous light conditions as compared to dark conditions. The differential response of purslane’s seed germination under NaCl and Na<sub>2</sub>SO<sub>4</sub> salinity and light conditions suggests weediness of this plant under adverse environmental conditions. The present work might be helpful for agricultural practices dealing with the problem of this weed.</p>

Genetic tools for advancement of Synechococcus sp. PCC 7002 as a cyanobacterial chassis.

BackgroundSuccessful implementation of modified cyanobacteria as hosts for industrial applications requires the development of a cyanobacterial chassis. The cyanobacterium Synechococcus sp. PCC 7002 embodies key attributes for an industrial host, including a fast growth rate and high salt, light, and temperature tolerances. This study addresses key limitations in the advancement of Synechococcus sp. PCC 7002 as an industrial chassis.ResultsTools for genome integration were developed and characterized, including several putative neutral sites for genome integration. The minimum homology arm length for genome integration in Synechococcus sp. PCC 7002 was determined to be approximately 250 bp. Three fluorescent protein reporters (hGFP, Ypet, and mOrange) were characterized for gene expression, microscopy, and flow cytometry applications in Synechococcus sp. PCC 7002. Of these three proteins, the yellow fluorescent protein (Ypet) had the best optical properties for minimal interference with the native photosynthetic pigments and for detection using standard microscopy and flow cytometry optics. Twenty-five native promoters were characterized as tools for recombinant gene expression in Synechococcus sp. PCC 7002 based on previous RNA-seq results. This characterization included comparisons of protein and mRNA levels as well as expression under both continuous and diurnal light conditions. Promoters A2520 and A2579 were found to have strong expression in Synechococcus sp. PCC 7002 while promoters A1930, A1961, A2531, and A2813 had moderate expression. Promoters A2520 and A2813 showed more than twofold increases in gene expression under light conditions compared to dark, suggesting these promoters may be useful tools for engineering diurnal regulation.ConclusionsThe genome integration, fluorescent protein, and promoter tools developed in this study will help to advance Synechococcus sp. PCC 7002 as a cyanobacterial chassis. The long minimum homology arm length for Synechococcus sp. PCC 7002 genome integration indicates native exonuclease activity or a low efficiency of homologous recombination. Low correlation between transcript and protein levels in Synechococcus sp. PCC 7002 suggests that transcriptomic data are poor selection criteria for promoter tool development. Lastly, the conventional strategy of using promoters from photosynthetic operons as strong promoter tools is debunked, as promoters from hypothetical proteins (A2520 and A2579) were found to have much higher expression levels.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0584-6) contains supplementary material, which is available to authorized users.

Engineering an Obligate Photoautotrophic Cyanobacterium to Utilize Glycerol for Growth and Chemical Production.

Cyanobacteria have attracted much attention as a means to directly recycle carbon dioxide into valuable chemicals that are currently produced from petroleum. However, the titers and productivities achieved are still far below the level required in industry. To make a more industrially applicable production scheme, glycerol, a byproduct of biodiesel production, can be used as an additional carbon source for photomixotrophic chemical production. Glycerol is an ideal candidate due to its availability and low cost. In this study, we found that a heterologous glycerol respiratory pathway enabled Synechococcus elongatus PCC 7942 to utilize extracellular glycerol. The engineered strain produced 761 mg/L of 2,3-butanediol in 48 h with a 290% increase over the control strain under continuous light conditions. Glycerol supplementation also allowed for continuous cell growth and 2,3-butanediol production in diurnal light conditions. These results highlight the potential of glycerol as an additional carbon source for photomixotrophic chemical production in cyanobacteria.

Transcript profiling reveals that cysteine protease inhibitors are up-regulated in tuber sprouts after extended darkness.

Potato (Solanum tuberosum L.) tubers are an excellent staple food due to its high nutritional value. When the tuber reaches physiological competence, sprouting proceeds accompanied by changes at mRNA and protein levels. Potato tubers become a source of carbon and energy until sprouts are capable of independent growth. Transcript profiling of sprouts grown under continuous light or dark conditions was performed using the TIGR 10K EST Solanaceae microarray. The profiles analyzed show a core of highly expressed transcripts that are associated to the reactivation of growth. Under light conditions, the photosynthetic machinery was fully activated; the highest up-regulation was observed for the Rubisco activase (RCA), the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the Photosystem II 22kDa protein (CP22) genes, among others. On the other hand, sprouts exposed to continuous darkness elongate longer, and after extended darkness, synthesis of chloroplast components was repressed, the expression of proteases was reduced while genes encoding cysteine protease inhibitors (CPIs) and metallocarboxypeptidase inhibitors (MPIs) were strongly induced. Northern blot and RT-PCR analysis confirmed that MPI levels correlated with the length of the dark period; however, CPI expression was strong only after longer periods of darkness, suggesting a feedback loop (regulation mechanism) in response to dark-induced senescence. Prevention of cysteine protease activity in etiolated sprouts exposed to extended darkness could delay senescence until they emerge to light.

2,3 Butanediol production in an obligate photoautotrophic cyanobacterium in dark conditions via diverse sugar consumption

Cyanobacteria are under investigation as a means to utilize light energy to directly recycle CO2 into chemical compounds currently derived from petroleum. Any large-scale photosynthetic production scheme must rely on natural sunlight for energy, thereby limiting production time to only lighted hours during the day. Here, an obligate photoautotrophic cyanobacterium was engineered for enhanced production of 2,3-butanediol (23BD) in continuous light, 12h:12h light-dark diurnal, and continuous dark conditions via supplementation with glucose or xylose. This study achieved 23BD production under diurnal conditions comparable to production under continuous light conditions. The maximum 23BD titer was 3.0gL−1 in 10d. Also achieving chemical production under dark conditions, this work enhances the feasibility of using cyanobacteria as industrial chemical-producing microbes.

Seed germination and emergence of Setaria pallidefusca and Pennisetum pedicellatum (Cyperales: Poaceae) in Nigeria.

Seed weight, viability, gennination and emergence of Setaria pallidefusca and Pennisetum pedicellatum were determined under controlled conditions. The seeds of S . pallidefusca and P. pedicellatum had 97% and 94% viability respectively. Optimum gennination ofall seeds occurred at 25°C. Maximum seedling emergence occurred at the soil surface, there was a progressive decrease at greater depth. Maximum depth for emergence were 5 cm (S . pallidefusca) and 7 cm (P. pedicellatum). Seeds of both species germinated well under varied light conditions. However, there was less gennination under continuous light or darlmess conditions than under altemating day and night conditions

Photoacclimation of natural phytoplankton communities

Phytoplankton regulate internal pigment concentrations in response to light and nutrient availability. Chlorophyll a to phytoplankton carbon ratios (chl:Cphyto) are commonly reported as a function of growth irradiance (Eg) for evaluating the photoacclimation response of phytoplankton. In contrast to most culture experiments, natural phytoplankton communities expe- rience fluctuating environmental conditions, making it difficult to compare field and lab observa- tions. Observing and understanding photoacclimation in nature is important for deciphering changes in chl:Cphyto resulting from environmental forcings and for accurately estimating net pri- mary production (NPP) in models which rely on a parameterized description of photoacclimation. Here we employ direct analytical measurements of Cphyto and parallel high-resolution biomass estimates from particulate backscattering (bbp) and flow cytometry to investigate chl:Cphyto in nat- ural phytoplankton communities. Chl:Cphyto observed over a wide range of Eg in the field was con- sistent with photoacclimation responses inferred from satellite observations. Field-based photoac- climation observations for a mixed natural community contrast with laboratory results for single species grown in continuous light and nutrient-replete conditions. Applying a carbon-based NPP model to our field data for a northsouth transect in the Atlantic Ocean results in estimates that closely match 14 C depth-integrated NPP for the same cruise and with historical records for the dis- tinct biogeographic regions of the Atlantic Ocean. Our results are consistent with previous satel- lite and model observations of cells growing in natural or fluctuating light and showcase how direct measurements of Cphyto can be applied to explore phytoplankton photophysiology, growth rates, and production at high spatial resolution in situ.

Spore Germination and Protonemal Development of Dolichomitriopsis diversiformis

Dolichomitriopsis diversiformis is an endemic and threatened moss in eastern Asia. In vitro culture and light microscopic observation were employed to study its developmental process from spore germination to the formation of young gametophyte, as well as effects of light and temperature on its spore germination and protonemal development. Microscopic observations revealed that its spores were positively photoblastic with exosporous germination, and sporelings were classified as the bryum-type. Light and dark conditions were compared to understand their effects on spore germination. In 24 h continuous illumination, all spores germinated in both 20 ℃ and 25 ℃. In contrast, in darkness at 20 ℃ from one to 30 days, spores did not germinate. However, when dark-cultured spores transferred to continuous light, they started to geminate in 48 hours. In addition, effects of 20 ℃ and 25 ℃ on sporeling were compared. In a continuous light condition, sporelings grew longer and developed more protonema branches in the 20 ℃ treatment than in the 25 ℃ treatment. It was interesting that a phenomenon of slow and hysteretic spore germination and protonematal development was observed in natural light and room temperature (5-10℃). These observations suggest that spore germination and sporeling development is regulated by light and temperature.

Efficient in vitro establishment and multiplication of Picrorhiza kurroa Royle ex Benth through in vitro raised seedlings

The aim of present investigation was to develop a highly reproducible and well documented protocol for in vitro germination and multiplication of highly valuable medicinal herb, Picrorhiza kurroa via callus mediated organogenesis using the axenic epicotyls originated from in vitro germinated seedlings. Highest germination percentage (88.6) was observed in stratified seeds (4°C for 5 days) treated with 100 mg/l GA3 and maintained at 25 ±1°C under continuous light conditions. Out of different combinations of plant growth regulators tested, Murashige and Skoog (MS) medium supplemented with 1.5 mg/l α naphthalene acetic acid (NAA)+0.75 mg/l kinetin (Kn)+0.75 mg/l 6-benzyladenine (BAP) was found best for callus induction and further proliferation. Addition of gibberellic acid (GA3) at 1.0 mg/l concentration in hormonal combination of 2.0 mg/l Kn and 0.75 mg/l indole-3-acetic acid (IAA) was found to be optimum to produce highest shooting response (95%) with an average number of 11.40 shoots per calli. The rooting was optimized using 0.5 mg/l IAA with 85% response. The plantlets with well-developed roots were hardened and were successfully acclimatized in field conditions. This protocol may offer the potential to substantially reduce the pressure of commercial need of this valuable herb on wild stock.

Effects of Melatonin on Morphological and Functional Parameters of the Pineal Gland and Organs of Immune System in Rats During Natural Light Cycle and Constant Illumination.

We studied the response of the pineal gland and organs of the immune system to melatonin treatment in Wistar rats kept under conditions of abnormal illumination regimen. The animals were kept under natural light regimen or continuous illumination for 14 days and then received daily injections of melatonin (once a day in the evening) for 7 days. Administration of melatonin to rats kept at natural light cycle was followed by a decrease in percent ratio of CD4+8+ splenocytes and CD4-8+ thymocytes. In 24-h light with the following melatonin injections were accompanied by an increase in percent rate and absolute amount of CD4+8+ cells in the spleen, and a decrease in percent rate of CD11b/c and CD4-8+ splenocytes. In the thymus amount of CD4-8+ cells increased, and absolute number of CD4+25+ cells reduced. Melatonin significantly decreased lipofuscin concentration in the pineal gland during continuous light. Direction and intensity of effects of melatonin on parameters of cell immunity and state of the pineal gland were different under normal and continuous light conditions. It should be taken into account during using of this hormone for correction of immune and endocrine impairments developing during change in light/dark rhythm.

Enhancing the vitamin B12 production and growth of Propionibacterium freudenreichii in tofu wastewater via a light-induced vitamin B12 riboswitch.

The vitamin B12-dependent riboswitch is a crucial factor that regulates gene transcription to mediate the growth of and vitamin B12 synthesis by Propionibacterium freudenreichii. In this study, the effect of various wavelengths of light on the growth rate and vitamin B12 synthesis was studied. Red, green, and blue light-emitting diodes (LEDs) were selected, and a dark condition was used as the control. The microorganism growth rate was measured using a spectrophotometer and plate counting, while the vitamin B12 content was determined using an HPLC-based method. The optical density at 600nm (OD600) values indicated that P. freudenreichii grew better under the continuous and discontinuous blue light conditions. Moreover, under the blue light condition, P. freudenreichii tended to have a higher growth rate (0.332h(-1)) and vitamin B12 synthesis (ca. 10μg/mL) in tofu wastewater than in dark conditions. HPLC analysis also showed that more methylcobalamin was produced under the blue light conditions than in the other conditions. The cbiB gene transcription results showed that blue light induced the synthesis of this vitamin B12 synthesis enzyme. Moreover, the results of inhibiting the expression of green fluorescent protein indicated that blue light removed the inhibition by the vitamin B12-dependent riboswitch. This method can be used to reduce fermentation time and produce more vitamin B12 in tofu wastewater.