Abscisic acid signaling through LANCL2 and PPARγ induces activation of p38MAPK resulting in dormancy of prostate cancer metastatic cells.

Prostate cancer (PCa) is one the most common malignancies in men. The high incidence of bone metastasis years after primary therapy suggests that disseminated tumor cells must become dormant, but maintain their ability to proliferate in the bone marrow. Abscisic acid (ABA) is a stress response molecule best known for its regulation of seed germination, stomal opening, root shoot growth and other stress responses in plants. ABA is also synthesized by mammalian cells and has been linked to human disease. The aim of the present study was to examine the role of ABA in regulating tumor dormancy via signaling through lanthionine synthetase C­like protein 2 (LANCL2) and peroxisome proliferator activated receptor γ (PPARγ) receptors. ABA signaling in human PCa cell lines was studied using targeted gene knockdown (KD), western blotting, quantitative PCR, cell proliferation, migration, invasion and soft agar assays, as well as co­culture assays with bone marrow stromal cells. The data demonstrated that ABA signaling increased the expression of p21, p27 and p16, while inhibiting viability, migration, invasion and colony size in a reversable manner without toxicity. ABA also induced p38MAPK activation and NR2F1 signaling. Targeted gene KD of LANCL2 and PPARγ abrogated the cellular responses to ABA. Taken together, these data demonstrate that ABA may induce dormancy in PCa cell lines through LANCL2 and PPARγ signaling, and suggest novel targets to manage metastatic PCa growth.

LIMK2 promotes melanoma tumor growth and metastasis through G3BP1-ESM1 pathway-mediated apoptosis inhibition.

Melanoma is the leading cause of skin cancer-related deaths, and current melanoma therapies, including targeted therapies and immunotherapies, benefit only a subset of metastatic melanoma patients due to either intrinsic or acquired resistance. LIM domain kinase 2 (LIMK2) is a serine/threonine kinase that plays an important role in the regulation of actin filament dynamics. Here, we show that LIMK2 is overexpressed in melanoma, and its genetic or pharmacological inhibition impairs melanoma tumor growth and metastasis in both cell culture and mice. To determine the mechanism by which LIMK2 promotes melanoma tumor growth and metastatic progression, we performed a phosphoproteomics analysis and identified G3BP1 as a key LIMK2 target, which mirrored the effects of LIMK2 inhibition when inhibited. To further determine the role of G3BP1 downstream of LIMK2, we knocked down the expression of G3BP1, performed RNA-seq analysis, and identified ESM1 as a downstream target of G3BP1. G3BP1 was required for ESM1 mRNA stability, and ESM1 ectopic expression rescued LIMK2 or G3BP1 inhibition-induced suppression of melanoma growth and metastatic attributes. These results collectively identify the LIMK2→G3BP1→ESM1 pathway as a facilitator of melanoma tumor growth and metastasis and document that LIMK2 is a therapeutically tractable target for melanoma therapy.

Phosphorus Accumulation in Extracellular Polymeric Substances (EPS) of Colony-Forming Cyanobacteria Challenges Imbalanced Nutrient Reduction Strategies in Eutrophic Lakes.

Extracellular polymeric substances (EPS) are crucial for cyanobacterial proliferation; however, certain queries, including how EPS affects cellular nutrient processes and what are the implications for nutrient management in lakes, are not well documented. Here, the dynamics of cyanobacterial EPS-associated phosphorus (EPS-P) were examined both in a shallow eutrophic lake (Lake Taihu, China) and in laboratory experiments with respect to nitrogen (N) and phosphorus (P) availability. Results indicated that 40-65% of the total cyanobacterial aggregate/particulate P presented as EPS-P (mainly labile P and Fe/Al-P). Phosphorus-starved cyanobacteria rapidly replenished their EPS-P pools after the P was resupplied, and the P concentration in this pool was stable for long afterward, although the environmental P concentration decreased dramatically. A low-N treatment enhanced the EPS production alongside two-fold EPS-P accumulation (particularly labile P) higher than the control. Such patterns occurred in the lake where EPS and EPS-P contents were high under N limitation. EPS-P enrichment increased the P content in cyanobacteria; subsequently, it could hold the total P concentration higher for longer and make bloom mitigation harder. The findings outline a new insight into EPS functions in the P process of cyanobacterial aggregates and encourage consideration of both N and P reductions in nutrient management.

Risk perception among residents living near industries in Godawari Municipality of Lalitpur, Nepal.

The industrial sector stands out as a significant contributor to environmental pollution. Those who reside in close proximity to industrial areas commonly harbor concerns about potential health and environmental hazards. This study aimed to find out the perception of risk and self-reported health impacts among individuals living near industries in Godawari Municipality, Lalitpur, Nepal. Conducted as a community-based cross-sectional study, it involved 270 households. Face-to-face interviews were employed, utilizing a pretested structured questionnaire. The study zone encompassed the communities of Godawari Municipality within a 3-kilometer radius of industrial sites. Specifically, stone mines, stone crushers, and brick kilns were purposefully selected, while study participants were randomly sampled using a random table. Data analysis was performed using IBM SPSS, incorporating both univariate and bivariate techniques. Among those residing near industrial zones, a mere 9.6 % reported experiencing wheezing or whistling in the past 12 months. A substantial 36.3% consistently felt stressed due to industrial activities in their vicinity. Approximately half (51.9 %) of the participants indicated that the contaminated air in the area had adverse effects on human health. Furthermore, a palpable perception of elevated risk was associated with the proximity of industries (p<0.001). Over half of the participants perceived a notable risk stemming from the presence of industries near their homes, largely due to pollutants. These individuals also disclosed various health repercussions and expressed significant apprehension regarding their future well-being in the area. The implications of these findings are substantial, particularly for local-level planning and the development of industrial sites. Addressing the concerns surrounding people's heightened perception of risk from nearby industries is pivotal in fostering harmonious coexistence and informed decision-making.

Fecal Carriage of Extended-Spectrum beta-Lactamase Producing Escherichia coli among Health Science Students.

BACKGROUND: The incidence of antibiotic resistance in commensal bacteria is increasing with the production of extended-spectrum beta-lactamase. Therefore, this study was conducted to understand the status of fecal carriage of such enzyme producing Escherichia coli among health science students of seven different faculties of Institute of Medicine, Tribhuvan University. METHODS: This was a cross-sectional study conducted over six months among the health science students. One stool sample collected from each student was cultured and Escherichia coli isolates were identified, antibiotic sensitivity profile was produced, and extended-spectrum beta-lactamase production was detected following Clinical and Laboratory Standards Institute guidelines. RESULTS: A total of 156 students participated in the study, and Escherichia coli was isolated from all. Out of the total 156 Escherichia coli isolates, 11.5% were extended-spectrum beta-lactamase-producers and 14.7% were multidrug-resistant. The highest rate of fecal carriage of extended-spectrum beta-lactamase-producing Escherichia coli was found among Bachelor of Medicine and Bachelor of Surgery students (17.5%) and Bachelor of Science in Medical Imaging Technology (16.7%) students. Such enzyme producing Escherichia coli was found in the range of 6.9% to 25.0% among second- to fifth-year students. A significant number of extended-spectrum beta-lactamase-producing isolates were resistant to ciprofloxacin and gentamicin, apart from other extended-spectrum beta-lactamase substrate antibiotics, when compared with non-producers. CONCLUSIONS: A high rate of extended-spectrum beta-lactamase-producing Escherichia coli was detected from the gut of healthy health science students which indicates their possible dissemination throughout the wider community resulting in potential outbreak of infections caused by such organisms.

Comparative study of Amsel's criteria and Nugent scoring for diagnosis of bacterial vaginosis in a tertiary care hospital, Nepal.

BACKGROUND: The most common pathological cause of abnormal vaginal discharge in reproductive-aged women is bacterial vaginosis (BV). Amsel's criteria and Nugent scoring systems are commonly employed approaches for the diagnosis of BV. Despite the Nugent scoring system being the gold standard method for diagnosing BV, Amsel's criteria are generally preferred in clinical setup owing to the fact Nugent scoring requires considerable time and expert microscopist. This study was conducted to determine the diagnostic value of Amsel's criteria by comparing it with the Nugent scoring system. METHODS: This was a descriptive cross-sectional study conducted at Tribhuvan University Teaching Hospital, Nepal from October 2016 to September 2017. Vaginal specimens were collected from a total of 141 women presenting with abnormal vaginal discharge. The sensitivity, specificity, positive predictive value, and negative predictive value of Amsel's criteria were calculated, and each component of Amsel's criteria was compared to the Nugent scoring system. RESULTS: The sensitivity, specificity, positive predictive value, and negative predictive value of Amsel's criteria were 50%, 98.2%, 87.5%, and 88.8% respectively. The clue cells showed 100% specificity and vaginal discharge with pH > 4.5 had 89.3% sensitivity while compared with Nugent's scoring system. CONCLUSIONS: Amsel's criteria can be used as an adjunct method to Nugent scoring for the diagnosis of BV in the hands of skilled manpower in resources limited countries. The presence of clue cell and positive whiff test of Amsel's criteria shows good match with Nugent's score.

Biofilm Formation by Pathogens Causing Ventilator-Associated Pneumonia at Intensive Care Units in a Tertiary Care Hospital: An Armor for Refuge.

BACKGROUND: Emerging threat of drug resistance among pathogens causing ventilator-associated pneumonia (VAP) has resulted in higher hospital costs, longer hospital stays, and increased hospital mortality. Biofilms in the endotracheal tube of ventilated patients act as protective shield from host immunity. They induce chronic and recurrent infections that defy common antibiotics. This study intended to determine the biofilm produced by pathogens causing VAP and their relation with drug resistance. METHODS: Bronchoalveolar lavage and deep tracheal aspirates (n = 70) were obtained from the patients mechanically ventilated for more than 48 hours in the intensive care units of Tribhuvan University Teaching Hospital, Kathmandu, and processed according to the protocol of the American Society for Microbiology (ASM). Antibiotic susceptibility testing was done following Clinical and Laboratory Standards Institute (CLSI) 2017 guidelines. Biofilm formation was determined using the microtiter plate method described by Christensen and modified by Stepanovoic et al. RESULTS: Significant microbial growth was seen in 78.6% of the total samples with 52.7% monomicrobial, 45.5% polymicrobial, and 1.8% fungal infection. Among the 71 isolates obtained, bulk was gram-negative (n = 64, 90.1%). Pseudomonas aeruginosa (31.0%) was the predominant isolate followed by Acinetobacter calcoaceticus baumannii complex (16.9%), Klebsiella pneumoniae (16.9%), Citrobacter freundii (15.5%), Staphylococcus aureus (7.0%), Escherichia coli (5.6%), Citrobacter koseri (2.8%), Enterococcus faecalis (1.4%), Burkholderia cepacia complex (1.4%), and Candida albicans (1.4%). Of the total isolates, 56.3% were biofilm producers. Multidrug-resistant (MDR) organisms, extended-spectrum ß-lactamase (ESBL), and metallo-ß-lactamase (MBL) producers were preeminent among the biofilm producers. The highest producer of biofilm was P. aeruginosa (19.7%). Among gram-negative biofilm producers, 42.2% were MDR, 21.9% were ESBL producers, and 7.8% were MBL producers. CONCLUSION: Gram-negative nonfermenter bacteria account for the bulk of nosocomial pneumonia. MDR, ESBL, and MBL production was preponderant among the biofilm producers. The rampant spread of drug resistance among biofilm producers is summoning novel interventions to combat multidrug resistance.

Scrub Typhus and Molecular Characterization of Orientia tsutsugamushi from Central Nepal.

Scrub typhus is a vector-borne, acute febrile illness caused by Orientia tsutsugamushi. Scrub typhus continues to be an important but neglected tropical disease in Nepal. Information on this pathogen in Nepal is limited to serological surveys with little information available on molecular methods to detect O. tsutsugamushi. Limited information exists on the genetic diversity of this pathogen. A total of 282 blood samples were obtained from patients with suspected scrub typhus from central Nepal and 84 (30%) were positive for O. tsutsugamushi by 16S rRNA qPCR. Positive samples were further subjected to 56 kDa and 47 kDa molecular typing and molecularly compared to other O. tsutsugamushi strains. Phylogenetic analysis revealed that Nepalese O. tsutsugamushi strains largely cluster together and cluster away from other O. tsutsugamushi strains from Asia and elsewhere. One exception was the sample of Nepal_1, with its partial 56 kDa sequence clustering more closely with non-Nepalese O. tsutsugamushi 56 kDa sequences, potentially indicating that homologous recombination may influence the genetic diversity of strains in this region. Knowledge on the circulating strains in Nepal is important to the development of diagnostic tests and vaccines to support public health measures to control scrub typhus in this country.

Circulating Genotypes of Rotavirus Prior to Rotarix?vaccine Introduction in Kathmandu, Nepal.

BACKGROUND: In Nepal, it is estimated that about 3 million children under 5 years of age are prone to diarrhea and previous studies have shown rotavirus as the major etiological agent. Given the high burden of rotavirus, Rotarix® vaccine was introduced in the national immunization schedule in July 2020. This study was carried out in a tertiary health center from January- September 2018 to determine the burden of rotavirus diarrhea as well as genotypic variations in the circulating virus prior to vaccine introduction in Kathmandu, Nepal. METHODS: Hospital based cross sectional study was conducted among children less than 5 years of age attending Kanti Children's Hospital. Rotavirus antigen detection was performed by enzyme immunoassay using ProSpecT Rotavirus Microplate Assay. Rotavirus A positive samples were further confirmed by genotyping using Reverse-Transcription Polymerase Chain Reaction. RESULTS: A total of 530 children that included 184 males and 346 females were enrolled in this study. Rotavirus antigen was detected in 112 (21.1%) stool samples. Of the total 112 positive EIA stool samples that were genotyped, G12P[6] (30.3%) was found to be the most common type, followed by G3P[8] (26.8%), mixed type (14.3%), and G1P[6] (13.4%). CONCLUSIONS: Continued surveillance should be carried out nationwide in Nepal to understand the effectiveness of the vaccination program and to report any new trends in the circulating genotypes.

Flocculation of Microcystis unicells induced by pH regulation: Mechanism and potential application.

In water treatment process, Microcystis colonies can be effectively removed by coagulants. However, the use of popular coagulants could cause adverse health effects in humans or increase the amount of sludge. Meanwhile, Microcystis unicells are much more difficult to remove than colonies, due to their small size and dispersed distribution. This study proposed and analyzed the flocculation of Microcystis unicells induced by pH regulation. The particle size, zeta potential, cell viability and integrity, cytochemical changes, and cell-to-cell connections were recorded during pH regulation. Results showed that when pH was adjusted in the range of 2.5 to 2 by HCl (1.2 M), Microcystis unicells aggregated to form flocs as large as 28 µm, which are easy to remove by filtration or sedimentation. The overwhelming majority of cells were intact and inactivated in the optimal pH range (2.5-2). Thus, pH regulation is an environment-friendly and cost-effective method to remove Microcystis unicells, which can be potentially applied to water treatment.

Bacteria on Medical Professionals' White Coats in a University Hospital.

The transient contamination of medical professional's attires including white coats is one of the major vehicles for the horizontal transmission of microorganisms in the hospital environment. This study was carried out to determine the degree of contamination by bacterial agents on the white coats in a tertiary care hospital in Nepal. Sterilized uniforms with fabric patches of 10 cm × 15 cm size attached to the right and left pockets were distributed to 12 nurses of six different wards of a teaching hospital at the beginning of their work shift. Worn coats were collected at the end of the shifts and the patches were subjected for total bacterial count and identification of selected bacterial pathogens, as prioritized by the World Health Organization (WHO). Fifty percent of the sampled swatches were found to be contaminated by pathogenic bacteria. The average colony growth per square inch of the patch was 524 and 857 during first and second workdays, respectively, indicating an increase of 63.6% in colony counts. The pathogens detected on patches were Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter sp. Additional bacteria identified included Bacillus sp., Micrococcus sp., and coagulase-negative staphylococci (CoNS). The nurses working in the maternity department had their white coats highly contaminated with bacteria. On the other hand, the least bacterial contamination was recorded from the nurses of the surgery ward. One S. aureus isolate from the maternity ward was resistant to methicillin. This study showed that pathogens belonging to the WHO list of critical priority and high priority have been isolated from white coats of nurses, thus posing the risk of transmission to patients. White coats must be worn, maintained, and washed properly to reduce bacterial contamination load and to prevent cross-contamination of potential superbugs. The practice of wearing white coats outside the healthcare zone should be strictly discouraged.

Pax4 Gene Delivery Improves Islet Transplantation Efficacy by Promoting ß Cell Survival and α-to-ß Cell Transdifferentiation.

The transcription factor Pax4 plays an essential role in the development of insulin-producing ß cells in pancreatic islets. Ectopic Pax4 expression not only promotes ß cell survival but also induces α-to-ß cell transdifferentiation. This dual functionality of Pax4 makes it an appealing therapeutic target for the treatment of insulin-deficient type 1 diabetes (T1D). In this study, we demonstrated that Pax4 gene delivery by an adenoviral vector, Ad5.Pax4, improved ß cell function of mouse and human islets by promoting islet cell survival and α-to-ß cell transdifferentiation, as assessed by multiple viability assays and lineage-tracing analysis. We then explored the therapeutic benefits of Pax4 gene delivery in the context of islet transplantation using T1D mouse models. Both mouse-to-mouse and human-to-mouse islet transplantation, via either kidney capsule or portal vein, were examined. In all settings, Ad5.Pax4-treated donor islets (mouse or human) showed substantially better therapeutic outcomes. These results suggest that Pax4 gene delivery into donor islets may be considered as an adjunct therapy for islet transplantation, which can either improve the therapeutic outcome of islet transplantation using the same amount of donor islets or allow the use of fewer donor islets to achieve normoglycemia.

Role of Death Receptors-associated Lipid Rafts in Oxaliplatin-induced Death Mode Regulation of HepG2 Cells.

BACKGROUND/AIM: We previously showed that oxaliplatin induces necrotic-like cell death in hepatocarcinomas, and combination with ursodexoycholic acid (UDCA) significantly shifts the necrotic-like death to apoptosis. Since cell death mode is crucial on inflammatory responses and chemotherapeutic efficacy, the mechanism underlying determination of cell death mode by UDCA was investigated in this study. MATERIALS AND METHODS: Apoptosis or necrosis was determined by apoptotic body formation, caspase-8 activity, LDH release and PI inclusion. The involvement of lipid rafts and death receptors was examined by rafts fractionation, confocal microscopy and gene silencing assays. RESULTS: UDCA combination enhanced recruitment of death receptors and adaptors into cholesterol-enriched lipid rafts, and induced a stronger raft clustering. Lipid raft disruption decreased the UDCA/oxaliplatin-mediated apoptosis and increased necrotic-like death. CONCLUSION: UDCA promotes lipid raft localization of multiple death receptors, thereby contributing to a shift of cell death mode from oxaliplatin-induced necrotic death to apoptosis in HepG2 cells.

KLF7 promotes pancreatic cancer growth and metastasis by up-regulating ISG expression and maintaining Golgi complex integrity.

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with a dismal prognosis. Currently, there is no effective therapy for PDAC, and a detailed molecular and functional evaluation of PDACs is needed to identify and develop better therapeutic strategies. Here we show that the transcription factor Krüppel-like factor 7 (KLF7) is overexpressed in PDACs, and that inhibition of KLF7 blocks PDAC tumor growth and metastasis in cell culture and in mice. KLF7 expression in PDACs can be up-regulated due to activation of a MAP kinase pathway or inactivation of the tumor suppressor p53, two alterations that occur in a large majority of PDACs. ShRNA-mediated knockdown of KLF7 inhibits the expression of IFN-stimulated genes (ISGs), which are necessary for KLF7-mediated PDAC tumor growth and metastasis. KLF7 knockdown also results in the down-regulation of Discs Large MAGUK Scaffold Protein 3 (DLG3), resulting in Golgi complex fragmentation, and reduced protein glycosylation, leading to reduced secretion of cancer-promoting growth factors, such as chemokines. Genetic or pharmacologic activation of Golgi complex fragmentation blocks PDAC growth and metastasis similar to KLF7 inhibition. Our results demonstrate a therapeutically amenable, KLF7-driven pathway that promotes PDAC growth and metastasis by activating ISGs and maintaining Golgi complex integrity.

Loss of HAT1 expression confers BRAFV600E inhibitor resistance to melanoma cells by activating MAPK signaling via IGF1R.

BRAF inhibitors (BRAFi) have been approved for the clinical treatment of BRAF-mutant metastatic melanoma. Although initial responses to BRAFi are generally favorable, acquired BRAFi resistance emerges rapidly, resulting in treatment failure. Only some of the underlying mechanisms responsible for BRAFi resistance are currently understood. Here, we showed that the genetic inhibition of histone acetyltransferase 1 (HAT1) in BRAF-mutant melanoma cells resulted in BRAFi resistance. Using quantitative immunofluorescence analysis of patient sample pairs, consisting of pre-treatment along with matched progressed BRAFi + MEKi-treated melanoma samples, HAT1 downregulation was observed in 7/11 progressed samples (~63%) in comparison with pre-treated samples. Employing NanoString-based nCounter PanCancer Pathway Panel-based gene expression analysis, we identified increased MAPK, Ras, transforming growth factor (TGF)-ß, and Wnt pathway activation in HAT1 expression inhibited cells. We further found that MAPK pathway activation following the loss of HAT1 expression was partially driven by increased insulin growth factor 1 receptor (IGF1R) signaling. We showed that both MAPK and IGF1R pathway inhibition, using the ERK inhibitor SCH772984 and the IGF1R inhibitor BMS-754807, respectively, restored BRAFi sensitivity in melanoma cells lacking HAT1. Collectively, we show that the loss of HAT1 expression confers acquired BRAFi resistance by activating the MAPK signaling pathway via IGF1R.

Diagnostic evaluation of IgM ELISA and IgM Immunofluorescence assay for the diagnosis of Acute Scrub Typhus in central Nepal.

BACKGROUND: Scrub typhus is an acute febrile illness caused by the obligate intracellular bacterium, Orientia tsutsugamushi. Immunochromatography (ICT) and IgM ELISA are two of the routinely employed antibody based assays for diagnosis of Scrub typhus fever in Nepal, although the recommended gold standard diagnostic test is IgM Immunofluorescence assay (IFA). This study evaluated InBios Scrub Typhus Detect™ Immunoglobulin M (IgM) ELISA and IgM Immunofluorescence assays in single serum sample at the time of admission. METHOD: Study participants (1585 suspected cases), were enrolled based on acute febrile illness with suspected scrub typhus cases in central Nepal. Blood sample was collected from the suspected patients of scrub typhus, presenting with acute febrile illness. IgM antibody to Orientia tsusugamushi was detected by using Scrub Typhus Detect™ Kit and an in-house IgM IFA. The IFA assay was performed with the Gilliam, Karp, Kato strains and O. chuto antigens following the ARRL protocol. RESULT: Statistical analysis of IgM ELISA results when compared to reference test, IgM IFA results demonstrated the following characteristics, sensitivity 84.0% (95%CI: 79.73-87.68%), specificity 94.82% (95% CI: 93.43-95.99%), positive likelihood ratio 16.21% (95% CI: 12.71-20.67%), negative likelihood ratio 0.17% (95% CI: 0.13-0.21%), disease prevalence 22.08% (95% CI: 20.06 -24.21%), positive predictive value 82.12% (95% CI: 78.28-85.42%) and negative predictive value 95.44% (95% CI: 94.27-96.38%) respectively. CONCLUSION: Although IgM IFA is considered the gold standard test for the diagnosis of scrub typhus cases, it is relatively expensive, requires trained personal and a microscope with fluorescence filters. Scrub typhus IgM ELISA may be the best alternative test and possible viable option for resource limited endemic countries like Nepal.

Effects of light color on interspecific competition between Microcystis aeruginosa and Chlorella pyrenoidosa in batch experiment.

In lakes, suspended inorganic particles and dissolved substance are able to absorb or scatter different light wavelengths, leading to the changes of underwater light spectra which are highly related to the water quality. In turn, such changes could form environmental filtering for phytoplankton community to select particular algal populations via intensive competition for light resources. As an example, eutrophic lakes where underwater light spectra changed dramatically have a result of cyanobacterial blooms. In this study, in order to test the effect of light spectrum on growth and competition of green algae and cyanobacteria, Chlorella pyrenoidosa (a common green alga) and Microcystis aeruginosa (a bloom-forming cyanobacterium) grew and competed under three light colors: white (400-700 nm), red (620-700 nm), and blue (410-490 nm) light. Mono- and co-cultured systems were designed and population dynamics of the two species were monitored. The Lotka-Volterra model was used to quantify interspecific competition. Moreover, their photosynthetic activities were measured in mono-cultures. Results showed that in mono-cultures, red light was more favorable for M. aeruginosa, while blue light promoted the growth of C. pyrenoidosa. In co-cultures, M. aeruginosa won in red light and white light, while C. pyrenoidosa dominated under blue light. Light color mainly affected the absorption flux of reaction center (ABS/RC) in photosynthetic system II (PSII) and its potential photosynthetic capacity (Fv/Fm). Fv/Fm of M. aeruginosa in red light (or C. pyrenoidosa in blue light) was significantly enhanced. This study revealed that light color showed a significant influence on interspecific competition between green algae and cyanobacteria, which offers new insights into the dominance establishment and bloom formation of Microcystis.

Characterization of Microcystis morphotypes: Implications for colony formation and intraspecific variation.

Groundworks on Microcystis colony formation and morphological variation are critical to understanding the whole eco-cycle of Microcystis blooms. In this study, we tested the cell adhesion effect, an important pathway for colony formation, among Microcystis colonies of different morphotypes, and examined the potential linkage between cell properties and morphological plasticity. Results showed that cell adhesion significantly contributed to the aggregation of Microcystis colonies, but such adhesion only occurred in colonies belonging to the same morphotype. This suggests that Microcystis cannot form large colonies through a direct adhesion effect among different morphotypes, possibly due to substantial differences in the chemical structures and compositions of their extracellular polymeric substances (EPS). Cell functional features also varied substantially with morphotypes, implying high intraspecific variation in competitive and defensive strategies of Microcystis. Our results offer new insights into colony formation of Microcystis and substantiate the importance of fundamental chemical characteristics of EPS in determining the morphological plasticity.

Effects of nitrogen on interspecific competition between two cell-size cyanobacteria: Microcystis aeruginosa and Synechococcus sp.

Micro-cyanobacteria and pico-cyanobacteria coexist in many lakes throughout the world. Their distinct cell sizes and nutrient utilization strategies may lead to dominance of one over the other at varying nutrient levels. In this study, Microcystis aeruginosa and Synechococcus sp. were chosen as representative organisms of micro- and pico-cyanobacteria, respectively. A series of nitrate and ammonia conditions (0.02, 0.1, 0.5, and 2.5 mg N L-1) were designed in mono- or co-cultured systems, respectively. Growth rates of the two species were calculated and fitted by the Monod and Logistic equations. Furthermore, the interspecific competition was analyzed using the Lotka-Volterra model. In mono-cultures, the two cyanobacteria displayed faster growth rates in ammonia than in nitrate. Meanwhile, Synechococcus sp. showed faster growth rates compared to M. aeruginosa in lower N groups (≤ 0.5 mg N L-1). However, in the highest nitrate treatment (2.5 mg N L-1), M. aeruginosa achieved much higher biomass and faster growth rates than Synechococcus sp.. In co-cultures, Synechococcus sp. dominated in the lowest N treatment (0.02 mg N L-1), but M. aeruginosa dominated under the highest nitrate condition (2.5 mg N L-1). Based on the analysis of Raman spectra of living cells in mono-cultures, nitrate (2.5 mg N L-1) upgraded the pigmentary contents of M. aeruginosa better than ammonia (2.5 mg N L-1), but nitrogen in different forms showed little effects on the pigments of Synechococcus sp.. Findings from this study can provide valuable information to predict cyanobacterial community succession and aquatic ecosystem stability.