Displaying publications 21 - 40 of 49 in total

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  1. Tee JY, Ng FL, Keng FS, Lee CW, Zhang B, Lin S, et al.
    iScience, 2024 Apr 19;27(4):109564.
    PMID: 38617563 DOI: 10.1016/j.isci.2024.109564
    The successful commercialization of algal biophotovoltaics (BPV) technology hinges upon a multifaceted approach, encompassing factors such as the development of a cost-efficient and highly conductive anode material. To address this issue, we developed an environmentally benign method of producing reduced graphene oxide (rGO), using concentrated Chlorella sp. UMACC 313 suspensions as the reducing agent. The produced rGO was subsequently coated on the carbon paper (rGO-CP) and used as the BPV device's anode. As a result, maximum power density was increased by 950% for Chlorella sp. UMACC 258 (0.210 mW m-2) and 781% for Synechococcus sp. UMACC 371 (0.555 mW m-2) compared to bare CP. The improved microalgae adhesion to the anode and improved electrical conductivity of rGO brought on by the effective removal of oxygen functional groups may be the causes of this. This study has demonstrated how microalgal-reduced GO may improve the efficiency of algal BPV for producing bioelectricity.
  2. Chau SC, Chong PS, Jin H, Tsui KC, Khairuddin S, Tse ACK, et al.
    Int J Mol Sci, 2023 Mar 23;24(7).
    PMID: 37047062 DOI: 10.3390/ijms24076089
    Cerebellar ataxia is a neurodegenerative disorder with no definitive treatment. Although previous study demonstrated the neuroprotective effects of Hericium erinaceus (H.E.), the mechanisms of H.E. treatment on the neuroinflammatory response, neurotransmission, and related metabolites remain largely unknown. We demonstrated that 3-AP rats treated with 25 mg/kg H.E. extracts had improved motor coordination and balance in the accelerated rotarod and rod tests. We showed that the H.E. treatment upregulated the expression of Tgfb1, Tgfb2, and Smad3 genes to levels comparable to those in the non-3-AP control group. Interestingly, we also observed a significant correlation between Tgfb2 gene expression and rod test performance in the 3-AP saline group, but not in the non-3-AP control or H.E.+3-AP groups, indicating a relationship between Tgfb2 gene expression and motor balance in the 3-AP rat model. Additionally, we also found that the H.E. treatment increased mitochondrial COX-IV protein expression and normalized dopamine-serotonin neurotransmission and metabolite levels in the cerebellum of the H.E.+3-AP group compared to the 3-AP saline group. In conclusion, our findings suggest that the H.E. treatment improved motor function in the 3-AP rat model, which was potentially mediated through neuroprotective mechanisms involving TGFB2-Smad3 signaling via normalization of neurotransmission and metabolic pathways.
  3. Sim EU, Chan SL, Ng KL, Lee CW, Narayanan K
    Dis Markers, 2016;2016:5179594.
    PMID: 28018022 DOI: 10.1155/2016/5179594
    Apart from their canonical role in ribosome biogenesis, there is increasing evidence of ribosomal protein genes' involvement in various cancers. A previous study by us revealed significant differential expression of three ribosomal protein genes (RPeL27, RPeL41, and RPeL43) between cell lines derived from tumor and normal nasopharyngeal epithelium. However, the results therein were based on a semiquantitative assay, thus preliminary in nature. Herein, we provide findings of a deeper analysis of these three genes in the context to nasopharyngeal carcinoma (NPC) tumorigenesis. Their expression patterns were analyzed in a more quantitative manner at transcript level. Their protein expression levels were also investigated. We showed results that are contrary to previous report. Rather than downregulation, these genes were significantly overexpressed in NPC cell lines compared to normal control at both transcript and protein levels. Nevertheless, their association with NPC has been established. Immunoprecipitation pulldown assays indicate the plausible interaction of either RPeL27 or RPeL43 with POTEE/TUBA1A and ACTB/ACTBL2 complexes. In addition, RPeL43 is shown to bind with MRAS and EIF2S1 proteins in a NPC cell line (HK1). Our findings support RPeL27, RPeL41, and RPeL43 as potential markers of NPC and provide insights into the interaction targets of RPeL27 and RPeL43 proteins.
  4. Chen Q, Lee CW, Sim EU, Narayanan K
    Hum Gene Ther Methods, 2014 Feb;25(1):40-7.
    PMID: 24134118 DOI: 10.1089/hgtb.2012.188
    Direct protein delivery into the cytosol of mammalian cells by invasive Escherichia coli (E. coli) bacterial vector will bypass the need to achieve nuclear entry and transcription of DNA, a major hurdle that is known to seriously limit gene transfer. The bacterial vector is induced to express the protein during its growth phase, before presentation for entry into mammalian cells and release of its content into the cellular environment. For this class of vector, crossing the plasma membrane becomes the primary step that determines the success of protein delivery. Yet, how the mechanics of protein expression within the vector affect its entry into the host is poorly understood. We found the vector's effectiveness to enter HeLa cells diminished together with its viability when phage N15 protelomerase (TelN) expression was induced continuously in the invasive E. coli despite producing an abundant amount of functional protein. By comparison, shorter induction, even as little as 3 hr, produced sufficient amounts of functional TelN and showed more effective invasion of HeLa cells, comparable to that of uninduced invasive E. coli. These results demonstrate that brief induction of protein expression during vector growth is essential for optimal entry into mammalian cells, an important step for achieving bacteria-mediated protein delivery.
  5. Lee CW, Lim JH, Heng PL, Marican NF, Narayanan K, Sim EUH, et al.
    Environ Monit Assess, 2020 Sep 25;192(10):660.
    PMID: 32975666 DOI: 10.1007/s10661-020-08625-3
    We sampled the Klang estuary during the inter-monsoon and northeast monsoon period (July-Nov 2011, Oct-Nov 2012), which coincided with higher rainfall and elevated Klang River flow. The increased freshwater inflow into the estuary resulted in water column stratification that was observed during both sampling periods. Dissolved oxygen (DO) dropped below 63 μM, and hypoxia was observed. Elevated river flow also transported dissolved inorganic nutrients, chlorophyll a and bacteria to the estuary. However, bacterial production did not correlate with DO concentration in this study. As hypoxia was probably not due to in situ heterotrophic processes, deoxygenated waters were probably from upstream. We surmised this as DO correlated with salinity (R2 = 0.664, df = 86, p  6.7 h), hypoxia could occur at the Klang estuary. Here, we presented a model that related riverine flow rate to the post-heavy rainfall hypoxia that explicated the episodic hypoxia at Klang estuary. As Klang estuary supports aquaculture and cockle culture, our results could help protect the aquaculture and cockle culture industry here.
  6. Akinsola RO, Lee CW, Sim EUH, Narayanan K
    Anal Biochem, 2021 03 01;616:114088.
    PMID: 33358938 DOI: 10.1016/j.ab.2020.114088
    Endosomal escape is considered a crucial barrier that needs to be overcome by integrin-mediated E. coli for gene delivery into mammalian cells. Bafilomycin, a potent inhibitor of the H+ proton pump commonly employed to lower endosomal pH, was evaluated as part of the E. coli protocol during delivery. We found an increase in green fluorescent protein expression up 6.9, 3.2, 5.0, 2.8, and 4.5 fold in HeLa, HEK-293, A549, HT1080, and MCF-7 respectively, compared to untreated cells. Our result showed for the first time that Inhibition of lysosomal V-ATPase enhances E. coli efficiency.
  7. Liu B, Lee CW, Bong CW, Wang AJ
    PeerJ, 2024;12:e16556.
    PMID: 38223759 DOI: 10.7717/peerj.16556
    BACKGROUND: Escherichia coli is a commonly used faecal indicator bacterium to assess the level of faecal contamination in aquatic habitats. However, extensive studies have reported that sediment acts as a natural reservoir of E. coli in the extraintestinal environment. E. coli can be released from the sediment, and this may lead to overestimating the level of faecal contamination during water quality surveillance. Thus, we aimed to investigate the effects of E. coli habitat transition from sediment to water on its abundance in the water column.

    METHODS: This study enumerated the abundance of E. coli in the water and sediment at five urban lakes in the Kuala Lumpur-Petaling Jaya area, state of Selangor, Malaysia. We developed a novel method for measuring habitat transition rate of sediment E. coli to the water column, and evaluated the effects of habitat transition on E. coli abundance in the water column after accounting for its decay in the water column.

    RESULTS: The abundance of E. coli in the sediment ranged from below detection to 12,000 cfu g-1, and was about one order higher than in the water column (1 to 2,300 cfu mL-1). The habitat transition rates ranged from 0.03 to 0.41 h-1. In contrast, the E. coli decay rates ranged from 0.02 to 0.16 h-1. In most cases (>80%), the habitat transition rates were higher than the decay rates in our study.

    DISCUSSION: Our study provided a possible explanation for the persistence of E. coli in tropical lakes. To the best of our knowledge, this is the first quantitative study on habitat transition of E. coli from sediments to water column.

  8. Lee CW, Ng AY, Bong CW, Narayanan K, Sim EU, Ng CC
    Water Res, 2011 Feb;45(4):1561-70.
    PMID: 21146847 DOI: 10.1016/j.watres.2010.11.025
    Using the size fractionation method, we measured the decay rates of Escherichia coli, Salmonella Typhi and Vibrio parahaemolyticus in the coastal waters of Peninsular Malaysia. The size fractions were total or unfiltered, <250 μm, <20 μm, <2 μm, <0.7 μm, <0.2 μm and <0.02 μm. We also carried out abiotic (inorganic nutrients) and biotic (bacterial abundance, production and protistan bacterivory) measurements at Port Dickson, Klang and Kuantan. Klang had highest nutrient concentrations whereas both bacterial production and protistan bacterivory rates were highest at Kuantan. We observed signs of protist-bacteria coupling via the following correlations: Protistan bacterivory-Bacterial Production: r = 0.773, df = 11, p < 0.01; Protist-Bacteria: r = 0.586, df = 12, p < 0.05. However none of the bacterial decay rates were correlated with the biotic variables measured. E. coli and Salmonella decay rates were generally higher in the larger fraction (>0.7 μm) than in the smaller fraction (<0.7 μm) suggesting the more important role played by protists. E. coli and Salmonella also decreased in the <0.02 μm fraction and suggested that these non-halophilic bacteria did not survive well in seawater. In contrast, Vibrio grew well in seawater. There was usually an increase in Vibrio after one day incubation. Our results confirmed that decay or loss rates of E. coli did not match that of Vibrio, and also did not correlate with Salmonella decay rates. However E. coli showed persistence where its decay rates were generally lower than Salmonella.
  9. Lee CW, Lim JH, Heng PL
    Environ Monit Assess, 2013 Dec;185(12):9697-704.
    PMID: 23748919 DOI: 10.1007/s10661-013-3283-3
    We sampled extensively (29 stations) at the Klang estuarine system over a 3-day scientific expedition. We measured physical and chemical variables (temperature, salinity, dissolved oxygen, total suspended solids, dissolved inorganic nutrients) and related them to the spatial distribution of phototrophic picoplankton (Ppico). Multivariate analysis of variance of the physicochemical variables showed the heterogeneity of the Klang estuarine system where the stations at each transect were significantly different (Rao's F₁₈, ₃₆ = 8.401, p < 0.001). Correlation analyses also showed that variables related to Ppico abundance and growth were mutually exclusive. Distribution of Ppico was best explained by the physical mixing between freshwater and seawater whereas Ppico growth was correlated with temperature.
  10. Du P, Liu X, Zhong G, Zhou Z, Thomes MW, Lee CW, et al.
    PMID: 32023897 DOI: 10.3390/ijerph17030889
    Southeast Asian countries including Malaysia play a major role in global drug trade and abuse. Use of amphetamine-type stimulants has increased in the past decade in Malaysia. This study aimed to apply wastewater-based epidemiology for the first time in Kuala Lumpur, Malaysia, to estimate the consumption of common illicit drugs in urban population. Influent wastewater samples were collected from two wastewater treatment plants in Kuala Lumpur in the summer of 2017. Concentrations of twenty-four drug biomarkers were analyzed for estimating drug consumption. Fourteen drug residues were detected with concentrations of up to 1640 ng/L. Among the monitored illicit drugs, 3,4-methylenedioxy-methamphetamine (MDMA) or ecstasy had the highest estimated per capita consumptions. Consumption and dose of amphetamine-type stimulants (methamphetamine and MDMA) were both an order of magnitude higher than those of opioids (heroin and codeine, methadone and tramadol). Amphetamine-type stimulants were the most prevalent drugs, replacing opioids in the drug market. The prevalence trend measured by wastewater-based epidemiology data reflected the shift to amphetamine-type stimulants as reported by the Association of Southeast Asian Nations Narcotics Cooperation Center. Most of the undetected drug residues were new psychoactive substances (NPSs), suggesting a low prevalence of NPSs in the drug market.
  11. Liew PS, Chen Q, Ng AWR, Chew YC, Ravin NV, Sim EUH, et al.
    Anal Biochem, 2019 10 15;583:113361.
    PMID: 31306622 DOI: 10.1016/j.ab.2019.113361
    Phage N15 protelomerase (TelN) cleaves double-stranded circular DNA containing a telomerase-occupancy-site (tos) and rejoins the resulting linear-ends to form closed-hairpin-telomeres in Escherichia coli (E. coli). Continued TelN expression is essential to support resolution of the linear structure. In mammalian cells, no enzyme with TelN-like activities has been found. In this work, we show that phage TelN, expressed transiently and stably in human and mouse cells, recapitulates its native activities in these exogenous environments. We found TelN to accurately resolve tos-DNA in vitro and in vivo within human and mouse cells into linear DNA-containing terminal telomeres that are resistant to RecBCD degradation, a hallmark of protelomerase processing. In stable cells, TelN activity was detectable for at least 60 days, which suggests the possibility of limited silencing of its expression. Correspondingly, linear plasmid containing a 100 kb human β-globin gene expressed for at least 120 h in non-β-globin-expressing mouse cells with TelN presence. Our results demonstrate TelN is able to cut and heal DNA as hairpin-telomeres within mammalian cells, providing a tool for creating novel structures by DNA resolution in these hosts. The TelN protelomerase may be useful for exploring novel technologies for genome interrogation and chromosome engineering.
  12. Wong YC, Ng AWR, Chen Q, Liew PS, Lee CW, Sim EUH, et al.
    ACS Synth Biol, 2023 Apr 21;12(4):909-921.
    PMID: 37026178 DOI: 10.1021/acssynbio.2c00580
    Bacteriophage N15 is the first virus known to deliver linear prophage into Escherichia coli. During its lysogenic cycle, N15 protelomerase (TelN) resolves its telomerase occupancy site (tos) into hairpin telomeres. This protects the N15 prophage from bacterial exonuclease degradation, enabling it to stably replicate as a linear plasmid in E. coli. Interestingly, purely proteinaceous TelN can retain phage DNA linearization and hairpin formation without involving host- or phage-derived intermediates or cofactors in the heterologous environment. This unique feature has led to the advent of synthetic linear DNA vector systems derived from the TelN-tos module for the genetic engineering of bacterial and mammalian cells. This review will focus on the development and advantages of N15-based novel cloning and expression vectors in the bacterial and mammalian environments. To date, N15 is the most widely exploited molecular tool for the development of linear vector systems, especially the production of therapeutically useful miniDNA vectors without a bacterial backbone. Compared to typical circular plasmids, linear N15-based plasmids display remarkable cloning fidelity in propagating unstable repetitive DNA sequences and large genomic fragments. Additionally, TelN-linearized vectors with the relevant origin of replication can replicate extrachromosomally and retain transgenes functionality in bacterial and mammalian cells without compromising host cell viability. Currently, this DNA linearization system has shown robust results in the development of gene delivery vehicles, DNA vaccines and engineering mammalian cells against infectious diseases or cancers, highlighting its multifaceted importance in genetic studies and gene medicine.
  13. Akinsola RO, Adewoyin M, Lee CW, Sim EU, Narayanan K
    Anal Biochem, 2021 12 01;634:114432.
    PMID: 34695391 DOI: 10.1016/j.ab.2021.114432
    Quantification of bacterial invasion into eukaryotic cells is a prerequisite to unfold the molecular mechanisms of this vector's function to obtain insights for improving its efficiency. Invasion is traditionally quantified by antibiotic protection assays that require dilution plating and counting of colony-forming units rescued from infected cells. However, to differentiate between attached and internalized bacteria vector, this assay requires supplementation by a time-consuming and tedious immunofluorescence staining, making it laborious and reduces its reliability and reproducibility. Here we describe a new red fluorescent protein (RFP)-based high-throughput and inexpensive method for tracking bacterial adherence and internalization through flow cytometry to provide a convenient and real-time quantification of bacterial invasiveness in a heterogeneous population of cells. We invaded MCF-7, A549, and HEK-293 cells with the E. coli vector and measured RFP using imaging flow cytometry. We found high cellular infection of up to 70.47% in MCF-7 compared to 27.4% and 26.2% in A549 and HEK-293 cells, respectively. The quantitative evaluation of internalized E. coli is rapid and cell-dependent, and it distinctively differentiates between attached and cytosolic bacteria while showing the degree of cellular invasiveness. This imaging flow cytometry approach can be applied broadly to study host-bacteria interaction.
  14. Osahor A, Deekonda K, Lee CW, Sim EU, Radu A, Narayanan K
    Anal Biochem, 2017 10 01;534:46-48.
    PMID: 28693990 DOI: 10.1016/j.ab.2017.07.008
    Sample preparation for scanning electron microscope analysis involves reagents and equipment that are expensive and often hazardous. Here we demonstrate a circumvention of Osmium tetroxide and critical point drying, greatly reducing the duration, complexity and cost of the process. We captured early stage interactions of invasive-bacteria and HeLa cells during the process of bacteria-mediated gene delivery and illustrate sufficient clarity can be obtained using this procedure to preserve and clearly visualize relevant cellular structures. This protocol is significantly cheaper and easier to adapt compared to conventional methods, and will allow routine preparation/viewing of eukaryotic or bacterial samples for basic morphological studies.
  15. Hung SK, Kou HW, Hsu KH, Wu CT, Lee CW, Leonard Goh ZN, et al.
    J Formos Med Assoc, 2021 Mar;120(3):997-1004.
    PMID: 32917483 DOI: 10.1016/j.jfma.2020.08.039
    BACKGROUND/PURPOSE: Splenic abscess is a life-threatening surgical emergency which requires early diagnosis and intervention to maximize patient outcomes. This can be achieved through accurate risk stratification in the emergency department (ED). Sarcopenia refers to an age-related loss of skeletal muscle mass and strength that is accompanied by major physiologic and clinical ramifications, and often signifies decreased physiologic reserves. It is associated with poor clinical outcomes in sepsis, acute respiratory failure, oncological surgery, and liver transplantation. This study evaluates the utility of sarcopenia as a radiological stratification tool to predict in-hospital mortality of splenic abscess patients in the ED. This will assist emergency physicians, internists and surgeons in rapid risk stratification, assessing treatment options, and communicating with family members.

    METHODS: 99 adult patients at four training and research hospitals who had undergone an abdominal contrast computed tomography scan in the ED with the final diagnosis of splenic abscess from January 2004 to November 2017 were recruited. Evaluation for sarcopenia was performed via calculating the psoas cross-sectional area at the level of the third lumbar vertebra and normalising for height, before checking it against pre-defined values. Univariate analyses were used to evaluate the differences between survivors and non-survivors. Sensitivity, specificity, and predictive values of the presence of sarcopenia in predicting in-hospital mortality were calculated. Kaplan-Meier methods, log-rank test, and Cox proportional hazards model were also performed to examine survival between groups with sarcopenia versus non-sarcopenia.

    RESULTS: Splenic abscess patients with sarcopenia were 7.56 times more at risk of in-hospital mortality than those without sarcopenia (multivariate-adjusted HR: 7.56; 95% CI: 1.55-36.93). Presence of sarcopenia was found to have 84.62% sensitivity and 96.49% negative predictive value in predicting mortality.

    CONCLUSION: Sarcopenia is associated with poor prognoses of in-hospital mortality in patients with splenic abscess presenting to the ED. We recommend its use in the ED to rapidly risk stratify and predict outcome to guide treatment strategies.

  16. Osahor AN, Tan CY, Sim EU, Lee CW, Narayanan K
    Anal Biochem, 2014 Oct 1;462:26-8.
    PMID: 24929088 DOI: 10.1016/j.ab.2014.05.030
    When recombineering bacterial artificial chromosomes (BACs), it is common practice to design the ends of the donor molecule with 50 bp of homology specifying its insertion site. We demonstrate that desired recombinants can be produced using intermolecular homologies as short as 15 bp. Although the use of shorter donor end regions decreases total recombinants by several fold, the frequency of recombinants with correctly inserted donor molecules was high enough for easy detection by simple polymerase chain reaction (PCR) screening. This observation may have important implications for the design of oligonucleotides for recombineering, including significant cost savings, especially for high-throughput projects that use large quantities of primers.
  17. Herr DR, Reolo MJ, Peh YX, Wang W, Lee CW, Rivera R, et al.
    Sci Rep, 2016 Apr 15;6:24541.
    PMID: 27080739 DOI: 10.1038/srep24541
    Ototoxic drugs, such as platinum-based chemotherapeutics, often lead to permanent hearing loss through apoptosis of neuroepithelial hair cells and afferent neurons of the cochlea. There is no approved therapy for preventing or reversing this process. Our previous studies identified a G protein-coupled receptor (GPCR), S1P2, as a potential mediator of otoprotection. We therefore sought to identify a pharmacological approach to prevent cochlear degeneration via activation of S1P2. The cochleae of S1pr2(-/-) knockout mice were evaluated for accumulation of reactive oxygen species (ROS) with a nitro blue tetrazolium (NBT) assay. This showed that loss of S1P2 results in accumulation of ROS that precedes progressive cochlear degeneration as previously reported. These findings were supported by in vitro cell-based assays to evaluate cell viability, induction of apoptosis, and accumulation of ROS following activation of S1P2 in the presence of cisplatin. We show for the first time, that activation of S1P2 with a selective receptor agonist increases cell viability and reduces cisplatin-mediated cell death by reducing ROS. Cumulatively, these results suggest that S1P2 may serve as a therapeutic target for attenuating cisplatin-mediated ototoxicity.
  18. Hu J, Pradit S, Loh PS, Chen Z, Guo C, Le TPQ, et al.
    Mar Pollut Bull, 2024 Jan 29;200:116064.
    PMID: 38290368 DOI: 10.1016/j.marpolbul.2024.116064
    Mangrove forests can help to mitigate climate change by storing a significant amount of carbon (C) in soils. Planted mangrove forests have been established to combat anthropogenic threats posed by climate change. However, the efficiency of planted forests in terms of soil organic carbon (SOC) storage and dynamics relative to that of natural forests is unclear. We assessed SOC and nutrient storage, SOC sources and drivers in a natural and a planted forest in southern Thailand. Although the planted forest stored more C and nutrients than the natural forest, the early-stage planted forest was not a strong sink relative to mudflat. Both forests were predominated by allochthonous organic C and nitrogen limited, with total nitrogen being a major driver of SOC in both cases. SOC showed a significant decline along land-to-sea and depth gradients as a result of soil texture, nutrient availability, and pH in the natural forest.
  19. Heng PL, Lim JH, Lee CW
    Environ Monit Assess, 2017 Mar;189(3):117.
    PMID: 28220442 DOI: 10.1007/s10661-017-5838-1
    Temporal variation of Synechococcus, its production (μ) and grazing loss (g) rates were studied for 2 years at nearshore stations, i.e. Port Dickson and Port Klang along the Straits of Malacca. Synechococcus abundance at Port Dickson (0.3-2.3 × 10(5) cell ml(-1)) was always higher than at Port Klang (0.3-7.1 × 10(4) cell ml(-1)) (p  0.25), but nutrient and light availability were important factors for their distribution. The relationship was modelled as log Synechococcus = 0.37Secchi - 0.01DIN + 4.52 where light availability (as Secchi disc depth) was a more important determinant. From a two-factorial experiment, nutrients were not significant for Synechococcus growth as in situ nutrient concentrations exceeded the threshold for saturated growth. However, light availability was important and elevated Synechococcus growth rates especially at Port Dickson (F = 5.94, p  0.30). In nearshore tropical waters, an estimated 69 % of Synechococcus production could be grazed.
  20. Lee CW, Bong CW, Hii YS
    Appl Environ Microbiol, 2009 Dec;75(24):7594-601.
    PMID: 19820145 DOI: 10.1128/AEM.01227-09
    We investigated the temporal variation of bacterial production, respiration, and growth efficiency in the tropical coastal waters of Peninsular Malaysia. We selected five stations including two estuaries and three coastal water stations. The temperature was relatively stable (averaging around 29.5 degrees C), whereas salinity was more variable in the estuaries. We also measured dissolved organic carbon and nitrogen (DOC and DON, respectively) concentrations. DOC generally ranged from 100 to 900 microM, whereas DON ranged from 0 to 32 microM. Bacterial respiration ranged from 0.5 to 3.2 microM O2 h(-1), whereas bacterial production ranged from 0.05 to 0.51 microM C h(-1). Bacterial growth efficiency was calculated as bacterial production/(bacterial production + respiration), and ranged from 0.02 to 0.40. Multiple correlation analyses revealed that bacterial production was dependent upon primary production (r2 = 0.169, df = 31, and P < 0.02) whereas bacterial respiration was dependent upon both substrate quality (i.e., DOC/DON ratio) (r2 = 0.137, df = 32, and P = 0.03) and temperature (r2 = 0.113, df = 36, and P = 0.04). Substrate quality was the most important factor (r2 = 0.119, df = 33, and P = 0.04) for the regulation of bacterial growth efficiency. Using bacterial growth efficiency values, the average bacterial carbon demand calculated was from 5.30 to 11.28 microM C h(-1). When the bacterial carbon demand was compared with primary productivity, we found that net heterotrophy was established at only two stations. The ratio of bacterial carbon demand to net primary production correlated significantly with bacterial growth efficiency (r2 = 0.341, df = 35, and P < 0.001). From nonlinear regression analysis, we found that net heterotrophy was established when bacterial growth efficiency was <0.08. Our study showed the extent of net heterotrophy in these waters and illustrated the importance of heterotrophic microbial processes in coastal aquatic food webs.
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