Facultative Anaerobic Conditions Research Articles

Recovery of nutrients from fish sludge to enhance the growth of microalga Chlorella sorokiniana CMBB276

Intensive aquaculture production generates large amounts of sludge. This waste could be considered as a potential source of nutrients that can be recovered and utilized. Little attention has been paid to nutrient recovery from fish sludge. In this study, bioconversion of sludge was evaluated in lab scale under anaerobic (AN), facultative anaerobic (FA) and aerobic (AE) conditions. After 40 days of fermentation, AN recovered the highest values of dissolved total nitrogen (82.7 mg L−1), while AE showed the highest dissolved total phosphorus (11.8 mg L−1) and the highest reduction of total suspended solids (36.0 %). Microbial analysis showed that AN exhibited a distinct bacterial community than that of FA and AE. Furthermore, C. sorokiniana grown in AN effluents collected after 12 days of fermentation achieved the highest biomass production (1.96 g L−1). These results suggest that AN has the best potential to recover nutrients from sludge for production of C. sorokiniana.

Enhancing microbial salt tolerance through low-voltage stimulation for improved p-chloronitrobenzene (p-CNB) removal in high-salinity wastewater

As an important raw material for the synthesis of chemical and pharmaceutical, hazardous carcinogen p-chloronitrobenzene (p-CNB) has been widely found in high-salinity wastewater which need to be treated carefully. Due to the high-salinity shock on microorganisms, conventional microbial treatment technologies usually show poor effluent quality. This study initially investigated the p-CNB removal performance of microorganisms stimulated by 1.2 V low-voltage in high-salinity wastewater under facultative anaerobic conditions and further revealed the enhanced mechanisms. The results showed that the p-CNB removal kinetic parameter kp-CNB in the electrostimulating microorganism reactor (EMR) increased by 104.37 % to 155.30 % compared to the microorganism reactor (MR) as the control group under the varying salinities (0–45 g/L NaCl). The secretion of extracellular polymeric substances (EPS) in halotolerant microorganisms mainly enhanced by 1.2 V voltage stimulation ranging from 0 g/L NaCl to 30 g/L NaCl. Protein concentration ratio of EMR to MR in loosely bound EPS achieved maximum value of 1.77 at the salinity of 15 g/L NaCl, and the same ratio in tightly bound EPS also peaked at 1.39 under the salinity of 30 g/L NaCl. At the salinity of 45 g/L NaCl, 1.2 V voltage stimulation mainly enhanced salt-in strategy of halotolerant microorganisms, and the intracellular Na+ and K+ concentration ratio of EMR to MR reached maximum and minimum values of 0.65 and 1.92, respectively. Furthermore, the results of microbial metagenomic and metatranscriptomic analysis showed the halotolerant microorganisms Pseudomonas_A and Nitratireductor with p-CNB removal ability were enriched significantly under 1.2 V voltage stimulation. And the gene expression of p-CNB removal, salt-in strategy and betaine transporter were enhanced under voltage stimulation at varying salinities. Our investigation provided a new solution which combined with 1.2 V voltage stimulation and halotolerant microorganisms for the treatment of high-salinity wastewater.

Performance evaluation of three constructed wetland-microbial fuel cell systems: wastewater treatment efficiency and electricity generation potential.

Constructed wetlands (CWs) have proven to be effective and environmentally friendly for removing pollutants, while microbial fuel cells (MFCs) offer the potential for electricity generation. Thus, this study evaluated the performance of three CW-MFC systems (zigzag, single-column, and triple-column continuous) for domestic wastewater treatment and electricity generation. Results showed that parallel connection of CW-MFCs significantly improved power generation compared to series connection. Additionally, using three copper wires to connect carbon fiber felt electrodes demonstrated superior pollutant capture capabilities compared to a single copper wire. During the 14-day testing period, the single-column system achieved the highest power density of 5.55 mW m-2, followed closely by the triple-column continuous system at 4.77 mW m-2. In contrast, the zigzag system exhibited a lower power density of 2.49 mW m-2. Interestingly, the implementation of facultative anaerobic conditions in the anode, along with the application of a plastic bag cover, facilitated the maintenance of anaerobic conditions in both the single-column and triple-column continuous systems. This resulted in increased power density and reduced internal resistance. In contrast, the zigzag system, with its larger surface area, aeration, and circulation, exhibited higher internal resistance and lower current dissipation. Despite its inferior electricity generation performance, the zigzag system demonstrated higher efficiency removal of chemical oxygen demand (COD), nitrate (NO3-), and phosphate (PO43-) than the single-column system. This can be attributed to the extended contact time, resulting in enhanced pollutant removal. Overall, the multi-column continuous system shows promise as a viable approach for simultaneous domestic wastewater treatment and electricity production, offering potential benefits for sustainable wastewater management.

Screening of skatole-degrading bacteria and control of human fecal odor by compound bacteria

PurposeThe biodegradation of skatole was used as a starting point in this study, and existing strains of degrading NH3 and H2S in the laboratory were combined to create a composite deodorant. The deodorization effect of the composite deodorant on human feces was investigated in order to provide a foundation for fecal odor gas treatment.MethodsSkatole-degrading bacteria were identified, degradation conditions were optimized, and skatole metabolites were identified using liquid chromatography-mass spectrometry (LC-MS). The skatole-degrading bacteria were combined with the existing strains of degrading NH3 and H2S in the laboratory to make a compound deodorizer, and the deodorizing effect of the compound deodorizer on fresh human feces and old human feces was compared. Liquid chromatography, specific sensors, and gas chromatography were used to determine the contents of skatole, NH3, H2S, and volatile organic compounds, and the microbial diversity was examined.ResultsMicrobial agents H and Y capable of utilizing skatole were screened out under aerobic and facultative anaerobic conditions, respectively. Within 48 h, the degradation rate of skatole by microbial agent Y was 88.52%. Following condition optimization, the optimum temperature for skatole degradation by microbial agent Y was 33 °C, and the optimum pH was 7. The main functional bacteria were Acinetobacter xiamenensis. The metabolites of skatole were determined by liquid chromatography-mass spectrometry (LC–MS), and six possible metabolites were found, including 3-aldehyde indole, 3-carboxyl indole, 1H-indole-2,3-dione, and 3-methyl indole pyruvate. The skatole-degrading bacteria Lactobacillus rhamnosus and Saccharomyces cerevisiae were then combined in proportion to form a composite deodorant. The 5-day degradation rate of skatole in the old manure group was 88.11%, while the 5-day degradation rate in the fresh manure group was 47.56%.ConclusionsThe compound microbial agent developed in this study has a solid deodorizing effect, particularly in the control of the odor of obsolete feces. The use of composite microbial agents can efficiently degrade skatole in human feces, providing a theoretical foundation for the use of microbial remediation in the actual world.Graphical

Utilization of bamboo as biorefinery feedstock: Co-production of xylo-oligosaccharide with succinic acid and lactic acid

Herein, we investigated the possibility of co-producing xylo-oligosaccharides (XOSs) from bamboo, as value-added products, along with succinic and lactic acids, as platform chemicals. Xylan was extracted from bamboo using the alkali method under mild conditions. From xylan, XOSs were produced by partial enzymatic hydrolysis at a conversion rate of 83.9%, and all reaction conditions resulted in similar degrees of polymerization. Hydrogen peroxide-acetic acid (HPAC) pretreatment effectively removed lignin from NaOH-treated bamboo, and the enzymatic hydrolytic yield of NaOH and HPAC-treated bamboo was 84.3% of the theoretical yield. The production of succinic and lactic acids from the hydrolysate resulted in conversion rates of approximately 63.2% and 91.3% of the theoretical yield using Corynebacterium glutamicum Δldh and Actinobacillus succinogenes, respectively, under facultative anaerobic conditions. This study demonstrates that bamboo has a high potential to produce value-added products using a biorefinery process and is an alternative resource for compounds typically derived from petroleum.

Single-step removal of calcium, fluoride, and phenol from contaminated water by Aquabacterium sp. CZ3 via facultative anaerobic microbially induced calcium precipitation: Kinetics, mechanism, and characterization

Confronting the complex contaminated water, Aquabacterium sp. CZ3 could perform microbially induced calcium precipitation (MICP) under facultative anaerobic condition using phenol as supplementary carbon source. Strain CZ3 exhibited a remarkable ability to remove nitrate, fluoride, calcium and phenol with removal rates of 100.00, 87.50, 66.24 and 100.00%, respectively. The Modified Gompertz model was used for kinetic analysis to determine the optimum conditions for denitrification and degradation of phenol. The mechanism of anaerobic MICP was enhanced by measuring the self-aggregation properties of the isolates. The mechanism of fluoride removal was identified as co-precipitation and adsorption by characterization analysis of the bioprecipitation. Furthermore, the changes in soluble metabolites under phenol stress explained the utilization of phenol as a co-substrate by microorganisms. This is a novel report on phenol degradation by anaerobic MICP, which provides a theoretical basis for expanding its practical application.

Abundance and characterization of microorganisms isolated from oil palm empty fruit bunches waste under aerobic, anaerobic, and facultative anaerobic conditions

Abstract. Dermiyati, Suharjo R, Telaumbanua M, Yosita R, Sari AW, Andayani AP. 2020. Abundance and characterization of microorganisms isolated from oil palm empty fruit bunches waste under aerobic, anaerobic, and facultative anaerobic conditions. Biodiversitas 21: 4213-4220. Increased production of palm oil causes an increase in oil palm empty fruit bunches waste, while the utilization of the waste has not been carried out optimally. Oil palm empty fruit bunches contain high cellulose content which promotes the development of various types of bacteria with different characteristics. This study was aimed to determine the abundance and the characterization of bacteria that were isolated from extract suspension of oil palm empty fruit bunches in the form of a local microorganism solution under aerobic, anaerobic, and facultative anaerobic conditions. For isolation, the oil palm empty fruit extract suspension was inoculated on media Plate Count Agar Peptone and bacterial abundance was determined. Various bacterial characterization test included bacterial morphology test in the form of color and shape of macroscopic isolates, gram test using KOH 3%, fermentative oxidative test, soft rot test on potato tubers, hypersensitivity test on tobacco plant leaves, and hypo virulent test which was indicated by the presence of symptoms of disease in cucumber sprouts and indicated in the disease severity index (DSI) was carried out. The results of local microorganism solution isolation from oil palm empty fruit bunches obtained as many as 220 bacterial isolates consisting of 84 isolates in aerobic condition, 68 isolates in anaerobic condition, and 68 isolates in facultative anaerobic condition. The highest bacterial abundance in aerobic conditions was equal to 285.60 x 1010 CFU mL-1. Each bacterial isolate had different characteristics. Most of the characteristics of bacteria were turbid white (34.55%), round (69.55%), gram-positive (76.36%), fermentative (89.55%), softrot negative (71.82%), hypersensitive negative (97.27%), and virulent (74.55%).

The characteristic and performance of reduced graphene oxide by marine bacterium Pseudoalteromonas sp. CF10-13

Reduced graphene oxide (rGO) has attracted enormous interest because of its excellent physicochemical properties compared to graphene oxide (GO). However, rGO applications are greatly restricted by the aggregation of graphene sheets, risks of sophisticated violent processes, environmental concerns, and high costs of GO reduction. In this study, a mild, eco-friendly, and simplified method for rGO material preparation was developed via a marine bacterium Pseudoalteromonas sp. CF10-13 (CF10-13) under facultative anaerobic conditions. Results showed that bacterial reduced graphene oxide (BRGO) had low oxygen content and decreased interlayer space (d-spacing 0.4 nm). The increased D band to G band ratio was 1.3 and a typical hexagonal crystal structure was observed. The prepared biocompatible three-dimensional hydrogel (BRGO balls) could decolorize both cationic dye (methyl blue) and azo dye (Congo red), with respective efficiencies of 87% and 92% and the equilibrium adsorptions were 72.5 mg/g and 76.0 mg/g at an initial dye concentration of 50 mg/L, respectively. This study provides one operable option for producing BRGO with better physicochemical properties with potential as a wastewater treatment method.

Effectiveness of bacterial attachment media to reduce organic matter from wastewater of catfish aquaculture

Sangkuriang catfish aquaculture produces waste in the form of organic matter from the remaining feed and metabolic waste. Previous study revealed that the organic matter found in the outlet part of the fishpond was three times higher than the inlet. The attempt to decrease organic matter in that study was performed using freshwater clam and Bacillus subtilis bacteria; however, the decrease was less than 80% within 5 days. This study aims to obtain a maximum decrease level of organic matter with the fastest time of degradation. The experimental method with a Completely Randomized Plot Design (Split Plot Design) was employed in this study. The primary treatments (main plot) were time while the sub-plot was the surface area of bacterial attachment media. The time was set within 72 hours with an observation interval of 12 hours. The areas of the attachment media were 25%, 50%, 75%, 100% of the surface diameter of the experimental pail. The attachment media used in this study was synthetic coir. The control treatment was done without the attachment media (0%). The experiment was conducted in a laboratory under a facultative anaerobic condition. The level of organic matter and the total of bacterial suspension (TPC) in the water were observed every 12 hours. Organic matter was measured using a KMnO4 oxidizer. The results study indicated that adhering 100% of the surface of the attachment media decreased organic matter by 93.7% within 72 hours (three days). The total bacteria in water media within 12 hours was 0.5x102 CFU/ml, while the total bacteria within 72 hours was 26x102 CFU/ml. It can be concluded that the utilization of the bacterial attachment media has accelerated the decrease of organic matter in the wastewater of Catfish aquaculture with a stable amount of bacterial suspension.

Degradation of rice straw at low temperature using a novel microbial consortium LTF-27 with efficient ability

In this study, a novel psychrotrophic lignocelluloses degrading microbial consortium LTF-27 was successfully obtained from cold perennial forest soil by successive enrichment culture under facultative anaerobic static conditions. The microbial consortium showed efficient degradation of rice straw, which cellulose, hemicelluloses and lignin lost 71.7%, 65.6% and 12.5% of its weigh, respectively, in 20 days at 15 °C. The predominant liquid products were acetic acid and butyric acid during degrading lignocellulose in anaerobic digestion (AD) process inoculated with the LTF-27. The consortium mainly composed of Parabacteroides, Alcaligenes, Lysinibacillus, Sphingobacterium, and Clostridium, along with some unclassified uncultured bacteria, indicating powerful synergistic interaction in AD process. A multi-species lignocellulolytic enzyme system working cooperatingly on lignocelluolse degradation was revealed by proteomics analysis of cellulose bound fraction of the crude extracellular enzyme, which provides key theoretical base for further exploration and application of LTF-27.

Effects of Air Injection on the Metabolic Activity of Emulsifier-Producing Bacteria from Oil Reservoirs

Oil emulsification is one of the major mechanisms for microbially enhanced oil recovery (MEOR). Although air injection is generally recommended for field trials of MEOR in China, its influence on the microbial community structure in oil reservoirs remains poorly understood, especially activation of emulsifier-producing bacteria. Herein, the effects of air injection on oil emulsification, nutrient consumption, oil properties, and microbial community structures were compared for activated cultures under four different oxygen content conditions: anaerobic, facultative anaerobic, intermittent aeration, and aerobic. The results showed that crude oil in aerobic and intermittent aeration cultures was emulsified effectively when nutrients were thoroughly depleted. The particle diameter of emulsified droplets was 4.74-10.02 μm. High-throughput sequencing results showed that Bacillus and Aeribacillus were effectively activated under aerobic and intermittent aeration conditions, while Tepidimicrobium and Coprothermobacter were activated under facultative anaerobic and anaerobic conditions. Real-time quantitative PCR results showed that the initial emulsifying effect was positively correlated with the abundance of Aeribacillus pallidus.

Biohydrogen Production by Antarctic Psychrotolerant Klebsiella sp. ABZ11.

Lower temperature biohydrogen production has always been attractive, due to the lower energy requirements. However, the slow metabolic rate of psychrotolerant biohydrogen-producing bacteria is a common problem that affects their biohydrogen yield. This study reports on the improved substrate synthesis and biohydrogen productivity by the psychrotolerant Klebsiella sp. strain ABZ11, isolated from Antarctic seawater sample. The isolate was screened for biohydrogen production at 30°C, under facultative anaerobic condition. The isolate is able to ferment glucose, fructose and sucrose with biohydrogen production rate and yield of 0.8 mol/l/h and 3.8 mol/g, respectively at 10 g/l glucose concentration. It also showed 74% carbohydrate uptake and 95% oxygen uptake ability, and a wide growth temperature range with optimum at 37°C. Klebsiella sp. ABZ11 has a short biohydrogen production lag phase, fast substrate uptake and is able to tolerate the presence of oxygen in the culture medium. Thus, the isolate has a potential to be used for lower temperature biohydrogen production process.

Microbial network of the carbonate precipitation process induced by microbial consortia and the potential application to crack healing in concrete

Current studies have employed various pure-cultures for improving concrete durability based on microbially induced carbonate precipitation (MICP). However, there have been very few reports concerned with microbial consortia, which could perform more complex tasks and be more robust in their resistance to environmental fluctuations. In this study, we constructed three microbial consortia that are capable of MICP under aerobic (AE), anaerobic (AN) and facultative anaerobic (FA) conditions. The results showed that AE consortia showed more positive effects on inorganic carbon conversion than AN and FA consortia. Pyrosequencing analysis showed that clear distinctions appeared in the community structure between different microbial consortia systems. Further investigation on microbial community networks revealed that the species in the three microbial consortia built thorough energetic and metabolic interaction networks regarding MICP, nitrate-reduction, bacterial endospores and fermentation communities. Crack-healing experiments showed that the selected cracks of the three consortia-based concrete specimens were almost completely healed in 28 days, which was consistent with the studies using pure cultures. Although the economic advantage might not be clear yet, this study highlights the potential implementation of microbial consortia on crack healing in concrete.

The use of constructed wetlands for the treatment of industrial wastewater

Abstract Constructed wetlands are characterized by specific conditions enabling simultaneous various physical and biochemical processes. This is the result of specific environment for the growth of microorganisms and hydrophytes (aquatic and semiaquatic plants) which are capable of living in aerobic, anaerobic and facultative anaerobic conditions. Their interaction contributes to the intensification of oxidation and reduction responsible for the removal and retention of pollutants. These processes are supported by sorption, sedimentation and assimilation. Thanks to these advantages, treatment wetland systems have been used in communal management for over 50 years. In recent years, thanks to its advantages, low operational costs and high removal efficiency, there is growing interest in the use of constructed wetlands for the treatment or pre-treatment of various types of industrial wastewater. The study analyzes current use of these facilities for the treatment of industrial wastewater in the world. The conditions of use and efficiency of pollutants removal from readily and slowly biodegradable wastewater, with special emphasis on specific and characteristic pollutants of particular industries were presented. The use of subsurface horizontal flow beds for the treatment of industrial wastewater, among others from crude oil processing, paper production, food industry including wineries and distillery, olive oil production and coffee processing was described. In Poland constructed wetlands are used for the treatment of sewage and sludge from milk processing in pilot scale or for dewatering of sewage sludge produced in municipal wastewater treatment plant treating domestic sewage with approximately 40% share of wastewater from dairy and fish industry. In all cases, constructed wetlands provided an appropriate level of treatment and in addition the so-called ecosystem service.

Bioleaching of Indian Ocean nodules with in situ iron precipitation by anaerobic Mn reducing consortia

In the present study selective iron-free extraction of Cu, Ni, Co and Mn from Indian Ocean manganese nodules by manganese reducing consortium is described. The consortium isolated from manganese ore mines of Joda, Odisha (India) and enriched with Indian Ocean manganese nodules was used for bioleaching under facultative anaerobic conditions in mineral salt media using organic carbon source. Bioleaching was carried out at 30°C without agitation. Recoveries of Mn, Ni and Co increased with time, while maximum Cu recovery occurred during the initial period followed by a decrease. A notable finding was that Fe dissolution remained extremely low, i.e. less than 42mgL−1 (3.0%), possibly due to in situ precipitation of iron. X-ray diffraction patterns of bioleach residues indicated formation of FePO4 and MnCO3 phases. Iron dissolution remained consistently low even with increasing pulp density and decreasing particle size. The Mn reducing consortia may thus help in selective leaching of Mn while preventing Fe from contaminating the leach liquor, which is desirable in downstream processing of metal production from Mn-nodule and ferromanganese ores.

Sequestration of Zn2+ from aqueous solution using Klebsiella pneumoniae: Batch kinetics and continuous studies

The present study was aimed to isolate, Klebsiella pneumoniae from activated sludge. It was used to remove Zn2+ from aqueous solution in batch and continuous modes. Batch study was conducted for 20–200mgL−1 of initial Zn2+ concentration to determine the optimum value of initial Zn2+ concentration. Batch bioremediation studies were also performed to determine the optimum values of solution pH, minimal salt medium (MSM) dosage, macronutrients amount, aerobic & facultative anaerobic conditions, temperature and inoculum volume. The optimum solution pH for the growth of K. pneumoniae was found as 7 for the Zn2+ bioremediation. The growth of K. pneumoniae was found optimum in aerobic condition and in the temperature range of 37–40°C. In continuous mode, the removal of Zn2+ from aqueous solution was investigated in a hybrid biofilter column packed with coal and compost as medium over a period of 60 days. K. pneumoniae was used as a potential metal removing agent. The maximum removal efficiency was obtained as 91.5% during phase II for 10mLmin−1 flow rate of Zn2+ and 20mgL−1 of Zn2+ inlet concentration. Biofilter column was run under shock loading conditions for 14days immediately after 60days of operation which revealed the stable nature of the column with fluctuating inputs. Field emission scanning electron microscopy with electron dispersive X-ray (FESEM-EDX) analysis confirmed the presence of Zn2+ and change in surface morphology after Zn2+ sorption on the outer surface of K. pneumoniae.

Sequential bioreduction–bioleaching and bioreduction–chemical leaching hybrid tests for enhanced copper recovery from a concentrator ball mill reject sample

Dumping of poor but metal containing industrial waste is associated with several environmental issues. Exposure of these wastes to the natural environment offers serious concerns for the mineral processing industries to utilize them for metal recovery and check environmental pollution. In the present study, a novel sequential bioreduction–bioleaching and bioreduction–chemical leaching route as a hybrid process is compared and discussed for the enhanced recovery of copper from an industrial concentrator plant ball milling unit rejected sample. A mixed consortium of metal reducing bacteria (DMRB) initially adapted to high Fe(III) concentrations was found to cause mineralogical/matrix alteration (possibly silicate weathering) including Fe(III) bioreduction in the sample and dissolute 29.73% copper during the first 35days under facultative anaerobic conditions. Sequential leaching of the bioreduced waste sample (generated from the first step) using a mixed meso-acidophilic bacterial consortium predominantly Acidithiobacillus ferrooxidans showed additional 28.72% copper dissolution within 2days using 1gL−1 Fe(II). On the other hand, a comparative chemical leaching of the same bioreduced sample using 0.5M H2SO4 yielded additional 32.17% copper within 4days of leaching and indicated better performance than the bioleaching tests.

A comprehensive study on the behavior of a novel bacterial strain Acinetobacter guillouiae for bioremediation of divalent copper

Biological methods have been successfully used to mitigate heavy metal pollution problem in wastewater. The present study was aimed towards isolation of a novel indigenous bacterial strain, Acinetobacter guillouiae from activated sludge and its subsequent application in remediation of copper (Cu(2+)) from aqueous solution. Kinetic study of bioremediation was performed for initial Cu(2+) concentrations ranging from 40 to 150mgL(-1). Optimum values of nutrient dosage, pH, macronutrients [Nitrogen (N)-Phosphorus (P)-Potassium (K)] dosage, aerobic and facultative anaerobic conditions, temperature, and inoculum volume were determined by conducting separate batch bioremediation studies at 80mgL(-1) initial concentration of Cu(2+). Kinetic study showed that A. guillouiae removed 98.7% Cu(2+) for 80mgL(-1) initial concentration of Cu(2+) after 16h at an optimum solution pH of 7.0. Results also revealed that A. guillouiae showed maximum growth at double the standard composition of N, P and standard composition of K in nutrient dosage. Experimental data obtained in present study were utilized to validate different growth kinetic models such as Monod, Powell, Haldane, Luong, and Edwards. Growth kinetics of A. guillouiae was better understood by Luong model (R (2)=0.97). Higher values of coefficient of determination (R (2)=0.97-0.99) confirmed the suitability of the three-half-order kinetic model for representing the Cu(2+) bioremediation. A. guillouiae showed a robust removal mechanism for the bioremediation of Cu(2+).

Bacterial Community Dynamics of Salted and Fermented Shrimp based on Denaturing Gradient Gel Electrophoresis

The Korean traditional seafood jeotgal is consumed directly or as an additive in other foods to improve flavor or fermentation efficiency. Saeujot, made from salted and fermented tiny shrimp (SFS; Acetes japonicus), is the best-selling jeotgal in Korea. In this study, we reveal the microbial diversity and dynamics in naturally fermented shrimp by denaturing gradient gel electrophoresis (DGGE). The population fingerprints of the predominant microbiota and its succession were generated by DGGE analysis of universal V3 16S rDNA polymerase chain reaction (PCR) amplicons. Overall, 17 strains were identified from sequencing of 30 DGGE bands. The DGGE profiles showed diverse bacterial populations in the sample, throughout the fermentation of SFS. Staphylococcus equorum, Halanaerobium saccharolyticum, Salimicrobium luteum, and Halomonas jeotgali were the dominant bacteria, and their levels steadily increased during the fermentation process. Certain other bacteria, such as Psychrobacter jeotgali and Halomonas alimentaria appeared during the early-fermentation process, while Alkalibacterium putridalgicola, Tetragenococcus muriaticus, and Salinicoccus jeotgali appeared during the late-fermentation process. The members of the order Bacillales were found to be predominant during the fermentation of SFS. Furthermore, S. equorum was identified as the dominant bacterial isolate by the traditional method of culturing under aerobic and facultative anaerobic conditions. We expect that this information will facilitate the design of autochthonous starter cultures for the production of SFS with desired characteristic sensory profiles and shorter ripening times.

Identification of genes essential for anaerobic growth of Listeria monocytogenes

The facultative anaerobic bacterium Listeria monocytogenes encounters microaerophilic or anaerobic conditions in various environments, e.g. in soil, in decaying plant material, in food products and in the host gut. To elucidate the adaptation of Listeria monocytogenes to variations in oxygen tension, global transcription analyses using DNA microarrays were performed. In total, 139 genes were found to be transcribed differently during aerobic and anaerobic growth; 111 genes were downregulated and 28 genes were upregulated anaerobically. The oxygen-dependent transcription of central metabolic genes is in agreement with results from earlier physiological studies. Of those genes more strongly expressed under lower oxygen tension, 20 were knocked out individually. Growth analysis of these knock out mutants did not indicate an essential function for the respective genes during anaerobiosis. However, even if not essential, transcriptional induction of several genes might optimize the bacterial fitness of Listeria monocytogenes in anaerobic niches, e.g. during colonization of the gut. For example, expression of the anaerobically upregulated gene lmo0355, encoding a fumarate reductase α chain, supported growth on 10 mM fumarate under anaerobic but not under aerobic growth conditions. Genes essential for anaerobic growth were identified by screening a mutant library. Eleven out of 1360 investigated mutants were sensitive to anaerobiosis. All 11 mutants were interrupted in the atp locus. These results were further confirmed by phenotypic analysis of respective in-frame deletion and complementation mutants, suggesting that the generation of a proton motive force via F1F0-ATPase is essential for anaerobic proliferation of Listeria monocytogenes.