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Applied Microbiology and Biotechnology (v.88, #3)

Lessons from the genomes of extremely acidophilic bacteria and archaea with special emphasis on bioleaching microorganisms by Juan Pablo Cárdenas; Jorge Valdés; Raquel Quatrini; Francisco Duarte; David S. Holmes (pp. 605-620).

This mini-review describes the current status of recent genome sequencing projects of extremely acidophilic microorganisms and highlights the most current scientific advances emerging from their analysis. There are now at least 56 draft or completely sequenced genomes of acidophiles including 30 bacteria and 26 archaea. There are also complete sequences for 38 plasmids, 29 viruses, and additional DNA sequence information of acidic environments is available from eight metagenomic projects. A special focus is provided on the genomics of acidophiles from industrial bioleaching operations. It is shown how this initial information provides a rich intellectual resource for microbiologists that has potential to open innovative and efficient research avenues. Examples presented illustrate the use of genomic information to construct preliminary models of metabolism of individual microorganisms. Most importantly, access to multiple genomes allows the prediction of metabolic and genetic interactions between members of the bioleaching microbial community (ecophysiology) and the investigation of major evolutionary trends that shape genome architecture and evolution. Despite these promising beginnings, a major conclusion is that the genome projects help focus attention on the tremendous effort still required to understand the biological principles that support life in extremely acidic environments, including those that might allow engineers to take appropriate action designed to improve the efficiency and rate of bioleaching and to protect the environment.

Keywords: Acidophiles; Genomics; Bioinformatics; Metabolic reconstruction; Ecophysiology

Biotechnological processes for biodiesel production using alternative oils by Laura Azócar; Gustavo Ciudad; Hermann J. Heipieper; Rodrigo Navia (pp. 621-636).

As biodiesel (fatty acid methyl ester (FAME)) is mainly produced from edible vegetable oils, crop soils are used for its production, increasing deforestation and producing a fuel more expensive than diesel. The use of waste lipids such as waste frying oils, waste fats, and soapstock has been proposed as low-cost alternative feedstocks. Non-edible oils such as jatropha, pongamia, and rubber seed oil are also economically attractive. In addition, microalgae, bacteria, yeast, and fungi with 20% or higher lipid content are oleaginous microorganisms known as single cell oil and have been proposed as feedstocks for FAME production. Alternative feedstocks are characterized by their elevated acid value due to the high level of free fatty acid (FFA) content, causing undesirable saponification reactions when an alkaline catalyst is used in the transesterification reaction. The production of soap consumes the conventional catalyst, diminishing FAME production yield and simultaneously preventing the effective separation of the produced FAME from the glycerin phase. These problems could be solved using biological catalysts, such as lipases or whole-cell catalysts, avoiding soap production as the FFAs are esterified to FAME. In addition, by-product glycerol can be easily recovered, and the purification of FAME is simplified using biological catalysts.

Keywords: Biodiesel; Waste lipids; Non-edible oils; Single cell oil; Lipase; Whole cell

Physiology and biochemistry of reduction of azo compounds by Shewanella strains relevant to electron transport chain by Yi-Guo Hong; Ji-Dong Gu (pp. 637-643).

Azo dyes are toxic, highly persistent, and ubiquitously distributed in the environments. The large-scale production and application of azo dyes result in serious environmental pollution of water and sediments. Bacterial azo reduction is an important process for removing this group of contaminants. Recent advances in this area of research reveal that azo reduction by Shewanella strains is coupled to the oxidation of electron donors and linked to the electron transport and energy conservation in the cell membrane. Up to date, several key molecular components involved in this reaction have been identified and the primary electron transportation system has been proposed. These new discoveries on the respiration pathways and electron transfer for bacterial azo reduction has potential biotechnological implications in cleaning up contaminated sites.

Keywords: Bacterial azo reduction; Electron transport chain; Physiology and biochemistry

Xanthophyllomyces dendrorhous for the industrial production of astaxanthin by Marta Rodríguez-Sáiz; Juan Luis de la Fuente; José Luis Barredo (pp. 645-658).

Astaxanthin is a red xanthophyll (oxygenated carotenoid) with large importance in the aquaculture, pharmaceutical, and food industries. The green alga Haematococcus pluvialis and the heterobasidiomycetous yeast Xanthophyllomyces dendrorhous are currently known as the main microorganisms useful for astaxanthin production at the industrial scale. The improvement of astaxanthin titer by microbial fermentation is a requirement to be competitive with the synthetic manufacture by chemical procedures, which at present is the major source in the market. In this review, we show how the isolation of new strains of X. dendrorhous from the environment, the selection of mutants by the classical methods of random mutation and screening, and the rational metabolic engineering, have provided improved strains with higher astaxanthin productivity. To reduce production costs and enhance competitiveness from an industrial point of view, low-cost raw materials from industrial and agricultural origin have been adopted to get the maximal astaxanthin productivity. Finally, fermentation parameters have been studied in depth, both at flask and fermenter scales, to get maximal astaxanthin titers of 4.7 mg/g dry cell matter (420 mg/l) when X. dendrorhous was fermented under continuous white light. The industrial scale-up of this biotechnological process will provide a cost-effective method, alternative to synthetic astaxanthin, for the commercial exploitation of the expensive astaxanthin (about $2,500 per kilogram of pure astaxanthin).

Keywords: Astaxanthin; Fermentation; Titer improvement; Industrial; Xanthophyllomyces dendrorhous

Clavulanic acid biosynthesis and genetic manipulation for its overproduction by Ju Yeon Song; Susan E. Jensen; Kye Joon Lee (pp. 659-669).

Clavulanic acid, a β-lactamase inhibitor, is used together with β-lactam antibiotics to create drug mixtures possessing potent antimicrobial activity. In view of the clinical and industrial importance of clavulanic acid, identification of the clavulanic acid biosynthetic pathway and the associated gene cluster(s) in the main producer species, Streptomyces clavuligerus, has been an intriguing research question. Clavulanic acid biosynthesis was revealed to involve an interesting mechanism common to all of the clavam metabolites produced by the organism, but different from that of other β-lactam compounds. Gene clusters involved in clavulanic acid biosynthesis in S. clavuligerus occupy large regions of nucleotide sequence in three loci of its genome. In this review, clavulanic acid biosynthesis and the associated gene clusters are discussed, and clavulanic acid improvement through genetic manipulation is explained.

Keywords: Clavulanic acid; Clavam; β-lactam antibiotics; Streptomyces clavuligerus

Succinic acid production from orange peel and wheat straw by batch fermentations of Fibrobacter succinogenes S85 by Qiang Li; Jose A. Siles; Ian P. Thompson (pp. 671-678).

Succinic acid is a platform molecule that has recently generated considerable interests. Production of succinate from waste orange peel and wheat straw by consolidated bioprocessing that combines cellulose hydrolysis and sugar fermentation, using a cellulolytic bacterium, Fibrobacter succinogenes S85, was studied. Orange peel contains d-limonene, which is a well-known antibacterial agent. Its effects on batch cultures of F. succinogenes S85 were examined. The minimal concentrations of limonene found to inhibit succinate and acetate generation and bacterial growth were 0.01%, 0.1%, and 0.06% (v/v), respectively. Both pre-treated orange peel by steam distillation to remove d-limonene and intact wheat straw were used as feedstocks. Increasing the substrate concentrations of both feedstocks, from 5 to 60 g/L, elevated succinate concentration and productivity but lowered the yield. In addition, pre-treated orange peel generated greater succinate productivities than wheat straw but had similar resultant titres. The greatest succinate titres were 1.9 and 2.0 g/L for pre-treated orange peel and wheat straw, respectively. This work demonstrated that agricultural waste such as wheat straw and orange peel can be biotransformed to succinic acid by a one-step consolidated bioprocessing. Measures to increase fermentation efficiency are also discussed.

Keywords: Succinic acid; Orange peel; Wheat straw; Fibrobacter succinogenes ; Bio-refinery

Isolation of basidiomycetous yeast Pseudozyma tsukubaensis and production of glycolipid biosurfactant, a diastereomer type of mannosylerythritol lipid-B by Tomotake Morita; Masako Takashima; Tokuma Fukuoka; Masaaki Konishi; Tomohiro Imura; Dai Kitamoto (pp. 679-688).

The producers of glycolipid biosurfactant, mannosylerythritol lipid-B (MEL-B), were isolated from leaves of Perilla frutescens on Ibaraki in Japan. Four isolates, 1D9, 1D10, 1D11, and 1E5, were identified as basidiomycetous yeast Pseudozyma tsukubaensis by rDNA sequence and biochemical properties. The structure of MEL-B produced by these strains was analyzed by ¹H nuclear magnetic resonance and gas chromatography–mass spectrometry methods, and was determined to be the same as the diastereomer MEL-B produced by P. tsukubaensis NBRC 1940. Of these isolates, P. tsukubaensis 1E5 (JCM 16987) is capable of producing the largest amount of the diastereomer MEL-B from vegetable oils. In order to progress the diastereomer MEL-B production by strain 1E5, factors affecting the production, such as carbon and organic nutrient sources, were further examined. Olive oil and yeast extract were the best carbon and nutrient sources, respectively. Under the optimal conditions, a maximum yield, productivity, and yield coefficient of 73.1 g/L, 10.4 g L⁻¹ day⁻¹, and 43.5 g/g were achieved by feeding of olive oil in a 5-L jar-fermenter culture using strain 1E5.

Keywords: Biosurfactant; Glycolipid; Mannosylerythritol lipid; Pseudozyma tsukubaensis ; Basidiomycetous yeast

Recombinant artificial forisomes provide ample quantities of smart biomaterials for use in technical devices by Boje Müller; Gundula A. Noll; Antonia M. Ernst; Boris Rüping; Sira Groscurth; Richard M. Twyman; Lawrence M. Kawchuk; Dirk Prüfer (pp. 689-698).

Forisomes are mechanoproteins that undergo ATP-independent contraction–expansion cycles triggered by divalent cations, pH changes, and electrical stimuli. Although native forisomes from Medicago truncatula comprise a number of subunits encoded by separate genes, here we show that at least two of those subunits (MtSEO1 and MtSEO4) can assemble into homomeric forisome bodies that are functionally similar to their native, multimeric counterparts. We expressed these subunits in plants and yeast, resulting in the purification of large quantities of artificial forisomes with unique characteristics depending on the expression platform. These artificial forisomes were able to contract and expand in vitro like native forisomes and could respond to electrical stimulation when immobilized between interdigital transducer electrodes. These results indicate that recombinant artificial forisomes with specific characteristics can be prepared in large amounts and used as components of microscale and nanoscale devices.

Keywords: Recombinant forisomes; Smart biomaterials; Sieve element occlusion; Yeast expression

Characterization of Xanthomonas campestris pv. campestris heat shock protein A (HspA), which possesses an intrinsic ability to reactivate inactivated proteins by Ching-Hsuan Lin; Chia-Ni Lee; Juey-Wen Lin; Wan-Ju Tsai; Szu-Wen Wang; Shu-Fen Weng; Yi-Hsiung Tseng (pp. 699-709).

hspA encodes a small heat shock protein (sHSP) in Xanthomonas campestris pv. campestris, the causative agent of black rot in cruciferous plants. In this study, two-dimensional gel electrophoresis, promoter activity assays, and Northern hybridization results revealed that HspA expression was induced by heat shock but not by other stresses, although low-level expression was detectable by reverse transcription-polymerase chain reaction (RT-PCR) under normal culture conditions. An hspA mutant exhibited reduced tolerance to heat, especially in the presence of MgSO₄, but no change in pathogenicity. Results of size-exclusion chromatography indicated that purified HspA_his, containing six C-terminal histidine residues, formed two different size classes of oligomeric complexes—410 and 820 kDa. In contrast, HspA_ter, the unmodified protein translated from the original hspA gene, formed only the 820-kDa complex. These results suggest that the C-terminus of HspA is important for oligomerization. Both HspA820_his and HspA410_his were able to partially protect luciferase against heat-induced aggregation. Unlike other reported sHSPs that commonly capture denaturing proteins in refoldable states until refolded by adenosine triphosphate-dependent chaperone systems, HspA_his alone was capable of reactivating heat-inactivated EcoRI. Thus, Xanthomonas campestris pv. campestris HspA has potential application as a protective agent during the storage of proteins.

Keywords: Small heat shock protein; Xanthomonas campestris ; HspA

Characterization of enzymes involved in the central metabolism of Gluconobacter oxydans by Bernadette Rauch; Jennifer Pahlke; Paul Schweiger; Uwe Deppenmeier (pp. 711-718).

Gluconobacter oxydans is an industrially important bacterium that lacks a complete Embden–Meyerhof pathway (glycolysis). The organism instead uses the pentose phosphate pathway to oxidize sugars and their phosphorylated intermediates. However, the lack of glycolysis limits the amount of NADH as electron donor for electron transport phosphorylation. It has been suggested that the pentose phosphate pathway contributes to NADH production. Six enzymes predicted to play central roles in intracellular glucose and gluconate flux were heterologously overproduced in Escherichia coli and characterized to investigate the intracellular flow of glucose and gluconates into the pentose phosphate pathway and to explore the contribution of the pentose phosphate pathway to NADH generation. The key pentose phosphate enzymes glucose 6-phosphate dehydrogenase (Gox0145) and 6-phosphogluconate dehydrogenase (Gox1705) had dual cofactor specificities but were physiologically NADP- and NAD-dependent, respectively. Putative glucose dehydrogenase (Gox2015) was NADP-dependent and exhibited a preference for mannose over glucose, whereas a 2-ketogluconate reductase (Gox0417) displayed dual cofactor specificity for NAD(P)H. Furthermore, a putative gluconokinase and a putative glucokinase were identified. The gluconokinase displayed high activities with gluconate and is thought to shuttle intracellular gluconate into the pentose phosphate pathway. A model for the trafficking of glucose and gluconates into the pentose phosphate pathway and its role in NADH generation is presented. The role of NADPH in chemiosmotic energy conservation is also discussed.

Keywords: Energy conservation; Pentose phosphate pathway; Respiratory chain; Acetic acid bacteria; Incomplete oxidation

Metabolic engineering of Escherichia coli to produce (2S, 3R, 4S)-4-hydroxyisoleucine by Sergey V. Smirnov; Tomohiro Kodera; Natalya N. Samsonova; Veronika А. Kotlyarovа; Natalya Yu Rushkevich; Аlexander D. Kivero; Pavel M. Sokolov; Makoto Hibi; Jun Ogawa; Sakayu Shimizu (pp. 719-726).

The stereo-specific l-isoleucine-4-hydroxylase (l-isoleucine dioxygenase (IDO)) was cloned and expressed in an Escherichia coli 2Δ strain lacking the activities of α-ketoglutarate dehydrogenase (EC 1.2.4.2), isocitrate liase (EC 4.1.3.1), and isocitrate dehydrogenase kinase/phosphatase (EC 2.7.11.5). The 2Δ strain could not grow in a minimal-salt/glucose/glycerol medium due to the blockage of TCA during succinate synthesis. The IDO activity in the 2Δ strain was able to “shunt” destroyed TCA, thereby coupling l-isoleucine hydroxylation and cell growth. Using this strain, we performed the direct biotransformation of l-isoleucine into 4-HIL with an 82% yield.

Keywords: 4-Hydroxyisoleucine; Diabetes; Dioxygenase; Biotransformation; Escherichia coli

Resveratrol content and expression of phenylalanine ammonia-lyase and stilbene synthase genes in rolC transgenic cell cultures of Vitis amurensis by Alexandra S. Dubrovina; Artem Y. Manyakhin; Yuri N. Zhuravlev; Konstantin V. Kiselev (pp. 727-736).

Resveratrol, a naturally occurring polyphenol, has been reported to exhibit a wide range of valuable biological and pharmacological properties. In the present investigation, we show that transformation of Vitis amurensis Rupr. with the oncogene rolC of Agrobacterium rhizogenes increased resveratrol production in the two transformed callus cultures 3.7 and 11.9 times. The rolC-transformed calli were capable of producing 0.099% and 0.144% dry weight of resveratrol. We characterized phenylalanine ammonia-lyase (PAL) and stilbene synthase (STS) gene expression in the two rolC transgenic callus cultures of V. amurensis. In the rolC transgenic culture with higher resveratrol content, expression of VaPAL3, VaSTS3, VaSTS4, VaSTS5, VaSTS6, VaSTS8, VaSTS9, and VaSTS10 was increased; while in the rolC culture with lower resveratrol content, expression of VaPAL3 and VaSTS9 was increased. We suggest that transformation of V. amurensis calli with the rolС gene induced resveratrol accumulation via selective enhancement of expression of individual PAL and STS genes involved in resveratrol biosynthesis. We compared the data on PAL and STS gene expression in rolC transgenic calli with the previously obtained results for rolB transgenic calli of V. amurensis. We propose that the transformation of V. amurensis with the rolC and rolB genes of A. rhizogenes increased resveratrol accumulation through different regulatory pathways.

Keywords: Callus culture; Resveratrol; rolС ; PAL ; STS ; Vitis amurensis

Transcriptional response of the catharanthine biosynthesis pathway to methyl jasmonate/nitric oxide elicitation in Catharanthus roseus hairy root culture by Mei-Liang Zhou; Xue-Mei Zhu; Ji-Rong Shao; Yan-Min Wu; Yi-Xiong Tang (pp. 737-750).

Jasmonates and nitric oxide (NO) play important roles in the regulation of the signaling network leading to the biosynthesis of plant secondary metabolites. In this work, we explore the effect of constitutive overexpression of CrORCA3 (octadecanoid-responsive Catharanthus AP2/ERF domain), methyl jasmonate (MeJA), and sodium nitroprusside (SNP) on the differentiated tissue of Catharanthus roseus hairy roots. The changes in catharanthine concentration and in the levels of mRNA transcripts of pathway genes and regulators were tracked for 192 h. ORCA3 overexpression led to a slight decrease of the accumulation of catharanthine, while MeJA treatment caused a large increase in the levels of transcripts of pathway genes and the catharanthine concentration. SNP treatment alone or SNP in combination with MeJA treatment caused a dramatic decrease of the cathanranthine concentration, while at the same time the levels of transcripts of zinc finger-binding proteins genes (ZCTs) increased. The latter treatment also caused a decrease of the levels of transcripts of type-I protein prenyltransferase gene (PGGT-I). This response of transcriptional repressors and pathway genes may explain the antagonistic effects of NO and MeJA on catharanthine biosynthesis in C. roseus hairy roots.

Keywords: Catharanthine; Methyl jasmonate; Metabolite regulation; Nitric oxide; Transcript profiling; Zinc finger-binding protein

Saccharomyces cerevisiae engineered to produce D-xylonate by Mervi H. Toivari; Laura Ruohonen; Peter Richard; Merja Penttilä; Marilyn G. Wiebe (pp. 751-760).

Saccharomyces cerevisiae was engineered to produce D-xylonate by introducing the Trichoderma reesei xyd1 gene, encoding a D-xylose dehydrogenase. D-xylonate was not toxic to S. cerevisiae, and the cells were able to export D-xylonate produced in the cytoplasm to the supernatant. Up to 3.8 g of D-xylonate per litre, at rates of 25–36 mg of D-xylonate per litre per hour, was produced. Up to 4.8 g of xylitol per litre was also produced. The yield of D-xylonate from D-xylose was approximately 0.4 g of D-xylonate per gramme of D-xylose consumed. Deletion of the aldose reductase encoding gene GRE3 in S. cerevisiae strains expressing xyd1 reduced xylitol production by 67%, increasing the yield of D-xylonate from D-xylose. However, D-xylose uptake was reduced compared to strains containing GRE3, and the total amount of D-xylonate produced was reduced. To determine whether the co-factor NADP⁺ was limiting for D-xylonate production the Escherichia coli transhydrogenase encoded by udhA, the Bacillus subtilis glyceraldehyde 3-phosphate dehydrogenase encoded by gapB or the S. cerevisiae glutamate dehydrogenase encoded by GDH2 was co-expressed with xyd1 in the parent and GRE3 deficient strains. Although each of these enzymes enhanced NADPH consumption on D-glucose, they did not enhance D-xylonate production, suggesting that NADP⁺ was not the main limitation in the current D-xylonate producing strains.

Keywords: D-xylonic acid; D-xylose; S. cerevisiae ; Phosphoglucose isomerase; Redox balance

Photoinactivation effects of hematoporphyrin monomethyl ether on Gram-positive and -negative bacteria detected by atomic force microscopy by Hua Jin; Xun Huang; Yong Chen; Hongxia Zhao; Hongyan Ye; Feicheng Huang; Xiaobo Xing; Jiye Cai (pp. 761-770).

The photodynamic antimicrobial chemotherapy as a promising approach for efficiently killing pathogenic microbes is attracting increasing interest. In this study, the cytotoxic and phototoxic effects of hematoporphyrin monomethyl ether (HMME) on the Gram-positive and Gram-negative bacteria were investigated. The cell viability was assessed by colony-forming unit method, and the results indicated that there was no significant cytotoxicity but high phototoxicity in the examined concentrations. Notably, the Gram-positive bacteria were more sensitive to HMME in phototoxicity. Simultaneously, an atomic force microscope (AFM) was used to detect the changes in morphological and nanomechanical properties of bacteria before and after HMME treatment. AFM images indicate that upon photoinactivation, the bacterial surface changed from a smooth, homogeneous architecture to a heterogenous, crackled morphology. The force spectroscopy measurements reveal that the cell wall became less rigid and the Young’s modulus decreased about 50%, whereas the tip-cell-surface adhesion forces increased significantly compared to those of native cells. It was speculated that the photodynamic effects of HMME induced the changes in the chemical composition of the outer membrane and exposure of some proteins inside the envelope. AFM can be utilized as a powerful and sensitive method for studying the interaction between bacteria and drugs.

Keywords: Hematoporphyrin monomethyl ether; APDT; Bacteria; Atomic force microscopy

Growth of wildtype and mutant E. coli strains in minimal media for optimal production of nucleic acids for preparing labeled nucleotides by Chandar S. Thakur; Margaret E. Brown; Jacob N. Sama; Melantha E. Jackson; T. Kwaku Dayie (pp. 771-779).

Since RNAs lie at the center of most cellular processes, there is a need for synthesizing large amounts of RNAs made from stable isotope-labeled nucleotides to advance the study of their structure and dynamics by nuclear magnetic resonance (NMR) spectroscopy. A particularly effective means of obtaining labeled nucleotides is to harvest these nucleotides from bacteria grown in defined minimal media supplemented with ¹⁵NH₄Cl and various carbon sources. Given the high cost of carbon precursors required for labeling nucleic acids for NMR studies, it becomes important to evaluate the optimal growth for commonly used strains under standard minimal media conditions. Such information is lacking. In this study, we characterize the growth for Escherichia coli strains K12, K10zwf, and DL323 in three minimal media with isotopic-labeled carbon sources of acetate, glycerol, and glycerol combined with formate. Of the three media, the LeMaster-Richards and the Studier media outperform the commonly used M9 media and both support optimal growth of E. coli for the production of nucleotides. However, the growth of all three E. coli strains in acetate is reduced almost twofold compared to growth in glycerol. Analysis of the metabolic pathway and previous gene array studies help to explain this differential growth in glycerol and acetate. These studies should benefit efforts to make selective ¹³C-¹⁵N isotopic-labeled nucleotides for synthesizing biologically important RNAs.

Keywords: Escherichia coli ; K12; K10zwf; DL323; BL21; Minimal media; Glycerol; Acetate; Formate

Arbuscular mycorrhizal fungus enhances P acquisition of wheat (Triticum aestivum L.) in a sandy loam soil with long-term inorganic fertilization regime by Junli Hu; Xiangui Lin; Junhua Wang; Xiangchao Cui; Jue Dai; Haiyan Chu; Jiabao Zhang (pp. 781-787).

The P efficiency, crop yield, and response of wheat to arbuscular mycorrhizal fungus (AMF) Glomus caledonium were tested in an experimental field with long-term (19 years) fertilizer management. The experiment included five fertilizer treatments: organic amendment (OA), half organic amendment plus half mineral fertilizer (1/2 OM), mineral fertilizer NPK, mineral fertilizer NK, and the control (without fertilization). AMF inoculation responsiveness (MIR) of wheat plants at acquiring P were estimated by comparing plants grown in unsterilized soil inoculated with G. caledonium and in untreated soil containing indigenous AMF. Without AMF inoculation, higher crop yields but lower colonization rates were observed in the NPK and two OA-inputted treatments, and NPK had significantly (P < 0.05) lower impacts on organic C and available P in soils and thereby P acquisition of wheat plants compared with OA and 1/2 OM. G. caledonium inoculation significantly (P < 0.05) increased colonization rates with the NPK and two P-deficient treatments but significantly (P < 0.05) increased vegetative biomass, crop yield, and P acquisition of wheat as well as soil alkaline phosphatase (ALP) activity, only with the NPK treatment. This gave an MIR of ca. 45% on total P acquisition of wheat plants. There were no other remarkable MIRs. It suggested that the MIR is determined by soil available P status, and rational combination of AMF with chemical NPK fertilizer can compensate for organic amendments by improving P-acquisition efficiency in arable soils.

Keywords: Glomus caledonium ; P efficiency; Soil alkaline phosphatase; Soil available P; Soil microbial biomass P; Soil organic C

The quorum-sensing effect of aerobic granules on bacterial adhesion, biofilm formation, and sludge granulation by Ting-ting Ren; Han-qing Yu; Xiao-yan Li (pp. 789-797).

Quorum sensing (QS) through signal chemical molecules is known to be essential to bacterial adhesion and biofilm formation. In this study, the QS ability of aerobic granules—a special form of biofilms used for biological wastewater treatment—was investigated and compared with that of conventional activated sludge flocs. A novel sectional membrane bioreactor was used together with a flow-cell to evaluate the possible influence of signal chemicals produced by the source sludge on the growth mode of bacterial cells. The results demonstrate the apparent production of QS chemicals from granules and its impact on initial cell attachment and granule formation. When granules were used as the signal-producing biomass, the attached-growth mode was dominant for the free cells, and the biofilm formation rate in the flow-cell was about ten times faster than in cases which used activated sludge as the signal source biomass. In addition, the intracellular extract from mature granules significantly accelerated the sludge granulation process. It is argued that the production and expression of QS signal chemicals from granules and granule precursors might have induced the gene expression of bacteria in suspension for attached growth rather than suspended growth, leading to granule formation and its stable structure.

Keywords: Aerobic granules; Biofilm; Biological wastewater treatment; Granulation; Quorum sensing; Signal chemical molecules

The effect of lipid content on the elemental composition and energy capacity of yeast biomass by Igor G. Minkevich; Emiliya G. Dedyukhina; Tat’yana I. Chistyakova (pp. 799-806).

Oleaginous yeasts (18 strains) were grown in ethanol media under various cultivation conditions (33 biomass samples). It was found that lipid and lipid-free fractions of dry biomass have elemental composition and biomass reductivity very close to values which can be considered as biological constants. The energy content of dry biomass strongly depended on the total lipid content. When the lipid content was 64%, the energy value of dry biomass reached 73% of diesel oil; therefore, oleaginous microorganisms can be a promising source of biodiesel fuel. The approach used in this work makes it possible to determine the energy value of biomass by its elemental composition without application of laborious and expensive calorimetric measurements of combustion heats.

Keywords: Oleaginous yeasts; Biomass composition; Lipids; Combustion heat; Mass–energy balance; Biological constants

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Applied Microbiology and Biotechnology (v.88, #3)

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Applied Microbiology and Biotechnology (v.88, #3)