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A variety of ecologically important processes are driven by bacterial motility and taxis, yet these basic bacterial behaviours remain understudied in cold habitats. Here, we present a series of experiments designed to test the chemotactic ability of the model marine psychrophilic bacterium Colwellia psychrerythraea 34H, when grown at optimal temperature and salinity (8°C, 35 ppt) or its original isolation conditions (-1°C, 35 ppt), towards serine and mannose at temperatures from -8°C to 27°C (above its upper growth temperature of 18°C), and at salinities of 15, 35 and 55 ppt (at 8°C and -1°C). Results indicate that C. psychrerythraea 34H is capable of chemotaxis at all temperatures tested, with strongest chemotaxis at the temperature at which it was first grown, whether 8°C or -1°C. This model marine psychrophile also showed significant halotaxis towards 15 and 55 ppt solutions, as well as strong substrate-specific chemohalotaxis. We suggest that such patterns of taxis may enable bacteria to colonize sea ice, position themselves optimally within its extremely cold, hypersaline and temporally fluctuating microenvironments, and respond to various chemical signals therein.

The &gamma, carbonic anhydrases (CAs, EC 4.2.1.1) present in the Antarctic marine bacteria Pseudoalteromonas haloplanktis and Colwellia psychrerythraea, herein referred to as PhaCA and CpsCA, respectively, were investigated for their activation with a panel of 24 amino acids and amines. Both bacteria are considered Antarctic models for the investigation of photosynthetic and metabolic pathways in organisms adapted to live in cold seawater. PhaCA was much more sensitive to activation by these compounds compared to the genetically related enzyme CpsCA. The most effective PhaCA activators were d-Phe, l-/d-DOPA, l-Tyr and 2-pyridyl-methylamine, with the activation constant KA values of 0.72&ndash, 3.27 &micro, M. d-His, l-Trp, d-Tyr, histamine, dopamine, serotonin anddicarboxylic amino acids were also effective activators of PhaCA, with KA values of 6.48&ndash, 9.85 &micro, M. CpsCA was activated by d-Phe, d-DOPA, l-Trp, l-/d-Tyr, 4-amino-l-Phe, histamine, 2-pyridyl-methylamine and l-/d-Glu with KA values of 11.2&ndash, 24.4 &micro, M. The most effective CpsCA activator was l-DOPA (KA of 4.79 &micro, M). Given that modulators of CAs from Antarctic bacteria have not been identified and investigated in detail for their metabolic roles to date, this research sheds some light on these poorly understood processes.

Oligomeric proteins are important targets for structure determination in solution. While in most cases the fold of individual subunits can be determined experimentally, or predicted by homology-based methods, protein-protein interfaces are challenging to determine de novo using conventional NMR structure determination protocols. Here we focus on a member of the bet-V1 superfamily, Aha1 from Colwellia psychrerythraea. This family displays a broad range of crystallographic interfaces none of which can be reconciled with the NMR and SAXS data collected for Aha1. Unlike conventional methods relying on a dense network of experimental restraints, the sparse data are used to limit conformational search during optimization of a physically realistic energy function. This work highlights a new approach for studying minor conformational changes due to structural plasticity within a single dimeric interface in solution.

The retention of salts in laboratory-grown ice was compared to the retention of extracellular polysaccharide substances (EPS) produced by the cold-adapted marine gammaproteobacterium, Colwellia psychrerythraea strain 34H. Saline ice was formed, by means of a cold-finger apparatus, from artificial sea-water solutions containing either native dissolved EPS from strain 34H, the same EPS but heat-treated, or dissolved EPS from the uninoculated growth medium. Results indicated that only the native (unheated) EPS of strain 34H was retained preferentially in the ice. Temperature and volumetric measurements of the ice further suggested a link between the heat-labile fraction of this EPS of marine bacterial origin and potential habitat alteration. Bacterial EPS may join algal EPS in our understanding of how extracellular polymers help to establish and sustain the microbial community that inhabits sea ice.

[Background]: Colwellia psychrerythraea 34H is a psychrophilic bacterium able to produce docosahexaenoic acid (DHA). Polyketide synthase pathway is assumed to be responsible for DHA production in marine bacteria. [Results]: Five pfa genes from strain 34H were confirmed to be responsible for DHA formation by heterogeneous expression in Escherichia coli. The complexity of fatty acid profile of this strain was revealed by GC and GC-MS. Treatment of cells with cerulenin resulted in significantly reduced level of C16 monounsaturated fatty acid (C16:1, C16:1). In contrast, the amount of saturated fatty acids (C10:0, C12:0, C14:0), hydroxyl fatty acids (3-OH C10:0 and 3-OH C12:0), as well as C20:4ω3, C20:5ω3 and C22:6ω3 were increased. RNA sequencing (RNA-Seq) revealed the altered gene expression pattern when C. psychrerythraea cells were treated with cerulenin. Genes involved in polyketide synthase pathway and fatty acid biosynthesis pathway were not obviously affected by cerulenin treatment. In contrast, several genes involved in fatty acid degradation or β-oxidation pathway were dramatically reduced at the transcriptional level. [Conclusions]: Genes responsible for DHA formation in C. psychrerythraea was first cloned and characterized. We revealed the complexity of fatty acid profile in this DHA-producing strain. Cerulenin could substantially change the fatty acid composition by affecting the fatty acid degradation at transcriptional level. Acyl-CoA dehydrogenase gene family involved in the first step of β-oxidation pathway may be important to the selectivity of degraded fatty acids. In addition, inhibition of FabB protein by cerulenin may lead to the accumulation of malonyl-CoA, which is the substrate for DHA formation., This work was supported by the National Natural Science Foundation of China (3100078) and 948 project (2015-Z3) to X Wan and by Grants BIO2010-14809 and BFU2014-55534-C2-2-P from the Spanish Ministry of Economy and Competitiveness to GM.

In the two cold-adapted monomeric isocitrate dehydrogenases from psychrophilic bacteria, Colwellia maris and Colwellia psychrerythraea (CmIDH and CpIDH, respectively), the combined substitutions of amino acid residues between the Leu693, Leu724 and Phe735 residues of CmIDH and the corresponding Phe693, Gln724 and Leu735 residues of CpIDH were introduced by site-directed mutagenesis. A double mutant of CmIDH substituted its Leu724 and Phe735 residues by the corresponding ones of CpIDH, CmL724Q/F735L, and the triple mutant of CpIDH, CpF693L/Q724L/L735F, showed the most decrease and increase of activity, respectively, of each wild-type and its all mutated enzymes. In the case of CmIDH, the substitutions of these three amino acid residues resulted in the decrease of catalytic activity and thermostability for activity, but the combined substitutions of amino acid residues did not necessarily exert additive effects on these properties. On the other hand, similar substitutions in CpIDH had quite opposite effects to CmIDH, and the effects of the combined substitutions were additive. All multiple mutants of CmIDH and CpIDH showed lower and higher catalytic efficiency (k (cat)/K (m)) values than the respective wild-type enzymes. Single and multiple mutations of the substituted amino acid residues in the CmIDH and CpIDH led to the increase and decrease of sensitivity to tryptic digestion, indicating that the stability of protein structure was decreased and increased by the mutations, respectively.

Monomeric isocitrate dehydrogenases from psychrophilic bacteria, Colwellia maris and Colwellia psychrerythraea (CmIDH-II and CpIDH-M, respectively) are cold-adapted enzymes and show a high degree of amino acid sequential identity to each other (77%). However, maximum activity of CpIDH-M at optimum temperature is much less than that of CmIDH-II. In the C-terminal region 3 of these enzymes, which was suggested from previous study to be responsible for their distinct catalytic ability, several sequential differences of amino acid residue are present. Among them, ten amino acid residues were exchanged between them by site-directed mutagenesis and several properties of the mutated enzymes were examined in this study. The mutated enzymes of CmIDH-II substituted its Gln671, Leu724 and Phe735 residues with the corresponding residues of CpIDH-M (termed Q671K, L724Q and F735L, respectively) showed lower specific activity and thermostability for activity than the wild-type enzyme. Furthermore, the decreased specific activity was also observed in L693F. In contrast, the corresponding mutants of CpIDH-M, F693L, Q724L and L735F, showed the increased specific activity and thermostability for activity. The catalytic efficiency (K-cat/K-m) values of these mutated CmIDH-II and CpIDH-M were lower and higher than those of their wild-type IDHs, respectively. These results suggest that the Gln671, Leu693, Leu724 and Phe735 residues of CmIDH-II are important for exerting its high catalytic ability. (C) 2013, The Society for Biotechnology, Japan. All rights reserved.

This issue inaugurates the second decade of publication of Acta Crystallographica Section F and, in keeping with the custom of the last decade, the cover features an artful arrangement of the best photomicrograph images of crystals published in the journal in the previous year. The custom has served as an annual testament to the commitment of Acta Cryst. F to serve the community of scientists whose focus includes the production of crystalline samples for macromolecular crystal structure determination. The crystals featured are as follows: keto-deoxy-d-galactarate (KDG) dehydratase from Agrobacterium tumefaciens, Taberman et al., 2014 ▶; glucose-1-phosphate uridylyltransferase (GalU) from Erwinia amylovora, Toccafondi et al., 2014 ▶; human farnesyl pyrophosphate synthase complexed with risedronate, Yokoyama et al., 2014 ▶; Xaa-Pro dipeptidase from Xanthomonas campestris, Kumar et al., 2014 ▶; Imp3 in complex with an Mpp10 peptide involved in yeast ribosome biogenesis, Zheng & Ye, 2014 ▶; C-terminal domain of guanylate kinase-associated protein from Rattus nor­vegicus, Tong et al., 2014 ▶; virus-like particles from a piscine betanodavirus, Luo et al., 2014 ▶; FMN-bound and FMN-free forms of aromatic acid decarboxylase (CpsUbiX) from the psychrophilic bacterium Colwellia psychrerythraea 34 H, Do et al., 2014 ▶; XoGroEL chaperonin from Xanthomonas oryzae pv. oryzae, Tran et al., 2014 ▶; an artificial molten-globular-like triosephosphate isomerase protein of mixed phylogenetic origin, Goyal et al., 2014 ▶; great cormorant (Phalacrocorax carbo) haemoglobin, Jagadeesan et al., 2014 ▶; FliP, an integral membrane component of the bacterial flagellar type III protein-export apparatus, Fukumura et al., 2014 ▶; feast/famine regulatory protein (Rv2779c) from Mycobacterium tuberculosis H37Rv, Dey & Ramachandran, 2014 ▶; Gos1p, a yeast SNARE protein, Cheng et al., 2014 ▶; d-lactate dehydrogenase from Lactobacillus jensenii, Kim et al., 2014 ▶; YfcM: an important factor for EF-P hydroxylation, Kobayashi et al., 2014 ▶; a novel β-l-arabinofuranosidase (HypBA1) from Bifidobacterium longum, Zhu et al., 2014 ▶; a dye-decolourizing peroxidase from Dictyostelium discoideum, Rai et al., 2014 ▶; a Fic protein from Clostridium difficile, Welner et al., 2014 ▶; human IL-18 and its extracellular complexes, Kimura et al., 2014 ▶; a surface mutant of the middle domain of PB2 from human influenza A (H1N1) virus, Tsurumura et al., 2014 ▶; the (S)-3-hydroxybutyryl-CoA dehydrogenase PaaH1 from Ralstonia eutropha H16, Kim & Kim, 2014 ▶; the putative type VI secretion immunity protein Tli5 (PA5088) from Pseudomonas aeruginosa, Chen et al., 2014 ▶; and a fungal type III polyketide synthase that produces the csypyrones, Yang et al., 2014 ▶. As indicated in the Editorial in the December 2014 issue (Hunter & Weiss, 2014 ▶), this new decade also inaugurates a new regime for articles reporting macromolecular crystallizations. We hope that our authors will respond to the new challenges presented by the changes. We are convinced that the changes will encourage the generation of articles of higher scientific import and of greater general interest. With this cover, and with this month’s article in our continuing International Year of Crystallography series, we emphasize our commitment to continue publication of macromolecular crystallization articles and welcome those that meet the new standards.