Chemotaxis of the marine bacterium Vibrio furnissii to sugars. A potential mechanism for initiating the chitin catabolic cascade

Molecular analysis of genes involved in chitin degradation from the chitinolytic bacterium Bacillus velezensis

Bacillus velezensis RB.IBE29 is a potent biocontrol agent with high chitinase activity isolated from the rhizosphere of black pepper cultivated in the Central Highlands, Vietnam. Genome sequences revealed that this species possesses some GH18 chitinases and AA10 protein(s); however, these enzymes have not been experimentally characterized. In this work, three genes were identified from the genomic DNA of this bacterium and cloned in Escherichia coli. Sequence analysis exhibited that the ORF of chiA consists of 1,203 bp and encodes deduced 45.46 kDa-chitinase A of 400 aa. The domain structure of chitinase A is composed of a CBM 50 domain at the N-terminus and a catalytic domain at the C-terminus. The ORF of chiB includes 1,263 bp and encodes deduced 47.59 kDa-chitinase B of 420 aa. Chitinase B consists of two CBM50 domains at the N-terminus and a catalytic domain at the C-terminus. The ORF of lpmo10 is 621 bp and encodes a deduced 22.44 kDa-AA10 protein, BvLPMO10 of 206 aa. BvLPMO10 contains a signal peptide and an AA10 catalytic domain. Chitinases A and B were grouped into subfamily A of family 18 chitinases. Amino acid sequences in their catalytic domains lack aromatic residues (Trp, Phe, Tyr) probably involved in processivity and substrate binding compared with well-known bacterial GH18 chitinases. chiB was successfully expressed in E. coli. Purified rBvChiB degraded insoluble chitin and was responsible for inhibition of fungal spore-germination and egg hatching of plant-parasitic nematode. This is the first report describing the analysis of the chitinase system from B. velezensis.

Evidence for reciprocal evolution of the global repressor Mlc and its cognate phosphotransferase system sugar transporter

Because the bacterial phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) is involved in the regulation of various physiological processes in addition to carbohydrate transport, its expression is precisely regulated in response to the availability of PTS sugars. The PTS consists of enzyme I and histidine phosphocarrier protein, and several sugar-specific enzymes II. In Escherichia coli, genes for enzymes II specific for glucose and related sugars are co-regulated by the global repressor Mlc, and glucose induction of the Mlc regulon genes is achieved by its interaction with glucose-specific enzyme II (EII^Glc ). In this study, we revealed that, in Vibrio species, which are phylogenetically older than Enterobacteriaceae, the membrane sequestration of Mlc and thereby the induction of its regulon genes is mediated by N-acetylglucosamine (NAG)-specific EII. While Vibrio Mlc interacts only with the EIIB domain of EII^Nag , E. coli Mlc interacts with the EIIB domain of both EII^Glc and EII^Nag . The present data suggest that EII^Nag may be the primordial regulator of Mlc, and EII^Glc has evolved to interact with Mlc since an EIIA domain was fused to EII^Nag in Enterobacteriaceae. Our findings provide insight into the coevolutionary dynamics between a transcription factor and its cognate regulator according to long-term resource availability in the bacterial natural habitat.

Diverse Horizontally-Acquired Gene Clusters Confer Sucrose Utilization to Different Lineages of the Marine Pathogen Photobacterium damselae subsp. damselae

The ability to metabolize sucrose is a variable trait within the family Vibrionaceae. The marine bacterium Photobacterium damselae subsp. damselae (Pdd), pathogenic for marine animals and humans, is generally described as negative for sucrose utilization (Scr⁻). Previous studies have reported sucrose-utilizing isolates (Scr⁺), but the genetic basis of this variable phenotype remains uncharacterized. Here, we carried out the genome sequencing of five Scr⁺ and two Scr⁻Pdd isolates and conducted a comparative genomics analysis with sixteen additional Pdd genomes sequenced in previous studies. We identified two different versions of a four-gene cluster (scr cluster) exclusive of Scr⁺ isolates encoding a PTS system sucrose-specific IIBC component (scrA), a fructokinase (scrK), a sucrose-6-phosphate hydrolase (scrB), and a sucrose operon repressor (scrR). A scrA deletion mutant did not ferment sucrose and was impaired for growth with sucrose as carbon source. Comparative genomics analyses suggested that scr clusters were acquired by horizontal transfer by different lineages of Pdd and were inserted into a recombination hot-spot in the Pdd genome. The incongruence of phylogenies based on housekeeping genes and on scr genes revealed that phylogenetically diverse gene clusters for sucrose utilization have undergone extensive horizontal transfer among species of Vibrio and Photobacterium.

Chitin Heterodisaccharide, Released from Chitin by Chitinase and Chitin Oligosaccharide Deacetylase, Enhances the Chitin-Metabolizing Ability of Vibrio parahaemolyticus

Vibrio parahaemolyticus RIMD2210633 secretes both chitinase and chitin oligosaccharide deacetylase and produces β-N-acetyl-d-glucosaminyl-(1,4)-d-glucosamine (GlcNAc-GlcN) from chitin. Previously, we reported that GlcNAc-GlcN induces chitinase production by several strains of Vibrio harboring chitin oligosaccharide deacetylase genes (T. Hirano, K. Kadokura, T. Ikegami, Y. Shigeta, et al., Glycobiology 19:1046-1053, 2009). The metabolism of chitin by Vibrio was speculated on the basis of the findings of previous studies, and the role of chitin oligosaccharide produced from chitin has been well studied. However, the role of GlcNAc-GlcN in the Vibrio chitin degradation system, with the exception of the above-mentioned function as an inducer of chitinase production, remains unclear. N,N'-Diacetylchitobiose, a homodisaccharide produced from chitin, is known to induce the expression of genes encoding several proteins involved in chitin metabolism in Vibrio strains (K. L. Meibom, X. B. Li, A. Nielsen, C. Wu, et al., Proc Natl Acad Sci U S A 101:2524-2529, 2004). We therefore hypothesized that GlcNAc-GlcN also affects the expression of enzymes involved in chitin metabolism in the same manner. In this study, we examined the induction of protein expression by several sugars released from chitin using peptide mass fingerprinting and confirmed the expression of genes encoding enzymes involved in chitin metabolism using real-time quantitative PCR analysis. We then confirmed that GlcNAc-GlcN induces the expression of genes encoding many soluble enzymes involved in chitin degradation in Vibrio parahaemolyticus Here, we demonstrate that GlcNAc-GlcN enhances the chitin-metabolizing ability of V. parahaemolyticus IMPORTANCE We demonstrate that β-N-acetyl-d-glucosaminyl-(1,4)-d-glucosamine (GlcNAc-GlcN) enhances the chitin-metabolizing ability of V. parahaemolyticus Members of the genus Vibrio are chitin-degrading bacteria, and some species of this genus are associated with diseases affecting fish and animals, including humans (F. L. Thompson, T. Iida, and J. Swings, Microbiol Mol Biol Rev 68:403-431, 2004; M. Y. Ina-Salwany, N. Al-Saari, A. Mohamad, F.-A. Mursidi, et al., J Aquat Anim Health 31:3-22, 2019). Studies on Vibrio are considered important, as they may facilitate the development of solutions related to health, food, and aquaculture problems attributed to this genus. This report enhances the current understanding of chitin degradation by Vibrio bacteria.

Bacteriophage Interactions with Marine Pathogenic Vibrios: Implications for Phage Therapy

A global distribution in marine, brackish, and freshwater ecosystems, in combination with high abundances and biomass, make vibrios key players in aquatic environments, as well as important pathogens for humans and marine animals. Incidents of Vibrio-associated diseases (vibriosis) in marine aquaculture are being increasingly reported on a global scale, due to the fast growth of the industry over the past few decades years. The administration of antibiotics has been the most commonly applied therapy used to control vibriosis outbreaks, giving rise to concerns about development and spreading of antibiotic-resistant bacteria in the environment. Hence, the idea of using lytic bacteriophages as therapeutic agents against bacterial diseases has been revived during the last years. Bacteriophage therapy constitutes a promising alternative not only for treatment, but also for prevention of vibriosis in aquaculture. However, several scientific and technological challenges still need further investigation before reliable, reproducible treatments with commercial potential are available for the aquaculture industry. The potential and the challenges of phage-based alternatives to antibiotic treatment of vibriosis are addressed in this review.

Identification and characterization of chitinolytic bacteria isolated from a freshwater lake

To develop a novel type of biocontrol agent, we focus on bacteria that are characterized by both chitinase activity and biofilm development. Chitinolytic bacteria were isolated from sediments and chitin flakes immersed in the water of a sand dune lake, Sakata, in Niigata, Japan. Thirty-one isolates from more than 5100 isolated strains were examined chitinase activity and biofilm formation. Phylogenetic analysis of these isolates based on the 16S rRNA gene sequences revealed that most isolates belonged to the family Aeromonadaceae, followed by Paenibacillaceae, Enterobacteriaceae, and Neisseriaceae. The specific activity of chitinase of four selected strains was higher than that of a reference strain. The molecular size of one chitinase produced by Andreprevotia was greater than that of typical bacterial chitinases. The dialyzed culture supernatant containing chitinases of the four strains suppressed hyphal growth of Trichoderma reesei. These results indicate that these four strains are good candidates for biocontrol agents.

Microbial Morphology and Motility as Biosignatures for Outer Planet Missions

Meaningful motion is an unambiguous biosignature, but because life in the Solar System is most likely to be microbial, the question is whether such motion may be detected effectively on the micrometer scale. Recent results on microbial motility in various Earth environments have provided insight into the physics and biology that determine whether and how microorganisms as small as bacteria and archaea swim, under which conditions, and at which speeds. These discoveries have not yet been reviewed in an astrobiological context. This paper discusses these findings in the context of Earth analog environments and environments expected to be encountered in the outer Solar System, particularly the jovian and saturnian moons. We also review the imaging technologies capable of recording motility of submicrometer-sized organisms and discuss how an instrument would interface with several types of sample-collection strategies. Key Words: In situ measurement-Biosignatures-Microbiology-Europa-Ice. Astrobiology 16, 755-774.

Aeromonas chitinase degrades chironomid egg masses

Chironomids are freshwater insects that undergo a complete metamorphosis of four life stages. Chironomid egg masses can be degraded by Vibrio cholerae and some Aeromonas species. Egg mass degradation by V. cholerae requires haemagglutinin protease activity. Our aim was to identify the egg mass degrading (EMD) factor secreted by Aeromonas dhkanesis 3K1C15. Following the hypothesis that the EMD factor of A. dhkanesis is also a protease, secreted proteases were screened, but none of them proved to have the same properties as the EMD factor. Using conventional protein purification methods, we found that the active fraction included chitinases. We further confirmed chitin as a building block of the egg masses. Interestingly, by supplementing bacterial growth media with chitin, we observed unexpected EMD factor activity in Aeromonas isolates that initially were not able to degrade egg masses. Accordingly, we concluded that although strain 3K1C15 secretes chitinases constitutively, most Aeromonas strains secrete chitinases inductively. Induction of chitinases in nature presumably occurs when bacteria are attached to the egg mass habitat, in which chitin is abundant. Considering that chitinases are highly conserved across bacteria phyla, we assume that the role of this enzyme in the bacteria-insect interplay could be wider than is currently thought.

Cold active hydrolytic enzymes production by psychrotrophic Bacilli isolated from three sub-glacial lakes of NW Indian Himalayas

The diversity of culturable, cold-active enzymes producing Bacilli was investigated from three sub-glacial lakes of north western Indian Himalayas. Amplified ribosomal DNA restriction analysis (ARDRA) using three restriction enzymes Alu I, Msp I, and Hae III led to the clustering of 136 Bacilli into 26, 23, and 22 clusters at 75% similarity index from Chandratal Lake, Dashair Lake, and Pangong Lake, respectively. Phylogenetic analysis based on 16S rRNA gene sequencing led to the identification of 35 Bacilli that could be grouped in seven families viz.: Bacillaceae (48%), Staphylococcaceae (14%), Bacillales incertae sedis (13%), Planococcaceae (12%), Paenibacillaceae (9%), Sporolactobacillaceae (3%), and Carnobacteriaceae (1%), which included twelve different genera Bacillus, Desemzia, Exiguobacterium, Jeotgalicoccus, Lysinibacillus, Paenibacillus, Planococcus, Pontibacillus, Sinobaca, Sporosarcina, Staphylococcus, and Virgibacillus. Based on their optimal temperature for growth, 35 Bacilli were grouped as psychrophilic (11 strains), psychrotrophic (17 strains), or psychrotolerant (7 strains), respectively. The representative isolates from each cluster were screened for cold-active enzyme activities. Amylase, β-glucosidase, pectinase, and protease activities at 4 °C were detected in more than 80% of the strains while approximately 40, 31, 23, 14, 11, and 9% of strains possessed cellulase, xylanase, β-galactosidase, laccase, chitinase, and lipase activity, respectively. Among 35 Bacilli, Bacillus amyloliquefaciens, Bacillus marisflavi, Exiguobacterium indicum, Paenibacillus terrae, Pontibacillus sp., Sporosarcina globispora, and Sporosarcina psychrophila were efficient producers of different cold-active enzymes. These cold-adapted Bacilli could play an important role in industrial and agricultural processes.

Defining the niche of Vibrio parahaemolyticus during pre- and post-monsoon seasons in the coastal Arabian Sea

The bacteria Vibrio parahaemolyticus is an important component of coastal ecosystems worldwide, and in recent years, V. parahaemolyticus has caused several cases of food-borne gastroenteritis. However, research investigating which parameters are important in regulating V. parahaemolyticus abundance in tropical areas with relatively stable temperatures and salinity are largely lacking. The objective here was to investigate which environmental forces are driving elevated abundances of V. parahaemolyticus in a tropical oligotrophic coastal area in the Arabian Sea. We analysed a large number of environmental parameters in parallel with cell densities of V. parahaemolyticus and Vibrio spp. Abundance data was obtained using real-time PCR, during two different sampling periods, representative for two distinct seasons. Water temperature and salinity were stable during and between sampling periods, but V. parahaemolyticus abundances were on average six times higher during the first sampling period in December, compared to the second period in February-March. V. parahaemolyticus abundance was found to be positively correlated to inorganic phosphate concentration and copepod abundance. We thus hypothesise that these are important factors regulating V. parahaemolyticus abundance in coastal tropical areas during these periods.

Ecology and physics of bacterial chemotaxis in the ocean

Intuitively, it may seem that from the perspective of an individual bacterium the ocean is a vast, dilute, and largely homogeneous environment. Microbial oceanographers have typically considered the ocean from this point of view. In reality, marine bacteria inhabit a chemical seascape that is highly heterogeneous down to the microscale, owing to ubiquitous nutrient patches, plumes, and gradients. Exudation and excretion of dissolved matter by larger organisms, lysis events, particles, animal surfaces, and fluxes from the sediment-water interface all contribute to create strong and pervasive heterogeneity, where chemotaxis may provide a significant fitness advantage to bacteria. The dynamic nature of the ocean imposes strong selective pressures on bacterial foraging strategies, and many marine bacteria indeed display adaptations that characterize their chemotactic motility as "high performance" compared to that of enteric model organisms. Fast swimming speeds, strongly directional responses, and effective turning and steering strategies ensure that marine bacteria can successfully use chemotaxis to very rapidly respond to chemical gradients in the ocean. These fast responses are advantageous in a broad range of ecological processes, including attaching to particles, exploiting particle plumes, retaining position close to phytoplankton cells, colonizing host animals, and hovering at a preferred height above the sediment-water interface. At larger scales, these responses can impact ocean biogeochemistry by increasing the rates of chemical transformation, influencing the flux of sinking material, and potentially altering the balance of biomass incorporation versus respiration. This review highlights the physical and ecological processes underpinning bacterial motility and chemotaxis in the ocean, describes the current state of knowledge of chemotaxis in marine bacteria, and summarizes our understanding of how these microscale dynamics scale up to affect ecosystem-scale processes in the sea.

The importance of chitin in the marine environment

Chitin is the most abundant renewable polymer in the oceans and is an important source of carbon and nitrogen for marine organisms. The process of chitin degradation is a key step in the cycling of nutrients in the oceans and chitinolytic bacteria play a significant role in this process. These bacteria are autochthonous to both marine and freshwater ecosystems and produce chitinases that degrade chitin, an insoluble polysaccharide, to a biologically useful form. In this brief review, a description of the structure of chitin and diversity of chitinolytic bacteria in the oceans is provided, in the context of the significance of chitin degradation for marine life.

Heterodisaccharide 4-O-(N-acetyl-β-D-glucosaminyl)-D-glucosamine is an effective chemotactic attractant for Vibrio bacteria that produce chitin oligosaccharide deacetylase

AIMS

To investigate the attractant effect of 4-O-(N-acetyl-β-D-glucosaminyl)-D-glucosamine (GlcNAc-GlcN) in the chemotaxis of Vibrio bacteria that produce carbohydrate esterase (CE) family 4 chitin oligosaccharide deacetylase (COD), an enzyme that catalyzes the production of GlcNAc-GlcN from N,N'-diacetylchitobiose (GlcNAc)(2).

METHODS AND RESULTS

The chemotactic effect of disaccharides from chitin on several strains of Vibrio bacteria was investigated using an agar gel lane-migration method. The results demonstrated that GlcNAc-GlcN functions as an effective chemoattractant in the CE family 4 COD-producing vibrios, Vibrio parahaemolyticus and Vibrio alginolyticus. In contrast, this phenomenon was not observed in Vibrio nereis or Vibrio furnissii, which lack genes encoding this enzyme. From transmission electron microscope observation of V. parahaemolyticus cells following the chemotaxis assay, GlcNAc-GlcN appears to stimulate polar flagellum rotation.

CONCLUSIONS

GlcNAc-GlcN is a specific chemoattractant for the CE family 4 COD-producing vibrios, V. parahaemolyticus and V. alginolyticus.

SIGNIFICANCE AND IMPACT OF THE STUDY

It was clarified for the first time that GlcNAc-GlcN functions as a signalling molecule in the chemotaxis of Vibrio bacteria that have an ability to produce CE family 4 COD, which generate GlcNAc-GlcN from (GlcNAc)(2).

Chitiniphilus shinanonensis gen. nov., sp. nov., a novel chitin-degrading bacterium belonging to Betaproteobacteria

A bacterial strain capable of degrading chitin, strain SAY3T, was isolated from moat water of Ueda Castle in Nagano Prefecture, Japan. The strain was gram-negative, curved rod-shaped, facultatively anaerobic, and motile with a single polar flagellum. It grew well with chitin as a sole carbon source. The cellular fatty acids profiles showed the presence of C16:1 omega7c and C16:0 as the major components. The G+C content of DNA was 67.6 mol% and Q-8 was the major respiratory quinone. A 16S rRNA gene sequence-based phylogenetic analysis showed the strain belonged to the family Neisseriaceae but was distantly related (94% identity) to any previously known species. Since the strain was clearly distinct from closely related genera in phenotypic and chemotaxonomic characteristics, it should be classified under a new genus and a new species. We propose the name Chitiniphilus shinanonensis gen. nov., sp. nov. The type strain is SAY3T (=NBRC 104970T=NICMB 14509T).

Heterodisaccharide 4-O-(N-acetyl-beta-D-glucosaminyl)-D-glucosamine is a specific inducer of chitinolytic enzyme production in Vibrios harboring chitin oligosaccharide deacetylase genes

Vibrio parahaemolyticus KN1699 produces 4-O-(N-acetyl-beta-d-glucosaminyl)-d-glucosamine (GlcNAc-GlcN) as a major end product from chitin using two extracellular hydrolases: glycoside hydrolase family 18 chitinase, which produces (GlcNAc)(2) from chitin, and carbohydrate esterase (CE) family 4 chitin oligosaccharide deacetylase (COD), which hydrolyzes the N-acetyl group at the reducing-end GlcNAc residue of (GlcNAc)(2). In this study, we clarified that this heterodisaccharide functions as an inducer of the production of the two above-mentioned chitinolytic enzymes, particularly chitinase. Similar results for chitinase production were obtained with other chitin-decomposing Vibrio strains harboring the CE family 4 COD gene; however, such an increase in chitinase production was not observed in chitinolytic Vibrio strains that did not harbor the COD gene. These results suggest that GlcNAc-GlcN is a unique inducer of chitinase production in Vibrio bacteria that have the COD-producing ability and that the COD involved in the synthesis of this signal compound is one of the key enzymes in the chitin catabolic cascade of these bacteria.

Cloning, expression, and characterization of a chitinase from the chitinolytic bacterium Aeromonas hydrophila strain SUWA-9

The chitinolytic bacterium Aeromonas hydrophila strain SUWA-9, which was isolated from freshwater in Lake Suwa (Nagano Prefecture, Japan), produced several kinds of chitin-degrading enzymes. A gene coding for an endo-type chitinase (chiA) was isolated from SUWA-9. The chiA ORF encodes a polypeptide of 865 amino acid residues with a molecular mass of 91.6 kDa. The deduced amino acid sequence showed high similarity to those of bacterial chitinases classified into family 18 of glycosyl hydrolases. chiA was expressed in Escherichia coli and the recombinant chitinase (ChiA) was purified and examined. The enzyme hydrolyzed N-acetylchitooligomers from trimer to pentamer and produced monomer and dimer as a final product. It also reacted toward colloidal chitin and chitosan with a low degree of deacetylation. When cells of SUWA-9 were grown in the presence of colloidal chitin, a 60 kDa-truncated form of ChiA that had lost the C-terminal chitin-binding domain was secreted.

Cloning, sequences, and characterization of two chitinase genes from the Antarctic Arthrobacter sp. strain TAD20: isolation and partial characterization of the enzymes

Arthrobacter sp. strain TAD20, a chitinolytic gram-positive organism, was isolated from the sea bottom along the Antarctic ice shell. Arthrobacter sp. strain TAD20 secretes two major chitinases, ChiA and ChiB (ArChiA and ArChiB), in response to chitin induction. A single chromosomal DNA fragment containing the genes coding for both chitinases was cloned in Escherichia coli. DNA sequencing analysis of this fragment revealed two contiguous open reading frames coding for the precursors of ArChiA (881 amino acids [aa]) and ArChiB (578 aa). ArChiA and ArChiB are modular enzymes consisting of a glycosyl-hydrolase family 18 catalytic domain as well as two and one chitin-binding domains, respectively. The catalytic domain of ArChiA exhibits 55% identity with a chitodextrinase from Vibrio furnissii. The ArChiB catalytic domain exhibits 33% identity with chitinase A of Bacillus circulans. The ArChiA chitin-binding domains are homologous to the chitin-binding domain of ArChiB. ArChiA and ArChiB were purified to homogeneity from the native Arthrobacter strain and partially characterized. Thermal unfolding of ArChiA, ArChiB, and chitinase A of Serratia marcescens was studied using differential scanning calorimetry. ArChiA and ArChiB, compared to their mesophilic counterpart, exhibited increased heat lability, similar to other cold-adapted enzymes.

Evolutionary conservation of methyl-accepting chemotaxis protein location in Bacteria and Archaea

The methyl-accepting chemotaxis proteins (MCPs) are concentrated at the cell poles in an evolutionarily diverse panel of bacteria and an archeon. In elongated cells, the MCPs are located both at the poles and at regions along the length of the cells. Together, these results suggest that MCP location is evolutionarily conserved.

The chitin disaccharide, N,N'-diacetylchitobiose, is catabolized by Escherichia coli and is transported/phosphorylated by the phosphoenolpyruvate:glycose phosphotransferase system

We have previously reported that wild type strains of Escherichia coli grow on the chitin disaccharide N,N'-diacetylchitobiose, (GlcNAc)(2), as the sole source of carbon (Keyhani, N. O., and Roseman, S. (1997) Proc. Natl. Acad. Sci., U. S. A. 94, 14367-14371). A nonhydrolyzable analogue of (GlcNAc)(2,) methyl beta-N, N'-[(3)H]diacetylthiochitobioside ([(3)H]Me-TCB), was used to characterize the disaccharide transport process, which was found to be mediated by the phosphoenolpyruvate:glycose phosphotransferase system (PTS). Here and in the accompanying papers (Keyhani, N. O., Boudker, O., and Roseman, S. (2000) J. Biol. Chem. 275, 33091-33101; Keyhani, N. O., Bacia, K., and Roseman, S. (2000) J. Biol. Chem. 275, 33102-33109; Keyhani, N. O., Rodgers, M., Demeler, B., Hansen, J., and Roseman, S. (2000) J. Biol. Chem. 275, 33110-33115), we report that transport of [(3)H]Me-TCB and (GlcNAc)(2) involves a specific PTS Enzyme II complex, requires Enzyme I and HPr of the PTS, and results in the accumulation of the sugar derivative as a phosphate ester. The phosphoryl group is linked to the C-6 position of the GlcNAc residue at the nonreducing end of the disaccharide. The [(3)H]Me-TCB uptake system was induced only by (GlcNAc)(n), n = 2 or 3. The apparent K(m) of transport was 50-100 micrometer, and effective inhibitors of uptake included (GlcNAc)(n), n = 2 or 3, cellobiose, and other PTS sugars, i.e. glucose and GlcNAc. Presumably the PTS sugars inhibit by competing for PTS components. Kinetic properties of the transport system are described.

Chitin catabolism in the marine bacterium Vibrio furnissii. Identification and molecular cloning of a chitoporin

Chitin catabolism by the marine bacterium Vibrio furnissii involves many genes and proteins, including two unique periplasmic hydrolases, a chitodextrinase and a beta-N-acetylglucosaminidase (Keyhani, N. O. , and Roseman, S. (1996) J. Biol. Chem. 271, 33414-33424 and 33425-33432). A specific chitoporin in the outer membrane may be required for these glycosidases to be accessible to extracellular chitooligosaccharides, (GlcNAc)(n), that are produced by chitinases. We report here the identification and molecular cloning of such a porin. An outer membrane protein, OMP (apparent molecular mass 40 kDa) was expressed when V. furnissii was induced by (GlcNAc)(n), n = 2-6, but not by GlcNAc or other sugars. Based on the N-terminal sequence of OMP, oligonucleotides were synthesized and used to clone the gene, chiP. The deduced amino acid sequence of ChiP is similar to several bacterial porins; OMP is a processed form of ChiP. In Escherichia coli, two recombinant proteins were observed, corresponding to processed and unprocessed forms of ChiP. A null mutant of chiP was constructed in V. furnissii. In contrast to the parental strain, the mutant did not grow on (GlcNAc)(3) and transported a nonmetabolizable analogue of (GlcNAc)(2) at a reduced rate. These results imply that ChiP is a specific chitoporin.

Chitin catabolism in the marine bacterium Vibrio furnissii. Identification, molecular cloning, and characterization of A N, N'-diacetylchitobiose phosphorylase

The major product of bacterial chitinases is N,N'-diacetylchitobiose or (GlcNAc)(2). We have previously demonstrated that (GlcNAc)(2) is taken up unchanged by a specific permease in Vibrio furnissii (unlike Escherichia coli). It is generally held that marine Vibrios further metabolize cytoplasmic (GlcNAc)(2) by hydrolyzing it to two GlcNAcs (i.e. a "chitobiase "). Here we report instead that V. furnissii expresses a novel phosphorylase. The gene, chbP, was cloned into E. coli; the enzyme, ChbP, was purified to apparent homogeneity, and characterized kinetically. The DNA sequence indicates that chbP encodes an 89-kDa protein. The enzymatic reaction was characterized as follows. (GlcNAc)(2)+P(i) GlcNAc-alpha-1-P+GlcNAc K'(cq)=1.0+/-0.2 Reaction 1 The K(m) values for the four substrates were in the range 0.3-1 mm. p-Nitrophenyl-(GlcNAc)(2) was cleaved at 8.5% the rate of (GlcNAc)(2), and p-nitrophenyl (PNP)-GlcNAc was 36% as active as GlcNAc in the reverse direction. All other compounds tested displayed </=1% of the activity of the indicated substrates including: for phosphorolysis, higher chitin oliogsaccharides, (GlcNAc)(n), n = 3-5, cellobiose, PNP-GlcNAc, and PNP-(GlcNAc)(3); for synthesis, (GlcNAc)(n) (n = 2-5), glucose, etc. (GlcNAc)(2) is a major regulator of the chitin catabolic cascade. Conceivably GlcNAc-alpha-1-P plays a similar but different role in regulation.

Physiological aspects of chitin catabolism in marine bacteria

Chitin, a carbohydrate polymer composed of alternating beta-1, 4-linked N-acetylglucosamine residues is the second most abundant organic compound in nature. In the aquatic biosphere alone, it is estimated that more than 10(11) metric tons of chitin are produced annually. If this enormous quantity of insoluble carbon and nitrogen was not converted to biologically useful material, the oceans would be depleted of these elements in a matter of decades. In fact, marine sediments contain only traces of chitin, and the turnover of the polysaccharide is attributed primarily to marine bacteria, but the overall process involves many steps, most of which remain to be elucidated. Marine bacteria possess complex signal transduction systems for: (1) finding chitin, (2) adhering to chitinaceous substrata, (3) degrading the chitin to oligosaccharides, (4) transporting the oligosaccharides to the cytoplasm, and (5) catabolizing the transport products to fructose-6-P, acetate and NH(3). The proteins and enzymes are located extracellularly, in the cell envelope, the periplasmic space, the inner membrane and the cytoplasm. In addition to these levels of complexity, the various components of these systems appear to be carefully coordinated by intricate regulatory mechanisms.

Sugar transport by the marine chitinolytic bacterium Vibrio furnissii. Molecular cloning and analysis of the glucose and N-acetylglucosamine permeases

Chitin catabolism by the marine bacterium Vibrio furnissii involves chemotaxis to and transport of N-acetyl-D-glucosamine (GlcNAc) and D-glucose. We report the properties of the respective permeases that complemented E. coli Glc- Man- mutants. Although the V. furnissii Glc-specific permease (55,941 Da) shares 38% identity with E. coli IIGlc (ptsG), it is 67% identical to MalX of the E. coli maltose operon (Reidl, J., and Boos, W. (1991) J. Bacteriol. 173, 4862-4876). An adjacent open reading frame encodes a protein with 52% identity to E. coli MalY. Glc phosphorylation requires only V. furnissii MalX and the accessory phosphoenolpyruvate:glycose phosphotransferase system proteins. The V. furnissii equivalent of IIGlc was not found in the 25,000 transformants screened. The GlcNAc/Glc-specific permease (52,894 Da) shares 47% identity with the N-terminal, hydrophobic domain of E. coli IINag, but is unique among IINag proteins in that it lacks the C-terminal domain and thus requires IIIGlc for sugar fermentation in vivo and phosphorylation in vitro. While there are similarities between the phosphoenolpyruvate:glycose phosphotransferase system of V. furnissii and enteric bacteria, the differences may be important for survival of V. furnissii in the marine environment.

The chitin catabolic cascade in the marine bacterium Vibrio furnissii. Characterization of an N,N'-diacetyl-chitobiose transport system

The disaccharide N,N'-diacetyl-chitobiose, (GlcNAc)2, is critical in chitin dissimilation by Vibrio furnissii and, as reported here, is taken up by a specific permease. Since (GlcNAc)2 is rapidly catabolized by V. furnissii, a non-hydrolyzable thioglycoside analogue was used: methyl beta-N,N'-[3H]diacetyl-thiochitobioside (Me-[3H]TCB). Me-TCB and TCB substitute for (GlcNAc)2 as chemoattractants and inducers of beta-N-acetylglucosaminidase activity. The [3H]Me-TCB uptake system was induced only by (GlcNAc)2 and by (GlcNAc)n that can be converted to (GlcNAc)2. The Km for [3H]Me-TCB uptake was </=1 microM and was not affected by Na+ or K+. Uptake appeared to be unidirectional, and in 0.4 M sucrose (+/- K+) the cells accumulated [3H]Me-TCB until it was depleted from the medium, giving an internal concentration of 0.1 M and an internal/external ratio > 1,000. The only effective inhibitors of uptake were: (GlcNAc)n, n = 2-4 > cellobiose > (GlcNAc)5. In 50% artificial sea water (or sucrose/Na+), [3H]Me-TCB accumulation attained a constant steady state level because of efflux, a Na+-dependent process. The physiological implications of these results are considered.

The chitin catabolic cascade in the marine bacterium Vibrio furnissii. Molecular cloning, isolation, and characterization of a periplasmic chitodextrinase

Chitin catabolism in Vibrio furnissii comprises several signal transducing systems and many proteins. Two of these enzymes are periplasmic and convert chitin oligosaccharides to GlcNAc and (GlcNAc)2. One of these unique enzymes, a chitodextrinase, designated EndoI, is described here. The protein, isolated from a recombinant Escherichia coli clone, exhibited (via SDS-polyacrylamide gel electrophoresis) two enzymatically active, close running bands ( approximately mass of 120 kDa) with identical N-terminal sequences. The chitodextrinase rapidly cleaved chitin oligosaccharides, (GlcNAc)4 to (GlcNAc)2, and (GlcNAc)5,6 to (GlcNAc)2 and (GlcNAc)3. EndoI was substrate inhibited in the millimolar range and was inactive with chitin, glucosamine oligosaccharides, glycoproteins, and glycopeptides containing (GlcNAc)2. The sequence of the cloned gene indicates that it encodes a 112,690-kDa protein (1046 amino acids). Both proteins lacked the predicted N-terminal 31 amino acids, corresponding to a consensus prokaryotic signal peptide. Thus, E. coli recognizes and processes this V. furnissii signal sequence. Although inactive with chitin, the predicted amino acid sequence of EndoI displayed similarities to many chitinases, with 8 amino acids completely conserved in 10 or more of the homologous proteins. There was, however, no "consensus" chitin-binding domain in EndoI.

Chitovibrin: a chitin-binding lectin from Vibrio parahemolyticus

A novel 134 kDa, calcium-independent chitin-binding lectin, 'chitovibrin', is secreted by the marine bacterium Vibrio parahemolyticus, inducible with chitin or chitin-oligomers. Chitovibrin shows no apparent enzymatic activity but exhibits a strong affinity for chitin and chito-oligomers > dp9. The protein has an isoelectric pH of 3.6, shows thermal tolerance, binds chitin with an optimum at pH 6 and is active in 0-4 M NaCl. Chitovibrin appears to be completely different from other reported Vibrio lectins and may function to bind V. parahemolyticus to chitin substrates, or to capture or sequester chito-oligomers. It may be a member of a large group of recently described proteins in Vibrios related to a complex chitinoclastic (chitinivorous) system.