Regulation of sugar uptake via the phosphoenolpyruvate-dependent phosphotransferase systems in Bacillus subtilis and Lactococcus lactis is mediated by ATP-dependent phosphorylation of seryl residue 46 in HPr

Gut Microbial Divergence Between Three Hadal Amphipod Species from the Isolated Hadal Trenches

Amphipods are the dominant scavenging metazoan species in the hadal trenches at water depths below 6,000 m. The gut microbiota have been considered to be contribution to the adaptation of deep-sea organisms; however, few comparative analyses of animal gut microbiota between different isolated hadal environments have been done so far. Here, we employed high-throughput 16S rRNA sequencing to compare the gut microbial taxonomic composition and functional potential diversity of three hadal amphipod species, Hirondellea gigas, Bathycallisoma schellenbergi, and Alicella gigantea, collected from the Mariana Trench, Marceau Trench, and New Britain Trench in the Pacific Ocean, respectively. Results showed that different community compositions were detected across all the amphipod specimens based on the analyses of alpha-diversity, hierarchical cluster tree, and PCoA (principal coordinate analysis). Moreover, almost no correlation was observed between genera overrepresented in different amphipods by microbe-microbe correlations analysis, which suggested that the colonization of symbionts were host-specific. At genus level, Psychromonas was dominant in H. gigas, and Candidatus Hepatoplasma was overall dominant in A. gigantea and B. schellenbergi. Comparison of the functional potential showed that, though three hadal amphipod species shared the same predominant functional pathways, the abundances of those most shared pathways showed distinct differences across all the specimens. These findings pointed to the enrichment of particular functional pathways in the gut microbiota of the different isolated trench amphipods. Moreover, in terms of species relative abundance, alpha-diversity and beta-diversity, there was high similarity of gut microbiota between the two A. gigantea populations, which dwelled in two different localities of the same hadal trench. Altogether, this study provides an initial investigation into the gut-microbial interactions and evolution at the hadal depths within amphipod. Each of these three amphipod species would be a model taxa for future studies investigating the influence habitat difference and geography on gut-microbial communities.

Post-translational Lysine Ac(et)ylation in Bacteria: A Biochemical, Structural, and Synthetic Biological Perspective

Ac(et)ylation is a post-translational modification present in all domains of life. First identified in mammals in histones to regulate RNA synthesis, today it is known that is regulates fundamental cellular processes also in bacteria: transcription, translation, metabolism, cell motility. Ac(et)ylation can occur at the ε-amino group of lysine side chains or at the α-amino group of a protein. Furthermore small molecules such as polyamines and antibiotics can be acetylated and deacetylated enzymatically at amino groups. While much research focused on N-(ε)-ac(et)ylation of lysine side chains, much less is known about the occurrence, the regulation and the physiological roles on N-(α)-ac(et)ylation of protein amino termini in bacteria. Lysine ac(et)ylation was shown to affect protein function by various mechanisms ranging from quenching of the positive charge, increasing the lysine side chains’ size affecting the protein surface complementarity, increasing the hydrophobicity and by interfering with other post-translational modifications. While N-(ε)-lysine ac(et)ylation was shown to be reversible, dynamically regulated by lysine acetyltransferases and lysine deacetylases, for N-(α)-ac(et)ylation only N-terminal acetyltransferases were identified and so far no deacetylases were discovered neither in bacteria nor in mammals. To this end, N-terminal ac(et)ylation is regarded as being irreversible. Besides enzymatic ac(et)ylation, recent data showed that ac(et)ylation of lysine side chains and of the proteins N-termini can also occur non-enzymatically by the high-energy molecules acetyl-coenzyme A and acetyl-phosphate. Acetyl-phosphate is supposed to be the key molecule that drives non-enzymatic ac(et)ylation in bacteria. Non-enzymatic ac(et)ylation can occur site-specifically with both, the protein primary sequence and the three dimensional structure affecting its efficiency. Ac(et)ylation is tightly controlled by the cellular metabolic state as acetyltransferases use ac(et)yl-CoA as donor molecule for the ac(et)ylation and sirtuin deacetylases use NAD⁺ as co-substrate for the deac(et)ylation. Moreover, the accumulation of ac(et)yl-CoA and acetyl-phosphate is dependent on the cellular metabolic state. This constitutes a feedback control mechanism as activities of many metabolic enzymes were shown to be regulated by lysine ac(et)ylation. Our knowledge on lysine ac(et)ylation significantly increased in the last decade predominantly due to the huge methodological advances that were made in fields such as mass-spectrometry, structural biology and synthetic biology. This also includes the identification of additional acylations occurring on lysine side chains with supposedly different regulatory potential. This review highlights recent advances in the research field. Our knowledge on enzymatic regulation of lysine ac(et)ylation will be summarized with a special focus on structural and mechanistic characterization of the enzymes, the mechanisms underlying non-enzymatic/chemical ac(et)ylation are explained, recent technological progress in the field are presented and selected examples highlighting the important physiological roles of lysine ac(et)ylation are summarized.

Metagenomic Insights Into the Structure and Function of Intestinal Microbiota of the Hadal Amphipods

Hadal trenches are the deepest known areas of the ocean. Amphipods are considered to be the dominant scavengers in the hadal food webs. The studies on the structure and function of the hadal intestinal microbiotas are largely lacking. Here, the intestinal microbiotas of three hadal amphipods, Hirondellea gigas, Scopelocheirus schellenbergi, and Alicella gigantea, from Mariana Trench, Marceau Trench, and New Britain Trench, respectively, were investigated. The taxonomic analysis identified 358 microbial genera commonly shared within the three amphipods. Different amphipod species possessed their own characteristic dominant microbial component, Psychromonas in H. gigas and Candidatus Hepatoplasma in A. gigantea and S. schellenbergi. Functional composition analysis showed that “Carbohydrate Metabolism,” “Lipid Metabolism,” “Cell Motility,” “Replication and Repair,” and “Membrane Transport” were among the most represented Gene Ontology (GO) Categories in the gut microbiotas. To test the possible functions of “Bacterial Chemotaxis” within the “Cell Motility” category, the methyl-accepting chemotaxis protein (MCP) gene involved in the “Bacterial Chemotaxis” pathway was obtained and used for swarming motility assays. Results showed that bacteria transformed with the gut bacterial MCP gene showed significantly faster growths compared with the control group, suggesting MCP promoted the bacterial swimming capability and nutrient utilization ability. This result suggested that hadal gut microbes could promote their survival in poor nutrient conditions by enhancing chemotaxis and motility. In addition, large quantities of probiotic genera were detected in the hadal amphipod gut microbiotas, which indicated that those probiotics would be possible contributors for promoting the host’s growth and development, which could facilitate adaptation of hadal amphipods to the extreme environment.

Role of Glutathione in Buffering Excess Intracellular Copper in Streptococcus pyogenes

Copper (Cu) is an essential metal for bacterial physiology but in excess it is bacteriotoxic. To limit Cu levels in the cytoplasm, most bacteria possess a transcriptionally responsive system for Cu export. In the Gram-positive human pathogen Streptococcus pyogenes (group A Streptococcus [GAS]), this system is encoded by the copYAZ operon. This study demonstrates that although the site of GAS infection represents a Cu-rich environment, inactivation of the copA Cu efflux gene does not reduce virulence in a mouse model of invasive disease. In vitro, Cu treatment leads to multiple observable phenotypes, including defects in growth and viability, decreased fermentation, inhibition of glyceraldehyde-3-phosphate dehydrogenase (GapA) activity, and misregulation of metal homeostasis, likely as a consequence of mismetalation of noncognate metal-binding sites by Cu. Surprisingly, the onset of these effects is delayed by ∼4 h even though expression of copZ is upregulated immediately upon exposure to Cu. Further biochemical investigations show that the onset of all phenotypes coincides with depletion of intracellular glutathione (GSH). Supplementation with extracellular GSH replenishes the intracellular pool of this thiol and suppresses all the observable effects of Cu treatment. These results indicate that GSH buffers excess intracellular Cu when the transcriptionally responsive Cu export system is overwhelmed. Thus, while the copYAZ operon is responsible for Cu homeostasis, GSH has a role in Cu tolerance and allows bacteria to maintain metabolism even in the presence of an excess of this metal ion.IMPORTANCE The control of intracellular metal availability is fundamental to bacterial physiology. In the case of copper (Cu), it has been established that rising intracellular Cu levels eventually fill the metal-sensing site of the endogenous Cu-sensing transcriptional regulator, which in turn induces transcription of a copper export pump. This response caps intracellular Cu availability below a well-defined threshold and prevents Cu toxicity. Glutathione, abundant in many bacteria, is known to bind Cu and has long been assumed to contribute to bacterial Cu handling. However, there is some ambiguity since neither its biosynthesis nor uptake is Cu-regulated. Furthermore, there is little experimental support for this physiological role of glutathione beyond measuring growth of glutathione-deficient mutants in the presence of Cu. Our work with group A Streptococcus provides new evidence that glutathione increases the threshold of intracellular Cu availability that can be tolerated by bacteria and thus advances fundamental understanding of bacterial Cu handling.

Gut Microbial Divergence between Two Populations of the Hadal Amphipod Hirondellea gigas

Hadal environments sustain diverse microorganisms. A few studies have investigated hadal microbial communities consisting of free-living or particle-associated bacteria and archaea. However, animal-associated microbial communities in hadal environments remain largely unexplored, and comparative analyses of animal gut microbiota between two isolated hadal environments have never been done so far. In the present study, 228 Gb of gut metagenomes of the giant amphipod Hirondellea gigas from two hadal trenches, the Mariana Trench and Japan Trench, were sequenced and analyzed. Taxonomic analysis identified 49 microbial genera commonly shared by the gut microbiota of the two H. gigas populations. However, the results of statistical analysis, in congruency with the alpha and beta diversity analyses, revealed significant differences in gut microbial composition across the two trenches. Abundance variation of Psychromonas, Propionibacterium, and Pseudoalteromonas species was observed. Microbial cooccurrence was demonstrated for microbes that were overrepresented in the Mariana trench. Comparison of functional potential showed that the percentage of carbohydrate metabolic genes among the total microbial genes was significantly higher in the guts of H. gigas specimens from the Mariana Trench. Integrating carbon input information and geological characters of the two hadal trenches, we propose that the differences in the community structure might be due to several selective factors, such as environmental variations and microbial interactions.IMPORTANCE The taxonomic composition and functional potential of animal gut microbiota in deep-sea environments remain largely unknown. Here, by performing comparative metagenomics, we suggest that the gut microbial compositions of two Hirondellea gigas populations from the Mariana Trench and the Japan Trench have undergone significant divergence. Through analyses of functional potentials and microbe-microbe correlations, our findings shed light on the contributions of animal gut microbiota to host adaptation to hadal environments.

Capacity for instantaneous catabolism of preferred and non-preferred carbon sources in Escherichia coli and Bacillus subtilis

Making the right choice for nutrient consumption in an ever-changing environment is a key factor for evolutionary success of bacteria. Here we investigate the regulatory mechanisms that enable dynamic adaptation between non-preferred and preferred carbon sources for the model Gram-negative and -positive species Escherichia coli and Bacillus subtilis, respectively. We focus on the ability for instantaneous catabolism of a gluconeogenic carbon source upon growth on a glycolytic carbon source and vice versa. By following isotopic tracer dynamics on a 1–2 minute scale, we show that flux reversal from the preferred glucose to non-preferred pyruvate as the sole carbon source is primarily transcriptionally regulated. In the opposite direction, however, E. coli can reverse its flux instantaneously by means of allosteric regulation, whereas in B. subtilis this flux reversal is transcriptionally regulated. Upon removal of transcriptional regulation, B. subtilis assumes the ability of instantaneous glucose catabolism. Using an approach that combines quantitative metabolomics and kinetic modelling, we then identify the additionally necessary key metabolite-enzyme interactions that implement the instantaneous flux reversal in the transcriptionally deregulated B. subtilis, and validate the most relevant allosteric interactions.

Carbon Catabolite Repression and the Related Genes of ccpA, ptsH and hprK in Thermoanaerobacterium aotearoense

The strictly anaerobic, Gram-positive bacterium, Thermoanaerobacterium aotearoense SCUT27, is capable of producing ethanol, hydrogen and lactic acid by directly fermenting glucan, xylan and various lignocellulosically derived sugars. By using non-metabolizable and metabolizable sugars as substrates, we found that cellobiose, galactose, arabinose and starch utilization was strongly inhibited by the existence of 2-deoxyglucose (2-DG). However, the xylose and mannose consumptions were not markedly affected by 2-DG at the concentration of one-tenth of the metabolizable sugar. Accordingly, T. aotearoense SCUT27 could consume xylose and mannose in the presence of glucose. The carbon catabolite repression (CCR) related genes, ccpA, ptsH and hprK were confirmed to exist in T. aotearoense SCUT27 through gene cloning and protein characterization. The highly purified Histidine-containing Protein (HPr) could be specifically phosphorylated at Serine 46 by HPr kinase/phosphatase (HPrK/P) with no need to add fructose-1,6-bisphosphate (FBP) or glucose-6-phosphate (Glc-6-P) in the reaction mixture. The specific protein-interaction of catabolite control protein A (CcpA) and phosphorylated HPr was proved via affinity chromatography in the absence of formaldehyde. The equilibrium binding constant (KD) of CcpA and HPrSerP was determined as 2.22 ± 0.36 nM by surface plasmon resonance (SPR) analysis, indicating the high affinity between these two proteins.

Carbon catabolite repression in Thermoanaerobacterium saccharolyticum

BACKGROUND

The thermophilic anaerobe Thermoanaerobacterium saccharolyticum is capable of directly fermenting xylan and the biomass-derived sugars glucose, cellobiose, xylose, mannose, galactose and arabinose. It has been metabolically engineered and developed as a biocatalyst for the production of ethanol.

RESULTS

We report the initial characterization of the carbon catabolite repression system in this organism. We find that sugar metabolism in T. saccharolyticum is regulated by histidine-containing protein HPr. We describe a mutation in HPr, His15Asp, that leads to derepression of less-favored carbon source utilization.

CONCLUSION

Co-utilization of sugars can be achieved by mutation of HPr in T. saccharolyticum. Further manipulation of CCR in this organism will be instrumental in achieving complete and rapid conversion of all available sugars to ethanol.

Regulation of sugar catabolism in Lactococcus lactis

The increasing number of genomic and post-genomic studies on Gram-positive organisms and especially on lactic acid bacteria brings a lot of information on sugar catabolism in these bacteria. Like for many other bacteria, glucose is the most preferred source of carbon and energy for Lactococcus lactis. Other carbon sources can induce their own utilization in the absence of well-metabolized sugar. These processes engage numbers of genes and undergo complex mechanisms of regulation. In this review, we discuss various biochemical and genetic control mechanisms involved in sugar catabolism, like regulation by repressors, activators, antiterminators or carbon catabolite repression control.

How phosphotransferase system-related protein phosphorylation regulates carbohydrate metabolism in bacteria

The phosphoenolpyruvate(PEP):carbohydrate phosphotransferase system (PTS) is found only in bacteria, where it catalyzes the transport and phosphorylation of numerous monosaccharides, disaccharides, amino sugars, polyols, and other sugar derivatives. To carry out its catalytic function in sugar transport and phosphorylation, the PTS uses PEP as an energy source and phosphoryl donor. The phosphoryl group of PEP is usually transferred via four distinct proteins (domains) to the transported sugar bound to the respective membrane component(s) (EIIC and EIID) of the PTS. The organization of the PTS as a four-step phosphoryl transfer system, in which all P derivatives exhibit similar energy (phosphorylation occurs at histidyl or cysteyl residues), is surprising, as a single protein (or domain) coupling energy transfer and sugar phosphorylation would be sufficient for PTS function. A possible explanation for the complexity of the PTS was provided by the discovery that the PTS also carries out numerous regulatory functions. Depending on their phosphorylation state, the four proteins (domains) forming the PTS phosphorylation cascade (EI, HPr, EIIA, and EIIB) can phosphorylate or interact with numerous non-PTS proteins and thereby regulate their activity. In addition, in certain bacteria, one of the PTS components (HPr) is phosphorylated by ATP at a seryl residue, which increases the complexity of PTS-mediated regulation. In this review, we try to summarize the known protein phosphorylation-related regulatory functions of the PTS. As we shall see, the PTS regulation network not only controls carbohydrate uptake and metabolism but also interferes with the utilization of nitrogen and phosphorus and the virulence of certain pathogens.

Inactivation of the Streptococcus mutans fxpC gene confers resistance to xylitol, a caries-preventive natural carbohydrate sweetener

Xylitol is transported by Streptococcus mutans via a constitutive phosphoenolpyruvate:fructose phosphotransferase system (PTS) composed of a IIABC protein. Spontaneous xylitol-resistant strains are depleted in constitutive fructose-PTS activity, exhibit additional phenotypes, and are associated with the caries-preventive properties of xylitol. Polymerase chain-reactions and chromosome walking were used to clone the fxp operon that codes for the constitutive fructose/xylitol-PTS. The operon contained three open reading frames: fxpA, which coded for a putative regulatory protein of the deoxyribose repressor (DeoR) family, fxpB, which coded for a 1-phosphofructokinase, and fxpC, which coded for a IIABC protein of the fructose-PTS family. Northern blot analysis revealed that these genes were co-transcribed into a 4.4-kb mRNA even in the absence of fructose. Inactivation of the fxpC gene conferred resistance to xylitol, confirming its function. The fxp operon is also present in the genomes of other xylitol-sensitive streptococci, which could explain their sensitivity to xylitol.

Glucose uptake in Clostridium beijerinckii NCIMB 8052 and the solvent-hyperproducing mutant BA101

Glucose uptake and accumulation by Clostridium beijerinckii BA101, a butanol hyperproducing mutant, were examined during various stages of growth. Glucose uptake in C. beijerinckii BA101 was repressed 20% by 2-deoxyglucose and 25% by mannose, while glucose uptake in C. beijerinckii 8052 was repressed 52 and 28% by these sugars, respectively. We confirmed the presence of a phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) associated with cell extracts of C. beijerinckii BA101 by glucose phosphorylation by PEP. The PTS activity associated with C. beijerinckii BA101 was 50% of that observed for C. beijerinckii 8052. C. beijerinckii BA101 also demonstrated lower PTS activity for fructose and glucitol. Glucose phosphorylation by cell extracts derived from both C. beijerinckii BA101 and 8052 was also dependent on the presence of ATP, a finding consistent with the presence of glucokinase activity in C. beijerinckii extracts. ATP-dependent glucose phosphorylation was predominant during the solventogenic stage, when PEP-dependent glucose phosphorylation was dramatically repressed. A nearly twofold-greater ATP-dependent phosphorylation rate was observed for solventogenic stage C. beijerinckii BA101 than for solventogenic stage C. beijerinckii 8052. These results suggest that C. beijerinckii BA101 is defective in PTS activity and that C. beijerinckii BA101 compensates for this defect with enhanced glucokinase activity, resulting in an ability to transport and utilize glucose during the solventogenic stage.

Effect of different cultivation conditions on Lactobacillus manihotivorans OND32T, an amylolytic lactobacillus isolated from sour starch cassava fermentation

Study of the cassava sour starch fermentation has led to the isolation of a new homofermentative amylolytic lactic acid bacterium, Lactobacillus manihotivorans OND32T, whose nutritional requirements have been investigated in this work. The main effect of deleting one of the substrate components of the MRS-starch medium was to reduce the amylase production. When starch fermentation with nitrogen as a gas phase was compared to fermentation under aerobic conditions, both growth and amylase production were reduced whereas lactic acid formation was not affected. Addition of carbon dioxide (> or = 20% v/v) to the nitrogen gas phase restored growth and amylase production. The amylase production was high with starch, maltose or cellobiose contrary to glucose, fructose and sucrose. During mixed fermentation of glucose and maltose, a diauxic growth was observed. The maltose consumption and the amylase production started after the glucose depletion. The presence of maltose altered the carbon assimilation from glucose, whereas the energetic pathway was not affected. It is concluded that the elimination of soluble sugars by the wet extraction of starch during the processing of cassava, together with the expected in situ CO2 production, are conditions favouring the growth and the amylase synthesis. However, these are likely to be limited by the low nitrogen content in cassava.

Mutations lowering the phosphatase activity of HPr kinase/phosphatase switch off carbon metabolism

The oligomeric bifunctional HPr kinase/P-Ser-HPr phosphatase (HprK/P) regulates many metabolic functions in Gram-positive bacteria by phosphorylating the phosphocarrier protein HPr at Ser46. We isolated Lactobacillus casei hprK alleles encoding mutant HprK/Ps exhibiting strongly reduced phosphatase, but almost normal kinase activity. Two mutations affected the Walker motif A of HprK/P and four a conserved C-terminal region in contact with the ATP-binding site of an adjacent subunit in the hexamer. Kinase and phosphatase activity appeared to be closely associated and linked to the Walker motif A, but dephosphorylation of seryl-phosphorylated HPr (P-Ser-HPr) is not simply a reversal of the kinase reaction. When the hprKV267F allele was expressed in Bacillus subtilis, the strongly reduced phosphatase activity of the mutant enzyme led to increased amounts of P-Ser-HPr. The hprKV267F mutant was unable to grow on carbohydrates transported by the phosphoenolpyruvate:glycose phosphotransferase system (PTS) and on most non-PTS carbohydrates. Disrupting ccpA relieved the growth defect only on non-PTS sugars, whereas replacing Ser46 in HPr with alanine also restored growth on PTS substrates.

Regulatory functions of serine-46-phosphorylated HPr in Lactococcus lactis

In most low-G+C gram-positive bacteria, the phosphoryl carrier protein HPr of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) becomes phosphorylated at Ser-46. This ATP-dependent reaction is catalyzed by the bifunctional HPr kinase/P-Ser-HPr phosphatase. We found that serine-phosphorylated HPr (P-Ser-HPr) of Lactococcus lactis participates not only in carbon catabolite repression of an operon encoding a beta-glucoside-specific EII and a 6-P-beta-glucosidase but also in inducer exclusion of the non-PTS carbohydrates maltose and ribose. In a wild-type strain, transport of these non-PTS carbohydrates is strongly inhibited by the presence of glucose, whereas in a ptsH1 mutant, in which Ser-46 of HPr is replaced with an alanine, glucose had lost its inhibitory effect. In vitro experiments carried out with L. lactis vesicles had suggested that P-Ser-HPr is also implicated in inducer expulsion of nonmetabolizable homologues of PTS sugars, such as methyl beta-D-thiogalactoside (TMG) and 2-deoxy-D-glucose (2-DG). In vivo experiments with the ptsH1 mutant established that P-Ser-HPr is not necessary for inducer expulsion. Glucose-activated 2-DG expulsion occurred at similar rates in wild-type and ptsH1 mutant strains, whereas TMG expulsion was slowed in the ptsH1 mutant. It therefore seems that P-Ser-HPr is not essential for inducer expulsion but that in certain cases it can play an indirect role in this regulatory process.

Expression of the phospho-beta-glycosidase ArbZ from Lactobacillus delbrueckii subsp. lactis in Lactobacillus helveticus: substrate induction and catabolite repression

ArbZ from Lactobacillus delbrueckii subsp. lactis was previously shown to enable utilization of the beta-glucoside arbutin by Escherichia coli. The arbZ gene was cloned and expressed in the industrially used beta-glucoside-negative strain Lactobacillus helveticus 3036(62). The transformants were able to ferment not only arbutin, but also cellobiose, salicin and methyl-beta-glucoside (MbetaGlc). Cleavage of beta-glucosides by the transformants depended on the integrity of the cytoplasmic membrane, whereas in cell-free extracts only C(6)-phosphorylated substrates were hydrolysed. This suggested that ArbZ is a phospho-beta-glycosidase. ArbZ activity in transformants of Lb. helveticus was subject to substrate induction mediated by the beta-glucosides arbutin, salicin and MbetaGlc, whereas cellobiose or the beta-galactoside lactose had no inducing effect. Northern blot analysis proved that induction by MbetaGlc was due to enhanced transcription of arbZ. Catabolite repression of arbZ induction was observed with glucose, mannose, fructose and galactose. The induction kinetics observed in the presence of these sugars indicated that at least two different mechanisms are operative in catabolite repression of arbZ in Lb. helveticus.

Mutational analysis of the role of HPr in Listeria monocytogenes

The regulatory role of HPr, a protein of the phosphotransferase system (PTS), was investigated in Listeria monocytogenes. By constructing mutations in the conserved histidine 15 and serine 46 residues of HPr, we were able to examine how HPr regulates PTS activity. The results indicated that histidine 15 was phosphorylated in a phosphoenolpyruvate (PEP)-dependent manner and was essential for PTS activity. Serine 46 was phosphorylated in an ATP-dependent manner by a membrane-associated kinase. ATP-dependent phosphorylation of serine 46 was significantly enhanced in the presence of fructose 1,6-diphosphate and resulted in a reduction of PTS activity. The presence of a charge at position 15 did not inhibit ATP-dependent phosphorylation of serine 46, a finding unique to gram-positive PEP-dependent PTSs studied to this point. Finally, HPr phosphorylated at serine 46 does not appear to possess self-phosphatase activity, suggesting a specific phosphatase protein may be essential for the recycling of HPr to its active form.

Cloning and expression of the Listeria monocytogenes scott A ptsH and ptsI genes, coding for HPr and enzyme I, respectively, of the phosphotransferase system

The phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS) utilizes high-energy phosphate present in PEP to drive the uptake of several different carbohydrates in bacteria. In order to examine the role of the PTS in the physiology of Listeria monocytogenes, we identified the ptsH and ptsI genes encoding the HPr and enzyme I proteins, respectively, of the PTS. Nucleotide sequence analysis indicated that the predicted proteins are nearly 70% similar to HPr and enzyme I proteins from other organisms. Purified L. monocytogenes HPr overexpressed in Escherichia coli was also capable of complementing an HPr defect in heterologous extracts of Staphylococcus aureus ptsH mutants. Additional studies of the transcriptional organization and control indicated that the ptsH and ptsI genes are organized into a transcription unit that is under the control of a consensus-like promoter and that expression of these genes is mediated by glucose availability and pH or by by-products of glucose metabolism.

Catabolite repression in Lactobacillus casei ATCC 393 is mediated by CcpA

The chromosomal ccpA gene from Lactobacillus casei ATCC 393 has been cloned and sequenced. It encodes the CcpA protein, a central catabolite regulator belonging to the LacI-GalR family of bacterial repressors, and shows 54% identity with CcpA proteins from Bacillus subtilis and Bacillus megaterium. The L. casei ccpA gene was able to complement a B. subtilis ccpA mutant. An L. casei ccpA mutant showed increased doubling times and a relief of the catabolite repression of some enzymatic activities, such as N-acetylglucosaminidase and phospho-beta-galactosidase. Detailed analysis of CcpA activity was performed by using the promoter region of the L. casei chromosomal lacTEGF operon which is subject to catabolite repression and contains a catabolite responsive element (cre) consensus sequence. Deletion of this cre site or the presence of the ccpA mutation abolished the catabolite repression of a lacp::gusA fusion. These data support the role of CcpA as a common regulatory element mediating catabolite repression in low-GC-content gram-positive bacteria.