Cloning and expression of the inorganic pyrophosphatase gene from the amino acid producer Brevibacterium lactofermentum ATCC 13869

Hidden diversity and potential ecological function of phosphorus acquisition genes in widespread terrestrial bacteriophages

Phosphorus (P) limitation of ecosystem processes is widespread in terrestrial habitats. While a few auxiliary metabolic genes (AMGs) in bacteriophages from aquatic habitats are reported to have the potential to enhance P-acquisition ability of their hosts, little is known about the diversity and potential ecological function of P-acquisition genes encoded by terrestrial bacteriophages. Here, we analyze 333 soil metagenomes from five terrestrial habitat types across China and identify 75 viral operational taxonomic units (vOTUs) that encode 105 P-acquisition AMGs. These AMGs span 17 distinct functional genes involved in four primary processes of microbial P-acquisition. Among them, over 60% (11/17) have not been reported previously. We experimentally verify in-vitro enzymatic activities of two pyrophosphatases and one alkaline phosphatase encoded by P-acquisition vOTUs. Thirty-six percent of the 75 P-acquisition vOTUs are detectable in a published global topsoil metagenome dataset. Further analyses reveal that, under certain circumstances, the identified P-acquisition AMGs have a greater influence on soil P availability and are more dominant in soil metatranscriptomes than their corresponding bacterial genes. Overall, our results reinforce the necessity of incorporating viral contributions into biogeochemical P cycling.

A novel fluorescence assay for inorganic pyrophosphatase based on modulated aggregation of graphene quantum dots

A simple and highly sensitive fluorometric method has been developed for inorganic pyrophosphatase (PPase) activity detection based on the disaggregation and aggregation of graphene quantum dots (GQDs).

Proteome of Gluconacetobacter diazotrophicus co-cultivated with sugarcane plantlets

Gluconacetobacter diazotrophicus is a micro-aerobic bacterium able to fix atmospheric nitrogen in endophytic mode. A proteomic approach was used to analyze proteins differentially expressed in the presence and absence of sugarcane plantlets. Two-dimensional gel electrophoresis (2-DE) showed 42 spots with altered levels of expression. Analysis of these spots by matrix-assisted laser desorption ionization time-of-flight in tandem (MALDI-TOF-TOF) identified 38 proteins. Differentially expressed proteins were associated with carbohydrate and energy metabolism, folding, sorting and degradation processes, and transcription and translation. Among proteins expressed in co-cultivated bacteria, four belong to membrane systems; others, like a transcription elongation factor (GreA), a 60 kDa chaperonin (GroEL), and an outer membrane lipoprotein (Omp16) have also been described in other plant-bacteria associations, indicating a common protein expression pattern as a result of symbiosis. A high protein content of 60kDa chaperonin isoforms was detected as non-differentially expressed proteins of the bacteria proteome. These results allow the assessment of the physiological significance of specific proteins to G. diazotrophicus metabolism and to the pathways involved in bacteria-host endophytic interaction.

Exopolyphosphatases PPX1 and PPX2 from Corynebacterium glutamicum

Corynebacterium glutamicum accumulates up to 300 mM of inorganic polyphosphate (PolyP) in the cytosol or in granules. The gene products of cg0488 (ppx1) and cg1115 (ppx2) were shown to be active as exopolyphosphatases (PPX), as overexpression of either gene resulted in higher exopolyphosphatase activities in crude extracts and deletion of either gene with lower activities than those of the wild-type strain. PPX1 and PPX2 from C. glutamicum share only 25% identical amino acids and belong to different protein groups, which are distinct from enterobacterial, archaeal, and yeast exopolyphosphatases. In comparison to that in the wild type, more intracellular PolyP accumulated in the Deltappx1 and Deltappx2 deletion mutations but less when either ppx1 or ppx2 was overexpressed. When C. glutamicum was shifted from phosphate-rich to phosphate-limiting conditions, a growth advantage of the deletion mutants and a growth disadvantage of the overexpression strains compared to the wild type were observed. Growth experiments, exopolyphosphatase activities, and intracellular PolyP concentrations revealed PPX2 as being a major exopolyphosphatase from C. glutamicum. PPX2(His) was purified to homogeneity and shown to be active as a monomer. The enzyme required Mg2+ or Mn2+ cations but was inhibited by millimolar concentrations of Mg2+, Mn2+, and Ca2+. PPX2 from C. glutamicum was active with short-chain polyphosphates, even accepting pyrophosphate, and was inhibited by nucleoside triphosphates.

Morphological changes and proteome response of Corynebacterium glutamicum to a partial depletion of FtsI

In Corynebacterium glutamicum, as in many Gram-positive bacteria, the cell division gene ftsI is located at the beginning of the dcw cluster, which comprises cell division- and cell wall-related genes. Transcriptional analysis of the cluster revealed that ftsI is transcribed as part of a polycistronic mRNA, which includes at least mraZ, mraW, ftsL, ftsI and murE, from a promoter that is located upstream of mraZ. ftsI appears also to be expressed from a minor promoter that is located in the intergenic ftsL–ftsI region. It is an essential gene in C. glutamicum, and a reduced expression of ftsI leads to the formation of larger and filamentous cells. A translational GFP-FtsI fusion protein was found to be functional and localized to the mid-cell of a growing bacterium, providing evidence of its role in cell division in C. glutamicum. This study involving proteomic analysis (using 2D SDS-PAGE) of a C. glutamicum strain that has partially depleted levels of FtsI reveals that at least 20 different proteins were overexpressed in the organism. Eight of these overexpressed proteins, which include DivIVA, were identified by MALDI-TOF. Overexpression of DivIVA was confirmed by Western blotting using anti-DivIVA antibodies, and also by fluorescence microscopy analysis of a C. glutamicum RESF1 strain expressing a chromosomal copy of a divIVA-gfp transcriptional fusion. Overexpression of DivIVA was not observed when FtsI was inhibited by cephalexin treatment or by partial depletion of FtsZ.

Altered morphology produced by ftsZ expression in Corynebacterium glutamicum ATCC 13869

Corynebacterium glutamicum is a Gram-positive bacterium that lacks the cell division FtsA protein and actin-like MreB proteins responsible for determining cylindrical cell shape. When the cell division ftsZ gene from C. glutamicum (ftsZCg ) was cloned in different multicopy plasmids, the resulting constructions could not be introduced into C. glutamicum; it was assumed that elevated levels of FtsZ Cg result in lethality. The presence of a truncated ftsZCg and a complete ftsZCg under the control of Plac led to a fourfold reduction in the intracellular levels of FtsZ, generating aberrant cells displaying buds, branches and knots, but no filaments. A 20-fold reduction of the FtsZ level by transformation with a plasmid carrying the Escherichia coli lacI gene dramatically reduced the growth rate of C. glutamicum, and the cells were larger and club-shaped. Immunofluorescence microscopy of FtsZ Cg or visualization of FtsZ Cg –GFP in C. glutamicum revealed that most cells showed one fluorescent band, most likely a ring, at the mid-cell, and some cells showed two fluorescent bands (septa of future daughter cells). When FtsZ Cg –GFP was expressed from Plac, FtsZ rings at mid-cell, or spirals, were also clearly visible in the aberrant cells; however, this morphology was not entirely due to GFP but also to the reduced levels of FtsZ expressed from Plac. Localization of FtsZ at the septum is not negatively regulated by the nucleoid, and therefore the well-known occlusion mechanism seems not to operate in C. glutamicum.

Formation of volutin granules in Corynebacterium glutamicum

Volutin granules are intracellular storages of complexed inorganic polyphosphate (poly P). Histochemical staining procedures differentiate between pathogenic corynebacteria such as Corynebacterum diphtheriae (containing volutin) and non-pathogenic species, such as C. glutamicum. Here we report that strains ATCC13032 and MH20-22B of the non-pathogenic C. glutamicum also formed subcellular entities (18-37% of the total cell volume) that had the typical characteristics of volutin granules: (i) volutin staining, (ii) green UV fluorescence when stained with 4',6-diamidino-2-phenylindole, (iii) electron-dense and rich in phosphorus when determined with transmission electron microscopy and X-ray microanalysis, and (iv) 31P NMR poly P resonances of isolated granules dissolved in EDTA. MgCl2 addition to the growth medium stimulated granule formation but did not effect expression of genes involved in poly P metabolism. Granular volutin fractions from lysed cells contained polyphosphate glucokinase as detected by SDS-PAGE/MALDI-TOF, indicating that this poly P metabolizing enzyme is present also in intact poly P granules. The results suggest that formation of volutin is a more widespread phenomenon than generally accepted.

Involvement of DivIVA in the morphology of the rod-shaped actinomycete Brevibacterium lactofermentum

In Brevibacterium lactofermentum, as in many Gram-positive bacteria, a divIVA gene is located downstream from the dcw cluster of cell-division- and cell-wall-related genes. This gene (divIVA(BL)) is mostly expressed during exponential growth, and the protein encoded, DivIVA(BL,) bears some sequence similarity to antigen 84 (Ag84) from mycobacteria and was detected with monoclonal antibodies against Ag84. Disruption experiments using an internal fragment of the divIVA(BL) gene or a disrupted divIVA(BL) cloned in a suicide conjugative plasmid were unsuccessful, suggesting that the divIVA(BL) gene is needed for cell viability in BREV: lactofermentum. Transformation of BREV: lactofermentum with a multicopy plasmid containing divIVA(BL) drastically altered the morphology of the corynebacterial cells, which became larger and bulkier, and a GFP fusion to DivIVA(BL) mainly localized to the ends of corynebacterial cells. This localization pattern, together with the overproduction phenotype, suggests that DivIVA may be important in regulating the apical growth of daughter cells.