Induction of pleomorphy and calcium ion deficiency in Lactobacillus bifidus

Bifid Shape Is Intrinsic to Bifidobacterium adolescentis

Although the genus Bifidobacterium was originally named for its bifid morphology, not all bifidobacterial species have a similar structure, and very few of them adopt a bifid shape under stress conditions. The exposure of respective bifidobacterial species to various conditions, such as different pH, temperatures, medium components, in vivo growth in Caenorhabditis elegans, and subculture, did not affect their diverse morphologies. Extensive scanning electron microscopy studies suggested that the bifid shape of B. adolescentis are maintained irrespective of the conditions. Hence, we conclude that the bifid morphology is intrinsic to B. adolescentis. Most bifidobacterial species are anaerobic and rod-shaped, whereas, after the first generation, they become microaerophilic or aerophilic. CaCl2 (treatment of B. animalis) signaling triggered a change from the rod shape to the bifid shape and vice versa in B. adolescentis.

Effects of ascorbic acid on α-l-arabinofuranosidase and α-l-arabinopyranosidase activities from Bifidobacterium longum RD47 and its application to whole cell bioconversion of ginsenoside

Bifidobacterium longum RD47 was cultured in 24 kinds of modified MRS broths containing various ingredients to select the most promising source that induces microbial enzymes. Among the various ingredients, ascorbic acid significantly enhanced α-l-arabinofuranosidase and α-l-arabinopyranosidase activities in Bifidobacterium longum RD47. Addition of 2 % ascorbic acid (w/v) to MRS showed the maximum enzyme activities. Both whole cell and disrupted cell homogenates showed efficient ρ-nitrophenyl-β-d-glucopyranoside and ρ-nitrophenyl-β-d-glucofuranoside hydrolysis activities. The initially enhanced α-l-arabinopyranosidase and α-l-arabinofuranosidase activities by ascorbic acid were maintained over the cell disruption process. The optimal pH of α-l-arabinofuranosidase and α-l-arabinopyranosidase was 5.0 and 7.0, respectively. Both enzymes showed the maximum activities at 40.0 °C. Under the controlled condition using Bifidobacterium longum RD47, ginsenoside Rb2, and Rc were converted to ginsenoside Rd.

Control of cell morphology of probiotic Lactobacillus acidophilus for enhanced cell stability during industrial processing

The viability of bacteria during industrial processing is an essential quality criterion for bacterial preparations, such as probiotics and starter cultures. Therefore, producing stable microbial cultures during proliferation is of great interest. A strong correlation between the culture medium and cellular morphology was observed for the lactic acid bacterium Lactobacillus acidophilus NCFM, which is commonly used in the dairy industry as a probiotic supplement and as a starter culture. The cell shapes ranged from single short rods to long filamentous rods. The culture medium composition could control this phenomenon of pleomorphism, especially the use of peptone in combination with an adequate heating of the medium during preparation. Furthermore, we observed a correlation between the cell size and stability of the microorganisms during industrial processing steps, such as freeze-drying, extrusion encapsulation and storage following dried preparations. The results revealed that short cells are more stable than long cells during each of the industrially relevant processing steps. As demonstrated for L. acidophilus NCFM, the adaptation of the medium composition and optimized medium preparation offer the possibility to increase the concentration of viable cells during up- and survival rate during down-stream processing.

Genomic insights into bifidobacteria

Since the discovery in 1899 of bifidobacteria as numerically dominant microbes in the feces of breast-fed infants, there have been numerous studies addressing their role in modulating gut microflora as well as their other potential health benefits. Because of this, they are frequently incorporated into foods as probiotic cultures. An understanding of their full interactions with intestinal microbes and the host is needed to scientifically validate any health benefits they may afford. Recently, the genome sequences of nine strains representing four species of Bifidobacterium became available. A comparative genome analysis of these genomes reveals a likely efficient capacity to adapt to their habitats, with B. longum subsp. infantis exhibiting more genomic potential to utilize human milk oligosaccharides, consistent with its habitat in the infant gut. Conversely, B. longum subsp. longum exhibits a higher genomic potential for utilization of plant-derived complex carbohydrates and polyols, consistent with its habitat in an adult gut. An intriguing observation is the loss of much of this genome potential when strains are adapted to pure culture environments, as highlighted by the genomes of B. animalis subsp. lactis strains, which exhibit the least potential for a gut habitat and are believed to have evolved from the B. animalis species during adaptation to dairy fermentation environments.

Phage-resistance linked to cell heterogeneity in the commercial strain Lactobacillus delbrueckii subsp. lactis Ab1

The aim of this work was to study the relationship between the cell morphological heterogeneity and the phage-resistance in the commercial strain Lactobacillus delbrueckii subsp. lactis Ab1. Two morphological variants (named C and T) were isolated from this strain. Phage-resistant derivatives were isolated from them and the percentage of occurrence of confirmed phage-resistant cells was 0.001% of the total cellular population. Within these phage-resistant cell derivatives there were T (3 out of 4 total isolates) and C (1 out of 4 total isolates) variants. The study of some technological properties (e.g. proteolytic and acidifying activities) demonstrated that most of phage-resistant derivatives were not as good as the parental strain. However, for one derivative (a T variant), the technological properties were better than those of the parental strain. On the other hand, it was possible to determinate that the system of phage-resistance in the T variants was interference in adsorption step, with adsorption rates <15%. For the C variant derivative it was possible to demonstrate the presence of a restriction/modification system and, moreover, to determinate that this system could be Type I R/M.

Staphylococcus aureus requires increased level of Ca(2+) or Mn(2+) to grow normally in a high-NaCl/low-Mg(2+) medium

Mg2+-availability in Staphylococcus aureus cells decreased significantly with increasing NaCl concentration in growth media. Cells grew in a NaCl-free, Chelex resin-treated complex medium only if the medium was supplemented with 50 microM MgCl2, while, growth was limited when the medium was further supplemented with 1.0 M NaCl. Cells grown in such a high-NaCl/low-Mg2+ medium exhibited the morphologic abnormality of larger than normal cells. Both sufficient growth and normal cell morphology were restored by increasing Mg2+ concentration in a high-NaCl medium, or by supplementation with either CaCl2 or MnSO4 in a high-NaCl/low-Mg2+ medium. Supplementing with BaCl2, SrCl2 or FeSO4, however, had no effect. These results indicate that Ca2+ and Mn2+ might play some essential role in the growth of Staphylococcus aureus in a high-NaCl/low-Mg2+ environment.

Cloning of pectate lyase gene pel from Pseudomonas fluorescens and detection of sequences homologous to pel in Pseudomonas viridiflava and Pseudomonas putida

Pectate lyase (PL) depolymerizes pectin and other polygalacturonates (PGAs) and is thought to play a role in bacterial invasion of plants. Production of PL by the soft-rotting pathogen Pseudomonas fluorescens CY091 is regulated by Ca2+. In the presence of Ca2+, this bacterium constitutively synthesizes PL in media containing glucose, glycerol, or PGA and excretes over 87% of total PL into culture fluids. In the absence of Ca2+, the organism fails to use PGA as a carbon source and produces very low levels of PL in media containing glucose or glycerol. Of the small amount of PL produced by the bacterium in Ca(2+)-deficient media, over 78% was detected within the cells, indicating that Ca2+ is critical not only for the production but also for the secretion of PL. The pel gene, encoding an alkaline PL (pI 10.0, Mr 41,000) was cloned and located on the overlapping region of a 4.3-kb SalI and a 7.1-kb EcoRI fragment. The 7.1-kb EcoRI fragment appears to contain a promoter for pel gene expression. A 1.7-kb SalI-XhoI subfragment of the 4.3-kb SalI fragment was cloned into pUC18 to give pROTM2. Escherichia coli cells carrying pROTM2 produce 50 to 100 times more PL than do cells carrying other pectolytic constructs. Production of PL by E. coli (pROTM2) was not affected by carbon sources or by Ca2+. The pI and Mr of PL from E. coli corresponded to values for its counterpart from P. fluorescens. A 0.7-kb BglII-ClaI fragment encoding the pel structural sequence was used to detect pel homologs in various species of fluorescent pseudomonads. Homologous sequences were observed in 10 of 11 strains of P. fluorescens, P. viridiflava, and P. putida. The pel gene in fluorescent pseudomonads is well conserved and may exist and remain repressed in certain strains or species which exhibit nonpectolytic phenotypes under laboratory conditions.

Calcium transport in membrane vesicles of Bacillus subtilis

Right-side-out membrane vesicles of Bacillus subtilis W23 grown on tryptone-citrate medium accumulated Ca2+ under aerobic conditions in the presence of a suitable electron donor. Ca2+ uptake was an electrogenic process which was completely inhibited by carbonyl cyanide m-chlorophenylhydrazone or valinomycin and not by nigericin. This electrogenic uptake of calcium was strongly dependent on the presence of phosphate and magnesium ions. The system had a low affinity for Ca2+. The kinetic constants in membrane vesicles were Km = 310 microM Ca2+ and Vmax = 16 nmol/mg of protein per min. B. subtilis also possesses a Ca2+ extrusion system. Right-side-out-oriented membrane vesicles accumulated Ca2+ upon the artificial imposition of a pH-gradient, inside acid. This system had a high affinity for Ca2+; Km = 17 microM Ca2+ and Vmax = 3.3 nmol/mg of protein per min. Also, a membrane potential, inside positive, drove Ca2+ transport via this Ca2+ extrusion system. Evidence for a Ca2+ extrusion system was also supplied by studies of inside-out-oriented membrane vesicles in which Ca2+ uptake was energized by respiratory chain-linked oxidation of NADH or ascorbate-phenazine methosulfate. Both components of the proton motive force, the pH gradient and the membrane potential, drove Ca2+ transport via the Ca2+ extrusion system, indicating a proton-calcium antiport system with a H+ to Ca2+ stoichiometry larger than 2. The kinetic parameters of this Ca2+ extrusion system in inside-out-oriented membranes were Km = 25 microM and Vmax = 0.7 nmol/mg of protein per min.

RNA synthesis in Yersinia pestis during growth restriction in calcium-deficient medium

Yersinia pestis requires 2.5 mM Ca(2+) for growth at 37 degrees C but not at 26 degrees C. After a shift from 26 to 37 degrees C in a Ca(2+)-deficient medium, an ordered series of metabolic alterations occur which result in transition from a growing cell to a viable but non-proliferating cell. The earliest known alteration in normal metabolism associated with this transition is a termination of net RNA synthesis. Competitive RNA/DNA hybridizations with uniformly labeled RNA and stable RNA competitor indicated identical mRNA to stable RNA ratios in growing cells and non-proliferating Ca(2+)-deprived cells. Similar hybridizations with pulse-labeled RNA demonstrated that growing cells synthesized 57% mRNA, 37% rRNA, and 5% tRNA, whereas Ca(2+)-deprived cells synthesized 95% mRNA, 4.7% rRNA, and 0.7% tRNA. After addition of radioactive uracil and rifampin to growing and Ca(2+)-deprived cells, decay of approximately 40 and 90% of the newly synthesized RNA was found for growing and Ca(2+)-deprived cells, respectively. The half-life of the mRNA was found to be 1.5 min for growing cells and 4.5 min for Ca(2+)-deprived cells. Y. pestis elicited increases in the levels of guanosine tetraphosphate and guanosine pentaphosphate in response to amino acid deprivation and yielded transient increases in the levels of these phosphorylated nucleotides after a shift from 26 to 37 degrees C. These increases were independent of Ca(2+) availability and preceded the alteration in RNA synthesis by more than 1 h. The levels of these phosphorylated nucleotides then stabilized at about 80 and 40 pmol for Ca(2+)-deprived and Ca(2+)-supplemented cultures, respectively, and did not increase further in the Ca(2+)-deprived culture at the time corresponding to the reduction in stable RNA synthesis. These findings indicate that the early lesion in RNA synthesis associated with the growth restriction of Ca(2+)-deprived Y. pestis reflects a block in stable RNA synthesis and that this effect is not mediated by guanosine tetraphosphate or guanosine pentaphosphate.

Growth Characteristics, Bile Sensitivity, and Freeze Damage in Colonial Variants of Lactobacillus acidophilus

Rough (R) and smooth (S) colonial variants were isolated from a heterogeneous culture of Lactobacillus acidophilus RL8K. R and S types were stable upon repeated transfer on agar, but revertant colonies did appear after broth transfers. When propagated in commercial MRS broth, R and S cultures showed similar growth characteristics, and both cell types were insensitive to freezing and frozen storage at −20°C. Alternatively, during growth in scratch MRS broth, R cultures shifted to a reduced rate of growth during the late logarithmic phase. R cells grown under these conditions were susceptible to death by freezing and injury at −20°C. Microscopically, R cells were observed as long gram-positive rods with small nonstainable blebs protruding from the cell wall. In bile sensitivity studies of R and S cells plated on MRS agar plus oxgall, the S culture was resistant to 1% bile, whereas the R culture was sensitive to 0.6% bile. Differences in the bile resistance and freeze damage of R and S cells suggest that colonial and cellular morphologies are important considerations for the selection of Lactobacillus strains as dietary adjuncts and for the development of growth conditions for preparing frozen concentrated cultures from either cell type.

Calcium-Induced Alteration of Cellular Morphology Affecting the Resistance of Lactobacillus acidophilus to Freezing

Examination of factors affecting the resistance of Lactobacillus acidophilus NCFM culture concentrates to freeze injury induced during frozen storage at -20°C revealed that calcium supplementation of the growth medium contributed to the storage stability of cells prepared in static culture. Culture concentrates of L. acidophilus NCFM were prepared from cells propagated in MRS broth or MRS broth supplemented with 0.1% calcium carbonate, calcium chloride, or calcium phosphate. After 28 days of frozen storage at -20°C, concentrated cells (3.2 × 10 9 colony-forming units per ml) prepared from MRS broth cultures showed an 84% reduction in viable cells. Of the remaining viable cells, 88% were sublethally injured and unable to form colonies on MRS agar supplemented with 0.15% bile. Cells prepared in calcium-supplemented MRS broths demonstrated more resistance to frozen storage. Viability and injury losses in the frozen concentrates were limited to 10 to 39% and 3 to 23%, respectively. It was observed that calcium supplementation of MRS medium resulted in a morphological transition of L. acidophilus NCFM from filamentous to bacilloid rods, and the bacilloid cells were more resistant to freezing and storage at conventional freezer temperatures. The results suggest that the morphology of the L. acidophilus cell may be an important consideration in the preparation of freeze-stable culture concentrates.

Consequences of Ca2+ deficiency on macromolecular synthesis and adenylate energy charge in Yersinia pestis

A 37 but not 26 degrees C virulent Yersinia pestis is known to require at least 2.5 mM Ca2+ for growth; this requirement is potentiated by Mg2+. After shift of log-phase cells (doubling time of 2 h) from 26 to 37 degrees C in Ca2+-deficient medium, shutoff of net ribonucleic acid synthesis preceded that of protein and cell mass. With 2.5 mM Mg2+, about two doublings in cell mass and number occurred before restriction with synthesis of sufficient deoxyribonucleic acid to account for initiation and termination of two postshift rounds of chromosome replication. Temperature shift with 20 mMMg2+ resulted in a single doubling of cell mass and number with one round of chromosome replication. Subsequent to shutoff of ribonucleic acid accumulation, ribonucleoside but not deoxyribonucleoside triphosphate pools became reduced to about 50% of normal values and the adenylate energy change fell from about 0.8, typical of growing cells, to about 0.6. Excretion of significant concentrations of adenine nucleotides under both permissive and restrictive conditions was observed. Only trace levels (less than 0.01 microM ol/g [dry weight]) of guaninosine 5'-diphosphate 3'-diphosphate accumulated under restrictive or permissive conditions; guanosine 5'-triphosphate 3'-diphosphate was not detected. Return of fully restricted cells from 37 to 26 degrees C with Ca2+ resulted in prompt growth, whereas addition of Ca2+ at 37 degrees C was ineffective. This finding indicates that the observed temperature-sensitive lesion in ribonucleic acid synthesis that results in restriction can be prevented but not reversed by cultivation with Ca2+.

Unidirectional growth and branch formation of a morphological mutant, Agrobacterium tumefaciens

Morphological characteristics of thermoconditional mutant Agrobacterium tumefaciens F-502 were investigated in relation to growth, division, and synthesis of cellular components. As a result of a shift from 27 to 37 C, mutant cells altered their morphology from short rods to elongated and branched forms; in addition, division and deoxyribonucleic acid synthesis were inhibited at 37 C. At 37 C unidirectional cell growth and branch formation occurred at one end of a cell, and the elongation rate of a cell was proportional to cell length. A hypothetical model for branch formation is presented in which the maximal elongation rate, 1.8 mum/h, at one end of a cell is an essential factor for initiation of branch formation.

Effect of Ca2+ on morphology and division of Yersinia pestis

Wild-type cells of Yersinia pestis are known to exhibit a nutritional requirement for physiological levels of Ca(2+) ( approximately 2.5 mM) at 37 but not 26 C. Upon shift of Ca(2+)-deficient cultures from 26 (permissive condition) to 37 C (restrictive condition), bacterial mass quadrupled as the organisms doubled in number and then became elongated to about twice their normal size. As shown in thin sections, the resulting static cells contained axial filaments which differed from the typical irregularly lobate nucleoids of normal yersiniae grown under the permissive condition. Following prolonged cultivation under the restrictive condition (12 h), the organisms generally exhibited apparent degenerative changes, including separation or infolding of the cell wall and cytoplasmic membrane, degeneration of deoxyribonucleic acid, and appearance of vacuoles within the cytoplasm. At this time, the cells were unable to reinitiate cell division at 37 C upon addition of Ca(2+) but divided in partial synchrony after return to 26 C. This observation indicated that, at 37 C, continuous exposure to Ca(2+) is necessary for yersiniae to maintain normal morphology and the ability to divide.

Biology of the bifidobacteria

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Influence of nutrition on the morphology of a strain of Bifidobacterium bifidum

A mucoid variant of Bifidobacterium bifidum was converted from its normal curved rod or bifid form to a highly branched form when grown in a chemically defined minimal medium. Branching could be prevented by the addition of a mixture of dl-alanine, dl-aspartic acid, l(+)-glutamic acid, and dl-serine, but not when any one of these four amino acids was omitted. Although sodium chloride induced pleomorphism, calcium ions were ineffective in suppressing the appearance of these pleomorphic forms. None of the cell wall precursors tested, viz., N-acetyl-d-glucosamine, alpha-epsilon-diaminopimelic acid, and muramic acid, inhibited branching.

Isolation of morphological mutants of Agrobacterium tumefaciens

Morphological mutants were isolated from a wild strain of Agrobacterium tumefaciens at a high frequency by treatment with a nitrosoguanidine. Seventeen of the 20 mutants isolated were temperature-sensitive. At 27 C, the mutant cells were rod-shaped and at 37 C, spherical or branched, whereas the wild-type cells were rod-shaped at both temperatures.

Necessity of calcium ion for cell division in Lactobacillus bifidus

Electron microscopy revealed that reversion of the bifid form to the bacilloid form of Lactobacillus bifidus takes place by cross wall formation, the process requiring available calcium ions.