Examining growth and survival of cowpea rhizobia in Jamaican peat

We have examined the survival of four cowpea rhizobia strains in Jamaican peat to determine its suitability as inoculant carrier. All strains survived well since more than 10⁷ cells of rhizobia per gram of peat were recovered from the inoculant after storage for 6 months at 30C. Survival of cowpea rhizobia was better when inoculants were stored at 4 than 30C. The native strains JRC29 and JRW3 (isolated in Jamaica) survived much better than the introduced strains MI-50A and IRC291 (isolated in West Africa). Survival of cowpea rhizobia was not significantly increased when peat was mixed with 1% sucrose. Our results suggest that Jamaican peat may be used as a carrier for inoculant production.     

The effect of moisture potential on growth and survival of root nodule bacteria in peat culture and on seed

Peat from three sources was dried, milled and packed separately in polyethylene bags and sterilized by irradiation. The carrier was impregnated with broth cultures of either Rhizobium leguminosarum bv. trifolii strain WU95, Bradyrhizobium japonicum strain CB1809 or B. lupini strain WU425 and sterile water to provide five moisture potentials in the range > - 1 × 10⁴ - 1 × 10⁶ Pa. The packets were stored at 26°C under conditions which restricted moisture loss. Numbers of root nodule bacteria were counted at intervals up to 12 weeks. No single moisture potential was optimum for all strains in all carriers because of a significant ( P < 0.05) interaction between moisture potential × strain × carrier × time. Where direct comparisons could be made, all strains survived best at - 1 × 10⁴ and/or −3.2 × 10⁴ Pa. Seeds of Trifolium subterraneum and polypropylene beads (used to avoid seed coat toxicity), were inoculated with WU95 prepared in two sources of peat and at each of the above moisture potentials and stored at 15°C. Seed coat toxicity significantly effected the log death rate ( k ) of WU95 on subterraneum clover seed for the period 0–0.25 d ( k 1.796) compared with k - 0.399 for polypropylene beads. In the first 24 h moisture did not affect survival but by 28 d rhizobia grown in Badenoch peat survived best at −3.2 × 10⁴ Pa. In Millicent peat, survival was equally as good at −3.2 × 10⁴ and −1 × 10⁴ Pa.     

Morphological changes of rhizobia in peat cultures

Morphological changes that take place in peat cultures of several species of rhizobia were examined. These changes seemed to be associated with enhanced survival of cells in peat and after inoculation onto plastic beads, which were used as a model system for seeds. Cell wall changes, in which the periplasmic space appeared to be occluded with electron-dense material, were observed in Rhizobium sp. strain SU343 and Bradyrhizobium lupini WU425 cells after 7 and 14 days in peat, respectively. Nutrient limitation and low O(2) concentration in peat are suggested to be factors involved in the induction of the morphological changes. Polyhydroxybutyrate reserves, which were present in broth-cultured cells of both species of rhizobia, were mobilized after transfer into peat but did not appear to influence survival after inoculation onto beads. Enhanced expression of an iron-manganese superoxide dismutase was also observed after the cells were transferred into peat. We conclude that cell wall thickening in rhizobia after transfer from broth cultures into peat is an adaptive response for long-term survival under nutrient-limited conditions in peat. Cells with thickened walls may also be more resistant to other types of stress, such as that encountered on a seed surface.     

Synergistic effect of relative humidity and temperature on the survival of rhizobia in inoculant carrier

Six strains of Rhizobium , three temperature-tolerant (U1, C13 and A19) and three temperature-sensitive strains (U10, C10 and A4) selected on the basis of previous study were used to screen the synergestic effect of different relative humidities (r.h. 50%, 65% and 90%) and temperatures (28°, 35°, 40° and 45°C) on the survival of rhizobia in inoculant carrier. At a particular temperature all the three r.h.'s were maintained. At a storage temperature of 28° and 35°C, the r.h. had little effect on the population of any of the rhizobial strains tested, but at 40° and 45°C, marked differences were observed and it was concluded that higher r.h. in conjunction with higher temperature resulted in low viable counts. The effect was similar but less obvious with the temperature-tolerant strains. It was found that 50% r.h. at different storage temperatures extended shelf life of rhizobial strains of blackgram, cowpea and arhar crops which were tested in this study in inoculant carrier.     

Wastewater sludge as a substrate for growth and carrier for rhizobia: the effect of storage conditions on survival of Sinorhizobium meliloti

The inoculation of legumes with rhizobia is used to maximise nitrogen fixation and enhance the plant yield without using N fertilisers. For this reason many inoculant types were developed and optimised. In our study, the effects of the growth medium, the carrier, the temperature and the storage period were determined on the survival of Sinorhizobium meloliti. Secondary sludge from Communauté Urbaine de Quebec wastewater treatment plant and standard medium (YMB) were used for rhizobial growth. Dehydrated sludge from Jonquière wastewater treatment plant, peat and a mixture of peat and sludge were used as carrier materials. Results showed that the wastewater sludge offered better protection for rhizobia survival during freezing and thawing at -20 degrees C than the standard medium. In general, results also showed the suitability of using sludge as a carrier because it had the same or a higher potential than peat to support survival of S. meliloti. In the case of YMB-grown rhizobia, peat- and sludge-based carriers appeared to be similar in terms of survival rate during the storage at 4 and 25 degrees C. For secondary sludge-grown rhizobia, the survival was better in sludge than in peat based carrier. Generally, the cell count remained higher than 10(8) cells/g for up to 80 days at 4 and 25 degrees C in both carriers (sludge and peat). However, for the secondary sludge-grown cells stored in peat-based carrier at 4 degrees C, the viable cells decreased under 10(8) cells/g at the 81st day of storage but remained acceptable compared to the standard (10(7) cells/g of carrier).     

The effect of water activity on Legionella spp. growth and survival

Growth and survival of Legionella spp. at various water activity (a_w) levels were determined. Compared with Escherichia coli , the growth of Legionella spp. was limited to a high a_w environment (≥0.98).     

The effect of water activity on Legionella spp. growth and survival

Growth and survival of Legionella spp. at various water activity (aw) levels were determined. Compared with Escherichia coli, the growth of Legionella spp. was limited to a high aw environment (greater than or equal to 0.98).     

The survival of plant growth promoting microorganisms in peat inoculant as measured by selective plate counting and enzyme-linked immunoassay

Achieving specific counting of plant growth promoting (PGP) microorganisms maintained at high numbers in inert carriers such as peat is an important objective for the inoculation of field crops such as cereals. In this paper, methods based on selective media together with strain-specific counting using enzyme-linked immunoassay (ELISA) were examined. Selective plate counting was developed by screening four commercial PGP biofertiliser strains for resistance to antibiotics. ELISAs for each strain were developed and calibrated by purifying polyclonal antibodies, testing sample pre-treatment strategies, and investigating the effect of culture age on standard curves. Selective plate counting proved to be more accurate than the ELISA methodology, confirming that all microbial strains survived for at least 1 month in sterile peat without loss in viable numbers, and further demonstrated growth inhibition of the strain Candida tropicalis HY when co-inoculated with the other strains Pseudomonas fluorescens 1 N, Bacillus amyloliquefaciens E19 and Bacillus subtilis B9. This is the first known study to have investigated the dynamics of PGP microorganisms in multi-strain inoculants and demonstrates the utility and hitherto unmentioned drawbacks of two different low-cost counting methods for biofertiliser quality control. Such information is vital for the adoption and success of non-rhizobial PGP biofertilisers for sustainable agriculture.     

The effect of ouabain on sensory neuron neurite growth in organotypic culture

Ouabain, a known inhibitor of Na+, K(+)-ATP, taken in a wide range of concentrations, was investigated in organotypic tissue culture of dorsal root ganglia cells of 10-11 day old chick embryos. Ouabain inhibited neurite growth in a dose-dependent manner. The Hill coefficient was defined as 1, and the Kp value was estimated as 1 x 10(-10) M. At inhibitor concentrations exceeding 1 x 10(-9) M, the growth of neurites was totally inhibited. It is assumed that Na+, K(+)-ATPase may play an important role in regulation of the process of neurite growth in sensory neurones.     

The effect of egg size and habitat on starling nestling growth and survival

In spite of the fact that hatchling size and energy reserves in birds are affected by egg size, many studies have failed to find an effect of egg size on offspring fitness. One possibility is that this is because they have been performed in areas with high food availability and that effects of egg size on offspring fitness are most apparent in areas of low food availability. To investigate this, egg size,␣offspring mass and survival of European starlings (Sturnus vulgaris) were measured in an agricultural landscape with a low but variable amount of pasture, the preferred foraging habitat of parent starlings. Offspring mass was related to egg size, but egg size explained a declining proportion of the variation in nestling mean mass as nestlings grew older. Offspring survival during the early, but not during the late nestling period was related to egg size. Throughout the nestling␣period, survival was related to the mass of the nestlings. It is suggested that the effect of egg size on␣offspring survival is through the effect of egg size on offspring mass, this effect declining as offspring grow older. Offspring survival during the early part of the nestling period was related to egg size when availability of pasture was low, but not when it was high. However, the interaction was not significant. Selection for␣larger egg size is discussed in relation to the structuring␣of starling populations into sources and sinks. Received: 22 September 1997 / Accepted: 22 January 1998     

The effect of a plasmid on growth and survival of E. coli

We studied the growth characteristics of a pair of Escherichia coli strains, isogenic apart from the possession of a nonconjugative plasmid. There was no difference between the two strains when they were grown separately. In mixed culture, a second slow phase of growth that normally occurred following the end of rapid exponential growth, was absent from the plasmid-carrying strain. This resulted in a considerable decrease in the proportion of the cells that carried the plasmid after overnight incubation. The effect of different conditions of growth is reported. The plasmid-carrying strain survived extended incubation (150 days at 37°C) as well as did the plasmid free strain separately. In a mixture, the proportion of plasmid-carrying cells declined rapidly, and none was detected after 100 days.     

Influence of growth phases and desiccation on the degrees of unsaturation of fatty acids and the survival rates of rhizobia

The influence of growth phase on the evolution of cellular fatty acids (CFA) and survival of Sinorhizobium and Bradyrhizobium during desiccation and storage at different levels of relative humidity (R.H.) was studied. Lactobacillic, cis vaccenic and palmitic acids were the major fatty acids of S. meliloti RCR 2011, B. elkanii USDA 120 and B. japonicum 3.2, whatever the growth phase. An exchange of cis vaccenic with lactobacillic acid was observed during the course of growth. The degree of unsaturation (% unsaturated CFA/% saturated CFA = u/s ratio) was significantly higher during the mid logarithmic phase of growth. Survival rates immediately after desiccation were unaffected by the growth phase and the R.H. Furthermore, no correlation was found between survival rate and u/s ratio. During the course of desiccation, the u/s ratio of rhizobia decreased but the decrease was largely independent of the R.H. Optimum R.H. values for storage were in the range 22–67·8%, and S. meliloti was significantly more tolerant than the bradyrhizobia. Cells of rhizobia harvested in the lag phase of growth were more resistant to protracted storage than cells at other growth phases. Again, no correlation was found between u/s ratio and survival rates, despite the expected practical significance for screening for drought-tolerant micro-organisms.     

The effect of chromosome constitution on growth in culture of human spontaneous abortions

Summary The effect of chromosome constitution on growth in culture was evaluated by comparing the length of time in culture until cytogenetic analysis among chromosomally normal and abnormal spontaneous abortions. We observed a significant effect of both tissue type and cell type, but not chromosome constitution, on the rate of growth of the cultures.     

The effect of buthionine sulfoximine on the growth of Leishmania donovani in culture

Changes in composition of the principal low molecular mass thiols of Leishmania donovani were monitored during the transformation of promastigotes, first to stationary phase metacyclic forms and then to amastigotes. No consistent variation in the thiol composition of the parasite which could account for the known increase in resistance of metacyclic and amastigote lifecycle forms to oxidant stress could be established. Amastigotes cultivated at 37 degrees C also produced ovothiol A, as judged by incorporation of radiolabel from [3-methyl]methionine and [14C]histidine, and the incorporation of radiolabel from [35S]cysteine into ovothiol A represented about 10-15% of the total label recovered in ovothiol A, glutathione and trypanothione. Amastigotes were less susceptible than promastigotes to the effects of the redox cyclers paraquat and menadione and grew in culture in the presence of up to 20 mM buthionine sulfoximine, which completely blocked the synthesis of glutathione and its spermidine conjugates. Glutathione and trypanothione biosynthesis is, therefore, not necessary for the replication of L. donovani amastigotes in culture. Inhibition of the formation of glutathione and trypanothione did not result in an upregulation of ovothiol A production.     

The effect of pH on the growth and metabolism of Streptococcus bovis in continuous culture

Streptococcus bovis H13/1 was grown anaerobically at pHs between 5.0 and 6.5 in a glucose-limited chemostat at a dilution rate of 0.05/h. The growth yield and the production of acetate, ethanol and formate decreased at pHs less than 6.5 whereas the production of lactate increased at the lower pH values. When a culture was subjected to sequential pH changes, growth yield and fermentation products were influenced not only by the pH existing in the culture medium but also by the metabolic activity of the cells at the preceding pHs in the sequence. The results are discussed in relation to the mechanisms available for the maintenance of pH homeo-stasis and for the metabolic control of fermentation pathways in Strep. bovis.