Lysis Of Microbial Cells Research Articles

Freeze–thaw cycle amplitude and freezing rate effects on extractable nitrogen in a temperate old field soil

Freeze–thaw cycles can promote soil N losses as a result of microbial and root cell lysis; however, minimal freeze–thaw effects have typically been observed in studies that have imposed moderate temperature cycles. We conducted laboratory incubations on surface soil (top 3 cm) collected in a temperate old field from late fall through mid-winter to examine how variation in freeze–thaw amplitude, number, timing of collection, and freezing rate altered soil extractable N. We varied freeze–thaw amplitude by imposing minimum cycle temperatures of 0, −1, −2, −5, and −10°C for a series of either one or two cycles and held control samples constant at 3°C. We also examined the effects of freezing rates of 1, 3, and 30°C h−1. We hypothesized that extractable N would be highest for both the maximum freezing amplitudes and rates. While multiple freeze–thaw cycles at −10°C and freeze–thaw cycles associated with artificially high freezing rates increased extractable N, freeze–thaw cycles representative of field conditions at our site had no effect on extractable N in late fall and early winter. By mid-winter there was a significant freeze–thaw cycle effect but, contrary to our prediction, less N was extracted from freeze–thaw treated samples than from the control samples, which remained thawed over the treatment period. Increased extractable N in control samples was driven by increased organic N rather than increased inorganic N. Our results suggest that freeze–thaw damage to soil organisms does not contribute substantially to N release in our system. Instead, soil extractable N may increase during mid-winter thaws as a result of increased soil proteolytic activity above freezing temperatures.

Internal Control for Nucleic Acid Testing Based on the Use of Purified Bacillus atrophaeus subsp. globigii Spores

Commonly used internal controls (ICs) to monitor the efficiency of nucleic acid testing (NAT) assays do not allow verification of nucleic acid extraction efficiency. Since microbial cells are often difficult to lyse, it is important to ensure that nucleic acids are efficiently extracted from any target organism. For this purpose, we developed a cellular IC based on the use of nonpathogenic Bacillus spores. Purified Bacillus atrophaeus subsp. globigii (referred to hereafter as simply B. atrophaeus) spores were added to vaginal and anal samples, which were then subjected to rapid DNA extraction and subsequent PCR amplification. The proof of concept of this cellular IC was made through the use of both manual and automated DNA extraction methods, using vaginal or anal samples spiked with B. atrophaeus spores, combined with a multiplex real-time PCR assay for the specific detection of group B streptococci (GBS) and B. atrophaeus. The performance of the cellular IC was compared to that of a standard IC plasmid added to PCRs. Approximately 500 B. atrophaeus spores per PCR was found to be optimal since this did not interfere significantly with GBS detection for either DNA extraction method and yielded reproducible amplification and/or detection of B. atrophaeus genomic DNA serving as an IC template. Performance of the cellular IC was comparable to that of the standard IC. This novel IC system using nonpathogenic and hard-to-lyse B. atrophaeus spores allowed validation of both the DNA extraction procedure and the amplification and detection process. Use of a spore-based control also provides a universal control for microbial cell lysis.

Enzymatic lysis of microbial cells

Cell wall lytic enzymes are valuable tools for the biotechnologist, with many applications in medicine, the food industry, and agriculture, and for recovering of intracellular products from yeast or bacteria. The diversity of potential applications has conducted to the development of lytic enzyme systems with specific characteristics, suitable for satisfying the requirements of each particular application. Since the first time the lytic enzyme of excellence, lysozyme, was discovered, many investigations have contributed to the understanding of the action mechanisms and other basic aspects of these interesting enzymes. Today, recombinant production and protein engineering have improved and expanded the area of potential applications. In this review, some of the recent advances in specific enzyme systems for bacteria and yeast cells rupture and other applications are examined. Emphasis is focused in biotechnological aspects of these enzymes.

Short-term carbon and nitrogen cycling in urine patches assessed by combined carbon-13 and nitrogen-15 labelling

Urine deposition by grazing animals is known to induce large N 2O emissions as a result of increased nitrification and denitrification in the soil. This is brought about by the increased N availability from the urine, in combination very likely also with increased organic C availability. Possible sources for C include the urine itself, increased solubility of soil C, lysis of microbial cells and leakage of C from scorched roots. The objective of this experiment was to test the hypothesis that: (i) urine deposition causes an increase in root-derived degradable C compounds in the soil, which (ii) fuel denitrification activity and N 2O production. The study took advantage of carbon-13 pulse labelling the plant tissue combined with application of nitrogen-15 labelled synthetic urine as an attempt to identify the sources of N 2O. Over a 6 weeks course, the CO 2 evolved in response to urine application was equal to the quantity of organic C added. Immediately after the application, 87% of the respired CO 2 appeared to be from the urine, and respiration of plant-derived C was temporarily decreased. The cumulated amount of respired 13C plant carbon, however, was unaltered by the urine treatment indicating that root death was not a significant source to available C. Nitrous oxide emissions accumulated to 7, 59, 142 and 77 mg N 2O-N m −2, respectively, for control (0N), low urine N (LUN), high urine N (HUN) and high mineral N (HMN) treatments. Pair-wise comparisons indicated that HUN > LUN ( P < 0.03), whereas HUN = HMN ( P < 0.18). The N 2O emission factors were 0.3% for the urine treatment, independent of urinary urea concentration and 0.15% for mineral N (NH 4 +). The 15N isotopic data indicated that denitrification of soil NO 3 − was the sole source for N 2O production in the urine-affected soil after 12 days of incubation. The initial source of N 2O could not be identified because of lack of ability to detect the soil 15NO 3 −. The source of N 2O from added NH 4 + was ambiguous since the isotopic signals of N 2O, NH 4 + and NO 3 − could not be discerned. Approximately, 50% of the urinary-N, independent of urea concentration, and 72% of the NH 4 +-was recovered after 6 weeks of incubation. This finding, in combination with the difference in the N 2O losses, emphasizes the potential to control N-emissions from urine patches through dietary control of the urine N-content.

Laboratory drying of organic-matter rich soils: Phosphorus solubility effects, influence of soil characteristics, and consequences for environmental interpretation

Agronomic soil test P (STP) and soil type data may be used to predict diffuse soluble P loss from soil to water (e.g. Withers, P.J.A., Dils, R.M., Hodgkinson, R.A., 1999. Transfer of phosphorus from small agricultural basins with variable soil types and land use. p. 41. In: Impact of Land use change on nutrient loads from different sources. IAHS publication no. 257; Daly, K., Mills, P., Coulter, B., McGarrigle, M., 2002. Modelling phosphorus concentrations in Irish rivers using land use, soil type, and soil phosphorus data. J. Environ. Qual., 31: 590–599). However, previous studies quantifying the effect of STP and soil type on P solubility have usually relied on laboratory analyses of dried soil samples to quantify P solubility. Drying soil samples has been found to substantially increase P solubility (e.g. Bartlett, R., James, B., 1980. Studying dried, stored soil samples—some pitfalls. Soil Sci. Soc. Am. J., 44: 721–724; Turner, B.L., Haygarth, P.M., 2001. Phosphorus solubilization in rewetted soils. Nature, 411: 258–258), and microbial biomass and organic matter (OM) have been implicated in this (e.g. Chepkwony, C.K., Haynes, R.J., Swift, R.S., Harrison, R., 2001. Mineralization of soil organic P induced by drying and rewetting as a source of plant-available P in limed and unlimed samples of an acid soil. Plant Soil, 234: 83–90; Turner, B.L., Driessen, J.P., Haygarth, P.M., McKelvie, I.D., 2003. Potential contribution of lysed bacterial cells to phosphorus solubilisation in two rewetted Australian pasture soils. Soil Biol. Biochem., 35: 187–189). Many grassland soils in western Ireland contain high OM and moisture contents, and may therefore be particularly susceptible to drying-induced soluble P release. This study quantifies drying-induced changes in P solubility, by measuring water-extractable P (P w) and desorbable P (P feo) contents in moist and dried samples of a range of 33, mainly grassland, soils from western Ireland. Molybdate analyses of P w extracts before and after acid digestion were used to quantify dissolved reactive P (P wDRP), taken to represent predominantly readily soluble inorganic P, and dissolved molybdate-unreactive P (MUP), taken to represent predominantly readily soluble organic P. Dried soil samples were analysed for a wide range of general and P-specific characteristics, including STP (Morgan P and Olsen P) and the degree of sorption saturation (DPSS). Based on OM content, soils were divided into peat (> 30% OM) and predominantly mineral (< 30% OM) soils after Daly et al. (2000). Almost all soils exhibited large increases in P solubility after drying, with the size of drying-induced soluble P increases increasing in the order P wDRP < P wMUP< P feo. Absolute drying-induced increases were statistically similar between peat and mineral soil groups (e.g. P feo mean increases of 9.06 and 13.81 for peat and mineral soil groups, respectively). However, when expressed as a proportion of moist sample P solubility, all soluble P increases were significantly greater for peat compared with mineral soils (e.g. P feo percentage increases 735% and 155% for peat and mineral soil groups, respectively). Consequently, some differentiation in P solubility between peat and mineral soil groups was lost after drying. Drying-induced P w increases appeared to be related to soil OM and moisture contents, indicating drying-induced P release through microbial cell lysis and OM destabilisation. Increases were not related to moist sample P solubility or STP, resulting in the loss of some differentiation in P solubility between high and low STP soils. Drying-induced P feo increases were positively related to DPSS, reflecting chemical equilibrium control of desorbable P released from dried samples. It was concluded that the standard practice of drying soils prior to P solubility analyses reduces the inferred importance of soil type and STP as risk factors in diffuse soluble P losses.

Freeze–thaw regime effects on carbon and nitrogen dynamics in sub-arctic heath tundra mesocosms

Freeze–thaw fluctuations in soil temperature may be critical events in the annual pattern of nutrient mobilisation that supplies plant growth requirements in some temperate, and most high latitude and high altitude ecosystems. We investigated the effects of two differing freeze–thaw regimes, each of which is realistic of in situ spatial and temporal variation in field conditions, on C and N dynamics in sub-arctic heath tundra mesocosms. In addition, 15N isotopic label was used to follow the partitioning of a labile N pool between major ecosystem components, both during the freeze–thaw treatments phase, and in a subsequent equilibration phase. A single deep freeze treatment phase enhanced dissolved total and labelled N pools in the soil solution at initial thaw, and resulted in reduced pool sizes at the end of the equilibration phase. By contrast, a multiple freeze–thaw cycling treatment directly enhanced the dissolved labelled N pool, but did not significantly affect dissolved total N. Furthermore, both dissolved labelled N and dissolved total N pools were significantly enhanced in the equilibration period following multiple freeze–thaw, the latter due to a marked increase in soil solution NH 4 +. Microbial biomass C was not significantly affected by either of the freezing treatments upon final thaw, but was significantly reduced over the combined treatment and equilibration phases of the multiple freeze–thaw regimes. Furthermore, the treatments had no significant effects on total or labelled N within the microbial biomass over either phase. Total mesocosm CO 2 efflux rates remained closely correlated with soil temperature throughout the experiment in both regimes, suggesting that respiratory flushes associated with treatment-induced microbial cell lysis were negligible. Together, these results indicate that moderate freeze–thaw fluctuations may have minimal influences on microbial biomass pools, but nevertheless can have strong contrasting effects on the amounts, forms, and timing of N and organic C supply into the soil solution. Ecosystem losses via N 2O effluxes were of greatest magnitude immediately upon thawing in both treatments, and were of similar total magnitude to inorganic N leachates in throughflow. Herb leaves, total fine roots, and vascular stems accumulated some 15N label in one or both of the freezing treatments by the end of the experiment. Together, these results indicating very small N losses relative to the magnitudes of internal transfers, suggest tight ecosystem N cycling both during and after freeze–thaw events. Furthermore, our small and subtle effects on microbial and soluble C and N pools relative to previous studies using more severe regimes, suggests that periods of moderate freeze–thaw fluctuations may have only a minor influence on the annual pattern of C and nutrient dynamics in seasonally cold ecosystems.

A Proposed Mechanism for the Pulse in Carbon Dioxide Production Commonly Observed Following the Rapid Rewetting of a Dry Soil

The rapid rewetting of a dry soil often yields a pulse in soil CO 2 production that persists for 2 to 6 d. This phenomenon is a common occurrence in surface soils, yet the mechanism responsible for producing the CO 2 pulse has not been positively identified, We studied the effects of a single drying and rewetting event on soil C pools, to identify which specific C substrates are mineralized to produce the observed pulse in respiration rates. We labeled two soils with C-glucose and measured the enrichment and pool sizes of the released CO 2 , extractable biomass C, and extractable soil organic matter (SOM-C) throughout a drying and rewetting cycle. After rewetting, respiration rates were 475 to 370% higher than the rates measured before the dry down. The enrichment of the released CO 2 was 1 to 2 times higher than the enrichment of the extractable biomass C pools and 10 to 20 times higher than the enrichment of the extractable organic C, suggesting that the CO 2 pulse was generated entirely from the mineralization of microbial biomass C. However, there was no evidence of substantial microbial cell lysis on rewetting. We hypothesize that the pulse of CO 2 is generated by the rapid mineralization of highly enriched intracellular compounds as a response by the microbial biomass to the rapid increase in soil water potentials. The drying and rewetting process also releases physically protected SOM, increasing the amount of extractable SOM-C by up to 200%. The additional SOM-C rendered soluble by the rewetting event did not contribute substantially to the rewetting CO 2 pulse. Overall, the rapid rewetting of a dry soil can influence soil C cycling in the short-term, by increasing the microbial mineralization of cytoplasmic solutes, and in the longer-term, by decreasing the total amount of SOM physically protected within microaggregates.

Initial investigations into the ultrasonic lysis of microbial cells for the release of adenosine triphosphate

Initial investigations into the ultrasonic lysis of microbial cells for the release of adenosine triphosphate

Microbial Biomass and Activity in a Laterite Soil Amended with Municipal Solid Waste Compost

The dynamics of soil quality indicators, such as microbial biomass‐C, soil respiration, and urease and acid phosphatase activities, in a laterite soil (Typic Haplustalf ) amended with different doses of Calcutta municipal solid waste compost (MSWC) were studied over 120 days of incubation at 30 °C under 60 % soil water holding capacity. The parameters were found to increase with the increase in doses of MSWC. Soil microbial biomass‐C (MBC) and soil respiration activity reached peak values at 30 days of incubation and then gradually decreased up to 120 days of incubation. Urease and acid phosphatase activities showed peak values at 60 and 90 days of incubation, respectively. The increase in soil enzyme activities with the fall in MBC suggested that the release of enzymes was associated with lysis of microbial cells at the end of their life cycle. There was no indication of any detrimental effect on soil quality indicators of application of MSWC to soil.

Excess sludge reduction in activated sludge processes by integrating biomass alkaline heat treatment

With new EC regulations, alternative treatment and disposal techniques of the excess sludge produced by activated sludge wastewater treatment plants have to be developed. To decrease activated sludge production yield, microbial cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline and a combination) were studied to generate Ralstonia eutropha (strain model) and waste activated sludge lysates and to evaluate their biodegradability. Gentle treatment conditions by alkaline waste treatment (20 min at 60 degrees C and pH 10 by NaOH addition) allowed waste activated sludge to be solubilized by a two step process (instantaneous and post-treatment) giving a dissolved organic carbon released by the total suspended solids treated of 267 mgDOC x g(-1)TSS. The biodegradation of the soluble fraction of the lysates by fresh sludge reached 75 and 90% after 48 and 350 hrs of incubation respectively. A validation on a laboratory scale by insertion of a liquor alkaline heat treatment loop in a biological synthetic wastewater treatment process was carried out. A reduction of 37% of the excess sludge was obtained without altering the purification yield of the process.

Ultrasonic waste activated sludge disintegration for improving anaerobic stabilization

The pretreatment of waste activated sludge by ultrasonic disintegration was studied in order to improve the anaerobic sludge stabilization. The ultrasound frequency was varied within a range from 41 to 3217kHz. The impact of different ultrasound intensities and treatment times was examined. Sludge disintegration was most significant at low frequencies. Low-frequency ultrasound creates large cavitation bubbles which upon collapse initiate powerful jet streams exerting strong shear forces in the liquid. The decreasing sludge disintegration efficiency observed at higher frequencies was attributed to smaller cavitation bubbles which do not allow the initiation of such strong shear forces. Short sonication times resulted in sludge floc deagglomeration without the destruction of bacteria cells. Longer sonication brought about the break-up of cell walls, the sludge solids were disintegrated and dissolved organic compounds were released. The anaerobic digestion of waste activated sludge following ultrasonic pretreatment causing microbial cell lysis was significantly improved. There was an increase in the volatile solids degradation as well as an increase in the biogas production. The increase in digestion efficiency was proportional to the degree of sludge disintegration. To a lesser degree the deagglomeration of sludge flocs also augmented the anaerobic volatile solids degradation.

Towards a reduction in excess sludge production in activated sludge processes: biomass physicochemical treatment and biodegradation.

To decrease activated sludge production, microbial cell lysis can be amplified to enhance cryptic growth (biomass growth on lysates). Cell breakage techniques (thermal, alkaline, acid) were studied to generate Alcaligenes eutrophus and sludge lysates and to evaluate their biodegradability. Gentle treatment conditions produced the best results. Complete cell deactivation was obtained for temperatures higher than 55 degrees C. The release kinetics were similar for temperatures varying from 60 degrees C to 100 degrees C. A 20-min incubation was suitable for reaching 80% of the maximum releasable carbon. In thermal-chemical hydrolysis, NaOH was the most efficient for inducing cell lysis. Carbon release was a two-step process. First an immediate release occurred, which was of the same order of magnitude for A. eutrophus and sludge [100-200 mg dissolved organic C (DOC) g total suspended solids (TSS)-1], followed by a post-treatment release. The second step was virtually equivalent to the first for sludge, and weaker for A. eutrophus (< 50 mg DOC g TSS-1). The biodegradability of the soluble fraction, both the immediate and the post-treatment carbon release, was investigated. The optimal degradation yield, obtained with sludge cells, reached 55% after 48 h of incubation and 80% after 350 h. The most consistent lysis and biodegradation results occurred at pH 10 and 60 degrees C after a 20-min incubation.

99/01270 Development of a low-cost oxy-hydrogen bio-fuel cell for generation of electricity using Nostoc as a source of hydrogen : Dawar, S. et al. Energy Research, 1998, 22, (12), 1019–1028

Urine deposition by grazing animals is known to induce large N2O emissions as a result of increased nitrification and denitrification in the soil. This is brought about by the increased N availability from the urine, in combination very likely also with increased organic C availability. Possible sources for C include the urine itself, increased solubility of soil C, lysis of microbial cells and leakage of C from scorched roots. The objective of this experiment was to test the hypothesis that: (i) urine deposition causes an increase in root-derived degradable C compounds in the soil, which (ii) fuel denitrification activity and N2O production. The study took advantage of carbon-13 pulse labelling the plant tissue combined with application of nitrogen-15 labelled synthetic urine as an attempt to identify the sources of N2O. Over a 6 weeks course, the CO2 evolved in response to urine application was equal to the quantity of organic C added. Immediately after the application, 87% of the respired CO2 appeared to be from the urine, and respiration of plant-derived C was temporarily decreased. The cumulated amount of respired 13C plant carbon, however, was unaltered by the urine treatment indicating that root death was not a significant source to available C. Nitrous oxide emissions accumulated to 7, 59, 142 and 77 mg N2O-N m−2, respectively, for control (0N), low urine N (LUN), high urine N (HUN) and high mineral N (HMN) treatments. Pair-wise comparisons indicated that HUN > LUN (P < 0.03), whereas HUN = HMN (P < 0.18). The N2O emission factors were 0.3% for the urine treatment, independent of urinary urea concentration and 0.15% for mineral N (NH4+). The 15N isotopic data indicated that denitrification of soil NO3− was the sole source for N2O production in the urine-affected soil after 12 days of incubation. The initial source of N2O could not be identified because of lack of ability to detect the soil 15NO3−. The source of N2O from added NH4+ was ambiguous since the isotopic signals of N2O, NH4+ and NO3− could not be discerned. Approximately, 50% of the urinary-N, independent of urea concentration, and 72% of the NH4+-was recovered after 6 weeks of incubation. This finding, in combination with the difference in the N2O losses, emphasizes the potential to control N-emissions from urine patches through dietary control of the urine N-content.

Preparations of immobilized lysozyme with reversibly soluble polymer for hydrolysis of microbial cells

Hen egg white lysozyme was immobilized by carbodiimide method to form amide bonds with a polymer (AS-L) showing reversibly soluble-insoluble characteristics with pH change. The immobilized enzyme (LY-AS) was soluble above pH 6 and precipitate below pH 4.5, offering advantages in that it can carry out hydrolysis of microbial cells in a soluble form yet be recovered after precipitation at low pH. The maximum specific activity of LY-AS was 66% of that of free lysozyme with M. lysodeikticus cells as substrate, which is much higher than the values reported in the literature using water-insoluble materials as carriers. The effects of pH and temperature on the activity of LY-AS were studied and compared with those of free lysozyme. With repeated pH cycles between 6.6 and 4.5, the operation half-life of immobilized enzyme activity was nine cycles. Repeated batch lysis of microbial cells could be carried out with intermittent enzyme precipitation and recovery steps. In such an operation the insoluble residual cells should be recovered together with the immobilized enzyme to minimize enzyme loss arising from adsorption to cells.

Influence of chloride and sulphate ions on soil enzymes

AbstractAmmonium chloride (AC) and ammonium sulphate (AS) are commonly used nitrogen fertilizers. But the effect of chloride and sulphate ions from these fertilizers on soil enzyme activity has received scant attention. Hence, we conducted a pot culture study to assess the influence of chloride (as AC) and sulphate (as AS) on the activities of urease, amidase, phosphatase and dehydrogenase in soil using rice as the test crop. Chloride and sulphate levels were fixed at 132, 264 and 396 kg ha−1 respectively. Controls were also performed. The enzymes were assayed at three stages of the crop growth viz., active tillering, panicle initiation and harvest.The enzyme activities decreased with increasing chloride and sulphate levels; however, the degree of inhibition varied among the enzymes assayed and the nature and amounts of salts added. The inhibition may be due to the specific effects of chloride and sulphate ions on microbial growth and subsequent enzyme synthesis, osmotic desiccation leading to microbial cell lysis, and a salting‐out effect modifying the ionic conformation of the active site of the enzyme protein.

Isolation and characterization of RNA from low-biomass deep-subsurface sediments.

Three methods for the isolation of microbial RNA from low-biomass deep-subsurface sediments have been developed and evaluated. RNA was isolated from samples taken from depths ranging from 173 to 217 m, and samples represented a variety of lithologies, including lacustrine, fluvial sand, and paleosol sediments. Cell numbers in these samples were estimated to be between log 4.0 and log 5.1/g on the basis of phospholipid fatty acid analysis. The most efficient method examined is based on the direct lysis of microbial cells followed by the extraction of RNA with alkaline phosphate buffers and subsequent inactivation of nucleases by extraction with guanidinium isothiocyanate. Estimated recoveries of mRNA for this method are approximately 26%. The recovered RNA included both mRNA and rRNA, as evidenced by the detection of sequences homologous to transcripts from the toluene-4-monooxygenase gene of Pseudomonas mendocina KR1 and bacterial, archaeal, and eukaryotic rRNA. An unexpectedly high relative concentration of archaeal rRNA (22 to 40%) was observed for these samples.

Lysis of Micrococcus lysodeikticus cells by lysozyme covalently immobilized on the lumen of hollow fibers

A lytic enzyme reactor for microbial cell lysis is described in which lysozyme is immobilized on the lumen of hemodialyzer hollow fibers using epichlorohydrin as a coupling agent. The cell suspension flows through the lumen without any hindrance where the cells are lyzed by the immobilized lysozyme efficiently. Micrococcus lysodeikticus cells at concentrations of 0.25 g/L and 5 g/L were successfully lyzed without clogging the hollow fiber. In comparison with lysozyme immobilized on submicron particles, the activity retention was at least 8 times higher.

Enhanced microbial cell lysis by the use of lysozyme immobilized on different carriers

Lysozyme was immobilized on chitosan and silica gel by adsorption, on cross-linked polystyrene divinylbenzene matrix (Deacidite KMP) by ionic binding and on non-porous glass beads by covalent attachment to improve the lytic activity towards complex substrates such as Micrococcus luteus. The lysozyme immobilization yields decreased on decreasing the amount of enzyme loaded, whereas the activation yields (defined as percentage ratio of immobilized active enzyme to immobilized enzyme) increased. Chitosan, silica gel, Deacidite KMP and non-porous glass bead preparations showed activation yields of 10%, 13·20%, 26·67% and 12·77%, respectively.

Micropitting of some clay materials adjacent structural pores

Micrometre-sized pits (micropits) were observed both in clay coatings within the upper B horizon of a Red Podzolic soil (Udic Haplustalf), and in the clay matrix adjacent structural pores within a calcitic buried soil. SEM-EDXRA and SEM-low temperature ashing were used to characterise these features and to determine their probable pedogenesis. The micropits in the Red Podzolic B horizon were around 2 μm in size, had either a hemi-ovoidal or a hemi-spheroidal morphology, and were formed by the lysis of microbial cells which had been partially buried during clay deposition on these surfaces. The micropits in the calcitic layer were up to 3 μm in size, were irregularly shaped, and were formed by the dissolution of calcite crystals embedded in the clay matrix.

A population balance model of enzymatic lysis of microbial cells

A model is proposed for enzymatic lysis of microbial cells based on number balances over the distribution of cell-wall mass in a population of cells. Analytical solutions to the population balance equations were obtained by the method of characteristics for simple reaction kinetics. The model has been used to analyze the following cases of lysis in a nonhomogeneous cell population: wall hydrolysis with cell rupture and product release, the effect of a distribution of lysis rates, and lysis of two-layer cell walls. Rate expressions for the reactions of lysis can be derived from bulk-phase experiments; the distributions of cell size and product content can be measured independently by flow cytometric techniques. The population model also provides an explanation for the initial lag seen in lysis kinetics for virtually any initial distribution. The model demonstrates patterns of lysis and product recovery for heterogeneous populations of cells and also applies to the more general problem of soluble-enzyme reactions with heterogeneous solid substrates.