191 SexedULTRA™, A NEW METHOD OF PROCESSING SEX SORTED BOVINE SPERM IMPROVES POST-THAW SPERM QUALITY AND IN VITRO FERTILITY

Since the first publications 30 years ago showing that flow cytometry was a reliable method to separate X and Y chromosome bearing sperm, the process has been subject to continual refinement. Numerous experiments have been performed in the last few years with the objective of developing an improved sex-sorted product, branded SexedULTRA™ (Sexing Technologies, Navasota, TX, USA) that retains sperm integrity to improve post-thaw sperm quality, in vitro embryo production, and field fertility compared with the previous XY method. Laboratory evaluations were performed on semen from 12 bulls at the Sexing Technologies laboratory in Navasota (TX, USA). Each ejaculate was divided in 2 aliquots and then processed in 1 of 2 methods (XY method or SexedULTRA™). Post-thaw sperm motilities were classified into percent total and progressively motile after thawing (0 h) and after a 3-h incubation at 37°C using a computer-assisted sperm motility analyzer (Hamilton Thorne IVOS II system, Hamilton Thorne Biosciences, Beverly, MA, USA). Percent intact acrosomes was also estimated after a 3-h incubation. Results were analysed by a mixed model ANOVA with the fixed effect of treatment and random effect of bull. Percent total motile SexedULTRA™ sperm was greater (P < 0.001) than sperm processed following the XY method at 0 (78.8 v. 67.2%) and 3 h (51.0% v. 39.0%) post-thaw. Likewise, there was a higher percent of progressively motile sperm both at 0 (50.7 v. 44.9%) and 3 h (31.5 v. 4.4%) post-thaw in the SexedULTRA™ sperm. Percent intact acrosomes was also greater in SexedULTRA™ sperm compared with the sperm processed following previous method (78.0 v. 64.0%). In vitro fertilizations were performed as a measure of sperm competence using 8 ejaculates from 2 bulls in Sexing Technologies IVF laboratory in Laceyville (PA, USA). Five to 10 oocytes and 5,000 motile sperm/oocyte were placed per IVF drop for the analysis. A total of 3 straws and a minimum of 800 oocytes per treatment group (ejaculate × treatment) were included in the comparison for development to 8-cell stage (cleavage rate) and to Day 7 blastocyst stage, measured as total (grades 1 to 4) and freezable (grades 1 and 2) embryos. Results were analysed using a mixed model ANOVA with treatment as a fixed effect and bull, ejaculate within bull, and IVF cycle as random effects. Results from IVF trials are shown in Table 1. Total and freezable embryo numbers were significantly higher (P < 0.05) when using SexedULTRA™ compared with XY sperm. Maintaining a suitable environment for sperm to progress through the various steps of the sex-sorting process results in better semen quality post-thaw as well as improved in vitro fertility. The SexedULTRA™ method confers a significant benefit in maintaining sperm integrity that, if translated into field fertility, could reduce the conception rate gap between conventional and sex-sorted bovine sperm. Table 1. Results from IVF and embryo culture using frozen-thawed, sex-sorted semen processed using the XY or the SexedULTRA™ method

190 SexedULTRA™, A NEW METHOD OF PROCESSING SEX-SORTED BOVINE SPERM IMPROVES CONCEPTION RATES

The gap in fertility between conventional and sex-sorted bovine sperm, known to be on the order of 10 percentage points, has never been bridged, even by increasing the number of sex-sorted sperm per inseminate. A concerted effort in the last few years has resulted in substantial changes in all stages of the sex-sorting process to develop an improved sex-sorted product called SexedULTRA™ (Sexing Technologies, Navasota, TX, USA). In vitro tests show that SexedULTRA™ maintained sperm integrity better than the previous XY method, and field trials were conducted to determine if this translated into improved bovine field fertility. The initial field trial was performed using ejaculates from 8 Holstein bulls located at Select Sires in Plain City (OH, USA). Each ejaculate was split in 2 aliquots that were then processed following the 2 methods (XY method or SexedULTRA™). A total of 6,930 Holstein heifers were inseminated across 41 commercial herds in the United States. Conception rate data were analysed using mixed model ANOVA (JMP 10.0.0; SAS Institute Inc., Cary, NC) with fixed effects of treatment, bull, bull by treatment interaction, and the random effect of herd. Sex-sorted bull sperm following the SexedULTRA™ method resulted in a greater (P < 0.001) conception rate compared with the XY method sperm (45.7 ± 1.7 v. 41.2 ± 1.6%). This is the first report of an improvement in conception rates using sex-sorted bovine semen in a decade since it became commercially available. A second field trial to investigate dose rate effects and compare against conventional semen was performed using 5 dairy bulls located at German Genetics International GmbH in Cloppenburg (Germany). Each ejaculate was split 4 ways, sex-sorted, and frozen in 0.25-mL straws as follows: XY 2.1 million/straw, SexedULTRA™ 2.1 million/straw, SexedULTRA™ 3.0 million/straw, and SexedULTRA™ 4.0 million/straw. A total of 7,855 heifers were inseminated with these sex-sorted straws, whereas 62,398 heifers were inseminated with conventional straws (15 million/straw) produced using contemporary ejaculates from the same bulls. The 56-day nonreturn rate was calculated by sire and treatment combination, and assigned a weight based on the total number of AI for each combination thereof. Table 1 contains the nonreturn rate weighted means and the relative fertility compared to conventional sperm. Data were analysed using a mixed model ANOVA (JMP 10.0.0; SAS Institute Inc.) with treatment and bull as fixed effects. SexedULTRA™ 4.0 sperm presented the greatest (P < 0.001) 56-day nonreturn rate followed by conventional 15.0 (66.73 v. 65.66%); XY 2.1 presented the lowest (P < 0.001) nonreturn rate. This is the first time a dose response effect with sex-sorted bovine sperm and parity in conception rates with conventional semen has been demonstrated. Table 1. Field trial results for number of inseminations, 56-day nonreturn rate (NRR) weighted means, and relative fertility1 compared with conventional sperm

Removing seminal plasma improves bovine sperm sex-sorting

Bull ejaculates with sperm concentrations of less than 1 billion sperm sort poorly for sex chromosomes, but whether this is because of the sperm concentration or the concomitant seminal plasma content has not been elucidated. Experiments were conducted to determine why ejaculates with lower sperm concentrations sort poorly and develop a protocol to increase sorting efficiency. In Experiment I, spermatozoa at 160 or 240 × 10⁶ sperm/mL were stained at 49, 65 or 81 μm Hoechst 33342 with 0 or 10% seminal plasma and then sex-sorted. In Experiment II, seminal plasma was adjusted to create samples with sperm concentrations of 0.7, 1.4 and 2.1 × 10⁹ sperm/mL, prior to sex-sorting. In Experiment III, spermatozoa were diluted to 0.7, 1.4 and 2.1 × 10⁹ sperm/mL using TALP containing 0 or 10% seminal plasma prior to sex-sorting and cryopreservation. In Experiment I, the optimal staining combination was 160 × 10⁶ sperm/mL stained with 65 μm Hoechst 33342 and no seminal plasma. In Experiment II, the percentages of membrane-impaired sperm were lower for sample concentrations of 2.1 × 10⁹ sperm/mL (15%) than for samples at 1.4 × 10⁹ (17%) or 0.7 × 10⁹ sperm/mL (18%; p < 0.01). The X sort rate was slower for samples stored at 0.7 × 10⁹ sperm/mL (3.45 × 10³ sperm/sec) than for samples stored at 1.4 × 10⁹ and 2.1 × 10⁹ sperm/mL (3.85 and 3.94 × 10³ sperm/sec, respectively; p < 0.05). In Experiment III, samples containing 0% seminal plasma had higher percentages of live-oriented cells (54 vs. 50%; p < 0.05), fewer dead sperm (19 vs. 22%; p < 0.01) and higher post-thaw motility (41 vs. 35%; p < 0.05) than samples containing 10% seminal plasma. Ejaculates with high sperm concentrations result in superior sorting because these samples have less seminal plasma during staining than ejaculates with lower initial sperm concentrations as all samples are diluted to 160 × 10⁶ sperm/mL for staining. Therefore, sorting efficiency appears to be affected by seminal plasma concentration, not by the original sperm concentration.

201 EFFECTS OF REMOVING SEMINAL PLASMA DURING 8-h STORAGE BEFORE SEX-SORTING BOVINE SPERM

We evaluated sex-sorting parameters and post-thaw motility for sperm stored with or without seminal plasma for 8 h before sorting. One first ejaculate was collected from each of 6 bulls routinely collected via artificial vagina; ejaculates contained at least 70% motile and 75% morphologically normal sperm and sperm concentrations ranged from 0.75 to 2.21 × 109 sperm mL–1. Ejaculates were divided into 2 samples and centrifuged at 1000 × g for 15 min. Seminal plasma from 1 sample was replaced with TALP (pH 7.4) to a sperm concentration of 1.4 × 109 sperm mL–1. The seminal plasma/sperm admixture of the other sample (control) was suspended to initial ejaculate sperm concentration. Both samples were stored for 8 h at 16°C before being subjected to standard sex-sorting procedures. Sperm were analyzed and bulk sorted on a MoFlo SX (XY Inc., Navasota, TX, USA) flow cytometer/cell sorter for percentage of live-oriented cells, percentage of membrane-impaired sperm (cell membranes permeable to red food colouring, which were discarded during sorting) and resolution between X- and Y-bearing sperm populations (peak to valley ratio). Sorted sperm were frozen according to standard procedures and post-thaw motility was determined immediately after thawing using computer-assisted sperm analysis. Treatments were compared using a paired t-test. Control sperm stored with seminal plasma resulted in a higher percentage of live-oriented cells (55%) versus those stored without seminal plasma (51%; P = 0.02). The percentage of membrane-impaired sperm was lower for control sperm (19%) than that of samples without seminal plasma (28%; P < 0.001). Resolution was greater for sperm stored without seminal plasma (34%) than for control sperm (10%; P = 0.04). Post-thaw, both total and progressively motile sperm were higher for samples without seminal plasma (63 and 53%, respectively) compared with those of the control samples (52 and 45%, respectively; P < 0.04). In conclusion, sperm stored for 8 h without seminal plasma had greater resolution between X- and Y-bearing populations and higher post-thaw motility than control sperm. However, these samples had a higher percentage of membrane-impaired sperm that were removed during sorting. Long-term storage of sperm in their seminal plasma before sex-sorting appears to be detrimental to post-sorting, post-thaw sperm motility.

DNA fragmentation kinetics and postthaw motility of flow cytometric-sorted white-tailed deer sperm

This study examined DNA damage and postthaw motility of white-tailed deer sperm (n = 28) before and after sex selection and conventional sorting using MoFlo XDP SX flow cytometry. Semen samples from the same individuals were treated in 4 different ways: 1) chilled-extended sperm samples (without glycerol); 2) cryopreserved conventional samples, samples directly cryopreserved after the addition of extenders; 3) cryopreserved conventionally sorted samples, sorted samples to remove the dead sperm subpopulation; and 4) cryopreserved sex-sorted samples; sorted samples to remove the dead sperm subpopulation and separation of X- and Y-chromosome-bearing sperm. In all the cases (n = 6), conventional samples showed decreased postthaw motilities (43 ± 26%) when compared with X-sorted samples (59 ± 20%; P < 0.05) and Y-sorted samples (54 ± 20%; P > 0.05). The DNA fragmentation baseline was <5% for frozen-thawed conventional samples, but even less after sex sorting and conventional sorting: 2.4 and 1.7%, respectively. On the other hand, conventional samples showed greater (P < 0.05) DNA fragmentation than the sex-sorted sperm (n = 6) at 96 h (average of 4.8 ± 4.5% and 5.3 ± 4%, respectively). Conventionally sorted samples (n = 8) did not have greater (P > 0.05) DNA fragmentation when compared with the sex-sorted samples. Fragmentation of DNA on X-chromosome and Y-chromosome-bearing sorted sperm were not significantly different (n = 10, P > 0.05) after 96 h (2.6 ± 3.6% and 2.2 ± 0.5%, respectively). Future research should be implemented for examining the fertilizing potential of sex-sorted white-tailed deer sperm (e.g., AI fertility trials).

A comparison of bovine seminal quality assessments using different viewing chambers with a computer-assisted semen analyzer

Computer-assisted sperm analysis of fresh and frozen-thawed bovine sperm requires proper handling and preparation, and the type of slide used in the assessment is critical if the resultant data are to be useful quality control measurements. In the present study, 4 different slide viewing chambers, a Makler chamber, a clean slide-coverslip, or a 2- or 4-cell chamber Leja slide, were compared with assess their utility in providing reliable measurements of sperm motility variables. A Hamilton-Thorne IVOS Computer-Assisted Semen Analyzer (CASA) was the instrument used to determine sperm measurements utilizing the 4 different chambers. Fifty-eight different freeze batches of bovine semen that had been collected from 47 bulls at 7 sites that sex-sort sperm using Sexing Technologies sorting criteria were incorporated into the trial. Neither the percentage of motile sperm nor the percentage of progressively motile sperm differed for the Makler chamber vs. slide-coverslip comparisons. Similarly, total and progressively motile sperm did not differ between the 2- and 4-cell chambered Leja slides. However, total and progressive motility of sperm determined with the Makler chamber and slide-coverslip were greater (P < 0.0001) than motilities recorded by the 2- or 4-cell chambered Leja slides. Based on the results, the type of viewing chamber can affect the range of sperm motility values when CASA is used for quality control evaluations of thawed, cryopreserved sex-sorted sperm samples.

277 EFFECTS OF SEMINAL PLASMA ON SEX-SORTING BOVINE SPERM

This experiment evaluated how characteristics of bovine ejaculates affect the sortability of X- and Y-bearing spermatozoa. Ejaculates were collected by artificial vagina, 2 each from 10 bulls with an average of 1 h between collections. Only ejaculates with at least 60% motile and 70% normal sperm were used. Semen was centrifuged at 1 000 × g for 15 min to separate sperm from seminal plasma; seminal plasma was clarified by 10 min of additional centrifugation at 2 000 × g. Sperm were rediluted to 160 million sperm/mL with TALP (pH 7.4) and 0, 5, 10, or 20% seminal plasma, from the same ejaculate or reciprocally from first/second ejaculates. Following incubation with Hoechst 33342 for 45 min, an equal volume of TALP (pH 5.5) containing red food dye was added, and sperm were analysed on a MoFlo (Dako, Glostrup, Denmark) flow cytometer for percentage live-oriented cells, X sort rate, coincidence rate, percentage dead or dying (sperm membrane permeable to red dye), and splitability (peaks to valley ratio). The percentage live-oriented sperm was higher for treatments with 0% seminal plasma (64.4%) than for 5 (59.6%), 10 (59.0%), and 20% (57.8%) seminal plasma (P < 0.01). The percentage live-oriented sperm was higher for second (63.0%) than for first ejaculates (56.2%). Sort rate was higher for 0% seminal plasma and second ejaculates (P < 0.05). Dead/dying rates were lower for 0% (16.5%) than for 5 (21.9%), 10 (23.6%), or 20% (23.4%) seminal plasma (P < 0.003); and for first ejaculates (25.9%) compared with second ejaculates (18.2%). Seminal plasma percentage and ejaculate had no effect on splitability, and there was no difference in sorting parameters whether the seminal plasma was from the first or second ejaculate. The initial sperm concentration of the ejaculate (range, 1.3 to 3.4 billion sperm/mL) did not affect any sperm sorting parameter. Thus, effects of sperm concentration on sortability need to be reconsidered, as current practice is to select ejaculates to sort based on initial sperm concentration. The initial pH, percentage morphological abnormalities, initial seminal plasma pH, and age of bull did not affect sorting parameters. In conclusion, the presence of seminal plasma during staining and sorting may decrease sort rate and percentage of live-oriented cells, as well as increase death rate. In addition, sorting second ejaculates may be more advantageous than sorting first ejaculates. Future studies are needed to determine if the results hold true if sperm are stored for several hours and how the various factors affect sperm post-thaw viability.

283 DNA FRAGMENTATION DYNAMICS AND POST-THAW MOTILITY OF WHITE-TAILED DEER SPERM

The main objective herein was to study the level of DNA damage and post-thaw motility of White-tailed deer sperm before (neat sample) and after sex-sorting and conventional-sorting using a MoFlo® SX flow cytometer (SX, Dako, Fort Collins, CO, USA). For assessing DNA damage, a comparison of frozen–thawed (F-T) neat sperm (control) was made with F-T sex-sorted, F-T conventional-sorted, and F-T conventional sperm samples. Sperm motility was assessed by bright field microscopy using a Nikon Eclipse 80i microscope and slide-coverslips (25.4 × 76.2 mm slides, 22 × 22 #1.5 coverslips). A direct comparison of all 4 aforementioned sperm groups could not be made for some bucks. Live/dead sorting of the sperm (i.e. conventional-sorted sperm) can remove membrane compromised sperm and nonaligned live sperm, which may result, in part, from abnormal morphologies. White-tailed deer (Odocoileus virginianus; n = 13) from 1 to 7 years old were used for the experiments. The White-tailed deer were selected based on a genetic predisposition for producing large antlers (i.e. Boone and Crockett antler scores ≥200 points). Sperm DNA fragmentation levels were assessed using the Sperm-Halomax® kit (Halotech DNA, Madrid, Spain), counting 300 sperm per sample. The level of baseline DNA fragmentation was similar for conventional F-T sperm samples (<5%), but even lower after sex-sorting and conventional-sorting (2.39 and 1.69%, respectively). The conventional sperm samples had lower post-thaw motilities compared with sex-sorted samples from the same individual bucks (n = 6), with average post-thaw motilities of 43 ± 26% and 56.5 ± 20%, respectively. The statistical comparison of the dynamic loss of DNA quality (i.e. DNA fragmentation of samples incubated in a 34°C water bath for 96 h) was assessed using the nonparametric maximum likelihood Kaplan-Meier estimator and a Breslow (Generalized Wilcoxon) test. When comparing sperm samples taken from the same bucks (n = 6), the conventional samples had significantly greater (P < 0.05) DNA fragmentation levels over time than the sex-sorted sperm. Conventional-sorted White-tailed deer (n = 8) sperm samples did not have significantly greater (P > 0.05) DNA fragmentation levels when compared with the sex–sorted sperm. When comparing X-chromosome sorted sperm to Y-chromosome sorted sperm, the DNA fragmentation levels were not significantly different (n = 10; P > 0.05), averaging 2.59 ± 3.61% and 2.18 ± 0.53% after 96 h. Based on the sperm DNA fragmentation and post-thaw motility results in the present study, the sex-sorting of White-tailed deer sperm may be a viable technique for the White-tailed deer industry and perhaps serve as a model for the conservation of endangered species such as the Eld’s deer (Cervus eldithamin). Future work should be implemented for examining the fertilizing potential of sex-sorted White-tailed deer sperm. The authors thank Maurice Rosenstein, Laura Belluzzo, Jared Templeton, Mike Bringans, Pat Cooper, Suzanne Menges, Miguel Ramirez, Altea Gosálbez, and Sexing Technologies staff for technical assistance. This research was funded by Sexing Technologies.

280 BOVINE SPERM DNA FRAGMENTATION RATES AND EXTENDER pH: A DYNAMIC EXPERIMENTAL APPROACH

Flow cytometry technology for the sorting of X- and Y-chromosome bearing sperm is currently utilised in research and for commercial applications. During sample preparation before the sex-sorting process, sperm go through different pH treatments that may affect their quality. The hypothesis to test in this study is that sperm DNA damage could occur due to differences in the pH of sperm extenders. Bull semen doses from 15 dairy and 15 beef bulls (2 ejaculates per individual), ranging in age between 13 and 96 months, were randomly selected from a bull stud in Texas (Sexing Technologies, Navasota, TX, USA). Each semen sample was divided into 4 separate aliquots. One neat semen sample was kept as a control and the other 3 aliquots were treated with 16 μL of 8.1 mM Hoechst 33342 (Molecular Probes, Eugene, OR, USA). A calculated amount of modified Tyrode’s albumin lactate pyruvate (Clear TALP), pH 7.4, was added based on neat ejaculate concentration. For the separation of live and dead sperm during the sex-sorting process, 2 mL of red TALP (Red Food Dye FD&C #40; Sensient Technologies Corp., Milwaukee, WI, USA) at 3 different pH treatment levels (5.5, 6.4, and 7.4) were added to the sperm samples. The dynamics of sperm DNA fragmentation were assessed immediately following the addition of red TALP treatment and after 24 h of incubation at 34°C. Sperm DNA fragmentation was measured using the commercial variant of the sperm chromatin dispersion test, the bull Sperm-Halomax® kit (Halotech DNA, Madrid, Spain), and counting 300 sperm cells under fluorescence microscopy. Analysis of variance was used to determine if there were statistical differences (α = 0.05) among mean values of the groups (SPSS v.17.0 for Windows, SPSS Inc., Chicago, IL, USA). Bonferroni post hoc tests were utilised to determine the pairwise directional differences between groups. Differences in DNA fragmentation were not observed at 0 h (P > 0.05); however, at 24 h this value was significantly higher (P < 0.05) in semen samples treated with red TALP, pH 6.4, v. samples treated with red TALP, pH 7.4, (44.0 ± 24.9% v. 34.8 ± 24.9%), and even higher when using red TALP pH 5.5 (50.8 ± 23.8%). Further experiments should be designed to demonstrate that the DNA molecule could be affected by pH fluctuations, which may be important in refining the sex-sorting process. Notably, the undiluted neat semen controls had greater levels of DNA fragmentation overall (57.5 ± 29.4%), suggesting a negative effect of high sperm concentrations and seminal plasma. The authors thank Mike Evans, Eddy Valenzuela, David Del Olmo, Jamie Jeffers, and the staff at Sexing Technologies for their technical assistance. This research was funded by Sexing Technologies and XY Inc.

362 STORAGE OF BOVINE SPERM FOR 20 H BETWEEN SEMEN COLLECTION AND SEXING

The objective of this study was to optimize bovine sperm storage for up to 20 h between semen collection and sex sorting followedby cryopreservation. Two successive ejaculates were obtained from mature dairy bulls (Holstein, n = 5; Jersey, n = 3) via artificial vagina. Treatments were then applied to the neat semen to which antibiotics were added as recommended by Certified Semen Services (Columbia, MO). Nothing further was added to the control samples until staining with Hoechst 33342 for sorting. For Treatment 1, semen was diluted 9:1 with a MOPS solution resulting in 24 mM MOPS and similarly, Treatment 2 resulted in 24 mM MOPS +2% egg yolk. A subsample of each treatment and control was sorted by flow cytometry shortly after collection, and sperm then were frozen following standard processing procedures. The other subsample was stored at 15-18°C and sorted 20 h after collection followed by cryopreservation. pH measurements were made before staining samples for sorting. Samples were evaluated post-thaw for subjective progressive and total sperm motility, by computer-assisted sperm analysis (CASA, Berkeley, CA, USA), and by flow cytometry for sperm viability using propidium iodide and SYBR-14. Treatment 1 performed better than the control (Table 1), while results for Treatment 2 were similar to the control. Second ejaculates were superior to first ejaculates. pH measurements showed that addition of MOPS kept the pH about 0.2 units higher than the control, but pH declined similarly over time in all groups. While responses for the 20 h sort were numerically lower than the 0 h sort (P > 0.1), the majority of responses were acceptable for most, but not all bulls. In conclusion, storing sperm in 24 mM MOPS was beneficial. Surprisingly, 2% egg yolk negated the beneficial effect of MOPS, possibly due to increasing osmolarity by ∼15mOsM/kg due to pH adjustment. Addition of MOPS provided better results than the control for both the 0 h and 20 h sorts. Table 1.Main effect means of semen characteristics

Effect of sex-sorted sperm dosage on conception rates in Holstein heifers and lactating cows

Ejaculates were collected by artificial vagina from 3 Holstein sires and sorted to 90% purity for X-chromosome-bearing spermatozoa (range 88 to 93%) using flow cytometry. Sorted sperm were diluted to 2.1, 3.5, or 5.0 x 10(6) sperm per dose in an egg yolk (20%), Tris, glycerol (7%) extender. Collections were repeated until >600 straws per sperm dose per sire were obtained. Each sperm dose was loaded into color-coded 0.25-mL French straws, with alternate colors used to define treatments across sires. Within sires, straws were packaged at 9 per cane (3 of each color) and strategically allocated to 75 Holstein herds with targets for 50% use in heifers and 50% in lactating cows. Straw color was recorded in the on-farm record-keeping system at the time of insemination. Data were analyzed separately for cows and heifers. Among heifers, a total of 2,125 usable records were retrieved from 51 herds (238 +/- 5.5 services/ sperm dose per sire, range: 218 to 263). Conception rates in heifers were influenced by the sire x sperm dosage interaction. Within sire A, conception rates of heifers were greater for the 5 x 10(6) (59.5%) than for the 2.1 x 10(6) (46.4%) sperm dose and intermediate for the 3.5 x 10(6) sperm dose (52.2%). However, across sires, sperm dosage had no effect on heifer conception rates (46.7, 51.2, and 52.5% for the 2.1, 3.5, and 5.0 x 10(6) sperm dosages, respectively). Among cows, a total of 2,369 services were retrieved from 56 herds (263 +/- 8.8 services/sperm dose per sire, range: 233 to 303). Conception rates of cows (29.4%) were not affected by sire or sperm dosage (27.0, 29.1, and 30.3% for the 2.1, 3.5, and 5.0 x 10(6) sperm dosages, respectively). In conclusion, these data indicate that an increased sperm dosage may enhance virgin heifer conception rates for some (but not all) sires, whereas neither sire nor sexed-sperm dosage affected conception rates of lactating cows. Additional studies of sexed-sperm dosage across a larger sampling of bulls are warranted to determine whether and how such a practice can be implemented cost effectively for the benefit of the dairy industry.

Plastics from bacteria and for bacteria: poly(beta-hydroxyalkanoates) as natural, biocompatible, and biodegradable polyesters

Hence, PHB belongs to the family of poly(beta-hydroxyalkanoates), PHA, all of which are usually formed as intracellular inclusions under unbalanced growth conditions. Recently, it became of industrial interest to evaluate PHA polyesters as natural, biodegradable, and biocompatible plastics for a wide range of possible applications such as surgical sutures or packaging containers. For industrial applications, the controlled incorporation of repeating units with different chain lengths into a series of copolymers is desirable in order to produce polyesters with a range of material properties because physical and chemical characteristics depend strongly on the polymer composition. Such "tailormade" copolymers can be produced under controlled growth conditions, in that if a defined mixture of substrates for a certain type of microorganisms is supplied, a well defined and reproducible copolymer is formed.

Biosynthesis and local sequence specific degradation of poly(3-hydroxyvalerate-co-4-hydroxybutyrate) in Hydrogenophaga pseudoflava

A novel copolymer that consisted of 3-hydroxyvalerate and 4-hydroxybutyrate, P(3HV-co-4HB), was synthesized in Hydrogenophaga pseudoflava by growing it in media containing gamma-valerolactone and gamma-butyrolactone as a carbon source. The monomer ratio in the copolymer was changed by altering the feed ratio of the two lactones. The cultivation technique was composed of three steps: the first-step for high cell production in Luria-Bertani medium, the second-step for intracellular degrading removal of poly(3-hydroxybutyrate) (P(3HB)), which was formed in the first step, by culturing the cells in carbon-source-free medium, and the final step for accumulation of P(3HV-co-4HB) in a mixed lactone medium. All the P(3HV-co-4HB) copolymers contained less than 1 mol % of 3HB unit. These copolymers were characterized by NMR spectroscopy, differential scanning calorimetry, wide-angle X-ray diffraction, and first-order kinetic analysis of intracellular degradation. The copolymer with an approximately equal ratio of the comonomers was found amorphous. The NMR microstructural analysis showed that the copolymers contained appreciable amounts of 3HV-rich or 4HB-rich chains. The (13)C NMR splitting patterns associated with the four carbons in the 4HB unit of P(3HV-co-4HB) bear close resemblance to those observed in the 4HB unit of P(3HB-co-4HB). The signals arising from the carbons in the 3HV unit of P(3HV-co-4HB) split in a manner similar to those in the 3HB unit of P(3HB-co-4HB). Thus the sequences were assigned by comparing the NMR splittings for P(3HV-co-4HB) with those for P(3HB-co-4HB) and P(3HB-co-3HV). The sequence assignment was further checked by comparing the signal intensities before and after degradation of the copolymers. This was considered reasonable because the H. pseudoflava intracellular PHA depolymerase is more specific to the 3HV unit than to the 4HB unit, which was also confirmed by the higher degradation rate constant for the 3HV unit in the first-order kinetic analysis.

Synthesis of poly(2-methyl-3-hydroxyoctanoate) via anionic polymerization of alpha-methyl-beta-pentyl-beta-propiolactone

Synthesis of an alpha,beta-alkyl branched polyester, i.e., poly(2-methyl-3-hydroxyoctanoate), has been accomplished via anionic polymerization of alpha-methyl-beta-pentyl-beta-propiolactone mediated by supramolecular complexes of potassium methoxide or potassium hydroxide, respectively. The structure of resulting polymers has been established by electrospray ionization multistage mass spectrometry (ESI-MSn), FT-IR, NMR, and GPC analyses. Previously proposed addition-elimination mechanism of the polymerization of beta-lactones containing alpha-hydrogen by alkoxide anion has been confirmed to operate also in the case of beta-lactone having alkyl substituents in both alpha and beta positions.

In vitro polymerization and copolymerization of 3-hydroxypropionyl-CoA with the PHB synthase from Ralstonia eutropha

The poly(3-hydroxybutyrate) (PHB) synthase of Ralstonia eutropha, which was produced by a recombinant strain of Escherichia coli and purified in one step with a methyl-HIC column to a purity of more than 90%, was used to polymerize 3-hydroxypropionyl-CoA (3HPCoA) and to copolymerize 3HPCoA with 3-hydroxybutyryl-CoA (3HBCoA). A Km of 189 microM and a kcat of 10 s-1 were determined for the activity of the enzyme in the polymerization reaction of 3HPCoA based on the assumption that the dimer form of PHB synthase was the active form. Free coenzyme A was found to be a very effective competitive inhibitor for the polymerization of 3HPCoA with a Ki of 85 microM. The maximum degree of conversion of 3HPCoA to polymer was less than 40%. In the simultaneous copolymerization reactions of these two monomers, both the turnover number for the copolymerization reaction and the maximum degree of conversion of 3HPCoA and 3HBCoA to copolymers increased with an increase in the amount of 3HBCoA in the monomer mixture. However, the maximum conversion of 3HPCoA to copolymer was always less than 35%, regardless of the ratio of 3HPCoA to 3HBCoA. Block copolymers were obtained by the sequential copolymerization of the two monomers and these copolymers had a much narrower molecular weight distribution than those obtained by the simultaneous copolymerization for the same molar ratio of 3HPCoA to 3HBCoA.

Kinetic and mechanistic characterization of the polyhydroxybutyrate synthase from Ralstonia eutropha

Purified Ralstonia eutropha polyhydroxybutyrate (PHB) synthase from recombinant cells can exist as monomer and dimer. The polymerization reaction catalyzed by this enzyme displays a lag phase, which causes difficulties for kinetic and mechanistic characterization of the enzymatic polymerization reaction. In this study, we developed a method to eliminate the lag phase of PHB synthase by physical means, i.e., adding multihydroxyl compounds to the enzyme solution. This method allows us to recognize the nature of the lag phase as a physical rather than a chemical process. With such lag-phase-free-enzyme, the kinetic properties of the enzyme were investigated. The results indicate that 3-hydroxybutyryl-CoA (3HBCoA) is the optimal substrate for the enzyme. A slower catalytic rate and lower binding ability account for a lower reactivity of 3-hydroxyvaleryl-CoA (3HVCoA) compared to that of 3HBCoA. The change of hydroxyl group from the beta to the gamma position causes dramatic decreases in the binding ability of 4-hydroxybutyryl-CoA (4HBCoA). By using a dilution strategy and size exclusion chromatographic technique, the active form of the enzyme was identified to be the dimeric form. The number of catalytic sites in the dimeric form of the enzyme was examined by comparing the molecular weight of polyhydroxybutyrate as a function of substrate-to-enzyme ratio. The results suggest that the dimeric enzyme has only one catalytic site. A revised model of polymerization reaction catalyzed by R. eutropha PHB synthase is described.

Enzymatic hydrolysis of oligomeric models of poly-3-hydroxybutyrate

The mechanism of the enzymatic degradation of poly([R]-3-hydroxybutyrate) (PHB) was investigated by using well-defined model substrates, including both linear and cyclic [R]-3-hydroxybutyrate (3HB) and [R]-3-hydroxyvalerate (3HV) oligomers, with two different PHB depolymerases. The linear and cyclic oligomers containing from 2 to 10 repeating units were hydrolyzed in solutions of the depolymerase isolated from Aspergillus fumigatus and Alcaligenes faecalis, and the rates of hydrolysis and types of products formed were characterized. Both of the depolymerases catalyzed the hydrolysis of the cyclic oligomers (macrolides) which contained more than three 3HB and 3HV repeating units. The degradation reactions of the linear and cyclic 3HB oligomers with the A. fumigatus depolymerase gave similar ratios of monomer-to-dimer products, but PHB itself formed mostly monomer on hydrolysis, indicating that the enzymatic hydrolysis reactions occurred by different mechanisms for these different types of substrates. The results of this study conclusively show that at least the endo mode of polymer hydrolysis occurs with the two enzymes studied, while the A. fumigatus depolymerase was found to utilize both endo and exo modes of hydrolysis to efficiently degrade PHB and 3HB oligomers.

Comparative study of the relationship between monomer structure and reactivity for two polyhydroxyalkanoate synthases

Using organically synthesized hydroxyalkanoate coenzyme A thioesters, the activities of two short-chain polyhydroxalkanoate (PHA) synthases were investigated--Ralstonia eutropha PHA synthase (a type I PHA synthase) and Ectothiorhodospira shaposhnikovii PHA synthase (a type III synthase). The results indicate that the two synthases have similar activities towards most of the monomers tested. 3-Hydroxybutyryl CoA was found to be the most efficient substrate for both synthases. Changes in the side-chain length of the monomers affect monomer reactivity, with shortening of the side-chain length having the more severe effect. Hydrophobicity in the side chain appears to play an important role in the catalytic reaction. The configuration and the position of the hydroxyl group also affect the reactivity of a monomer. Monomers with the [S] configuration can not be recognized by either synthase. Moving the hydroxyl group from the beta carbon to the alpha carbon has a much more severe effect on the reactivity of the monomer than moving the hydroxyl group to the gamma carbon. The results demonstrate that the in vitro system can be used to prepare entirely novel polymers that may not be obtainable from living cells because of metabolic restrictions.

Polyesters from microorganisms

Bacterial polyesters have been found to have useful properties for applications as thermoplastics, elastomers, and adhesives and are biodegradable and biocompatible. Poly(3-hydroxyalkanoates) (PHAs) and poly(beta-malate) are the most representative polyesters synthesized by microorganisms. PHAs containing a wide variety of repeating units can be produced by bacteria, including those containing many types of pendant functional groups which can be synthesized by microorganisms that are grown on unnatural organic substrates. Poly(beta-malate) is of interest primarily for medical applications, especially for drug delivery systems. In this chapter, the bacterial production and properties of poly(3-hydroxyalkanoates) and poly(beta-malate) are described with emphasis on the former.

Characterization, seasonal occurrence, and diel fluctuation of poly(hydroxyalkanoate) in photosynthetic microbial mats

In situ poly(hydroxyalkanoate) (PHA) levels and repeating-unit compositions were examined in stratified photosynthetic microbial mats from Great Sippewissett Salt Marsh, Mass., and Ebro Delta, Spain. Unlike what has been observed in pure cultures of phototrophic bacteria, the prevalence of hydroxyvalerate (HV) repeating units relative to hydroxybutyrate (HB) repeating units was striking. In the cyanobacteria-dominated green material of Sippewissett mats, the mole percent ratio of repeating units was generally 1HB:1HV. In the purple sulfur bacteria-dominated pink material the relationship was typically 1HB:2HV. In Sippewissett mats, PHA contributed about 0.5 to 1% of the organic carbon in the green layer and up to 6% in the pink layer. In Ebro Delta mats, PHA of approximately 1HB:2HV-repeating-unit distribution contributed about 2% of the organic carbon of the composite photosynthetic layers (the green and pink layers were not separated). Great Sippewissett Salt Marsh mats were utilized for more extensive investigation of seasonal, diel, and exogenous carbon effects. When the total PHA content was normalized to organic carbon, there was little seasonal variation in PHA levels. However, routine daily variation was evident at all sites and seasons. In every case, PHA levels increased during the night and decreased during the day. This phenomenon was conspicuous in the pink layer, where PHA levels doubled overnight. The daytime declines could be inhibited by artificial shading. Addition of exogenous acetate, lactate, and propionate induced two- to fivefold increases in the total PHA levels when applied in the daylight but had no effect when applied at night. The distinct diel pattern of in situ PHA accumulation at night appears to be related, in some phototrophs, to routine dark energy metabolism and is not influenced by the availability of organic nutrients.

Characterization by mass spectrometry of poly(3-hydroxyalkanoates) produced by Rhodospirillum rubrum from 3-hydroxyacids

The sequence distributions of two microbial copolyesters obtained by fermentation of Rhodospirillum rubrum, grown with 3-hydroxyhexanoic or 3-hydroxyheptanoic acids, were determined by analyzing the oligomers prepared by partial pyrolysis or partial methanolysis of these copolyesters using fast atom bombardment mass spectrometry (FAB-MS). Oligomers up to pentamers were identified in the case of partial pyrolysis and up to tetradecamers in the case of partial methanolysis. The comparison between the experimental and calculated peak intensities of FAB mass spectra allows the calculation of compositions and sequence distributions, which in these copolyesters follow Bernoullian statistics, indicating that they are random terpolyesters.

Intracellular depolymerase activity in isolated inclusion bodies containing polyhydroxyalkanoates with long alkyl and functional substituents in the side chain

The in vitro degradation of isolated Pseudomonas oleovorans inclusion bodies containing either poly-3-hydroxynonanoate (PHN), or poly(-3-hydroxy-5-phenylvalerate) (PHPV), or a mixture of these two polymers was investigated. When incubated at 30 degrees C and pH 9, inclusion bodies containing either polyhydroxyoctanoate (PHO), PHN or PHPV exhibited similar degradation rates of approximately 0.94 (+/- 3%) mg/h. The PHN and PHPV components for inclusion bodies containing a mixture of PHN and PHPV showed similar degradation rates; that is the ratios showed little change and remained at approximately 50 wt.% (+/- 3%) for each component. These results contrast markedly with in vivo studies for similar inclusion bodies in whole cells. The results suggest that the synthesis and degradation of these novel polyhydroxyalkanoates by P. oleovorans proceeds by the same enzymatic pathway. In addition, comparisons between the in vivo and in vitro polymer degradation suggest that the activity of the intracellular depolymerase does not control the rate limiting step of PHPV degradation in vivo. Instead, the presence of an aromatic group in the repeating units of this polymer may inhibit the utilization of the monomeric units of PHPV as a reserve carbon source by the cells.

In vivo biocompatibility and degradation studies of polyhydroxyoctanoate in the rat: a new sealant for the polyester arterial prosthesis

The present study examined the biocompatibility and degradation properties of poly (beta-hydroxy octanoate) (PHO) as an impregnation substrate on arterial prostheses. PHO-impregnated polyester grafts sterilized by ethylene oxide (EO) or gamma (gamma) radiation, and polyester Dacron(R) prostheses impregnated with fluoropolymer, gelatin, or albumin were implanted subcutaneously in rats for periods ranging from 2 to 180 days. The biocompatibility was assessed by quantifying the alkaline and acid phosphatase secretion while performing histological studies at the tissue/prosthesis interface. The degradation was determined by chemical analysis of the EO and gamma-sterilized PHO after implantation using differential scanning calorimetry (DSC), wide angle x-ray diffraction (WAXD), and size exclusion chromatography (SEC). Alkaline phosphatase activity by the sterilized PHO and by the gelatin and albumin grafts was significantly elevated early after implantation in contrast to that of the Dacron and fluoropolymer grafts that occurred later, at 7 and 5 days, respectively The peak of acid phosphatase activity for all of the grafts occurred between 5 and 10 days postimplantation, with the gamma-sterilized PHO grafts recording the greatest activity. Histological study revealed that the tissue incorporation into the graft wall was earlier and more complete for the Dacron and fluoropolymer grafts after 6 months than for the gelatin and albumin grafts, because the latter induced important inflammatory reactions during the resorption of the cross-linked protein substrates. The EO and gamma-sterilized PHO grafts exhibited a similar healing sequence characterized by the development of a collagenous tissue surrounding the prostheses. However, no infiltration of tissue into the graft wall was observed after 6 months, mainly because of the presence of the PHO. Degradation of the EO and gamma-sterilized PHO occurred preferentially by a hydrolytic mechanism as shown by a 30% molecular weight decrease after 6 months. In conclusion, PHO showed good biocompatibility in terms of enzyme activity and tissue reaction. Degradation was a slow, in vivo process controlled primarily by a random hydrolytic reaction and by a local enzymatic attack by macrophages and giant cells.

Extracellular polymerization of 3-hydroxyalkanoate monomers with the polymerase of Alcaligenes eutrophus

Previous investigations on the role of the polymerase in the synthesis of poly-3-hydroxybutyrate (PHB) are reviewed, and the results from earlier in vitro studies on the activity and selectivity of the polymerase of Alcaligenes eutrophus are discussed. In the present study the effect of glycerol on stabilizing the polymerase after purification and on eliminating the lag phase in in vitro polymerization reactions of 3-hydroxybutyl CoA (HBCoA), and 3-hydroxyvaleryl CoA (HVCoA) are described. K(M) values were determined for the activity of the polymerase with both HBCoA and HVCoA, and the rates of propagation for both monomers were estimated. With a racemic mixture of HBCoA, the enzyme polymerized only the [R] monomer.

Extracellular degradation of medium chain length poly(beta-hydroxyalkanoates) by Comamonas sp

The PHA-degrading isolate, strain P37C, was enriched from residential compost for its ability to hydrolyze the medium chain length PHA, poly(beta-hydroxyoctanoate) (PHO). It was subsequently found to grow on a wide range of PHAs, including both short chain length and medium chain length PHAs. The isolate was identified as belonging to the genus Comamonas. Strain P37C formed clear zones on poly(beta-hydroxybutyrate) (PHB), (PHO) and poly(beta-hydroxyphenylvalerate) (PHPV) overlay plates. PHA clear zone tubes were prepared using seven different kinds of PHAs, ranging from PHB with four-carbon repeating units, to poly(beta-hydroxyoctanoate-co-beta-hydroxyundecanoate) (PHOU) with 8- and 11-carbon repeating units. There was a direct correlation between PHA side chain length and rate of hydrolysis of the PHAs. A series of PHOUs containing varying percentages of unsaturated bonds were used to make a series of epoxidized PHOUs (PHOEs) with varying percentages of epoxy functions. Results of clear zone tube assays showed that these functionalized PHAs were all biodegradable by strain P37C, and there was no apparent correlation between rate of biodegradation and the proportion of functional groups in the PHAs. Biodegradability of these PHAs was verified using respirometry and enzyme assays. Cell-free supernatants containing activity toward PHAs were prepared, and strain P37C was shown to synthesize at least two distinct PHA depolymerases for the hydrolysis of SCL and MCL PHAs.

Production of poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) and poly(4-hydroxybutyric acid) without subsequent degradation by Hydrogenophaga pseudoflava

A Hydrogenophaga pseudoflava strain was able to synthesize poly(3-hydroxybutyric acid-co-4-hydroxybutyric acid) [P(3HB-co-4HB)] having a high level of 4-hydroxybutyric acid monomer unit (4HB) from gamma-butyrolactone. In a two-step process in which the first step involved production of cells containing a minimum amount of poly(3-hydroxybutyric acid) [P(3HB)] and the second step involved polyester accumulation from the lactone, approximately 5 to 10 mol% of the 3-hydroxybutyric acid (3HB) derived from the first-step culture was unavoidably reincorporated into the polymer in the second cultivation step. Reincorporation of the 3HB units produced from degradation of the first-step residual P(3HB) was confirmed by high-resolution 13C nuclear magnetic resonance spectroscopy. In order to synthesize 3HB-free poly(4-hydroxybutyric acid) [P(4HB)] homopolymer, a three-stage cultivation technique was developed by adding a nitrogen addition step, which completely removed the residual P(3HB). The resulting polymer was free of 3HB. However, when the strain was grown on gamma-butyrolactone as the sole carbon source in a synthesis medium, a copolyester of P(3HB-co-4HB) containing 45 mol% 3HB was produced. One-step cultivation on gamma-butyrolactone required a rather long induction time (3 to 4 days). On the basis of the results of an enzymatic study performed with crude extracts, we suggest that the inability of cells to produce 3HB in the multistep culture was due to a low level of 4-hydroxybutyric acid (4HBA) dehydrogenase activity, which resulted in a low level of acetyl coenzyme A. Thus, 3HB formation from gamma-butyrolactone is driven by a high level of 4HBA dehydrogenase activity induced by long exposure to gamma-butyrolactone, as is the case for a one-step culture. In addition, intracellular degradation kinetics studies showed that P(3HB) in cells was completely degraded within 30 h of cultivation after being transferred to a carbon-free mineral medium containing additional ammonium sulfate, while P(3HB-co-4HB) containing 5 mol% 3HB and 95 mol% 4HB was totally inert in interactions with the intracellular depolymerases. Intracellular inertness could be a useful factor for efficient synthesis of the P(4HB) homopolymer and of 4HB-rich P(3HB-co-4HB) by the strain used in this study.

Protein organization on the PHA inclusion cytoplasmic boundary

Polyhydroxyalkanoate (PHA) cellular inclusions consist of polyesters, phospholipids, and proteins. Both the polymerase and the depolymerase enzymes are active components of the structure. Recently, proteins associated with these inclusions have been described in a number of bacterial species. In order to further clarify the structure and function of these proteins in relation to polymer inclusions, ultrastructural studies of isolated polymer inclusions were initiated. The surface boundary characteristics of polymer inclusions, produced by several genera of bacteria, two different Pseudomonas putida deletion mutants and by Escherichia coli recombinants, were examined. The recombinant E. coli carried either the PHB biosynthesis operon (phaCAB) from Ralstonia eutropha alone, or both this operon and a gene encoding an inclusion surface protein of R. eutropha (phaP). The results support two suggestions: (i) specific genes in the PHA gene cluster code for the proteins forming the surface boundary arrays which characterize the polymer inclusion; and (ii) transfer of such a gene would result in subcellular compartmentalization of accumulating polymer. Although the proteins appear to serve a similar function among different genera, nevertheless, the different surface proteins are encoded by a variety of non-homologous genetic sequences.

Investigation of the function of proteins associated to polyhydroxyalkanoate inclusions in Pseudomonas putida BMO1

Polyhydroxyalkanoate (PHA) granule associated proteins from Pseudomonas oleovorans were purified and the N-terminal sequences of two major proteins migrating in sodium dodecyl sulfate polyacrylamide gels with a relative molecular mass of 18 and 43 kDa (GA1 and GA2, respectively) were analyzed. Radiolabeled degenerate probes deduced from these amino acid sequences were used to identify genomic DNA fragments from P. oleovorans and Pseudomonas putida encoding GA1 and GA2. DNA sequence analysis of the fragments obtained from P. putida revealed that the genes encoding these proteins were adjacent to phaC2 and ORF3, the PHA synthase II gene and an open reading frame of unknown function, respectively, found at the P. oleovorans and P. aeruginosa PHA synthase gene locus. The open reading frames encoding GA1, GA2 and ORF3 or smaller fragments beginning at GA1 were inactivated by chromosomal insertion of the Tn5 kanamycin resistance gene block (neo). When these mutants were grown on mineral salts agar media under nitrogen limitation, containing gluconate or decanoate as carbon sources, they appeared more translucent than the wild-type grown under similar conditions. Gas-chromatographic analysis of the cellular dry mass revealed that the mutant strains accumulated 30-50% less PHA than the P. putida wild type.