Long-term Outcomes with Spinal versus General Anesthesia for Hip Fracture Surgery: A Randomized Trial

BACKGROUND

The effects of spinal versus general anesthesia on long-term outcomes have not been well studied. This study tested the hypothesis that spinal anesthesia is associated with better long-term survival and functional recovery than general anesthesia.

METHODS

A prespecified analysis was conducted of long-term outcomes of a completed randomized superiority trial that compared spinal anesthesia versus general anesthesia for hip fracture repair. Participants included previously ambulatory patients 50 yr of age or older at 46 U.S. and Canadian hospitals. Patients were randomized 1:1 to spinal or general anesthesia, stratified by sex, fracture type, and study site. Outcome assessors and investigators involved in the data analysis were masked to the treatment arm. Outcomes included survival at up to 365 days after randomization (primary); recovery of ambulation among 365-day survivors; and composite endpoints for death or new inability to ambulate and death or new nursing home residence at 365 days. Patients were included in the analysis as randomized.

RESULTS

A total of 1,600 patients were enrolled between February 12, 2016, and February 18, 2021; 795 were assigned to spinal anesthesia, and 805 were assigned to general anesthesia. Among 1,599 patients who underwent surgery, vital status information at or beyond the final study interview (conducted at approximately 365 days after randomization) was available for 1,427 (89.2%). Survival did not differ by treatment arm; at 365 days after randomization, there were 98 deaths in patients assigned to spinal anesthesia versus 92 deaths in patients assigned to general anesthesia (hazard ratio, 1.08; 95% CI, 0.81 to 1.44, P = 0.59). Recovery of ambulation among patients who survived a year did not differ by type of anesthesia (adjusted odds ratio for spinal vs. general, 0.87; 95% CI, 0.67 to 1.14; P = 0.31). Other outcomes did not differ by treatment arm.

CONCLUSIONS

Long-term outcomes were similar with spinal versus general anesthesia.

EDITOR’S PERSPECTIVE

Outcomes with spinal versus general anesthesia for patients with and without preoperative cognitive impairment: Secondary analysis of a randomized clinical trial

INTRODUCTION

The effect of spinal versus general anesthesia on the risk of postoperative delirium or other outcomes for patients with or without cognitive impairment (including dementia) is unknown.

METHODS

Post hoc secondary analysis of a multicenter pragmatic trial comparing spinal versus general anesthesia for adults aged 50 years or older undergoing hip fracture surgery.

RESULTS

Among patients randomized to spinal versus general anesthesia, new or worsened delirium occurred in 100/295 (33.9%) versus 107/283 (37.8%; odds ratio [OR] 0.85; 95% confidence interval [CI] 0.60 to 1.19) among persons with cognitive impairment and 70/432 (16.2%) versus 71/445 (16.0%) among persons without cognitive impairment (OR 1.02; 95% CI 0.71 to 1.47, p = 0.46 for interaction). Delirium severity, in-hospital complications, and 60-day functional recovery did not differ by anesthesia type in patients with or without cognitive impairment.

DISCUSSION

Anesthesia type is not associated with differences in delirium and functional outcomes among persons with or without cognitive impairment.

Pain, Analgesic Use, and Patient Satisfaction With Spinal Versus General Anesthesia for Hip Fracture Surgery : A Randomized Clinical Trial

BACKGROUND

The REGAIN (Regional versus General Anesthesia for Promoting Independence after Hip Fracture) trial found similar ambulation and survival at 60 days with spinal versus general anesthesia for hip fracture surgery. Trial outcomes evaluating pain, prescription analgesic use, and patient satisfaction have not yet been reported.

OBJECTIVE

To compare pain, analgesic use, and satisfaction after hip fracture surgery with spinal versus general anesthesia.

DESIGN

Preplanned secondary analysis of a pragmatic randomized trial. (ClinicalTrials.gov: NCT02507505).

SETTING

46 U.S. and Canadian hospitals.

PARTICIPANTS

Patients aged 50 years or older undergoing hip fracture surgery.

INTERVENTION

Spinal or general anesthesia.

MEASUREMENTS

Pain on postoperative days 1 through 3; 60-, 180-, and 365-day pain and prescription analgesic use; and satisfaction with care.

RESULTS

A total of 1600 patients were enrolled. The average age was 78 years, and 77% were women. A total of 73.5% (1050 of 1428) of patients reported severe pain during the first 24 hours after surgery. Worst pain over the first 24 hours after surgery was greater with spinal anesthesia (rated from 0 [no pain] to 10 [worst pain imaginable]; mean difference, 0.40 [95% CI, 0.12 to 0.68]). Pain did not differ across groups at other time points. Prescription analgesic use at 60 days occurred in 25% (141 of 563) and 18.8% (108 of 574) of patients assigned to spinal and general anesthesia, respectively (relative risk, 1.33 [CI, 1.06 to 1.65]). Satisfaction was similar across groups.

LIMITATION

Missing outcome data and multiple outcomes assessed.

CONCLUSION

Severe pain is common after hip fracture. Spinal anesthesia was associated with more pain in the first 24 hours after surgery and more prescription analgesic use at 60 days compared with general anesthesia.

PRIMARY FUNDING SOURCE

Patient-Centered Outcomes Research Institute.

Spinal Anesthesia or General Anesthesia for Hip Surgery in Older Adults

BACKGROUND

The effects of spinal anesthesia as compared with general anesthesia on the ability to walk in older adults undergoing surgery for hip fracture have not been well studied.

METHODS

We conducted a pragmatic, randomized superiority trial to evaluate spinal anesthesia as compared with general anesthesia in previously ambulatory patients 50 years of age or older who were undergoing surgery for hip fracture at 46 U.S. and Canadian hospitals. Patients were randomly assigned in a 1:1 ratio to receive spinal or general anesthesia. The primary outcome was a composite of death or an inability to walk approximately 10 ft (3 m) independently or with a walker or cane at 60 days after randomization. Secondary outcomes included death within 60 days, delirium, time to discharge, and ambulation at 60 days.

RESULTS

A total of 1600 patients were enrolled; 795 were assigned to receive spinal anesthesia and 805 to receive general anesthesia. The mean age was 78 years, and 67.0% of the patients were women. A total of 666 patients (83.8%) assigned to spinal anesthesia and 769 patients (95.5%) assigned to general anesthesia received their assigned anesthesia. Among patients in the modified intention-to-treat population for whom data were available, the composite primary outcome occurred in 132 of 712 patients (18.5%) in the spinal anesthesia group and 132 of 733 (18.0%) in the general anesthesia group (relative risk, 1.03; 95% confidence interval [CI], 0.84 to 1.27; P = 0.83). An inability to walk independently at 60 days was reported in 104 of 684 patients (15.2%) and 101 of 702 patients (14.4%), respectively (relative risk, 1.06; 95% CI, 0.82 to 1.36), and death within 60 days occurred in 30 of 768 (3.9%) and 32 of 784 (4.1%), respectively (relative risk, 0.97; 95% CI, 0.59 to 1.57). Delirium occurred in 130 of 633 patients (20.5%) in the spinal anesthesia group and in 124 of 629 (19.7%) in the general anesthesia group (relative risk, 1.04; 95% CI, 0.84 to 1.30).

CONCLUSIONS

Spinal anesthesia for hip-fracture surgery in older adults was not superior to general anesthesia with respect to survival and recovery of ambulation at 60 days. The incidence of postoperative delirium was similar with the two types of anesthesia. (Funded by the Patient-Centered Outcomes Research Institute; REGAIN ClinicalTrials.gov number, NCT02507505.).

Continuous erector spinae plane block versus thoracic epidural analgesia in video-assisted thoracic surgery: a study protocol for a prospective randomized open label non-inferiority trial

BACKGROUND

Thoracic epidural analgesia is considered the gold standard for pain relief in video-assisted thoracoscopic surgery. This neuraxial technique blocks pain sensation by injecting a local anesthetic agent in the epidural space near the spinal cord to block spinal nerve roots. Recently, the erector spinae plane block has been introduced as a practical alternative to the thoracic epidural. This interfascial regional anesthesia technique interrupts pain sensation by injecting a local anesthetic agent in between the muscular layers of the thoracic wall. Several case series and three RCTs described it as an effective pain management technique in video-assisted thoracoscopic surgery (Scimia et al., Reg Anesth Pain Med 42:537, 2017; Adhikary et al., Indian J Anaesth 62:75-8, 2018; Kim, A randomized controlled trial comparing continuous erector spinae plane block with thoracic epidural analgesia for postoperative pain management in video-assisted thoracic surgery, n.d.; Yao et al., J Clin Anesth 63:109783, 2020; Ciftci et al., J Cardiothorac Vasc Anesth 34:444-9, 2020). The objective of this study is to test the hypothesis that a continuous erector spinae plane block incorporated into an opioid-based systemic multimodal analgesia regimen is non-inferior in terms of the quality of postoperative recovery compared to continuous thoracic epidural local anesthetic-opioid analgesia in patients undergoing elective unilateral video-assisted thoracoscopic surgery.

METHODS

This is a prospective randomized open label non-inferiority trial. A total of 90 adult patients undergoing video-assisted thoracoscopic surgery will be randomized 1:1 to receive pain treatment with either (1) continuous erector spinae plane block plus intravenous patient-controlled analgesia with piritramide (study group) or (2) continuous thoracic epidural analgesia with a local anesthetic-opioid infusate (control group). All patients will receive additional systemic multimodal analgesia with paracetamol and non-steroidal anti-inflammatory drugs. The primary endpoint is the quality of recovery as measured by the Quality of Recovery-15 score. Secondary endpoints are postoperative pain as Numerical Rating Score scores, length of hospital stay, failure of analgesic technique, postoperative morphine-equivalent consumption, itching, nausea and vomiting, total operative time, complications related to surgery, perioperative hypotension, complications related to pain treatment, duration of bladder catheterization, and time of first assisted mobilization > 20 m and of mobilization to sitting in a chair.

DISCUSSION

This randomized controlled trial aims to confirm whether continuous erector spinae plane block plus patient-controlled opioid analgesia can equal the analgesic effect of a thoracic epidural local anesthetic-opioid infusion in patients undergoing video-assisted thoracoscopic surgery.

TRIAL REGISTRATION

Netherlands Trial Register NL6433 . Registered on 1 March 2018. This trial was prospectively registered.

Ultrasound-guided fascial plane blocks of the chest wall: a state-of-the-art review

Ultrasound-guided fascial plane blocks of the chest wall are increasingly popular alternatives to established techniques such as thoracic epidural or paravertebral blockade, as they are simple to perform and have an appealing safety profile. Many different techniques have been described, which can be broadly categorised into anteromedial, anterolateral and posterior chest wall blocks. Understanding the relevant clinical anatomy is critical not only for block performance, but also to match block techniques appropriately with surgical procedures. The sensory innervation of tissues deep to the skin (e.g. muscles, ligaments and bone) can be overlooked, but is often a significant source of pain. The primary mechanism of action for these blocks is a conduction blockade of sensory afferents travelling in the targeted fascial planes, as well as of peripheral nociceptors in the surrounding tissues. A systemic action of absorbed local anaesthetic is plausible but unlikely to be a major contributor. The current evidence for their clinical applications indicates that certain chest wall techniques provide significant benefit in breast and thoracic surgery, similar to that provided by thoracic paravertebral blockade. Their role in trauma and cardiac surgery is evolving and holds great potential. Further avenues of research into these versatile techniques include: optimal local anaesthetic dosing strategies; high-quality randomised controlled trials focusing on patient-centred outcomes beyond acute pain; and comparative studies to determine which of the myriad blocks currently on offer should be core competencies in anaesthetic practice.

Risks to healthcare workers following tracheal intubation of patients with COVID-19: a prospective international multicentre cohort study

Healthcare workers involved in aerosol‐generating procedures, such as tracheal intubation, may be at elevated risk of acquiring COVID‐19. However, the magnitude of this risk is unknown. We conducted a prospective international multicentre cohort study recruiting healthcare workers participating in tracheal intubation of patients with suspected or confirmed COVID‐19. Information on tracheal intubation episodes, personal protective equipment use and subsequent provider health status was collected via self‐reporting. The primary endpoint was the incidence of laboratory‐confirmed COVID‐19 diagnosis or new symptoms requiring self‐isolation or hospitalisation after a tracheal intubation episode. Cox regression analysis examined associations between the primary endpoint and healthcare worker characteristics, procedure‐related factors and personal protective equipment use. Between 23 March and 2 June 2020, 1718 healthcare workers from 503 hospitals in 17 countries reported 5148 tracheal intubation episodes. The overall incidence of the primary endpoint was 10.7% over a median (IQR [range]) follow‐up of 32 (18–48 [0–116]) days. The cumulative incidence within 7, 14 and 21 days of the first tracheal intubation episode was 3.6%, 6.1% and 8.5%, respectively. The risk of the primary endpoint varied by country and was higher in women, but was not associated with other factors. Around 1 in 10 healthcare workers involved in tracheal intubation of patients with suspected or confirmed COVID‐19 subsequently reported a COVID‐19 outcome. This has human resource implications for institutional capacity to deliver essential healthcare services, and wider societal implications for COVID‐19 transmission.

Advances in regional anaesthesia and acute pain management: a narrative review

Regional anaesthesia has undergone several exciting advances in the past few decades. Ultrasound-guided techniques of peripheral nerve blockade have become the gold standard thanks to the associated improvements in efficacy, ease of performance and safety. This has increased the accessibility and utilisation of regional anaesthesia in the anaesthesia community at large and is timely given the mounting evidence for its potential benefits on various patient-centred outcomes, including major morbidity, cancer recurrence and persistent postoperative pain. Ultrasound guidance has also paved the way for refinement of the technical performance of existing blocks concerning simplicity and safety, as well as the development of new regional anaesthesia techniques. In particular, the emergence of fascial plane blocks has further broadened the application of regional anaesthesia in the management of painful conditions of the thorax and abdomen. The preliminary results of investigations into these fascial plane blocks are promising but require further research to establish their true value and role in clinical care. One of the challenges that remains is how best to prolong regional anaesthesia to maximise its benefits while avoiding undue harm. There is ongoing research into optimising continuous catheter techniques and their management, intravenous and perineural pharmacological adjuncts, and sustained-release local anaesthetic molecules. Finally, there is a growing appreciation for the critical role that regional anaesthesia can play in an overall multimodal anaesthetic strategy. This is especially pertinent given the current focus on eliminating unnecessary peri-operative opioid administration.

A Comparison of 5% Dextrose in 0.9% Normal Saline versus Non-Dextrose-Containing Crystalloids as the Initial Intravenous Replacement Fluid in Elective Surgery

Intravenous fluid replacement in adult elective surgery is often initiated with dextrose-containing fluids. We sought to determine if this practice resulted in significant hyperglycaemia and if there was a risk of hypoglycaemia if non-dextrose-containing crystalloids were used instead.

We conducted a randomized controlled trial in 50 non-diabetic adult patients undergoing elective surgery which did not involve entry into major body cavities, large fluid shifts, or require administration of > 500 ml of intravenous fluid in the first two hours of peri-operative care. Patients received 500 ml of either 5% dextrose in 0.9% normal saline, lactated Ringer's solution, or 0.9% normal saline over 45 to 60 minutes. Plasma glucose, electrolytes and osmolality were measured prior to infusion, and at 15 minutes and one hour after completion of infusion.

None of the patients had preoperative hypoglycaemia despite average fasting times of almost 13 hours. Patients receiving lactated Ringer's and normal saline remained normoglycaemic throughout the study period. Patients receiving dextrose saline had significantly elevated plasma glucose 15 minutes after completion of infusion (11.1 (9.9–12.2, 95% CI) mmol/l). Plasma glucose exceeded 10 mmol/l in 72% of patients receiving dextrose saline. There was no significant difference in plasma glucose between the groups at one hour after infusion, but 33% of patients receiving DS had plasma glucose ≥8 mmol/l.

We conclude that initiation of intravenous fluid replacement with dextrose-containing solutions is not required to prevent hypoglycaemia in elective surgery. On the contrary, a relatively small volume of 500 ml causes significant, albeit transient, hyperglycaemia, even in non-diabetic patients.

Erector spinae plane block in abdominal surgery: Case series

The aim of this study is to report 11 cases of erector spinae plane (ESP) block used for unilateral or bilateral abdominal surgery, adding to the overall limited experience with abdominal ESP block. The procedures were carried out at a teaching hospital in 11 patients (eight males, three females, ages 36–80 years) requiring abdominal surgery, including laparoscopic surgery. Each patient required surgery under different physical circumstances and likely different conceptions of what constituted pain. Two of the eleven patients were administered the ESP block and did not require general anaesthesia. Most of the patients with the ESP block maintained a numerical rating scale (NRS) for pain of 0–2/10 postoperatively. An occasional patient required paracetamol analgesia. There were no cases of opiate rescue. Obesity in a 46-year-old woman was believed to cause unclear ultrasonographic visualisation, interfering with entry of the ESP catheter. She, however, had no post-operative pain. She was given the usual intravenous metamizole 2 g for 10 h and required only analgesics at 16 h. ESP block, which produces analgesia by blocking trunk nerves, is an appropriate approach to patients requiring abdominal surgery, whether laparoscopic or open.

The analgesic efficacy of pre-operative bilateral erector spinae plane (ESP) blocks in patients having ventral hernia repair

Laparoscopic ventral hernia repair is an operation associated with significant postoperative pain, and regional anaesthetic techniques are of potential benefit. The erector spinae plane (ESP) block performed at the level of the T5 transverse process has recently been described for thoracic surgery, and we hypothesised that performing the ESP block at a lower vertebral level would provide effective abdominal analgesia. We performed pre-operative bilateral ESP blocks with 20-30 ml ropivacaine 0.5% at the level of the T7 transverse process in four patients undergoing laparoscopic ventral hernia repair. Median (range) 24-h opioid consumption was 18.7 mg (0.0-43.0 mg) oral morphine. The highest and lowest median (range) pain scores in the first 24 h were 3.5 (3.0-5.0) and 2.5 (0.0-3.0) on an 11-point numerical rating scale. We also performed the block in a fresh cadaver and assessed the extent of injectate spread using computerised tomography. There was radiographic evidence of spread extending cranially to the upper thoracic levels and caudally as far as the L2-L3 transverse processes. We conclude that the ESP block is a promising regional anaesthetic technique for laparoscopic ventral hernia repair and other abdominal surgery when performed at the level of the T7 transverse process. Its advantages are the ability to block both supra-umbilical and infra-umbilical dermatomes with a single-level injection and its relative simplicity.

Real-time ultrasound-guided spinal anesthesia in patients with a challenging spinal anatomy: two case reports

Spinal anesthesia may be challenging in patients with poorly palpable surface landmarks or abnormal spinal anatomy. Pre-procedural ultrasound imaging of the lumbar spine can help by providing additional anatomical information, thus permitting a more accurate estimation of the appropriate needle insertion site and trajectory. However, actual needle insertion in the pre-puncture ultrasound-assisted technique remains a 'blind' procedure. We describe two patients with an abnormal spinal anatomy in whom ultrasound-assisted spinal anesthesia was unsuccessful. Successful dural puncture was subsequently achieved using a technique of real-time ultrasound-guided spinal anesthesia. This may be a useful option in patients in whom landmark-guided and ultrasound-assisted techniques have failed.

Anaesthetic Management of Awake Craniotomy for Tumour Resection

Introduction: Awake craniotomy allows accurate localisation of the eloquent brain, which is crucial during brain tumour resection in order to minimise risk of neurologic injury. The role of the anaesthesiologist is to provide adequate analgesia and sedation while maintaining ventilation and haemodynamic stability in an awake patient who needs to be cooperative during neurological testing. We reviewed the anaesthetic management of patients undergoing an awake craniotomy procedure. Materials and Methods: The records of all the patients who had an awake craniotomy at our institution from July 2004 till June 2006 were reviewed. The anaesthesia techniques and management were examined. The perioperative complications and the outcome of the patients were noted. Results: There were 17 procedures carried out during the study period. Local anaesthesia with moderate to deep sedation was the technique used in all the patients. Respiratory complications occurred in 24% of the patients. Hypertension was observed in 24% of the patients. All the complications were transient and easily treated. During cortical stimulation, motor function was assessed in 16 patients (94%). Three patients (16%) had lesions in the temporalparietal region and speech was assessed intraoperatively. Postoperative motor weakness was seen in 1 patient despite uneventful intraoperative testing. No patient required intensive care unit stay. The median length of stay in the high dependency unit was 1 day and the median length of hospital stay was 9 days. There was no in-hospital mortality. Conclusion: Awake craniotomy for brain tumour excision can be successfully performed under good anaesthetic conditions with careful titration of sedation. Our series showed it to be a well-tolerated procedure with a low rate of complications. The benefits of maximal tumour excision can be achieved, leading to potentially better patient outcome. Key words: Brain neoplasm, Neurosurgery, Postoperative complications

Anaesthetic management of awake craniotomy for tumour resection

INTRODUCTION

Awake craniotomy allows accurate localisation of the eloquent brain, which is crucial during brain tumour resection in order to minimise risk of neurologic injury. The role of the anaesthesiologist is to provide adequate analgesia and sedation while maintaining ventilation and haemodynamic stability in an awake patient who needs to be cooperative during neurological testing. We reviewed the anaesthetic management of patients undergoing an awake craniotomy procedure.

MATERIALS AND METHODS

The records of all the patients who had an awake craniotomy at our institution from July 2004 till June 2006 were reviewed. The anaesthesia techniques and management were examined. The perioperative complications and the outcome of the patients were noted.

RESULTS

There were 17 procedures carried out during the study period. Local anaesthesia with moderate to deep sedation was the technique used in all the patients. Respiratory complications occurred in 24% of the patients. Hypertension was observed in 24% of the patients. All the complications were transient and easily treated. During cortical stimulation, motor function was assessed in 16 patients (94%). Three patients (16%) had lesions in the temporal-parietal region and speech was assessed intraoperatively. Postoperative motor weakness was seen in 1 patient despite uneventful intraoperative testing. No patient required intensive care unit stay. The median length of stay in the high dependency unit was 1 day and the median length of hospital stay was 9 days. There was no in-hospital mortality.

CONCLUSION

Awake craniotomy for brain tumour excision can be successfully performed under good anaesthetic conditions with careful titration of sedation. Our series showed it to be a well-tolerated procedure with a low rate of complications. The benefits of maximal tumour excision can be achieved, leading to potentially better patient outcome.

A BIS-guided study of sevoflurane requirements for adequate depth of anaesthesia in Caesarean section

Caesarean section carries a high risk of awareness, especially in the period prior to neonatal delivery. We investigated the concentration of sevoflurane required to maintain bispectral index (BIS) < 60 until delivery occurred. We enrolled 23 parturients into an up-down sequential allocation study. The median effective end-tidal concentration (EC(50)) of sevoflurane was defined as that which maintained BIS < 60 between skin incision and delivery in 50% of patients. This was calculated using Dixon and Massey's method. Receiver operating characteristic curve analysis was used to establish BIS response probability thresholds. The EC(50) for sevoflurane was 1.22% (1.08-1.33, 95% CI). The probability of maintaining BIS < 60 was < 55% at a concentration of < 1.1%; this increased to 80% at concentrations of 1.2-1.3%. We conclude that sevoflurane concentrations of at least 1.2-1.3% should be administered in uncomplicated Caesarean section, so as to minimise the risk of awareness and recall.

Opitutus terrae gen. nov., sp. nov., to accommodate novel strains of the division 'Verrucomicrobia' isolated from rice paddy soil

Three strains of obligately anaerobic bacteria were isolated from rice paddy soil microcosms. Comparative analysis of the 16S rRNA genes showed that these novel isolates have identical gene sequences and are members of the division 'Verrucomicrobia'. The novel strains are phenotypically and phylogenetically distinct from species described previously. One strain, PB90-1T, was characterized in more detail. The cells are cocci and are motile by means of a flagellum. Catalase and oxidase activities are absent. Growth-supporting substrates include mono-, di- and polysaccharides, while alcohols, amino acids and organic acids do not support growth. Propionate and acetate are the major end-products of fermentation. Nitrate is reduced to nitrite, but other external electron acceptors are not utilized. The G+C content of the genomic DNA is 74 mol%. This strain represents a taxon that has not yet been formally recognized, for which the name Opitutus terrae gen. nov., sp. nov. is proposed. The type strain is PB90-1T (= DSM 11246T).

Evidence for anaerobic syntrophic acetate oxidation during methane production in the profundal sediment of subtropical Lake Kinneret (Israel)

Methane production was measured in samples of the profundal sediment from Lake Kinneret. Production rates of CH(4) were higher at 30 degrees C than at the in situ temperature of 15 degrees C and were higher in the top 5 cm layer than below. Turnover of [2-(14)C]-acetate resulted in the production of (14)CH(4) and (14)CO(2) with turnover times of < 42 min. However, < 30% of the added radioactivity was converted to gaseous products, indicating that only part of the acetate pool was microbially available. The calculated acetate turnover rates were sufficient to account for total CH(4) production, indicating that CH(4) was produced exclusively from acetate. This conclusion was confirmed by inhibition of methanogens with chloroform, which resulted in an almost stoichiometric accumulation of acetate. However, a large percentage (30-60%) of [2-(14)C]-acetate was converted to (14)CO(2), despite lack of reducible sulphate or other oxidants in the sediment. Anoxic preincubation of the sediment did not result in reduced production of (14)CO(2). Therefore, part of the acetate must have been oxidized rather than methanogenically cleaved. Conversion of [(14)C]-bicarbonate to (14)CH(4) indicated that 30-50% of total CH(4) production originated from reduction of CO(2). To reconcile the relatively high contribution of H(2)/CO(2)-dependent methanogenesis with the relatively high oxidative conversion of acetate, we assume that part of the acetate was used syntrophically by consortia of acetate-oxidizing bacteria and H(2)/CO(2)-using methanogens. This conclusion is supported by favourable thermodynamic conditions for syntrophic acetate oxidation under in situ conditions and complete inhibition of [2-(14)C]-acetate turnover at high H(2) partial pressures. Further evidence to support this conclusion comes from the analysis of the structure of the archaeal community. Terminal restriction fragment length polymorphism (T-RFLP) and partial sequence analysis of the SSU rRNA genes amplified from DNA extracts of the sediment showed Methanomicrobiaceae as the dominant methanogenic group, whereas acetoclastic methanogens could not be detected.

Functional patterns and temperature response of cellulose-fermenting microbial cultures containing different methanogenic communities

The effect of microbial composition on the methanogenic degradation of cellulose was studied using two lines of anaerobic cellulose-fermenting methanogenic microbial cultures at two different temperatures: that at 15 degrees C being dominated by Methanosaeta and that at 30 degrees C by Methanosarcina. In both cultures, CH4 production and acetate consumption were completely inhibited by either 2-bromoethanesulfonate or chloroform, whereas H2 consumption was only inhibited by chloroform, suggesting that homoacetogens utilized H2 concomitantly with methanogens. Hydrogen was the intermediate that was consumed first, while acetate continued to accumulate. At 15 degrees C, acetoclastic methanogenesis smoothly followed H2-dependent CH4 production. Fluorescence in situ hybridization showed that populations of Methanosaeta steadily increased with time from 5 to 25% of total cell counts. At 30 degrees C, two phases of CH4 production were obtained, with acetate consumed after the abrupt increase of Methanosarcina from 0 to 45% of total cell counts. Whereas populations of Methanosaeta were able to adapt after transfer from 15 to 30 degrees C, those of Methanosarcina were not, irrespective of during which phase the cultures were transferred from 30 degrees C to 15 degrees C. Our results thus show that the community structure of methanogens indeed affects the function of a cellulose-fermenting community with respect to temperature response.

Thermophilic methanogens in rice field soil

The soil temperature in flooded Italian rice fields is generally lower than 30 degrees C. However, two temperature optima at approximately 41 degrees C and 50 degrees C were found when soil slurries were anoxically incubated at a temperature range of 10-80 degrees C. The second temperature optimum indicates the presence of thermophilic methanogens in the rice field soil. Experiments with 14C-labelled bicarbonate showed that the thermophilic CH4 was exclusively produced from H2/CO2. Terminal restriction fragment length polymorphism (T-RFLP) of archaeal SSU rRNA gene fragments revealed a dramatic change in the archaeal community structure at temperatures > 37 degrees C, with the euryarchaeotal rice cluster I becoming the dominant group (about 80%). A clone library of archaeal SSU rRNA gene fragments generated at 49 degrees C was also dominated (10 out of 11 clones) by rice cluster I. Our results demonstrate that Italian rice field soil contains thermophilic methanogenic activity that was most probably a result of members of the as yet uncultivated euryarchaeotal rice cluster I.

Molecular analyses of methyl-coenzyme M reductase alpha-subunit (mcrA) genes in rice field soil and enrichment cultures reveal the methanogenic phenotype of a novel archaeal lineage

The diversity of methanogen-specific methyl-coenzyme M reductase alpha-subunit (mcrA/mrtA) genes in Italian rice field soil was analysed using a combination of molecular techniques and enrichment cultures. From 75 mcrA/mrtA clones retrieved from rice field soil, 52 were related to members of the Methanosarcinaceae, Methanosaetaceae and Methanobacteriaceae. However, 19 and four clones formed two novel clusters of deeply branching mcrA sequences, respectively, which could not be affiliated to known methanogens. A new methanogen-specific fingerprinting assay based on terminal restriction fragment length polymorphism (T-RFLP) analysis of fluorescently labelled polymerase chain reaction (PCR) products allowed us to distinguish all environmental mcrA/mrtA sequences via group-specific Sau96I restriction sites. Even genes for the isoenzyme methyl-coenzyme M reductase two (mrtA) of Methanobacteriaceae present in rice field soil were represented by a unique 470 bp terminal restriction fragment (T-RF). Both cloning and T-RFLP analysis indicated a significant representation of novel environmental mcrA sequences in rice field soil (238 bp T-RF). To identify these mcrA sequences, methanogenic enrichment cultures with rice field soil as inoculum were established with H2/CO2 as substrates at a temperature of 50 degrees C, and these were monitored using molecular tools. In subsequent transfers of these enrichment cultures, cloning and T-RFLP analysis detected predominantly SSU rRNA genes of rice cluster I (RC-I), an uncultivated euryarchaeotal lineage discovered previously in anoxic rice field soil. In parallel, both mcrA cloning and T-RFLP analyses of the enrichment culture identified the more frequent cluster of novel environmental mcrA sequences as belonging to members of RC-I. Thus, we could demonstrate the genotype and phenotype of RC-I Archaea by the presence of a catabolic gene in a methanogenic enrichment culture before the isolation of pure cultures.

Characterization and identification of numerically abundant culturable bacteria from the anoxic bulk soil of rice paddy microcosms

Most-probable-number (liquid serial dilution culture) counts were obtained for polysaccharolytic and saccharolytic fermenting bacteria in the anoxic bulk soil of flooded microcosms containing rice plants. The highest viable counts (up to 2.5 x 10(8) cells per g [dry weight] of soil) were obtained by using xylan, pectin, or a mixture of seven mono- and disaccharides as the growth substrate. The total cell count for the soil, as determined by using 4', 6-diamidino-2-phenylindole staining, was 4.8 x 10(8) cells per g (dry weight) of soil. The nine strains isolated from the terminal positive tubes in counting experiments which yielded culturable populations that were equivalent to about 5% or more of the total microscopic count population belonged to the division Verrucomicrobia, the Cytophaga-Flavobacterium-Bacteroides division, clostridial cluster XIVa, clostridial cluster IX, Bacillus spp., and the class Actinobacteria. Isolates originating from the terminal positive tubes of liquid dilution series can be expected to be representatives of species whose populations in the soil are large. None of the isolates had 16S rRNA gene sequences identical to 16S rRNA gene sequences of previously described species for which data are available. Eight of the nine strains isolated fermented sugars to acetate and propionate (and some also fermented sugars to succinate). The closest relatives of these strains (except for the two strains of actinobacteria) were as-yet-uncultivated bacteria detected in the same soil sample by cloning PCR-amplified 16S rRNA genes (U. Hengstmann, K.-J. Chin, P. H. Janssen, and W. Liesack, Appl. Environ. Microbiol. 65:5050-5058, 1999). Twelve other isolates, which originated from most-probable-number counting series indicating that the culturable populations were smaller, were less closely related to cloned 16S rRNA genes.

Comparative phylogenetic assignment of environmental sequences of genes encoding 16S rRNA and numerically abundant culturable bacteria from an anoxic rice paddy soil

We used both cultivation and direct recovery of bacterial 16S rRNA gene (rDNA) sequences to investigate the structure of the bacterial community in anoxic rice paddy soil. Isolation and phenotypic characterization of 19 saccharolytic and cellulolytic strains are described in the accompanying paper (K.-J. Chin, D. Hahn, U. Hengstmann, W. Liesack, and P. H. Janssen, Appl. Environ. Microbiol. 65:5042-5049, 1999). Here we describe the phylogenetic positions of these strains in relation to 57 environmental 16S rDNA clone sequences. Close matches between the two data sets were obtained for isolates from the culturable populations determined by the most-probable-number counting method to be large (3 x 10(7) to 2.5 x 10(8) cells per g [dry weight] of soil). This included matches with 16S rDNA similarity values greater than 98% within distinct lineages of the division Verrucomicrobia (strain PB90-1) and the Cytophaga-Flavobacterium-Bacteroides group (strains XB45 and PB90-2), as well as matches with similarity values greater than 95% within distinct lines of descent of clostridial cluster XIVa (strain XB90) and the family Bacillaceae (strain SB45). In addition, close matches with similarity values greater than 95% were obtained for cloned 16S rDNA sequences and bacteria (strains DR1/8 and RPec1) isolated from the same type of rice paddy soil during previous investigations. The correspondence between culture methods and direct recovery of environmental 16S rDNA suggests that the isolates obtained are representative geno- and phenotypes of predominant bacterial groups which account for 5 to 52% of the total cells in the anoxic rice paddy soil. Furthermore, our findings clearly indicate that a dual approach results in a more objective view of the structural and functional composition of a soil bacterial community than either cultivation or direct recovery of 16S rDNA sequences alone.

Effect of temperature on structure and function of the methanogenic archaeal community in an anoxic rice field soil

Soil temperatures in Italian rice fields typically range between about 15 and 30 degrees C. A change in the incubation temperature of anoxic methanogenic soil slurry from 30 degrees C to 15 degrees C typically resulted in a decrease in the CH4 production rate, a decrease in the steady-state H2 partial pressure, and a transient accumulation of acetate. Previous experiments have shown that these changes were due to an alteration of the carbon and electron flow in the methanogenic degradation pathway of organic matter caused by the temperature shift (K. J. Chin and R. Conrad, FEMS Microbiol. Ecol. 18:85-102, 1995). To investigate how temperature affects the structure of the methanogenic archaeal community, total DNA was extracted from soil slurries incubated at 30 and 15 degrees C. The archaeal small-subunit (SSU) rRNA-encoding genes (rDNA) of these environmental DNA samples were amplified by PCR with an archaeal-specific primer system and used for the generation of clone libraries. Representative rDNA clones (n = 90) were characterized by terminal restriction fragment length polymorphism (T-RFLP) and sequence analysis. T-RFLP analysis produced for the clones terminally labeled fragments with a characteristic length of mostly 185, 284, or 392 bp. Sequence analysis allowed determination of the phylogenetic affiliation of the individual clones with their characteristic T-RFLP fragment lengths and showed that the archaeal community of the anoxic rice soil slurry was dominated by members of the families Methanosarcinaceae (185 bp) and Methanosaetaceae (284 bp), the kingdom Crenarchaeota (185 or 284 bp), and a novel, deeply branching lineage of the (probably methanogenic) kingdom Euryarchaeota (392 bp) that has recently been detected on rice roots (R. Grosskopf, S. Stubner, and W. Liesack, Appl. Environ. Microbiol. 64:4983-4989, 1998). The structure of the archaeal community changed when the temperature was shifted from 30 degrees C to 15 degrees C. Before the temperature shift, the clones (n = 30) retrieved from the community were dominated by Crenarchaeota (70%), "novel Euryarchaeota" (23%), and Methanosarcinacaeae (7%). Further incubation at 30 degrees C (n = 30 clones) resulted in a relative increase in members of the Methanosarcinaceae (77%), whereas further incubation at 15 degrees C (n = 30 clones) resulted in a much more diverse community consisting of 33% Methanosarcinaceae, 23% Crenarchaeota, 20% Methanosaetaceae, and 17% novel Euryarchaeota. The appearance of Methanosaetaceae at 15 degrees C was conspicuous. These results demonstrate that the structure of the archaeal community in anoxic rice field soil changed with time and incubation temperature.

Altered expression of an L1-specific, O-linked cuticle surface glycoprotein in mutants of the nematode Caenorhabditis elegans

Mouse mAb M38 was used in indirect immunofluorescence experiments to detect a stage-specific antigen on the surface of the first larval stage (L1) of the free-living nematode Caenorhabditis elegans, and to detect alterations in the apparent expression of this antigen in two distinct classes of C. elegans mutants. In previously described srf-2 and srf-3 mutants (Politz S. M., M. T. Philipp, M. Estevez, P.J. O'Brien, and K. J. Chin. 1990. Proc. Natl. Acad. Sci. USA. 87:2901-2905), the antigen is not detected on the surface of any stage. Conversely, in srf-(yj43) and other similar mutants, the antigen is expressed on the surface of the first through the fourth (L4) larval stages. To understand the molecular basis of these alterations, the antigen was characterized in gel immunoblotting experiments. After SDS-PAGE separation and transfer to nitrocellulose, M38 detected a protein antigen in extracts of wild-type L1 populations. The antigen was sensitive to digestion by Pronase and O-glycanase (endo-alpha-N-acetylgalactosaminidase), suggesting that it is an O-linked glycoprotein. This antigen was not detected in corresponding extracts of wild-type L4s or srf-2 or srf-3 L1s, but was detected in extracts of srf-(yj43) L4s. The antigen-defective phenotype of srf-3 was epistatic to the heterochronic mutant phenotype of srf-(yj43) in immunofluorescence tests of the srf-3 srf-(yj43) double mutant, suggesting that srf-(yj43) causes incorrect regulation of a pathway of antigen formation that requires wild-type srf-3 activity.

Genes that can be mutated to unmask hidden antigenic determinants in the cuticle of the nematode Caenorhabditis elegans

Rabbit antisera directed against a mixture of proteins solubilized from the wild-type adult Caenorhabditis elegans cuticle were used to isolate mutants, induced by ethyl methanesulfonate treatment, that exhibit alterations in surface antigenicity by immunofluorescence. Genetic mapping and complementation data for four such mutations define two genes, srf-2(I) and srf-3(IV). The mutant phenotypes observed by immunofluorescence appear to result from unmasking of antigenic determinants that are normally hidden in the wild-type cuticle. In support of this hypothesis, surface radioiodination experiments indicate that components labeled on the wild-type surface are missing or less readily labeled on the surface of srf-2 and srf-3 mutants.

Genetic analysis of adult-specific surface antigenic differences between varieties of the nematode Caenorhabditis elegans

We have studied developmental stage-specificity and genetic specification of surface antigens in the nematode Caenorhabditis elegans. Rabbit antisera directed against the adult C. elegans cuticle were used in conjunction with antiserum adsorption experiments to obtain antibody reagents with specificity for the adult surface. Adult-specific antibodies were used to identify several varietal strains of C. elegans that display antigen-negative phenotypes as adults. Genetic mapping results using the surface antigen phenotype as a marker indicated that a single gene (designated srf-1) or cluster of genes on linkage group II determines the adult surface antigen phenotype.