Phylogenetic diversity, abundance, and axial distribution of bacteria in the intestinal tract of two soil-feeding termites (Cubitermes spp.)

The hindgut of soil-feeding termites is highly compartmentalized and characterized by pronounced axial dynamics of the intestinal pH and microbial processes such as hydrogen production, methanogenesis, and reductive acetogenesis. Nothing is known about the bacterial diversity and the abundance or axial distribution of the major phylogenetic groups in the different gut compartments. In this study, we showed that the variety of physicochemical conditions is reflected in the diversity of the microbial communities in the different gut compartments of two Cubitermes species (TERMITIDAE: Termitinae). 16S rRNA gene clones from the highly alkaline first proctodeal segment (P1) of Cubitermes orthognathus represented almost exclusively gram-positive bacteria with low G+C content (LGC bacteria). In the posterior gut segments, their proportion decreased progressively, and the clone libraries comprised a variety of phyla, including the Cytophaga-Flexibacter-Bacteroides group, various subgroups of Proteobacteria, and the spirochetes. Phylogenetic analysis revealed that many of the clones clustered with sequences from the guts of other termites, and some even formed clusters containing only clones from C. orthognathus. The abundance and axial distribution of major phylogenetic groups in the gut of Cubitermes ugandensis were determined by fluorescence in situ hybridization with group-specific oligonucleotide probes. While the results were generally in good agreement with those of the clonal analysis, direct counts with probes specific for the Planctomycetales revealed a severe underestimation of representatives of this phylum in the clone libraries. Results obtained with newly designed FISH probes directed against two clusters of LGC clones from C. orthognathus indicated that the clones were restricted to specific gut regions. A molecular fingerprinting analysis published in a companion paper (D. Schmitt-Wagner, M. W. Friedrich, B. Wagner, and A. Brune, Appl. Environ. Microbiol. 69:6018-6024, 2003) corroborated the presence of compartment-specific bacterial communities in the gut of different Cubitermes species.     

Localization and in situ activities of homoacetogenic bacteria in the highly compartmentalized hindgut of soil-feeding higher termites (Cubitermes spp.).

Methanogenesis and homoacetogenesis occur simultaneously in the hindguts of almost all termites, but the reasons for the apparent predominance of methanogenesis over homoacetogenesis in the hindgut of the humivorous species is not known. We found that in gut homogenates of soil-feeding Cubitermes spp., methanogens outcompete homoacetogens for endogenous reductant. The rates of methanogenesis were always significantly higher than those of reductive acetogenesis, whereas the stimulation of acetogenesis by the addition of exogenous H(2) or formate was more pronounced than that of methanogenesis. In a companion paper, we reported that the anterior gut regions of Cubitermes spp. accumulated hydrogen to high partial pressures, whereas H(2) was always below the detection limit (<100 Pa) in the posterior hindgut, and that all hindgut compartments turned into efficient H(2) sinks when external H(2) was provided (D. Schmitt-Wagner and A. Brune, Appl. Environ. Microbiol. 65:4490-4496, 1999). Using a microinjection technique, we found that only the posterior gut sections P3/4a and P4b, which harbored methanogenic activities, formed labeled acetate from H(14)CO(3)(-). Enumeration of methanogenic and homoacetogenic populations in the different gut sections confirmed the coexistence of both metabolic groups in the same compartments. However, the in situ rates of acetogenesis were strongly hydrogen limited; in the P4b section, no activity was detected unless external H(2) was added. Endogenous rates of reductive acetogenesis in isolated guts were about 10-fold lower than the in vivo rates of methanogenesis, but were almost equal when exogenous H(2) was supplied. We conclude that the homoacetogenic populations in the posterior hindgut are supported by either substrates other than H(2) or by a cross-epithelial H(2) transfer from the anterior gut regions, which may create microniches favorable for H(2)-dependent acetogenesis.     

Microbiological study of lactic acid fermentation of Caper berries by molecular and culture-dependent methods

Fermentation of capers (the fruits of Capparis sp.) was studied by molecular and culture-independent methods. A lactic acid fermentation occurred following immersion of caper berries in water, resulting in fast acidification and development of the organoleptic properties typical of this fermented food. A collection of 133 isolates obtained at different times of fermentation was reduced to 75 after randomly amplified polymorphic DNA (RAPD)-PCR analysis. Isolates were identified by PCR or 16S rRNA gene sequencing as Lactobacillus plantarum (37 isolates), Lactobacillus paraplantarum (1 isolate), Lactobacillus pentosus (5 isolates), Lactobacillus brevis (9 isolates), Lactobacillus fermentum (6 isolates), Pediococcus pentosaceus (14 isolates), Pediococcus acidilactici (1 isolate), and Enterococcus faecium (2 isolates). Cluster analysis of RAPD-PCR patterns revealed a high degree of diversity among lactobacilli (with four major groups and five subgroups), while pediococci clustered in two closely related groups. A culture-independent analysis of fermentation samples by temporal temperature gradient electrophoresis (TTGE) also indicated that L. plantarum is the predominant species in this fermentation, in agreement with culture-dependent results. The distribution of L. brevis and L. fermentum in samples was also determined by TTGE, but identification of Pediococcus at the species level was not possible. TTGE also allowed a more precise estimation of the distribution of E. faecium, and the detection of Enterococcus casseliflavus (which was not revealed by the culture-dependent analysis). Results from this study indicate that complementary data from molecular and culture-dependent analysis provide a more accurate determination of the microbial community dynamics during caper fermentation.     

Species diversity and relative abundance of vaginal lactic acid bacteria from women in Uganda and Korea

AIMS: Lactobacilli play an important role in maintaining vaginal health of women. The aim of this study was to compare the species richness and relative abundance of Lactobacillus and other lactic acid bacteria in women of two geographically distant countries, Uganda and Korea. METHODS AND RESULTS: Vaginal samples were obtained from two women populations in Uganda and Korea. The Lactobacillus Rogosa SL agar was used for initial isolation of lactic acid bacteria. After phenotypic analyses, the 16S rRNA gene was amplified by polymerase-chain reaction and analysed by the BLAST program and phylogenetic tree construction. A total of 338 (128 Korean and 210 Ugandan) vaginal lactic acid bacterial strains were isolated, including five genera: Lactobacillus, Leuconostoc, Pediococcus, Streptococcus and Weissella. While Lactobacillus crispatus was common in both populations, Lactobacillus fermentum was common only in Korean women, and Lactobacillus gasseri, Lactobacillus reuteri and Lactobacillus vaginalis only in Ugandan women. Among other lactic acid bacteria, Weissella was more common in Ugandan, and Pediococcus in Korean women. All Weissella strains produced hydrogen peroxide, and all Pediococcus strains inhibited Candida species. CONCLUSION: Although many lactic acid bacteria colonize women, their species distributions may be different in women of geographically separated communities. SIGNIFICANCE AND IMPACT OF THE STUDY: The knowledge of species richness and relative abundance of vaginal lactic acid bacteria, including Lactobacillus, Pediococcus and Weissella, may lead to the design of better probiotic products as bacterial replacement therapy.     

Dynamics of lactic acid bacteria populations in Rioja wines by PCR-DGGE, comparison with culture-dependent methods

Lactic acid bacteria populations of red wine samples from industrial fermentations, including two different vinification methods were studied. For this investigation, polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE) analysis was employed to supplement previous results that were obtained by culture-dependent methods. PCR-DGGE was aimed to study two targeted genes, 16S ribosomal DNA (rDNA) and rpoB, and the results were useful to evaluate the microbial populations in wine samples. Moreover, an improvement of a detection limit determined so far for DGGE analysis was obtained with the method described in this study, what made possible to identify lactic acid bacteria populations below 10¹ colony-forming unit/mL. The species Oenococcus oeni was the most frequently detected bacterium, but identifications close to species Oenococcus kitaharae and Lactococcus lactis that are not often found in wine were firstly identified in samples of this research. PCR-DGGE allowed to detect 9 out of 11 lactic acid bacteria species identified in this study (nine by PCR-16S rDNA/DGGE and four by PCR-rpoB/DGGE), while five species were detected using the modified de Man, Rogosa and Sharpe agar. Therefore, the two methods were demonstrated to be complementary. This finding suggests that analysis of the lactic acid bacteria population structure in wine should be carried out using both culture-dependent and culture-independent techniques with more than one primer pair.     

Hydrogen profiles and localization of methanogenic activities in the highly compartmentalized hindgut of soil-feeding higher termites (Cubitermes spp.).

It has been shown that the coexistence of methanogenesis and reductive acetogenesis in the hindgut of the wood-feeding termite Reticulitermes flavipes is based largely on the radial distribution of the respective microbial populations and relatively high hydrogen partial pressures in the gut lumen. Using Clark-type microelectrodes, we showed that the situation in Cubitermes orthognathus and other soil-feeding members of the subfamily Termitinae is different and much more complex. All major compartments of agarose-embedded hindguts were anoxic at the gut center, and high H(2) partial pressures (1 to 10 kPa) in the alkaline anterior region rendered the mixed segment and the third proctodeal segment (P3) significant sources of H(2). Posterior to the P3 segment, however, H(2) concentrations were generally below the detection limit (<100 Pa). All hindgut compartments turned into efficient hydrogen sinks when external H(2) was supplied, but methane was formed mainly in the P3/4a and P4b compartments, and in the latter only when H(2) or formate was added. Addition of H(2) to the gas headspace stimulated CH(4) emission of living termites, indicating that endogenous H(2) production limits methanogenesis also in vivo. At the low H(2) partial pressures in the posterior hindgut, methanogens would most likely outcompete homoacetogens for this electron donor. This might explain the apparent predominance of methanogenesis over reductive acetogenesis in the hindgut of soil-feeding termites, although the presence of homoacetogens in the anterior, highly alkaline region cannot yet be excluded. In addition, the direct contact of anterior and posterior hindgut compartments in situ permits a cross-epithelial transfer of H(2) or formate, which would not only fuel methanogenesis in these compartments, but would also create favorable microniches for reductive acetogenesis. In situ rates and spatial distribution of H(2)-dependent acetogenic activities are addressed in a companion paper (A. Tholen and A. Brune, Appl. Environ. Microbiol. 65:4497-4505, 1999).     

Species diversity and relative abundance of lactic acid bacteria in the milk of rhesus monkeys (Macaca mulatta)

Background Mother’s milk is a source of bacteria that influences the development of the infant commensal gut microbiota. To date, the species diversity and relative abundance of lactic acid bacteria in the milk of non‐human primates have not been described. Methods Milk samples were aseptically obtained from 54 female rhesus monkeys (Macaca mulatta) at peak lactation. Following GM17 and MRS agar plating, single bacterial colonies were isolated based on difference in morphotypes, then grouped based on whole‐cell protein profiles on SDS–PAGE. Bacterial DNA was isolated and the sequence the 16S rRNA gene was analyzed. Results A total of 106 strains of 19 distinct bacterial species, belonging to five genera, Bacillus, Enterococcus, Lactobacillus, Pediococcus, and Streptococcus, were identified. Conclusions Maternal gut and oral commensal bacteria may be translocated to the mammary gland during lactation and present in milk. This pathway can be an important source of commensal bacteria to the infant gut and oral cavity.     

Evaluation of the spoilage lactic acid bacteria in modified-atmosphere-packaged artisan-type cooked ham using culture-dependent and culture-independent approaches

Aims: To investigate microbial diversity and population dynamics of spoilage-sensitive modified-atmosphere-packaged (MAP) artisan-type cooked ham in relation to storage temperature. Methods and Results: Modified-atmosphere-packaged cooked ham samples were stored at different temperatures (4, 7, 12 and 26°C). Traditional methods were combined with polymerase chain reaction (PCR)-based techniques, i.e. a culture-dependent, repetitive DNA sequence-based method (rep-PCR) and a culture-independent approach (PCR-denaturing gradient gel electrophoresis of 16S rRNA gene fragments; PCR-DGGE). rep-PCR on DNA extracted from MRS isolates indicated that Leuconostoc carnosum and Enterococcus faecalis prevailed at all temperatures, with the latter becoming more important above 7°C. PCR-DGGE indicated the additional presence of Carnobacterium divergens and Brochothrix thermosphacta at all temperatures. Discriminant analysis related variation within the Leuc. carnosum cluster to the storage temperature. High performance liquid chromatography revealed that lactic acid was the main metabolite because of glucose consumption. Conclusions: Leuconostoc carnosum, C. divergens, E. faecalis and Br. thermosphacta are the main spoilage bacteria of artisan-type MAP cooked ham. Their population dynamics are affected by storage temperature. Significance and Impact of the Study: Temperature can condition the development of spoilage in artisan-type MAP cooked ham, acting at both species and biotype level.     

Application of 13C NMR to investigate the transformations and biodegradation of organic materials by wood- and soil-feeding termites, and a coprophagous litter-dwelling dipteran larva

Solid-state 13C nuclear magnetic resonance spectroscopy has been used to characterize the C in samples of the food (wood), gut contents and faeces from the wood-feeding termite, Microcerotermes parvus; soil in the guts and mound material from the soil-feeding termite, Thoracotermes macrothorax; and the food and faeces from the litter-feeding, coprophagous larvae of the dipteran fly, Bibio marci. Spectra from the wood-feeding termite indicated preferential loss of polysaccharide and accumulation of lignin with some modification to the O-aromatic-C and methoxyl-C (O-methyl-C) components during passage through the gut. Spectra for the soil-feeding termite indicated little change in the distribution of 13C between resonances following passage through the gut, except for some evidence of preferential polysaccharide loss. Interpretation of the spectra from these organisms was restricted by the relatively low C content of the soils and mound material, and by the large contribution to the NMR spectra from the gut tissue rather than the gut contents. Spectra for the litter-feeding dipteran larvae indicated preferential feeding on the polysaccharide-rich component of the litter and then overall loss of polysaccharide-C and accumulation of both aromatic-C and methoxyl-C in the gut. These changes were greater for the second passage than for the first passage through the gut, suggesting that principally mechanical and physical changes occurred initially and that chemical digestion was prevalent during the second passage.     

Role of bacteria in maintaining the redox potential in the hindgut of termites and preventing entry of foreign bacteria

The hindgut of the lower termites, Mastotermes darwiniensis and Coptotermes lacteus and the higher termite Nasutitermes exitiosus were made aerobic by exposure of the termites to pure oxygen, a procedure which killed their spirochaetes and their protozoa (lower termites only). The time taken for the hindgut to become anaerobic after the termites were restored to normal atmospheric conditions ranged from 2 to 4.5 hr. After oxygen treatment the number of gut bacteria increased some six- to ten-fold in all termite species, indicating that the bacteria are poised to use oxygen entering the gut. Removal of all the hindgut microbiota by feeding tetracycline caused the hindgut to become aerobic in M. darwiniensis and N. exitiosus. The transferring of M. darwiniensis to fresh wood, free of antibiotic, resulted in the return of the normal flora and the eventual establishment of anaerobic conditions in the hindgut. Thus the bacteria appear to be important in maintaining anaerobic conditions in the gut. Attempts to determine whether the protozoa (in the lower termites) played any part in maintaining the Eh of the hindgut were unsuccessful. Serratia marcescens failed to colonise the gut of normal C. lacteus and transiently colonized (for 5 days) the gut of normal N. exitiosus. Transient colonization by S. marcescens (from 6 to 10 days) occurred in N. exitiosus when its hindgut spirochaetes were killed and in C. lacteus when its spirochaetes and protozoa were killed, indicating a possible role for the spirochaetes and/or protozoa in influencing the bacteria allowed to reside in the hindgut. Exposure of normal termites to Serratia provoked an increase in the numbers of the normal gut bacteria.     

Characterization of lactic acid bacteria isolated from seafood

Lactic acid bacteria were isolated from various samples of seafood: fresh pollock, brine shrimp, gravad fish, vacuum-packed seafood (surimi, smoked tuna, salted cod), and fish stored under 100% CO₂ at 5°C (smoked tuna, fresh and salted cod, salmon). Eighty-six independent isolates were obtained and were grouped according to cell morphology, presence or absence of diaminopimelic acid in the cell wall, and lactate configuration. Fifty-four isolates were identified as belonging to the genus Lactococcus and most of them exhibited DNA homologies with L. lactis subsp. lactis. Four strains were identified as Lactobacillus plantarum , eight strains as genus Leuconostoc and 16 belonged to the genus Carnobacterium. One facultative heterofermentative Lactobacillus and three other isolates were not identified. Of the strains 47% showed similar patterns of carbohydrate fermentations especially among strains belonging to the genera Lactococcus and Carnobacterium. Most of the strains (64%) grew at 5°C, in salted media and in fish extract medium without added sugar. Carnobacterium piscicola and Carn. divergens were the only reference strains able to grow in the same conditions as well as psychrotroph strains isolated from seafood. A numerical analysis could not be used because of the divergent properties of isolates of the same genus and strong similarities between different genera.     

Antibacterial metabolites of lactic acid bacteria: their diversity and properties

The review is devoted to literature data on antimicrobial metabolites produced by lactic acid bacteria (LAB), which have long been used for the preparation of cultured dairy products. This paper summarizes data on low-molecular-weight antimicrobial substances, which are primary products or by-products of lactic fermentation. Individual sections are devoted to a variety of antifungal agents and bacteriocins produced by LAB; their potential use as food preservatives has been discussed. The characteristics and classification of bacteriocins are presented in a greater detail; their synthesis and mechanism of action are described using the example of nisin A, which belongs to class I lantibiotics synthesized by the bacterium Lactococcus lactis subsp. lactis. The mechanism of action of class II bacteriocins has been demonstrated with lacticin. Prospective directions for using LAB antimicrobial metabolites in industry and medicine are discussed in the Conclusion.     

柳枝稷青贮用乳酸菌复合系的组成多样性及其代谢特性

摘要:【目的】筛选一组乳酸产量高、组成稳定的柳枝稷青贮用乳酸菌复合系。【方法】通过连续限制性培养方法获得乳酸菌复合系SGL,使用变性梯度凝胶电泳(DGGE)和高通量测序技术分别分析其群落结构的稳定性和组成多样性。在培养基中添加不同氮源,测定氮源对SGL菌体生长和代谢产酸的影响。【结果】连续限制性培养8代,SGL的菌群结构趋于稳定,主要菌种为同型发酵乳酸菌,包括Lactobacillus nantensis (78.78%)、Lactobacillus plantarum(7.92%)、Lactobacillus pantheris(5.27%)、Bacillus coagulans(4.41%)和Lactococcus lactics(3.31%),是现有唯一的同时包含Lactobacillus、Lactococcus和Bacillus的乳酸菌复合系。酵母浸粉是促进SGL菌体生长和产乳酸的最好氮源,最适添加量为20 g/L。当(NH4)2SO4和酵母浸粉中N的比例为1:4时,菌体生长量和乳酸产量与20 g/L 酵母浸粉等同。【结论】乳酸菌复合系SGL 多样性高、组成稳定、可利用无机氮源,作为青贮饲料添加剂,具有很大的应用潜力,本研究为SGL的培养和应用提供了理论依据。     

Antibacterial metabolites of lactic acid bacteria: Their diversity and properties

The review is devoted to literature data on antimicrobial metabolites produced by lactic acid bacteria (LAB), which have long been used for the preparation of cultured dairy products. This paper summarizes data on low-molecular-weight antimicrobial substances, which are primary products or by-products of lactic fermentation. Individual sections are devoted to a variety of antifungal agents and bacteriocins produced by LAB; their potential use as food preservatives has been discussed. The characteristics and classification of bacteriocins are presented in a greater detail; their synthesis and mechanism of action are described using the example of nisin A, which belongs to class I lantibiotics synthesized by the bacterium Lactococcus lactis subsp. lactis. The mechanism of action of class II bacteriocins has been demonstrated with lacticin. Prospective directions for using LAB antimicrobial metabolites in industry and medicine are discussed in the Conclusion.     

Genetic diversity of lactic acid bacteria in the intestine of Persian sturgeon fingerlings

Lactic acid bacteria (LAB) are often found as sub‐dominant microbial components in the gastrointestinal (GI) tract of fish and have positive effects on the host. They are generally promising candidates for probiotics and can act as substances to improving both native immune responses and growth performance of animals including fish. In the present study the Persian sturgeon Acipenser persicus autochthonous intestinal LAB were investigated. A total of 90 sturgeon fingerlings were sampled and LAB were isolated and enumerated on MRS agar. Initial identification of 47 LAB isolates using standard biochemical and phenotypic tests revealed five dominant phenotypes. Twenty‐one isolates, representatives from each of these phenotypes, were subsequently identified by 16S rRNA sequence analysis. The results showed that cultivable authochthonous LAB ranged from log 2.93 to 5.61 CFU g^?1 intestine, with a mean of 4.38 ± 0.58 CFU g^?1. 16S rRNA sequence analysis revealed that the LAB community was dominated by Lactococcus spp., with Lactococcus garvieae and Lactococcus lactis accounting for 42.55 and 36.17% of the LAB population, respectively. Pediococcus pentosaceus (14.90%), Weissella cibaria (4.25%) and Enterococcus faecalis (2.13%) were identified as minor components of the LAB community. This is the first report of these LAB as members of the microbial community in the intestine of Acipenser persicus. The results show that both potentially pathogenic (i.e. Lactococcus garvieae) and probiotic (i.e. Lactococcus lactis and Weissella cibaria) LAB inhabit the Persian sturgeon GI tract. Future studies should seek to elucidate the relevance of these species to the host.     

The genetic diversity of lactic acid producing bacteria in the equine gastrointestinal tract

Seventy-two lactic acid producing bacterial isolates (excluding streptococci) were cultured from the gastrointestinal tract of six horses. Two of the horses were orally dosed with raftilose to induce lactic acidosis and laminitis while the remaining four were maintained on a roughage diet. Near complete 16S rDNA was amplified by PCR from the genomic DNA of each isolate. Following RFLP analysis with the restriction enzymes MboI, HhaI and HinfI, the PCR products from the 18 isolates that produced L- and/or D-lactate were subsequently cloned and sequenced. DNA sequence analysis indicated that the majority of the isolates were closely related to species within the genus Lactobacillus, including Lactobacillus salivarius, Lactobacillus mucosae and Lactobacillus delbrueckii. Four isolates were closely related to Mitsuokella jalaludinii. Lactic acid producing bacteria (LAB) from the equine gastrointestinal tract was dominated by representatives from the genus Lactobacillus, but also included D-lactate-producing bacteria closely related to M. jalaludinii. Identification and characterization of LAB from the equine gastrointestinal tract should contribute to our understanding and management of fermentative acidosis, ulceration of the stomach and laminitis.     

Comparison of pattern recognition techniques for the identification of lactic acid bacteria

AIMS: The goal of this study was to evaluate three pattern recognition methods for use in the identification of lactic acid bacteria. METHODS AND RESULTS: Lactic acid bacteria (21 unknown isolates and 30 well-characterized strains), including the Lactobacillus, Lactococcus, Streptococcus, Pediococcus and Oenococcus genera, were tested for 49 phenotypic responses (acid production on carbon sources). The results were scored in several ways. Three procedures, k-nearest neighbour analysis (KNN), k-means clustering and fuzzy c-means clustering (FCM), were applied to the data. CONCLUSION: k-Nearest neighbour analysis performed better with five-point-scaled than with binary data, indicating that intermediate values are helpful to classification. k-Means clustering performed slightly better than KNN and was best with fuzzified data. The best overall results were obtained with FCM. Genus level classification was best with FCM using an exponent of 1.25. SIGNIFICANCE AND IMPACT OF THE STUDY: The three pattern recognition methods offer some advantages over other approaches to organism classification.     

Metabolic diversity in biohydrogenation of polyunsaturated fatty acids by lactic acid bacteria involving conjugated fatty acid production

Lactobacillus plantarum AKU 1009a effectively transforms linoleic acid to conjugated linoleic acids of cis-9,trans-11-octadecadienoic acid (18:2) and trans-9,trans-11–18:2. The transformation of various polyunsaturated fatty acids by washed cells of L. plantarum AKU 1009a was investigated. Besides linoleic acid, α-linolenic acid [cis-9,cis-12,cis-15-octadecatrienoic acid (18:3)], γ-linolenic acid (cis-6,cis-9,cis-12–18:3), columbinic acid (trans-5,cis-9,cis-12–18:3), and stearidonic acid [cis-6,cis-9,cis-12,cis-15-octadecatetraenoic acid (18:4)] were found to be transformed. The fatty acids transformed by the strain had the common structure of a C18 fatty acid with the cis-9,cis-12 diene system. Three major fatty acids were produced from α-linolenic acid, which were identified as cis-9,trans-11,cis-15–18:3, trans-9,trans-11,cis-15–18:3, and trans-10,cis-15–18:2. Four major fatty acids were produced from γ-linolenic acid, which were identified as cis-6,cis-9,trans-11–18:3, cis-6,trans-9,trans-11–18:3, cis-6,trans-10–18:2, and trans-10-octadecenoic acid. The strain transformed the cis-9,cis-12 diene system of C18 fatty acids into conjugated diene systems of cis-9,trans-11 and trans-9,trans-11. These conjugated dienes were further saturated into the trans-10 monoene system by the strain. The results provide valuable information for understanding the pathway of biohydrogenation by anaerobic bacteria and for establishing microbial processes for the practical production of conjugated fatty acids, especially those produced from α-linolenic acid and γ-linolenic acid. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Anaerobic carbon monoxide dehydrogenase diversity in the homoacetogenic hindgut microbial communities of lower termites and the wood roach

Anaerobic carbon monoxide dehydrogenase (CODH) is a key enzyme in the Wood-Ljungdahl (acetyl-CoA) pathway for acetogenesis performed by homoacetogenic bacteria. Acetate generated by gut bacteria via the acetyl-CoA pathway provides considerable nutrition to wood-feeding dictyopteran insects making CODH important to the obligate mutualism occurring between termites and their hindgut microbiota. To investigate CODH diversity in insect gut communities, we developed the first degenerate primers designed to amplify cooS genes, which encode the catalytic (β) subunit of anaerobic CODH enzyme complexes. These primers target over 68 million combinations of potential forward and reverse cooS primer-binding sequences. We used the primers to identify cooS genes in bacterial isolates from the hindgut of a phylogenetically lower termite and to sample cooS diversity present in a variety of insect hindgut microbial communities including those of three phylogenetically-lower termites, Zootermopsis nevadensis, Reticulitermes hesperus, and Incisitermes minor, a wood-feeding cockroach, Cryptocercus punctulatus, and an omnivorous cockroach, Periplaneta americana. In total, we sequenced and analyzed 151 different cooS genes. These genes encode proteins that group within one of three highly divergent CODH phylogenetic clades. Each insect gut community contained CODH variants from all three of these clades. The patterns of CODH diversity in these communities likely reflect differences in enzyme or physiological function, and suggest that a diversity of microbial species participate in homoacetogenesis in these communities.