Differentiation of Yam Virus Isolates Using Symptomatology, Western Blot Assay, and Monoclonal Antibodies

Monoclonal antibodies (mAbs) were prepared against a yam mosaic virus (YMV) isolate from the Côte d'Ivoire. Symptomatology, Western immunoblotting, and ELISA were used to discriminate 69 isolates of YMV originating from different Dioscorea species and from various yam producing areas. These isolates induced two types of symptoms, were of four different electrophoretic mobilities and formed two serogroups. These results suggest that at least six differetit groups of isolates exist, three of which infect the main cultivated species in various geographical areas while two others were from unusual samples in our collection. An isolate from 'Pilimpikou Yam' from Central Burkina Faso was serologically distinct. It is concluded that there is a significant variability among yam virus isolates which is unrelated to the origin of the isolate (geographic or host species). It is suggested that precautions should be taken in order to avoid international exchange of infected material.     

Dental anomalies in Upper Eocene Anthracotheriidae: a possible case of inbreeding

Three fragmentary maxillae and an isolated upper molar from the Upper Eocene locality of Wai Lek (Krabi Basin, South Thailand) belonging to the small anthracotheriid Siamotherium krabiense display strongly abnormal morphologies that are particularly unusual among the dental anomalies recorded in both extant and fossil mammals. Variation and atavism can be ruled out, and the other hypothetical origins of these anomalies, particularly the occurrence of odontomes and inbreeding, are discussed. Dental anomalies, Anthracotheriidae, Asia, atavism, variation, inbreeding.
Stéphane Ducrocq and Jean-Jacques Jaeger, Laboratoire de Paléontologie, Institut des Sciences de l'Evolution, Case Courrier 064, Université Montpellier II, Place Eugéne Bataillon, F-34095 Montpellier Cédex 5, France (SD's current address: Staatliches Museum für Naturkunde, Rosenstein 1, D-70191 Stuttgart, Germany); Yaowalak Chaimanee and Varavudh Suteethorn, Department of Mineral Resources, Geological Survey, Rama VI Road, Bangkok 10400, Thailand; 14th November, 1994; revised 27th July. 1995.     

不同地理种群尖音库蚊复组抗性动态和遗传多样性

通过生物测定、蛋白质电泳和等位酶分析等方法对5个不同地区的尖音库蚊复组蚊虫Culex pipiens complex的抗性水平、种群中非特异性酯酶基因表型分布和种群遗传多样性进行了研究。不同地理种群的抗性检测结果表明：5个种群分别对敌敌畏、对硫磷、氯菊酯和溴氰菊酯的抗性较高,对残杀威、巴沙和胺菊酯的抗性较低;朝阳种群对敌敌畏抗性最高（55.7倍）,武汉种群次之;佛山种群对氯菊酯和溴氰菊酯的抗性比率高达123倍和23.9倍。酯酶电泳结果显示：5个种群间酯酶多态性存在差异,广州和佛山两个库蚊种群酯酶表型多态性最高,有B1,A2-B2,A8-B8,A9-B9,B10和A11-B11等6种酯酶表型,提示高活性酯酶是主要的抗性机制。群体遗传学研究表明：每位点平均等位基因数（A）为2.76,平均多态位点百分率（P）为64.45％,平均预期杂合度（He）为0.1943,种群间遗传分化系数（Fst）值为0.10,平均基因流(Nm)＝2.57,说明5个种群有较丰富的遗传多样性,种群内遗传多样性高于种群之间。据此推测,种群间可以通过迁徙等方式进行基因交流,使得遗传结构、抗性水平朝一致性方向变化。本研究对我国尖音库蚊复组蚊虫的综合治理有一定指导意义。     

拟除虫菊酯抗性家蝇的交互抗药性研究

拟除虫菊酯的广泛使用使家蝇普遍产生了抗药性,为有效的控制家蝇的危害,需要了解家蝇对轮换或新杀虫剂的交互抗性状况。作者用点滴法测定了两个实验室汰选的拟除虫菊酯抗性家蝇品系对几种杀虫剂的交互抗性,结果表明:二氯苯醚菊酯和溴氰菊酯之间存在较高程度的交互抗药性;拟除虫菊酯抗性较高的家蝇对作用机制不同的新农药(多杀菌素、氟虫腈)表现较低程度的交互抗性。     

神经递质释放与家蝇对拟除虫菊酯抗性关系研究

通过生物测定比较溴氰菊酯、氯菊酯和DDT对Dec-R,2C1-R,DDT-R和敏感(SP)家蝇Musca domestica vicina的毒力,表明三个抗性品系对溴氰菊酯、氯菊酯和DDT均有很高的抗性,抗性倍数分别达120 912,6 032和112.2倍,并对上述三种杀虫剂有明显的交互抗性和抗击倒效应。杂交试验表明Dec-R对溴氰菊酯的抗性是一个隐性基因,电生理试验表明抗性家蝇中枢神经系统(CNS)对药剂敏感度的降低是其产生抗性和交互抗性的重要机制。研究结果表明Dec-R和2CLR家蝇品系中存在有击倒抗性因子(Kdr)。当用1×10^-7mol/L溴氰菊酯对SP家蝇脑突触体在提高K+浓度去极化后,可加强3H-胆碱的释放,而在Dec-R品系中,溴氰菊酯浓度提高到1×10^-4m0l/L也未能加强³H-胆碱的释放,表明溴氰菊酯与神经递质的释放和钠通道亲和性的降低是抗性的主要机制。     

Identification of two distinct amplifications of the esterase B locus inCulex pipiens (L.) mosquitoes from mediterranean countries

Two new highly active esterases were detected by starch electrophoretic studies inCulex pipiens mosquitoes from the area of Montpellier (France) and from Cyprus. We demonstrate here that both the French and the Cyprus esterases B are overproduced due to amplification of the coding gene. The production of the esterase B is approximately 50- and 500-fold higher in mosquitoes from France and Cyprus, respectively, than in susceptible insects, whereas the number of gene copies is about 25 and 250. Differences of about 7- and 95-fold were also found in the degree of chlorpyrifos resistance. RFLP comparison of the amplified region containing the esterase B gene revealed large differences between French and Cyprus mosquitoes. It thus appears that two distinct haplotypes with an esterase B gene coding an enzyme with identical electrophoretic mobility have been amplified. We therefore named the haplotypes in mosquitoes from France and Cyprus B4 and B5, respectively. The estimated genetic distance between these two haplotypes is not smaller than those observed in all pair comparisons of other known esterase B haplotypes. These results are discussed in the context of amplification phenomena.This work was supported in part by Grant 89.1540 from the Ministère de l'Education Nationale and by the CNRS/Programme Environnement.     

Comparative evaluation of carbosulfan- and permethrin-impregnated curtains for preventing house-entry by the malaria vector Anopheles gambiae in Burkina Faso

Pyrethroid-impregnated bednets and curtains are widely employed to reduce the risk of malaria transmission, but pyrethroid-resistance is becoming more prevalent among malaria vector Anopheles mosquitoes (Diptera: Culicidae). As an alternative treatment for curtains, we assessed carbosulfan (a carbamate insecticide) in comparison with permethrin as the standard pyrethroid, against endophilic female mosquitoes of the Anopheles gambiae Giles complex in a village near Ouagadougou, Burkina Faso. The main criterion evaluated was the impact of curtains (hung inside windows, eaves and doorways) on the number of An. gambiae s.l. females active indoors at night. Light-traps were operated overnight (21.00-06.00 hours beside occupied untreated bednets) to sample mosquitoes in houses fitted with net curtains treated with carbosulfan 0.2 g ai/m2 or permethrin 1 g ai/m2 or untreated, compared with houses without curtains. The treated and untreated curtains significantly reduced the numbers of mosquitoes collected indoors, compared with houses without curtains. Carbosulfan-treated curtains had a highly significantly greater effect than permethrin-treated or untreated curtains, the scale of the difference being estimated as three-fold. However, there was no significant difference between the impact of untreated and permethrin-treated curtains on densities of An. gambiae s.l. trapped indoors. Samples of the An. gambiae complex comprised An. arabiensis Patton and both the S- and M-forms of An. gambiae Giles s.s. Susceptibility tests revealed some resistance to DDT and low frequencies of permethrin-resistance, insufficient to explain the poor performance of permethrin on curtains. Among survivors from the diagnostic dosage of permethrin were some specimens of all three members of the An. gambiae complex, but the kdr resistance mechanism was detected only in the S-form of An. gambiae s.s. Questions arising for further investigation include clarification of resistance mechanisms in, and foraging behaviour of, each member of the An. gambiae complex in this situation and the need to decide whether carbosulfan-treated curtains are acceptably safe for use to reduce risks of malaria transmission.     

Parasitism of cowpea by Striga gesnerioides: variation in virulence and discovery of a new source of host resistance

In glasshouse experiments in the United Kingdom, Striga gesnerioides-resistant cowpea varieties, Suvita-2 and 58–57, were assessed alongside a susceptible variety for their responses to seventeen samples of S. gesnerioides from four West African countries. The susceptible variety was attacked by all samples, while Suvita-2 was resistant to samples from Burkina Faso and Mali, and 58–57 was resistant only to samples from Burkina Faso.
At least three physiological groups of the parasite can be distinguished: samples from Burkina Faso attacking the smallest range of cowpea varieties; those from Mali being intermediate; those from Niger and Nigeria attacking all the cowpea varieties. A sample from Cameroon behaved slightly differently and may represent a fourth type.
A cowpea line from Botswana, B.301, selected for its field resistance to Alectra vogelii proved resistant to all Striga populations to which it was exposed, including those from Niger and Cameroon.     

Pyrethroid resistance in Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and implications for its management in Australia

Abstract  The study was conducted to characterise the underlying resistance mechanisms responsible for high levels of pyrethroid resistance in Frankliniella occidentalis (Pergande) in Australia. Seven commercially available pyrethroids (acrinathrin, alpha-cypermethrin, bifenthrin, deltamethrin, esfenvalerate, permethrin and tau-fluvalinate) were evaluated against seven F. occidentalis strains collected from ornamentals, fruit and vegetables in three states of Australia. A Potter spray tower was used to test for pyrethroid resistance and all field strains were found to be resistant, with resistance ratios ranging from 15-fold deltamethrin to 1300-fold tau-fluvalinate. The two most resistant strains were further tested for detoxification enzymes that could be involved in resistance. Three synergists, piperonyl butoxide (PBO), diethyl maleate (DEM) and profenofos, which, respectively, inhibit the enzymes cytochrome P-450 monooxygenases, glutathione S -transferases and esterases, were used. The synergism data indicate that multiple mechanisms may be involved in pyrethroid resistance in Australian populations of F. occidentalis . Among the three synergists, PBO considerably reduced pyrethroid resistance in the selected strains compared with DEM and profenofos. The practical implication for PBO use to suppress pyrethroid resistance in F. occidentalis is elaborated.     

Esterases in the mosquito Culex pipiens pipiens L.: Formal genetics and polymorphism of adult esterases

The genetics of two esterase loci active in autogenous adults of the mosquito Culex pipiens pipiens L. has been studied by means of starch gel electrophoresis. Three alleles at the Est-1 locus and eight at the Est-2 locus are described. Both loci have a null allele. Active alleles are codominant and there is no hybrid enzyme in heterozygotes. The Est-1 locus codes esterases preferentially hydrolyzing -naphthylacetate and the Est-2 locus esterases preferentially hydrolyzing -naphthylacetate. Strains homozygous for both loci were selected. Linkage studies of the two loci have shown that they are not sex linked but are linked to each other, the crossover frequency being 8.6%. The polymorphism of two laboratory and two natural populations is described for both loci. Phenotypic distributions are in good agreement with Hardy-Weinberg expectations.This work was conducted at the Université des Sciences et Techniques du Languedoc (Laboratoire de Génétique Expérimentale des Populations), Montpellier, France, in partial fulfillment of the requirements for the degree of Docteur de spécialité.     

Regional Fragmentation of Rain Forest in West Africa and Its Effect on Local Dung Beetle Assemblage Structure

Data from Ghana and Côte d'Ivoire, for local dung beetle assemblages of rain forest, plantations, and savanna, suggest that a subset of the savanna fauna has expanded its range across the Eastern Guinean Forest ecoregion, presumably in response to its conversion from continuous rain forest into an archipelago of forest fragments within a disturbance matrix of less shady plantation and farmland vegetation that more resembles moist savanna.     

Three years of insecticide resistance monitoring in Anopheles gambiae in Burkina Faso: resistance on the rise?

ABSTRACT: Background and methods A longitudinal Anopheles gambiae s.l. insecticide-resistance monitoring programme was established in four sentinel sites in Burkina Faso. For three years, between 2008 and 2010, WHO diagnostic dose assays were used to measure the prevalence of resistance to all the major classes of insecticides at the beginning and end of the malaria transmission season. Species identification and genotyping for target site mutations was also performed and the sporozoite rate in adults determined. RESULTS: At the onset of the study, resistance to DDT and pyrethroids was already prevalent in An. gambiae s.l. from the south-west of the country but mosquitoes from the two sites in central Burkina Faso were largely susceptible. Within three years, DDT and permethrin resistance was established in all four sites. Carbamate and organophosphate resistance remains relatively rare and largely confined to the south-western areas although a small number of bendiocarb survivors were found in all sites by the final round of monitoring. The ace-1R target site resistance allele was present in all localities and its frequency exceeded 20% in 2010 in two of the sites. The frequency of the 1014 F kdr mutation increased throughout the three years and by 2010, the frequency of 1014 F in all sites combined was 0.02 in Anopheles arabiensis, 0.56 in An. gambiae M form and 0.96 in An. gambiae S form. This frequency did not differ significantly between the sites. The 1014 S kdr allele was only found in An. arabiensis but its frequency increased significantly throughout the study (P = 0.0003) and in 2010 the 1014 S allele frequency was 0.08 in An. arabiensis. Maximum sporozoite rates (12%) were observed in Soumousso in 2009 and the difference between sites is significant for each year. CONCLUSION: Pyrethroid and DDT resistance is now established in An. gambiae s.l. throughout Burkina Faso. Results from diagnostic dose assays are highly variable within and between rounds of testing, and hence it is important that resistance monitoring is carried out on more than one occasion before decisions on insecticide procurement for vector control are made. The presence of 1014 S in An. gambiae s.l., in addition to 1014 F, is not unexpected given the recent report of 1014 S in Benin but highlights the importance of monitoring for both mutations throughout the continent. Future research must now focus on the impact that this resistance is having on malaria control in Burkina Faso.     

Identification and distribution of a GABA receptor mutation conferring dieldrin resistance in the malaria vector Anopheles funestus in Africa

Growing problems of pyrethroid resistance in Anopheles funestus have intensified efforts to identify alternative insecticides. Many agrochemicals target the GABA receptors, but cross-resistance from dieldrin resistance may preclude their introduction.Dieldrin resistance was detected in An. funestus populations from West (Burkina Faso) and central (Cameroon) Africa, but populations from East (Uganda) and Southern Africa (Mozambique and Malawi) were fully susceptible to this insecticide. Partial sequencing of the dieldrin target site, the ??-aminobutyric acid (GABA) receptor, identified two amino acid substitutions, A296S and V327I. The A296S mutation has been associated with dieldrin resistance in other species. The V327I mutations was detected in the resistant sample from Burkina Faso and Cameroon and consistently associated with the A296S substitution. The full-length of the An. funestus GABA-receptor gene, amplified by RT-PCR, generated a sequence of 1674 bp encoding 557 amino acid of the protein in An. funestus with 98% similarity to that of Anopheles gambiae. Two diagnostic assays were developed to genotype the A296S mutation (pyrosequencing and PCR-RFLP), and use of these assays revealed high frequency of the resistant allele in Burkina Faso (60%) and Cameroon (82%), moderate level in Benin (16%) while low frequency or absence of the mutation was observed respectively in Uganda (7.5%) or 0% in Malawi and Mozambique.The distribution of the Rdl^R mutation in An. funestus populations in Africa suggests extensive barriers to gene flow between populations from different regions.     

Modifications of pyrethroid effects associated with kdr mutation in Anopheles gambiae

Effects of knockdown resistance (kdr) were investigated in three pyrethroid‐resistant (RR) strains of the Afrotropical mosquito Anopheles gambiae Giles (Diptera: Culicidae): Kou from Burkina Faso, Tola and Yao from Côte d'Ivoire; compared with a standard susceptible (SS) strain from Kisumu, Kenya. The kdr factor was incompletely recessive, conferring 43‐fold resistance ratio at LD₅₀ level and 29‐fold at LD₉₅ level, as determined by topical application tests with Kou strain. When adult mosquitoes were exposed to 0.25% permethrin‐impregnated papers, the 50% and 95% knockdown times (KdT) were 23 and 42 min for SS females, compared with 40 and 62 min for RS (F₁ Kou × Kisumu) females. On 1% permethrin the KdT₅₀ and KdT₉₅ were 11 and 21 min for SS compared with 18 and 33 min for RS females. Following 1 h exposure to permethrin (0.25% or 1%), no significant knockdown of Kou RR females occurred within 24 h. Permethrin irritancy to An. gambiae was assessed by comparing ‘time to first take‐off’ (TO) for females. The standard TO₅₀ and TO₉₅ values for Kisumu SS on untreated paper were 58 and 1044 s, respectively, vs. 3.7 and 16.5 s on 1% permethrin. For Kou RR females the comparable values were 27.3 s for TO₅₀ and 294 s for TO₉₅, with intermediate RS values of 10.1 s for TO₅₀ and 71.9 s for TO₉₅. Thus, TO values for RS were 2.7–4.4 times more than for SS, and those for RR were 7–18 times longer than for SS. Experiments with pyrethroid‐impregnated nets were designed to induce hungry female mosquitoes to pass through holes cut in the netting. Laboratory ‘tunnel tests’ used a bait guinea‐pig to attract mosquitoes through circular holes (5 × 1 cm) in a net screen. With untreated netting, 75–83% of laboratory‐reared females passed through the holes overnight, 63–69% blood‐fed successfully and 9–17% died, with no significant differences between SS and RR genotypes. When the netting was treated with permethrin 250 mg ai/m² the proportions that passed through the holes overnight were only 10% of SS vs. 40–46% of RR (Tola & Kou); mortality rates were 100% of SS compared with 59–82% of RR; bloodmeals were obtained by 9% of Kou RR and 17% of Tola RR, but none of the Kisumu SS females. When the net was treated with deltamethrin 25 mg ai/m² the proportions of An. gambiae that went through the holes and blood‐fed successfully were 3.9% of Kisumu SS and 3.5% of Yaokoffikro field population (94% R). Mortality rates were 97% of Kisumu SS vs. 47% of Yaokoffikro R. Evidently this deltamethrin treatment was sufficient to kill nearly all SS and half of the Yaokoffikro R An. gambiae population despite its high kdr frequency. Experimental huts at Yaokoffikro were used for overnight evaluation of bednets against An. gambiae females. The huts were sealed to prevent egress of mosquitoes released at 20.00 hours and collected at 05.00 hours. Each net was perforated with 225 square holes (2 × 2 cm). A man slept under the net as bait. With untreated nets, only 4–6% of mosquitoes died overnight and bloodmeals were taken by 17% of SS vs. 29% of Yaokoffikro R (P < 0.05). Nets treated with permethrin 500 mg/m² caused mortality rates of 95% Kisumu SS and 45% Yao R (P < 0.001) and blood‐feeding rates were reduced to 1.3% of SS vs. 8.1% of Yao R (P < 0.05). Nets treated with deltamethrin 25 mg/m² caused mortality rates of 91% Kisumu SS and 54% Yao R (P < 0.001) and reduced blood‐feeding rates to zero for SS vs. 2.5% for Yao R (P > 0.05). Pyrethroid‐impregnated bednets in experimental huts and ‘tunnel tests’ gave equivalent results, showing that nets impregnated with permethrin or deltamethrin provided good levels of protection against kdr homozygous strains of An. gambiae (Kou and Tola), and against the field population at Yaokoffikro with 94% kdr frequency. The explanation seems to be that (a) high proportions of kdr females are killed by prolonged contact with pyrethroids through diminished sensitivity to the usual irritant and repellent effects, and (b) relatively few kdr females take advantage of this prolonged contact to ingest a bloodmeal.     

神经递质3H-去甲肾上腺素释放与家蝇对拟除虫菊酯抗性的关系

在用K⁺去极化条件下,研究了溴氰菊酯和氯菊酯分别对敏感、抗溴氰菊酯和抗氯菊酯家蝇Musca domestica 品系脑突触体释放神经递质去甲肾上腺素的影响。结果表明：在用K⁺去极化后,神经递质去甲肾上腺素的释放在抗溴氰菊酯和抗氯菊酯家蝇品系中比敏感品系分别下降47.0%和51.0%;当用10^-5 mol/L溴氰菊酯预处理家蝇脑突触体,用K+去极化后对敏感、抗溴氰菊酯和抗氯菊酯家蝇品系释放去甲肾上腺素的加强作用分别提高80.3%、26.5%和70.5%;用10^-5 mol/L氯菊酯预处理3个家蝇品系的突触体对去甲肾上腺素释放均无加强作用。由此表明,家蝇对溴氰菊酯的抗性是与Na+通道的亲和性降低有关,而氯菊酯的抗性与Na+通道的亲和性关系不大。     

Production of l-lactic acid by Rhizopus species

Of 19 Rhizopus spp. only four produced l-lactic acid in shake-flask culture. Aerobically and in the presence of a neutralizing agent, Rhizopus oryzae NRRL 395 produced the highest concentration of l-lactic acid (65 g/l) but with O₂-limited growth ethanol was produced instead.C.R. Soccol and V.I. Stonoga are with the Laboratório de Processos Biotecnológicos, Departmento de Engenharia Química da Universidade Federal do Paraná, 81531-970 Curitiba, PR, Brazil; M. Raimbault is with the Centre ORSTOM, Laboratoire de Biotecnologie, Physiologie et Métabolisme Cellulaires, 911, Avenue Agropolis, 34032 Montpellier, Cedex 1, France.     

Experimental hut comparisons of nets treated with carbamate or pyrethroid insecticides, washed or unwashed, against pyrethroid-resistant mosquitoes

Abstract. The efficacy against mosquitoes (Diptera: Culicidae) of a bednet treated with carbamate insecticide [carbosulfan capsule suspension (CS) 200 mg/m²] was compared with four types of pyrethroid‐treated nets in veranda‐trap huts at Yaokoffikro near Bouaké, Côte d'Ivoire, where the malaria vector Anopheles gambiae Giles carries the kdr gene (conferring pyrethroid resistance) at high frequency and Culex quinquefasciatus Say is also pyrethroid resistant. Pyrethroids compared were lambdacyhalothrin CS 18 mg/m², alphacypermethrin water dispersible granules (WG) 20 mg/m², deltamethrin 50 mg/m² (Permanet?) and permethrin emulsifiable concentrate (EC) 500 mg/m². Insecticidal power and personal protection from mosquito bites were assessed before and after the nets were used for 8 months and hand washed five times in cold soapy water. Before washing, all treatments except permethrin significantly reduced blood‐feeding and all had significant insecticidal activity against An. gambiae. The carbosulfan net gave significantly higher killing of An. gambiae than all pyrethroid treatments except the Permanet. Against Culex spp., carbosulfan was more insecticidal and gave a significantly better protective effect than any of the pyrethroid treatments. After washing, treated nets retained various degrees of efficacy against both mosquito genera – but least for the carbosulfan net. Washed nets with three types of pyrethroid treatment (alphacypermethrin, lambdacyhalothrin, permethrin) gave significantly higher mortality rates of Culex than in huts with the same pyrethroid‐treated nets before washing. After five washes, the Permanet?, which is sold as a long‐lasting insecticidal product, performed no better than the other nets in our experimental conditions.     

Comparison of the structure and composition of bacterial communities from temperate and tropical freshwater ecosystems

We used a partial 16S rRNA sequencing approach to compare the structure and composition of the bacterial communities in three large, deep subalpine lakes in France with those of communities in six shallow tropical reservoirs in Burkina Faso. Despite the very different characteristics of these ecosystems, we found that their bacterial communities share the same composition in regard to the relative proportions of the different phyla, suggesting that freshwater environmental conditions lead to convergence in this composition. In the same way, we found no significant difference in the richness and diversity of the bacterial communities in France and Burkina Faso. We defined core and satellite operational taxonomic units (OTUs) (sequences sharing at least 98% identity) on the basis of their abundance and their geographical distribution. The core OTUs were found either ubiquitously or only in temperate or tropical and subtropical areas, and they contained more than 70% of all the sequences retrieved in this study. In contrast, satellite OTUs were characterized by having a more restricted geographical distribution and by lower abundance. Finally, the bacterial community composition of these freshwater ecosystems in France and Burkina Faso was markedly different, showing that the history of these ecosystems and regional environmental parameters have a greater impact on the relative abundances of the different OTUs in each bacterial community than the local environmental conditions.