Co-Metabolic Biodegradation of DBP by Paenibacillus sp. S-3 and H-2

Two di-n-butyl phthalate (DBP)-degrading strains, designated as S-3 and H-2, were isolated from DBP-polluted soil and both identified as Paenibacillus sp. When DBP was provided as the sole carbon source, about 45.5 and 71.7 % of DBP (100 mg/L) were degraded by strain S-3 and H-2, respectively, after incubation for 48 h. However, DBP (100 mg/L) was degraded completely by co-culture of strain S-3 and H-2 after incubation for 60 h. Four phthalic acid (PA) esters could be utilized by co-metabolism in the study and the degradation rates followed the order of dimethyl phthalate > diethyl phthalate > DBP > dioctyl phthalate. The metabolic pathway of DBP was elucidated based on the results of metabolites identification and enzyme assays. For strain S-3, DBP was degraded into butyl hydrogen phthalate which was degraded to PA by carboxyesterase further. But PA could be not hydrolyzed further because strain S-3 lacked 3,4-phthalate dioxygenase. Different with S-3, strain H-2 could hydrolyze PA into 3,4-dihydroxy-PA by 3,4-phthalate dioxygenase. Then 3,4-dihydroxy-PA was converted to protocatechuate and benzoic acid. Finally, the aromatic ring was cleavage and mineralized to CO₂ and H₂O. Above all, co-metabolism could increase the activity of 3,4-phthalate dioxygenase and accelerated the degradation of DBP. This study highlights an important potential use of co-metabolic biodegradation for the in situ bioremediation of DBP and its metabolites-contaminated environment.     

Single cell oil production by <Emphasis Type="Italic">Gordonia</Emphasis> sp. DG using agro-industrial wastes

Lipid accumulation by Gordonia sp. DG using sodium gluconate as carbon source in comparison with Rhodococcus opacus PD630 was studied. Maximum lipid content 80% was observed at the beginning of the stationary phase for R. opacus and 72% at the end of stationary phase for Gordonia sp. Different agro-industrial wastes were used as carbon source. The cells of the two organism accumulated lipid more than 50% of the biomass with most tested agro-industrial wastes. The maximum value was in presence of sugar cane molasses (93 and 96%) for R. opacus and Gordonia sp. respectively. Maximum triacyglycerols (TAGs), 88.9 and 57.8 mg/l, was obtained using carob and orange waste by R. opacus and Gordonia sp. respectively. The use of orange waste as carbon source by R. opacus, increased lipid unsaturation with C18:3 as the major unsaturated fatty acid. On the other hand, C22:0 and C6:0 were the dominant fatty acids (54.5% of the total identified fatty acids) produced by Gordonia sp. in presence of orange waste as carbon source. Statistical optimization of the medium revealed that maximum lipid content was achieved with 60% orange waste, 0.05 g/l ammonium chloride and 0.2 g/l magnesium sulphate.     

Molecular detection of <Emphasis Type="Italic">Rickettsia</Emphasis>, <Emphasis Type="Italic">Coxiella</Emphasis> and <Emphasis Type="Italic">Rickettsiella</Emphasis> DNA in three native Australian tick species

Three Australian native animal species yielded 60 samples composed of three indigenous ticks. Hosts included twelve koalas, two echidnas and one wombat from Victoria, and ticks were of the species Ixodes tasmani (n = 42), Bothriocroton concolor (n = 8) and B. auruginans (n = 10), respectively. PCR screening and sequencing detected a species of Coxiella, sharing closest sequence identity to C. burnetii (>98%), in all B. auruginans, as well as a species of Rickettsia, matching closest to R. massiliae, in 70% of the same samples. A genotype sharing closest similarity to Rickettsia bellii (>99%) was identified in three female B. concolor collected from one of the echidnas. Three samples of I. tasmani, taken from three koalas, yielded different genotypes of Rickettsiella. These results represent the first detection of the three genera in each tick species and identify a high level of previously undetected bacterial diversity in Australian ticks.     

Arginine-dependent acid-resistance pathway in <Emphasis Type="Italic">Shigella boydii</Emphasis>

Ability to survive the low pH of the human stomach is considered be an important virulent determinant. It was suggested that the unique acid tolerance of Shigella boydii 18 CDPH, the strain implicated in a 1998 outbreak, may have played an important role in surviving the acidic food (bean salad). The strain was capable of inducing arginine-dependent acid-resistance (ADAR) pathway. This pathway was assumed to be absent in Shigella sp. Here, we have examined occurrence and efficacy of ADAR pathway in 21 S. boydii strains obtained from the American Type Culture Collection (ATCC) along with strains of S. flexneri (n = 7), S. sonnei (n = 4), and S. dysenteriae (n = 2). The eight S. boydii strains were able to induce ADAR to survive the acid challenge at pH 2.0; additional 8 strains could tolerate acid challenge at pH 2.5 but not at pH 2.0. The remaining five S. boydii strains were not able to induce ADAR pathway and could not survive acid challenge even at pH 2.5. ADAR pathway also appears to be present in all four Shigella sp. Shigella ADAR pathway was induced when cells were grown under partial oxygen pressure while its expression in E. coli required mere fermentative growth on glucose.     

Phylogenetic Studies of <Emphasis Type="Italic">Gordonia</Emphasis> Species Based on <Emphasis Type="Italic">gyrB</Emphasis> and <Emphasis Type="Italic">secA1</Emphasis> Gene Analyses

Phylogenetic relations within the genus Gordonia were analyzed using partial gyrB and secA1 gene sequences of 23 type species in comparison with those of 16S rRNA gene. The gyrB and secA1 phylogenies showed agreement with that constructed using 16S rRNA gene sequences. The degrees of divergence of the gyrB and secA1 genes were approximately 3.4 and 1.7 times greater, respectively, than that of 16S rRNA gene. The gyrB gene showed more discriminatory power than either the secA1 or 16S rRNA gene, facilitating clear differentiation of any two Gordonia species using gyrB gene analysis. Our data indicate that gyrB and secA1 gene sequences are useful as markers for phylogenetic study and identification at the species level of the genus Gordonia.     

Phthalate catabolic gene cluster is linked to the angular dioxygenase gene in <Emphasis Type="Italic">Terrabacter</Emphasis> sp. strain DBF63

Phthalate is a metabolic intermediate of the pathway of fluorene (FN) degradation via angular dioxygenation. A gene cluster responsible for the conversion of phthalate to protocatechuate was cloned from the dibenzofuran (DF)- and FN-degrading bacterium Terrabacter sp. strain DBF63 and sequenced. The genes encoding seven catabolic enzymes, oxygenase large subunit of phthalate 3,4-dioxygenase (phtA1), oxygenase small subunit of phthalate 3,4-dioxygenase (phtA2), cis-3,4-dihydroxy-3,4-dihydrophthalate dehydrogenase (phtB), [3Fe-4S] or [4Fe-4S] type of ferredoxin (phtA3), ferredoxin reductase (phtA4), 3,4-dihydroxyphthalate decarboxylase (phtC) and putative regulatory protein (phtR), were found in the upstream region of the angular dioxygenase gene (dbfA1A2), encoded in this order. Escherichia coli carrying phtA1A2BA3A4 genes converted phthalate to 3,4-dihydroxyphthalate, and the 3,4-dihydroxyphthalate decarboxylase activity by E. coli cells carrying phtC was finally detected with the introduction of a Shine-Dalgarno sequence in the upstream region of its initiation codon. Homology analysis on the upstream region of the pht gene cluster revealed that there was an insertion sequence (IS) (ISTesp2; ORF14 and its flanking region), part of which was almost 100% identical to the orf1 and its flanking region adjacent to the extradiol dioxygenase gene ( bphC1) involved in the DF degradation of Terrabacter sp. strain DPO360 [Schmid et al. (1997) J Bacteriol 179:53-62]. This suggests that ISTesp2 plays a role in the metabolism of aromatic compounds in Terrabacter sp. strains DBF63 and DPO360.     

Identification of the di-<Emphasis Type="Italic">n</Emphasis>-butyl phthalate-biodegrading strains and the biodegradation pathway in strain LMB-1

DNA isolated from a greenhouse soil (Nanjing, Jiangsu Province, China) was suitable for PCR amplification of gene segment coding for the 16S rRNA. Diverse PCR products were characterized by cloning and sequencing, and analysis of bacterial colonies showed the presence over 26 phyla. The most bacteria belonged to Proteobacteria, Actinobacteria, Gemmatimonadetes, Acidobacteria and Planctomycetes. Furthermore, after the enrichment procedure of DBP-degrading microorganisms, 4 strains were isolated from the soil sample with di-n-butyl phthalate (DBP) biodegradability, and they were identified to be Rhizobium sp., Streptomyces sp., Pseudomonas sp. and Acinetobacter sp. Analysis of the degradation products by LC-MS led to identification of metabolites of DBP in strain LMB-1 (identified as Rhizobium sp.) which suggests that DBP was degraded through β-oxidation, demethylation, de-esterification and cleavage of aromatic ring.     

<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> in Poland and Japan is nodulated by <Emphasis Type="Italic">Mesorhizobium amorphae</Emphasis> strains

Robinia pseudoacacia microsymbionts from plants growing in Poland and Japan were evaluated for phylogeny and taxonomic position by genomic approach. Based on the comparative analyses of atpD (368 bp) and dnaK (573 bp) gene sequences as well as 16S rDNA restriction analysis (RFLP-16S rDNA), R. pseudoacacia microsymbionts were identified as Mesorhizobium strains. In dnaK and atpD gene phylograms R. pseudoacacia nodulators formed robust, monophyletic clusters with Mesorhizobium species with the nucleotide sequence similarity of 91–98% and 90–98%, respectively. The classification of R. pseudoacacia rhizobia to the genus Mesorhizobium was also supported by amplified 16S rDNA restriction analysis. The studied bacteria formed common clusters with Mesorhizobium species, and their DNA patterns were identical or nearly identical to Mesorhizobium genus strains. When DNA-DNA hybridization was performed, the total DNA of the representative R. pseudoacacia rhizobia exhibited 51–75% relatedness to DNA of Mesorhizobium amorphae ICMP15022 strain and below 41% to DNA of other Mesorhizobium species. These results showed that R. pseudoacacia and M. amorphae belong to the same genomospecies. The G+C content of DNA of R. pseudoacacia two microsymbionts was 59.7 and 60.6 mol% compared to 61–64 mol% across M. amorphae strains.     

Cyanobactericidal effect of <Emphasis Type="Italic">Rhodococcus</Emphasis> sp. isolated from eutrophic lake on <Emphasis Type="Italic">Microcystis</Emphasis> sp

A bacterium, which was observed in all cultivations of Microcystis sp., was isolated and designated as Rhodococcus sp. KWR2. The growth of bloom-forming cyanobacteria, including four strains of Microcystis aeruginosa and Anabaena variabilis, was suppressed by up to 75–88% by 2% (v/v) culture broth of KWR2 after 5 days. But KWR2 did not inhibit eukaryotic algae, Chlorella vulgaris and Scenedesmus sp. An extracellular algicidal substance produced by KWR2 showed a cyanobactericidal activity of 94% and was water-soluble with a molecular weight of lower than 8 kDa.     

Impact of biological control agents on fusaric acid secreted from <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">gladioli</Emphasis> (Massey) Snyder and Hansen in <Emphasis Type="Italic">Gladiolus grandiflorus</Emphasis> corms

Fusaric acid (FA) (5-n-butylpuridine 2-carboxyl acid), a highly toxic secondary metabolite produced by Fusarium oxysporum strains, plays a significant role in disease development. The abilities of three F. oxysporum f. sp. gladioli (Massey) Snyder and Hansen isolates (G010; 649-91; and 160-57) to produce FA in infected Gladiolus corm tissues was evaluated in vitro in relation to the presence of two biological control agents, Trichoderma harzianum T22, and Aneurinobacillus migulanus. Pathogenicity tests were used to differentiate between the abilities of the F. oxysporum strains to secrete FA. FA was identified using LC/MS and quantified using HPLC. Isolate G010 was significantly more virulent (P < 0.01) on Gladiolus grandiflorus corms; it secretes 1.8 μM FA/g fresh weight corm into inoculated Gladiolus. Moreover, G010 was the only isolate that produced FA among the three examined isolates. There was a correlation between the corm lesion area and the FA secretion ability of F. oxysporum f. sp. gladioli (P < 0.001; r ² = 0.96). No FA was detected in PDA cultures of F.oxysporum f. sp. gladioli isolates. The presence of T. harzianum T22 appeared to prevent FA secretion into the corms. In the presence of A. migulanus, however, the amount of FA secreted into the corm tissues increased. These results support the use of T. harzianum as an effective biological control agent against F. oxysporum f. sp. gladioli.     

Rhizoremediation of diesel-contaminated soil using the plant growth-promoting rhizobacterium <Emphasis Type="Italic">Gordonia</Emphasis> sp. S2RP-17

A plant growth-promoting rhizobacterium (PGPR) was isolated and identified as Gordonia sp. S2RP-17, which showed ACC deaminase and siderophore synthesizing activities. Its maximum specific growth rate was 0.54 ± 0.12 d⁻¹ at 5,000 mg L⁻¹ of total petroleum hydrocarbon (TPH), and its maximum diesel degradation rate was 2,434.0 ± 124.4 mg L⁻¹ d⁻¹ at 20,000 mg L⁻¹ of TPH. The growth of Zea mays was significantly promoted by the inoculation of Gordonia sp. S2RP-17 in the diesel-contaminated soil. Measured TPH removal efficiencies by various means were 13% by natural attenuation, 84.5% by planting Zea mays, and 95.8% by the combination of Zea mays and Gordonia sp. S2RP-17. The S2RP-17 cell counts were maintained at 1 × 10⁶ CFU g-soil⁻¹ during the remediation period, although they slightly decreased from their initial numbers (2.94 × 10⁷ CFU g-soil⁻¹). These results indicate that rhizoremediation using both Zea mays and Gordonia sp. S2RP-17 is a promising strategy for enhancing remediation efficiency of diesel-contaminated soils.     

<Emphasis Type="Italic">Ogataea phyllophila</Emphasis> sp. nov., <Emphasis Type="Italic">Candida chumphonensis</Emphasis> sp. nov. and <Emphasis Type="Italic">Candida mattranensis</Emphasis> sp. nov., three methylotrophic yeast species from phylloplane in Thailand

Five strains (LN12, LN14^T, LN15^T, LN16 and LN17^T) representing three novel methylotrophic yeast species were isolated from the external surface of plant leaves by three-consecutive enrichments. On the basis of morphological, biochemical, physiological and chemotaxonomic characteristics, the sequence analysis of the D1/D2 domain of the large subunit (LSU) rRNA gene and the phylogenetic analysis, the five strains were assigned to be one novel Ogataea species and two novel Candida species. Three strains (LN12, LN14^T and LN16) represent a single novel species of the genus Ogataea, for which the name Ogataea phyllophila sp. nov. is proposed. The type strain is LN14^T (= BCC 42666^T = NBRC 107780^T = CBS 12095^T). Strain LN15^T was assigned to be Candida chumphonensis sp. nov. (type strain LN15^T = BCC 42667^T = NBRC 107781^T = CBS 12096^T). Strain LN17^T represented another novel species of Candida that was named Candida mattranensis sp. nov. (type strain LN17^T = BCC 42668^T = NBRC 107782^T = CBS 12097^T).     

Effects of three phthalate esters on the life-table demography of freshwater rotifer <Emphasis Type="Italic">Brachionus calyciflorus</Emphasis> Pallas

Phthalate esters (PAEs) are mainly used in the polymer industry as external plasticizers in PVC, and tend to migrate slowly out of the plastic, either into the air by volatilization or into water or other solvents by dissolution. Di-n-butyl phthalate (DBP), butyl benzyl phthalate (BBP) and di-2-ethylhexyl phthalate (DEHP) are three members of PAEs, identified as priority controlled hazardous substances by the United States Environmental Protection Agency, and have been shown to have potential for endocrine disrupting effects on vertebrates and humans. The effects of DBP, BBP and DEHP on survival and reproduction of the freshwater rotifer Brachionus calyciflorus were studied using life-table demographic methods. The results showed that all the life-table demographic parameters of B. calyciflorus were markedly affected by DBP and BBP, but not by DEHP. The net reproductive rate representing the output of reproduction was more affected than all the other parameters representing population growth, development or survival of the rotifers. Compared to the solvent control, DBP and BBP, both at 500 μg l⁻¹, significantly increased the net reproductive rate, and prolonged the generation time and the life expectancy at hatching of the rotifers. DBP at 50 μg l⁻¹ markedly decreased the intrinsic rate of population increase of the rotifers, but the reverse was true for BBP at 50 and 500 μg l⁻¹. Among all the parameters, the intrinsic rate of population increase was the most sensitive to DBP and BBP. The levels of PAEs in water from all the studied rivers and lakes in the world did not affect the population growth of rotifers.     

Urban Pigeons (<Emphasis Type="Italic">Columba livia</Emphasis>) as a Potential Source of Pathogenic Yeasts: A Focus on Antifungal Susceptibility of <Emphasis Type="Italic">Cryptococcus</Emphasis> Strains in Northeast Brazil

To investigate pigeons as a potential source of pathogenic yeast species, 47 samples of pigeon droppings and 322 samples from pigeon cloacae were evaluated. The samples were also collected from trees located near the pigeon habitats, in the city of Fortaleza, Ceará, Northeast Brazil. In addition, we evaluated the in vitro antifungal susceptibility of these environmental Cryptococcus strains to amphotericin B, azoles and caspofungin. C. neoformans var. neoformans (n = 10), C. laurentii (n = 3), Candida spp. (n = 14), Rhodotorula mucilaginosa (n = 6) and Trichosporon sp. (n = 3) were isolated from pigeon droppings. In contrast, only Candida spp. (n = 4), Trichosporon sp. (n = 3) and R. mucilaginosa (n = 2) were recovered from cloacae specimens. Only Candida glabrata (n = 1) was recovered from plant samples. Azole resistance was detected in only one environmental strain of Cryptococcus, which was resistant to itraconazole (MIC = 1 μg/ml). As expected, all Cryptococcus strains were resistant to caspofungin. In summary, the present study confirms that urban pigeons are a potential source of Cryptococcus spp. and other pathogenic yeasts. Additionally, antifungal resistance was observed in one environmental strain of Cryptococcus neoformans var. neoformans in Northeast Brazil.     

Phylogeny of members of the <Emphasis Type="Italic">Frankia</Emphasis> genus based on <Emphasis Type="Italic">gyr</Emphasis>B, <Emphasis Type="Italic">nif</Emphasis>H and <Emphasis Type="Italic">gln</Emphasis>II sequences

To construct an evolutionary hypothesis for the genus Frankia, gyrB (encoding gyrase B), nifH (encoding nitrogenase reductase) and glnII (encoding glutamine synthetase II) gene sequences were considered for 38 strains. The overall clustering pattern among Frankia strains based on the three analyzed sequences varied among themselves and with the previously established 16S rRNA gene phylogeny and they did not reliably reflect clear evolution of the four discerned Frankia clusters (1, 2, 3 and 4). Based on concatenated gyrB, nifH and glnII, robust phylogenetic trees were observed with the three treeing methods (Maximum Likelihood, Parsimony and Neighbor-Joining) and supported by strong bootstrap and posterior probability values (>75%) for overall branching. Cluster 4 (non-infective and/or non-nitrogen-fixing Frankia) was positioned at a deeper branch followed by cluster 3 (Rhamnaceae and Elaeagnaceae infective Frankia), while cluster 2 represents uncultured Frankia microsymbionts of the Coriariaceae, Datiscaceae, Rosaceae and of Ceanothus sp. (Rhamnaceae); Cluster 1 (Betulaceae, Myricaceae and Casuarinaceae infective Frankia) appears to have diverged more recently. The present study demonstrates the utility of phylogenetic analyses based upon concatenated gyrB, nifH and glnII sequences to help resolve previously unresolved or poorly resolved nodes and will aid in describing species among the genus Frankia.     

<Emphasis Type="Italic">n</Emphasis>-Alkane assimilation and <Emphasis Type="Italic">tert</Emphasis>-butyl alcohol (TBA) oxidation capacity in <Emphasis Type="Italic">Mycobacterium austroafricanum</Emphasis> strains

Mycobacterium austroafricanum IFP 2012, which grows on methyl tert-butyl ether (MTBE) and on tert-butyl alcohol (TBA), the main intermediate of MTBE degradation, also grows on a broad range of n-alkanes (C₂ to C₁₆). A single alkB gene copy, encoding a non-heme alkane monooxygenase, was partially amplified from the genome of this bacterium. Its expression was induced after growth on n-propane, n-hexane, n-hexadecane and on TBA but not after growth on LB. The capacity of other fast-growing mycobacteria to grow on n-alkanes (C₁ to C₁₆) and to degrade TBA after growth on n-alkanes was compared to that of M. austroafricanum IFP 2012. We studied M. austroafricanum IFP 2012 and IFP 2015 able to grow on MTBE, M. austroafricanum IFP 2173 able to grow on isooctane, Mycobacterium sp. IFP 2009 able to grow on ethyl tert-butyl ether (ETBE), M. vaccae JOB5 (M. austroaafricanum ATCC 29678) able to degrade MTBE and TBA and M. smegmatis mc2 155 with no known degradation capacity towards fuel oxygenates. The M. austroafricanum strains grew on a broad range of n-alkanes and three were able to degrade TBA after growth on propane, hexane and hexadecane. An alkB gene was partially amplified from the genome of all mycobacteria and a sequence comparison demonstrated a close relationship among the M. austroafricanum strains. This is the first report suggesting the involvement of an alkane hydroxylase in TBA oxidation, a key step during MTBE metabolism.     

<Emphasis Type="Italic">Rhizobium sphaerophysae</Emphasis> sp. nov., a novel species isolated from root nodules of <Emphasis Type="Italic">Sphaerophysa salsula</Emphasis> in China

Four gram-negative, aerobic, motile, non-spore, forming rods with a wide pH and temperature range for growth (pH 7.0–11.0, optimum pH 8.0; 20–45°C, optimum 28°C) strains were isolated from root nodules of Sphaerophysa salsula and characterized by means of a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the four strains formed a new lineage related to the genus Rhizobium and the sequence similarities between the isolate and the most related type strain Rhizobium giardinii was 96.5%. These strains also formed a distinctive group from the reference strains for defined Rhizobium species based on housekeeping gene sequences (atpD and recA), BOX-PCR fingerprinting, phenotypic features and symbiotic properties. The representative strain CCNWGS0238^T has DNA-DNA relatedness of less than 33.4% with the most closely related species R. giardinii. It is therefore proposed as a new species, Rhizobium sphaerophysae sp. nov., with isolate CCNWGS0238^T (=ACCC17498^T = HAMBI3074^T) as the type strain.     

Phenotype changes inherited by crossing pyrethroid susceptible and resistant genotypes from the cattle tick <Emphasis Type="Italic">Riphicephalus</Emphasis> (<Emphasis Type="Italic">Boophilus</Emphasis>) <Emphasis Type="Italic">microplus</Emphasis>

Dialelic crosses and backcrosses of pyrethroid resistant (RR) and susceptible (SS) Rhipicephalus (Boophilus) microplus tick strains were carried out and the substitution (Phe-Ile) within the sodium channel gene was monitored in order to analyze the effects of the genotype on the pyrethroid resistance phenotype as measured by the larval packet test (LPT). Parental strains: susceptible (SS) and resistant (RR); dialelic crosses: RS (♂RR × ♀SS), and SR (♂SS × ♀RR); and backcrosses: RS × SS, RS × RR, SR × SS and SR × RR were infested on 280 kg calves. Resistance type (monogenic or polygenic) and effective dominance were determined based on the discriminant concentration (DC) for cipermethrine (0.5%), deltamethrine (0.09%) and flumethrine (0.01%). Allele specific PCR (AS-PCR) was used for genotyping, looking at a sodium channel mutation (Phe-Ile substitution). The mortality rates and allele frequency of susceptible and pyrethroid resistant reference strains were 0% mortality and 90% RR alleles for resistant strain, and 100% mortality and 0% RR alleles as measured by the larval packet test (LPT) and allele specific PCR (AS-PCR) respectively. Backcrossed strain SR × RR showed an effective dominance (D_ML) of 0.605 for cypermethrin, 0.639 for deltamethrin and 0.498 for flumethrin, while survival of backcrosses RS × SS, RS × RR and SR × SS showed a significant tendency to recesivity. Backcrossed strain SR × RR (69.4%) also showed a higher RR genotype frequency with regards to RS × SS (25.5%), RS × RR (36.7%) and SR × SS (32.0%), however, susceptible allele was inherited in general as an incomplete dominant trait. Monogenic inheritance hypothesis was tested and the results showed monogenic inheritance for cypermethrin and flumethrin (P < 0.05) but not for deltamethrin (P > 0.05). However, significant correlation was found between RR genotype and the survival rate for all three pyrethroids used (P < 0.05), suggesting that a single substitution on the sodium channel gene can be responsible for resistance to pyrethroids as a class, due to the high frequency for RR genotypes. Combination with different mutations or metabolic resistance mechanisms cannot be excluded.