Local Vibrio Isolates Exhibit Molecular Characteristics Distinct from Reference V. harveyi and V. campbellii Strains

Six Vibrio isolates identified biochemically as Vibrio campbellii from Southeast Asian Fisheries Development Center (SEAFDEC) in Tigbauan, Iloilo, were characterized by 16 rDNA sequence, total protein profile, and DNA profile analyses. Genomic DNA from the isolates were subjected to PCR using four sets of primers targeting gene fragments of hemolysin and toxR based on sequences from reference Vibrio harveyi (IFO15634), V. campbellii (IFO1563), and local isolates identified as V. harveyi. Total protein profile could not distinguish the isolates from one another and from the reference V. harveyi (IFO15634) and V. campbellii (IFO15631). Analysis of 16s rDNA sequences revealed high degree of sequence similarity (96% - 99%) of the six local isolates with other Vibrio species including V. campbellii and V. parahaemolyticus, indicating that this analysis will not be useful in resolving their identity. All six isolates exhibited characteristic reference V. harveyi PCR profile when a primer set designed to amplify a 308-bp fragment of hemolysin gene in that species was used. However, no amplicons were generated for these isolates using primers that amplify toxR gene fragments in V. harveyi. This suggests that the six isolates were not bonafide V. harveyi strains. The isolates also did not exhibit V. campbellii characteristics since the primer designed to target the toxR gene in V. campbellii could not amplify DNA from any of the six isolates, suggesting that they were not bonafide V. campbellii strains either. The toxR gene from the six isolates could be amplified using a primer based on toxR gene sequences from a SEAFDEC isolate previously identified as V. harveyi (PN-9801). These data suggest that the six isolates previously identified as V. campbellii as well as PN-9801 may be classified in one group separate from bonafide reference V. harveyi and reference V. campbellii strains, based on the identical results in the molecular analyses performed in this study

Identification of a possible cytadherence regulatory locus in Mycoplasma pneumoniae

Transposon mutagenesis was used to analyze Mycoplasma pneumoniae cytadherence. Mycoplasmas were electroporated with Tn4001, and transformants were identified by antibiotic selection using gentamicin. The resulting colonies were screened for hemadsorption (HA) as an indicator for cytadherence. Six HA- colonies from independent transformations were isolated, filter cloned, and characterized in more detail. Southern hybridization analysis revealed that all six transposon insertions mapped to the same 252-kbp ApaI fragment and 19.5-kbp XhoI fragment. More detailed analysis localized the insertion to two adjacent EcoRI fragments. This site is distinct from the locus containing the genes for the high-molecular weight cytadherence-accessory proteins HMW1 and HMW3, and yet these proteins were absent from the protein profiles of all six transformants. To determine if transposon insertion was responsible for the HA- phenotype, reversion frequencies of the transformants were assessed after passage in the presence of antibiotic selection. In contrast to a spontaneously arising HMW-deficient variant, which reverted to an HA+ phenotype readily, no HA+ revertants were identified for any of the six transformants. These observations suggest that a potential regulatory locus that may be important in the expression of the HMW cytadherence-accessory proteins has been identified.</jats:p

Species identification of thermo-tolerant bacillus isolates using 16s rDNA, gyraseB Gene (gyrB) and enzyme gene sequence analysis

© 2017, Department of Science and Technology. All rights reserved. Twenty four thermo-tolerant Bacillus isolates that tested positive in preliminary enzyme plate assays were subjected to 16S rDNA sequence analysis, which revealed that identification results were not consistent with conventional biochemical identification in eighteen isolates. Identification inconsistencies were resolved in sixteen isolates by gyrB sequence analysis that gave single species identification, consistent with 16S rDNA sequence analysis. One isolate was identified as B. subtilis based on similar results from the conventional approach and 16S rDNA analysis. Ambiguous identification was observed in seven isolates with16S rDNA and gyrB sequences exhibiting 96-100% sequence identity with two or more closely related Bacillus species. Four isolates with ambiguous identification exhibited significant 16S rDNA and gyrB sequence identity with a group of Bacillus that includes B. cereus, B. thuringiensis, and B. anthracis. Each of three remaining isolates with ambiguous identification exhibited significant rDNA and/or gyrB sequence identity with a different group, a group of bacteria that includes B. vietnamensis and B. aquimaris, a group with B. safensis and B. pumilus and another with B. methylotrophicus and B. amyloliquefaciens. Enzyme gene-targeted polymerase chain reaction (PCR) amplified partial gene sequences of at least one of the enzymes protease, cellulase, amylase, and phytase in each of fourteen isolates. The enzyme genes exhibited 98-99% sequence identity with genes reported in the database for Bacillus species that matched the identification results. Additional phenotypic and molecular markers that could distinguish closely related Bacillus species are necessary to resolve ambiguous identification

Transposon mutagenesis reinforces the correlation between Mycoplasma pneumoniae cytoskeletal protein HMW2 and cytadherence

A new genetic locus associated with Mycoplasma pneumoniae cytadherence was previously identified by transposon mutagenesis with Tn4001. This locus maps approximately 160 kbp from the genes encoding cytadherence-associated proteins HMW1 and HMW3, and yet insertions therein result in loss of these proteins and a hemadsorption-negative (HA-) phenotype, prompting the designation cytadherence-regulatory locus (crl). In the current study, passage of transformants in the absence of antibiotic selection resulted in loss of the transposon, a wild-type protein profile, and a HA+ phenotype, underscoring the correlation between crl and M. pneumoniae cytadherence. Nucleotide sequence analysis of crl revealed open reading frames (ORFs) orfp65, orfp216, orfp41, and orfp24, arranged in tandem and flanked by a promoter-like and a terminator-like sequence, suggesting a single transcriptional unit, the P65 operon. The 5' end of orfp65 mRNA was mapped by primer extension, and a likely promoter was identified just upstream. The product of each ORF was identified by using antisera prepared against fusion proteins. The previously characterized surface protein P65 is encoded by orfp65, while the 190,000 Mr cytadherence-associated protein HMW2 is a product of orfp216. Proteins with sizes of 47,000 and 41,000 Mr and unknown function were identified for orfp41 and orfp24, respectively. Structural analyses of HMW2 predict a periodicity highly characteristic of a coiled-coil conformation and five leucine zipper motifs, indicating that HMW2 probably forms dimers in vivo, which is consistent with a structural role in cytadherence. Each transposon insertion mapped to orfp216 but affected the levels of all products of the P65 operon. HMW2 is thought to form a disulfide-linked dimer, formerly designated HMW5, and examination of an hmw2 deletion mutant confirms that HMW5 is a product of the hmw2 gene.</jats:p

Differential detection of vibrios pathogenic to shrimp by multiplex PCR

The research was focused on the multiplex polymerase chain reaction (PCR) differential detection of shrimp pathogens Vibrio harveyi, Vibrio campbellii and isolates from a variant strain of Vibrio (referred to as Philippine Vibrio isolates in this study) exhibiting characteristics distinct from these two species. Sequence alignment of the hemolysin gene from type strains Vibrio harveyi (NBRC 15634) and Vibrio campbellii (NBRC 15631), as well as 10 variant Philippine Vibrio isolates, was performed in order to design a set of hemolysin-targeted primers for the specific detection of the Philippine Vibrio isolates. Primer PNhemo amplified a 320-bp hemolysin gene fragment of the Philippine Vibrio isolates in PCR using 65°C annealing temperature; but did not amplify the target gene fragment in type strains V. harveyi and V. campbellii. Another new primer (VcatoxR) targeting the toxR gene was designed for the specific detection of type strain V. Campbellii under stringent 65°C annealing temperature. PCR using VcatoxR primer resulted in the specific amplification of a 245-bp V. campbellii toxR fragment. The simultaneous use of three primer sets in PCR, including PNhemo and VcatoxR (the two new primers designed in this study), and a primer VhtoxR (previously reported for the specific detection of V. harveyi), resulted in differential profiles with 390-bp, 245-bp, and 320-bp amplicons for V. harveyi, V. campbellii, and variant Philippine Vibrio isolates, respectively. Presence of all three types of Vibrio shrimp pathogens in the sample could be detected with a multiplex PCR profile containing all the expected size amplicons

Local Vibrio isolates exhibit molecular characteristics distinct from reference V. harveyi and V. campbellii strains

Six Vibrio isolates identified biochemically as Vibrio campbellii from Southeast Asian Fisheries Development Center (SEAFDEC) in Tigbauan, Iloilo, were characterized by 16 rDNA sequence, total protein profile, and DNA profile analyses. Genomic DNA from the isolates were subjected to PCR using four sets of primers targeting gene fragments of hemolysin and toxR based on sequences from reference Vibrio harveyi (IFO15634), V. campbellii (IFO1563), and local isolates identified as V. harveyi. Total protein profile could not distinguish the isolates from one another and from the reference V. harveyi (IFO15634) and V. campbellii (IFO15631). Analysis of 16s rDNA sequences revealed high degree of sequence similarity (96% - 99%) of the six local isolates with other Vibrio species including V. campbellii and V. parahaemolyticus, indicating that this analysis will not be useful in resolving their identity. All six isolates exhibited characteristic reference V. harveyi PCR profile when a primer set designed to amplify a 308-bp fragment of hemolysin gene in that species was used. However, no amplicons were generated for these isolates using primers that amplify toxR gene fragments in V. harveyi. This suggests that the six isolates were not bonafide V. harveyi strains. The isolates also did not exhibit V. campbellii characteristics since the primer designed to target the toxR gene in V. campbellii could not amplify DNA from any of the six isolates, suggesting that they were not bonafide V. campbellii strains either. The toxR gene from the six isolates could be amplified using a primer based on toxR gene sequences from a SEAFDEC isolate previously identified as V. harveyi (PN-9801). These data suggest that the six isolates previously identified as V. campbellii as well as PN-9801 may be classified in one group separate from bonafide reference V. harveyi and reference V. campbellii strains, based on the identical results in the molecular analyses performed in this study