Distribution of mosquito larvae in rice field habitats: A spatial scale analysis in semi-field condition

The distribution of the mosquito larvae in the breeding habitats varies at the spatial scale depending on the availability of the resources and the predators. This proposition was assessed through the observation of the spatial distribution of Culex larvae (Culex tritaeniorhynchus) in artificially constructed rice field habitats. Using a binomial generalized linear model with logit link, the disparity in the abundance of the larvae was evaluated to justify the effects of light (light vs shade), vertical (surface vs bottom), and horizontal (wall vs center) distribution as explanatory variables. Under light availability, the spatial occupancy of the mosquito larvae was higher in the center than in the walls of the mesocosms. However, the larval orientation was higher on the surface than at the bottom of the mesocosms in all instances. In comparison to open spaces, the larval aggregation was higher in the presence of the floating vegetations like Azolla and Lemna, indicating that the habitat heterogeneity of the mesocosms influenced the distribution of the mosquito larvae in the available spaces. A reduction in the larval aggregation pattern in the spaces was observed in the presence of the predator (Anisops sp.) reflecting the possible evasion tactics of the mosquito larvae. The observations suggest that the mosquito larvae may utilize the vegetation in the rice field habitats quite effectively and occupy empty spaces of predators. The results may be considered as a prototype of the prospective localization of the mosquito larvae in the rice fields and help to frame the strategies of spraying the biopesticides to achieve optimal efficacy in mosquito regulation

Phenotyping and molecular characterization of Lysinibacillus sp. P-011 (GU288531) and their role in the development of Drosophila melanogaster

The bacterial strain Lysinibacillus sp. (P-011) was isolated from the midgut of the Drosophila melanogaster larvae. The bacteria were gram positive, spore forming, rod shaped ranging from 1.86 to 2.5µm in length and 0.50 to 0.67 µm in diameter, positive for catalase, indole, oxidase, nitrate reduction, starch and gelatin hydrolysis, sensitive to tetracycline, chloramphenicol, doxycycline hydrochloride, gatifloxacin, ofloxacin, vancomycin, rifampicin, levofloxacin, ciprofloxacin, nalidixic acid, but resistant to ampicillin, streptomycin, gentamycin and kanamycin. The phylogenetic tree showed that the strain Lysinibacillus sp. P-011 (GU288531) branched with Lysinibacillus boronitolerans with 89% bootstrap support. Lysinibacillus sp. P-011 (~105 cfu/ml) played an important role on larval development of D. melanogaster under controlled environmental condition. Wild larvae when fed on normal food as well as normal food mixed with ineffective antibiotics, developed puparium within seven days whereas took more than 10 days when fed on normal food mixed with anti P-011 antibiotics and sterile food mixed with bacterial suspension and anti P-011 antibiotics. 94 to 98% cured larvae developed puparium within seven days when fed on only sterile food mixed with bacterial suspension (P-011) or sterile food mixed with bacterial suspension (P-011) and ineffective antibiotics.Key words: Drosophila melanogaster, gut-bacteria, larval development, Lysinibacillus sp. P-011 (GU288531), 16S rRNA gene sequence, phylogenetic tree

Virulence of Bacillus cereus as natural facultative pathogen of Anopheles subpictus Grassi (Diptera: Culicidae) larvae in submerged rice-fields and shallow ponds

Out of 4407 Anopheles subpictus larvae collected from submerged rice-fields and shallow ponds, 1412 were found to be unhealthy and 2.8% of unhealthy larvae were naturally infected by Bacillus cereus. B. cereus formed circular, white and flat colonies. Bacteria were gram positive, ellipsoidal/oval spore forming aerobic rods. Although the isolate was positive for catalase, urease, gelatinase, lipase, nitrate reduction and H2S production, it was negative for indole production, Vogues-Proskauer test, oxidase test and acid/gas production from carbon sources. Through biochemical characterization and fatty acid methyl ester (FAME) analysis, the bacterial isolate was identified as Bacillus cereus. In the laboratory condition, B. cereus suspension resulted in 43.57% and 93.78% death of A. subpictus larvae within 3 and 6 h, respectively. The organisms were sensitive to recommended doses of kanamycin, gatifloxacin, gentamycin, levofloxacin, doxycyclin,  tetracyclin, streptomycin, rifampicin, vancomycin, ciprofloxacin, but found resistant to ampicillin.Key words: Bacillus cereus, fatty acid methyl ester analysis, scanning electron micrograph, biochemicalcharacterization, pathogen, Anopheles subpictus larva

Combined effect of physico-chemical and microbial quality of breeding habitat water on oviposition of malarial vector Anopheles subpictus.

Mosquitoes prefer diverse water bodies for egg laying and larval survival. Present study was performed with an objective to characterize physico-chemical properties and microbial profiling of breeding habitat water bodies of Anopheles subpictus mosquitoes. A field survey was accomplished to check the presence of An. subpictus larvae to record per dip larval density in various breeding habitats throughout the year. Physico-chemical and bacteriological properties in relation to mosquito oviposition were assessed. Dissolved oxygen content, pH and alkalinity were found to have major impacts and ponderosity on the prevalence of An. subpictus larvae. Larval density showed significant positive correlation with dissolved oxygen content of water and significant negative correlation with pH and alkalinity of habitat water. Comparatively higher population (cfu/mL) of Bacillus spp. competent with starch hydrolyzing and nitrate reducing properties were recorded all the breeding habitat water bodies of An. subpictus. Higher amplitude of anopheline larvae was portrayed during monsoon and post-monsoon season in clear water with an inclining trend to high dissolved oxygen content and neutral pH. B. cereus, B. megaterium, B. subtilis and B. tequilensis prevalent in all habitat water bodies were marked as oviposition attractants of gravid An. subpictus mosquitoes. Microbial population played key roles in the modulation of physico-chemical parameters of habitat water with a view to enhance its acceptability by gravid mosquitoes in relation to their oviposition. Better understanding of the interactions along with the control of oviposition attractant bacterial strains from mosquito breeding habitats might contribute to the vector management programme

Seasonal Fluctuation of the Population and Characterization of Bacillus

Seasonal fluctuation of the population of Bacillus spp. in the coastal soils of Digha, West Bengal, India, was determined and it has been found that, during summer, monsoon, and winter season, the Bacillus population density varied in the range of 0.01–0.236 × 106, 0.11–0.202 × 106, and 0.098–0.155 × 106, respectively. Two-way ANOVA, agglomerative hierarchial cluster (AHC) analysis, and principal component analysis (PCA) were performed to determine the diversity of Bacillus spp. in both spatial and temporal aspects. During summer season, the population of Bacillus spp. reached a comparatively higher density than monsoon or winter. Spatial variation was also exhibited among the Bacillus spp. in different coastal villages. A total of 25 strains of Bacillus spp. (DSB1–DSB25) were isolated from the coastal soils of different village areas of Digha, during the study period. The isolates were characterized morphologically, physiologically, and biochemically. Colony morphology of each of the isolates was thoroughly studied. Biochemical tests along with fermentation tests, NaCl, pH, and temperature tolerance tests were done. The antibiotic sensitivity of the isolated Bacillus spp. against different standard antibiotics was also assessed. The study revealed that the coastal soils of Digha area were rich in different strains of Bacillus spp. showing significant differences in the morphophysiological and biochemical properties

Isolation and characterization of arsenic-resistant bacteria and possible application in bioremediation

Ground water arsenic contamination is a widespread problem in many developing countries including Bangladesh and India. In recent years development of modern innovative technologies for the removal of arsenic from aqueous system has become an interesting topic for research. In this present study, two rod shaped Gram-positive bacteria are being reported, isolated from arsenic affected ground water of Purbasthali block of Burdwan, West Bengal, India, which can tolerate arsenate concentration up to 4500 ppm and 550 ppm of arsenite concentration. From biochemical analysis and 16S rRNA sequencing, they were identified as Bacillus sp. and Aneurinibacillus aneurinilyticus respectively. The isolates SW2 and SW4 can remove 51.45% and 51.99% of arsenite and 53.29% and 50.37% of arsenate, respectively from arsenic containing culture media. Both of the isolate can oxidize arsenite to less toxic arsenate. These two arsenic resistant bacteria can be used as a novel pathway for the bioremediation of arsenic