Abstract:The objective of this research is to develop fermentation methodology for the production of the biocontrol agent Heterorhabditis bacteriophora. Deployment of this organism will reduce the use of chemical insecticides which threaten the environment. This study shows how to produce the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora and its bacterial symbiont Photorhabdus luminescens utilizing an in vitro, monoxenic liquid culture. EPNs were cultured in three different bioreactor working volumes of 1.5, 4 and 7 liters with initial nematode inoculation concentrations of approximately 2x10 3 /mL. Liquid nematode media was conditioned with the bacterial symbiont 24 hours prior to nematode inoculation. Within three days after inoculation, infective juveniles (IJs) developed into self-fertilizing hermaphrodites and eventually produced IJ offspring. Maximum nematode densities were obtained seven days post-nematode inoculation. All three working volumes (1.5, 4 and 7 liters) produced final yields of 4.6x10 4 ± 2000 IJs/mL, 4.2x10 4 ± 2200 IJs/mL and 3.9x10 4 ± 2000 IJs/mL, respectively. In vitro scale-up technology can be further optimized for production of this biocontrol agent by improving media formulation, process parameters, bioreactor design and inoculation times that will maximize nematode yield.
The present study deals with the batch and fed-batch mass production of Steinernema carpocapsae. S. carpocapsae is an entomoparasitic nematode that is used as a biological control agent of soil-borne crop insect pests. The ability and efficiency of fed-batch culture process was successful through the utilization of the nematode’s bacterial symbiont Xenorhabdus nematophila. Results from the fed-batch process were compared to those obtain from the standard batch process. The fed-batch process successively improved the mass production process of S. carpocapsae employing liquid medium technology. Within the first week of the fed-batch process (day six), the nematode density obtained was 202,000 nematodes mL−1; whereas on day six, batch culture mode resulted in a nematode density of 23,000 nematodes mL−1. The fed-batch process was superior to that of batch production with a yield approximately 8.8-fold higher. In fed-batch process, the nematode yield was improved 88.6 % higher within a short amount of time compared to the batch process. Fed-batch seems to make the process more efficient and possibly economically viable.
The present work aimed to make an assessment of physicochemical parameters and bacteriological contamination associated with 24 ground water resources used by more than 5% of total population, classified under four characteristic locations of Bhavnagar, a growing city of Gujarat. Ground water quality was evaluated with respect to most probable number of Escherichia coli, and presence of heterotrophic bacteria including some pathogens. Based on morphological differences and sites, 27 isolates were randomly selected and identified accurately. Scanning electron microscopy was also performed for each representative genus to understand morphology. Resources from thickly crowded areas were dominated by Aeromonas and Acinetobacter, residential area by Citrobacter and Serratia and sites adjacent to drainage canals by Pseudomonas spp. Further, bacterial community structure of 24 different resources was determined by Biolog EcoPlates™ and species richness and diversity were evaluated. Antibiotic resistance pattern revealed emergence of multidrug resistance among some of the identified strains. To the best of our knowledge, this is the first report on detailed bacteriological analysis of ground water resources of Bhavnagar city including bacterial identification using polyphasic approach, community study, antibiotics resistance profiling, and interpretation of data using suitable statistical tools. Furthermore, this study can be considered as a model for understanding ground water quality of other cities also.
Heterorhabditis bacteriophora and Steinernema carpocapsae are microscopic entomoparasitic nematodes (EPNs) that are attractive, organic alternatives for controlling a wide range of crop insect pests. EPNs evolved with parasitic adaptations that enable them to "feast" upon insect hosts. The infective juvenile, a non-feeding, developmentally arrested nematode stage, is destined to seek out insect hosts and initiates parasitism. After an insect host is located, EPNs enter the insect body through natural openings or by cuticle penetration. Upon access to the insect hemolymph, bacterial symbionts (Photorhabdus luminescens for H. bacteriophora and Xenorhabdus nematophila for S. carpocapsae) are regurgitated from the nematode gut and rapidly proliferate. During population growth, bacterial symbionts secrete numerous toxins and degradative enzymes that exterminate and bioconvert the host insect. During development and reproduction, EPNs obtain their nutrition by feeding upon both the bioconverted host and proliferated symbiont. Throughout the EPN life cycle, similar characteristics are seen. In general, EPNs are analogous to each other by the fact that their life cycle consists of five stages of development. Furthermore, reproduction is much more complex and varies between genera and species. In other words, infective juveniles of S. carpocapsae are destined to become males and females, whereas H. bacteriophora develop into hermaphrodites that produce subsequent generations of males and females. Other differences include insect host range, population growth rates, specificity of bacterial phase variants, etc. This review attempts to compare EPNs, their bacterial counterparts and symbiotic relationships for further enhancement of mass producing EPNs in liquid media.
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