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...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.展开更多
Vibrio harveyi, like other luminescent bacteria, is capable of producing extracellular chitinases. Microbial chitinases are utilized to depolymerize chitin into chitooligosaccharides and N-acetylglucosamine for the ac...Vibrio harveyi, like other luminescent bacteria, is capable of producing extracellular chitinases. Microbial chitinases are utilized to depolymerize chitin into chitooligosaccharides and N-acetylglucosamine for the acquisition of carbon and possibly nitrogen, needed for survival. For many luminous marine bacteria （Vibrio spp.）, quorum-sensing is highly speculated to be responsible for bioluminescence; however, in terrestrial species （Photorhabdus spp.） luminosity seems to be controlled through unknown mechanism of phase variation. In the present work, the correlation between bacterial luminosity and chitinase production of F. harveyi was studied. The utilization of bioluminescence could prove to be an easier and more convenient method to monitor chitin fermentations that employ luminous bacteria. Results from the fermentation study indicate that luminosity of F. harveyi inversely correlates with chitinase production. In other words, during chitin fermentation, chitinase production was seen to increase while luminosity decreased with respect to growth and growth conditions. Furthermore, the results also suggest that V. harveyi may utilize an alternate mechanism that can counter quorum-sensing mechanisms to ensure bacterial survival under deteriorating growth conditions. The inverse relationship observed in this study may lead to a basic understanding of monitoring and studying chitin fermentations and anti-quorum-sensing/phase variation mechanisms exhibited by luminous bacteria.展开更多
文摘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.
文摘Vibrio harveyi, like other luminescent bacteria, is capable of producing extracellular chitinases. Microbial chitinases are utilized to depolymerize chitin into chitooligosaccharides and N-acetylglucosamine for the acquisition of carbon and possibly nitrogen, needed for survival. For many luminous marine bacteria （Vibrio spp.）, quorum-sensing is highly speculated to be responsible for bioluminescence; however, in terrestrial species （Photorhabdus spp.） luminosity seems to be controlled through unknown mechanism of phase variation. In the present work, the correlation between bacterial luminosity and chitinase production of F. harveyi was studied. The utilization of bioluminescence could prove to be an easier and more convenient method to monitor chitin fermentations that employ luminous bacteria. Results from the fermentation study indicate that luminosity of F. harveyi inversely correlates with chitinase production. In other words, during chitin fermentation, chitinase production was seen to increase while luminosity decreased with respect to growth and growth conditions. Furthermore, the results also suggest that V. harveyi may utilize an alternate mechanism that can counter quorum-sensing mechanisms to ensure bacterial survival under deteriorating growth conditions. The inverse relationship observed in this study may lead to a basic understanding of monitoring and studying chitin fermentations and anti-quorum-sensing/phase variation mechanisms exhibited by luminous bacteria.
