Libri sul tema "Microbial taxonomy"

The goal of this chapter is to introduce the field of microbial ecology and some terms used in the rest of the book. Microbial ecology, which is the study of microbes in natural environments, is important for several reasons. Although most are beneficial, some microbes cause diseases of higher plants and animals in aquatic environments and on land. Microbes are also important because they are directly or indirectly responsible for the food we eat. They degrade pesticides and other pollutants contaminating natural environments. Finally, they are important in another “pollution” problem: the increase in greenhouse gases such as carbon dioxide and methane in the atmosphere. Because microbes are crucial for many biogeochemical processes, the field of microbial ecology is crucial for understanding the effect of greenhouse gases on the biosphere and for predicting the impact of climate change on aquatic and terrestrial ecosystems. Even if the problem of climate change were solved, microbes would be fascinating to study because of the weird and wonderful things they do. The chapter ends by pointing out the difficulties in isolating and cultivating microbes in the laboratory. In many environments, less than one percent of all bacteria and other microbes can be grown in the laboratory. The cultivation problem has many ramifications for identifying especially viruses, bacteria, and archaea in natural environments, and for connecting up taxonomic information with biogeochemical processes.

El material que se presenta en este libro es una actualización de los protocolos de laboratorio en lo que respecta a los patógenos de insectos: virus, bacterias, hongos, protozoos y nematodes. El objetivo principal del libro ha sido reunir toda la información para dar a conocer el estado actual del estudio de los patógenos de insectos, su taxonomía, métodos diagnósticos y enfoques para el uso en control microbiano de insectos plaga y vectores.

Community structure refers to the taxonomic types of microbes and their relative abundance in an environment. This chapter focuses on bacteria with a few words about fungi; protists and viruses are discussed in Chapters 9 and 10. Traditional methods for identifying microbes rely on biochemical testing of phenotype observable in the laboratory. Even for cultivated microbes and larger organisms, the traditional, phenotype approach has been replaced by comparing sequences of specific genes, those for 16S rRNA (archaea and bacteria) or 18S rRNA (microbial eukaryotes). Cultivation-independent approaches based on 16S rRNA gene sequencing have revealed that natural microbial communities have a few abundant types and many rare ones. These organisms differ substantially from those that can be grown in the laboratory using cultivation-dependent approaches. The abundant types of microbes found in soils, freshwater lakes, and oceans all differ. Once thought to be confined to extreme habitats, Archaea are now known to occur everywhere, but are particularly abundant in the deep ocean, where they make up as much as 50% of the total microbial abundance. Dispersal of bacteria and other small microbes is thought to be easy, leading to the Bass Becking hypothesis that “everything is everywhere, but the environment selects.” Among several factors known to affect community structure, salinity and temperature are very important, as is pH especially in soils. In addition to bottom-up factors, both top-down factors, grazing and viral lysis, also shape community structure. According to the Kill the Winner hypothesis, viruses select for fast-growing types, allowing slower growing defensive specialists to survive. Cultivation-independent approaches indicate that fungi are more diverse than previously appreciated, but they are less diverse than bacteria, especially in aquatic habitats. The community structure of fungi is affected by many of the same factors shaping bacterial community structure, but the dispersal of fungi is more limited than that of bacteria. The chapter ends with a discussion about the relationship between community structure and biogeochemical processes. The value of community structure information varies with the process and the degree of metabolic redundancy among the community members for the process.