The use of colony development for the characterization of bacterial communities in soil and on roots

Abstract

A simple agar plating method for the description of microbial communities is described. This method is based on the quantification of the numbers of bacterial colonies in 6-7 age-based classes as they appear on agar media over a period of 6-10 days. The method can be used to quantify microbial communities in different habitats (roots and soil) and can be related to the ecophysiology of the microbial communities present. Significant differences in distribution patterns were found in time and depth on the roots. In general, as roots matured, the microbial communities changed from one dominated by r-strategists to one that was more distributed towards K-strategists. The soil had the greatest percentage of organisms that could be characterized as K-strategists. The method was also used to compare microbial communities on wheat roots and in soil in both the field and in microcosms in the glasshouse. In general, the method enabled differentiation between r- and K-strategists in environmental samples, something that could not be done using an ecophysiological index (a modification of the Shannon diversity index) or total bacterial numbers alone.

Plant mediated interactions between Pseudomonas fluorescens, Rhizobium leguminosarum and arbuscular mycorrhizae on pea

“…Higher levels of easily degradable carbon sources in the rhizosphere leads to enhanced establishment of zygomogenic organisms, such as Pseudomonas spp. (Bowen 1980 ;De Leij et al 1993). This is supported by the fact that the total population of indigenous fluorescent pseudomonads was significantly higher on plants inoculated with Ps.…”

Impact of temperature on the biological properties of soil

“…N 10 /10] 100, where N 1 , N 2 , N 3 ,…. N 10 is a proportional count of colonies grown in (Sarathchandra et al, 1997), and the ecophysiological diversity index EP = -∑(pi log pi), where pi is the number of microbial colonies from a given day divided by the total number of colonies (De Leij et al, 1993), were then calculated. Enzyme activity, similarly to the microbial count, was determined in the individual soil samples.…”

Response of microorganisms and enzymes to soil contamination with a mixture of pethoxamid terbuthylazine

“…N 3 /3…N 10 /10] 9 100, where N 1 , N 2 , N 3 ,…N 10 were proportional counts of colonies that emerged on day 1, 2, 3,…,10. According to the formula proposed by De Leij et al (1993) the ecophysiological diversity index (EP) for the microorganisms was determined EP = -P (pi 9 log pi) where pi-counts of colonies that emerged on a given day divided by total counts of colonies.…”