Number Of Bacterial Populations Research Articles

Soil microbial population numbers and enzyme activities in relation to altitude and forest degradation

Microbial population numbers and their enzyme activities in terms of different enzymes, namely dehydrogenase, urease and phosphatase, were estimated in four forest stands (two at low and two at higher altitudes). The two forest stands at each altitude were at different stages of regeneration. At both altitudes, fungal and bacterial population numbers were higher in the less degraded forests than in the more degraded ones. Consequently, the different enzyme activities were also greater in the less degraded forest soils. A correlation coefficient was calculated between fungal population numbers, bacterial population numbers, soil moisture, organic C and the various enzymes activities. Dehydrogenase activity showed a positive correlation with fungal population numbers in all of the forest stands. However, the bacterial population numbers only showed a significant correlation ( r = 0.639, P < 0.05) with dehydrogenase enzyme in the less degraded forest at the lower altitude. A significant positive correlation was established between urease activity and fungal and bacterial population numbers at the lower altitude, but only with the fungal population numbers at the higher altitude. At the higher altitude no significant correlation could be established with phosphatase and any of these traits. At the lower altitude, however, phosphatase showed a positive correlation with organic C and fungal population numbers. These enzymes showed a marked seasonality. The results of the investigation indicated that disturbance of soil and vegetation has an adverse effect on microbial population numbers and microbial enzyme activities.

Role of Seed in Survival and Transmission of Xanthomonas campestris pv. oryzae Causing Bacterial Blight of Rice

AbstractSurvival period and possibility of seed transmission of X. campestris pv. oryzae were studied. The bacterium survived for longer (170–180 days) in kharif than rabi (120–130 days) harvested seed. The percentage of infected seeds was higher in kharif than rabi. The infected seed when sown failed to produce the symptoms on respective seedlings due to the low number of bacterial population. Present studies indicated that infected seed though may not produce symptoms on the seedlings directly but serve as a source of inoculum form season to season.

Pesticide Levels and Fluctuation in Soil Bacteria in an Irrigated Field and a Pond of Southwest Texas

The Presidio area in Texas is now being studied in detail for the effects of pesticides2 upon the ecosystem. A typical irrigated field was studied for the effects of pesticides on bacterial populations from June through August 1966. Bacterial population numbers were found to fluctuate directly with the influences of irrigation. Soil that was not irrigated but had adequate moisture for bacterial growth yielded an inverse relation between pesticide levels and bacterial numbers. A connection between bacterial populations and pesticide breakdown was suggested. Microbial numbers and pesticide levels were examined in a stagnate body of water located adjacent to cultivated fields. Pesticide levels and bacterial counts were found to vary directly with silt washed into the pond from adjacent areas following substantial rainfalls. Pesticide persistence in soil has been a topic of study for several years. DDT and other chlorinated hydrocarbons have been reported to remain in soil for up to ten years by Ginsburg and Reed (1954), Lichtenstein and Schultz (1959), Lichtenstein and Polivka (1959), MacPhee et al., (1960) and Woodwell and Martin (1964). Little breakdown of DDT in soil during the first year after application was shown by Jones (1952). However, he presented data showing that breakdown after the first year occurred in soils with high organic matter and bacterial counts. Bollen et al., (1954) and Martin et al., (1959) presented data which showed that the total number of bacteria in soil had not been affected even though pesticide residues at phytotoxic levels for higher plants had been reached. Ahmed et al., (1958), 1 Technical Article No. 7228, Texas Agricultural Experiment Station, College Station, Texas. This research was supported in part by Grant AP 28-02 from the Division of Air Pollution, Bureau of State Services, Public Health Service. 2 Abbreviations used in this paper are: DDT = 2,2-bis(p-chlorophenyl)-1,1,1trichloroethane; DDD = 1,1-Dichloro-2,2-bis(p-chlorophenyl) -ethane; DDE = 1,1dichloro-2,2-bis(p-chlorophenyl) ethylene; methyl parathion =0,0-dimethyl O-pnitrophenyl phosphorothioate; ethyl parathion 0,0-diethyl 0-p-nitrophenyl phosphorothioate.