The Efficiency of Several Liquid Carriers to Increase the Survival of Enterobacter cloacae S16-3 and the Effects of their Produced Inocula on Germination and Growth of Wheat Seedlings

Biofertilizers play major role in sustainable agriculture. For provide them, different carriers are used to increase the longevity and survival of the bacteria. Biofertilizers are being used in two general forms; solid or liquid. For making biofertilizers, various types of material are used to inoculate seed or soil. A suitable material for carrying microorganisms should have certain characteristics such as high water holding capacity, chemical and physical uniformity, easy to sterilize by autoclaving or gamma-irradiation, absence of toxic compounds for microbial strains, and environmental safety. At the same time, these materials should have a near-neutral or easily adjustable pH and be locally abundant at reasonable cost. Liquid or solid biofertilizers have their own advantages or disadvantages. The aim of this study was to investigate the survival of Enterobacter cloacae S16-3 bacterium on different liquid carriers during one year.

The liquid carrier consisted of 9 treatments containing glycerol, polyethylene glycol (PEG), trehalose, carboxymethyl cellulose (CMC), arabic gum, polyvinyl pyrrolidone (PVP), glucose and starch with different amounts and in different combinations. In this study, bacterial inoculants prepared with the same initial population (109 CFU mL-1) after storage at room temperature were compared for the survival of the bacterium. The bacterial population was counted at 0, 15, 30, 60, 90, 120, 180, 270 and 365 days. For counting the bacteria in microbial carriers, after dilution series preparation, bacterial suspension was used in strip culture in a plate. In this research, the effects of prepared inoculants on germination and growth of wheat seedlings in sterile conditions in a plate and pot culture at the end of the fourth month were investigated. In pot culture, characteristics such as shoot and root length, the wet and dry weight of shoot and root, total wet and dry weight of shoot and root were measured.

The bacterial counting results showed that among the tested carriers, the most population was counted after one year in formulation F5 (arabic gum, starch and PEG) (107 CFU mL-1) and the lowest population was counted in formulation F7 (glycerol, trehalose, glucose, arabic gum, and PEG), so that after 6 months no alive cells of bacteria were counted. Also, the results of germination test and growth of wheat seedlings cultivating in a plate showed that the materials used in microbial carriers did not have any inhibitory effect on germination of the seeds, and even, in some cases, they could encourage their germination and growth. So that ten seeds in each inoculum started to germination simultaneously. In pot culture, F9 formulations (glycerol, glucose, arabic gum and PEG), and F4 (trehalose, arabic gum, and PEG) in terms of root fresh weight and total fresh weight had better means. The root fresh weight of the formulations were 1020 and 740 mg and the total fresh weight of 1800 and 1390 mg, respectively. The comparison of these carriers with control (without bacteria and carrier) and suspension of bacteria (non-carrier inoculation) showed that these carriers could be more effective in all measured characteristics.

Currently, the application of different materials in bacterial liquid formulation is considered to be of high importance as an innovative technological strategy to maintain the metabolic stability of microorganisms. Finally, according to the results of this experiment and the convenience and availability of the carriers, the F5 and F9 formulations can be suggested for further studies.