As dryland farming becomes more important for food production, the goal to find a sustainable method to promote crop growth under arid conditions is imperative. Thus, we looked to the Mojave Desert for a solution as it is home to plants living under year-round extreme climate and soil conditions. We isolated bacteria from the rhizosphere of Larrea tridentata, commonly found in the Mojave Desert, and studied their plant growth promoting (PGP) traits as we hypothesized that these plants depend on the microbial community for their growth and survival. We isolated a total of 30 unique bacterial colonies and characterized them through four cultivation-dependent assays: 1) siderophore production; 2) phosphate solubilization; 3) antibiotic production; and 4) cellulase activity. Many isolates exhibited siderophore production whereas only a few demonstrated phosphate-solubilizing and cellulase activity. Only a single colony exhibited antibiotic production. Following a PCR of the 16S ribosomal gene and sequencing, 16 of the original 30 isolates were identified as actinomycete and Bacillus strains. eDNA isolation was also performed. A trapping experiment in which legume plants are inoculated with the original soil samples showed effective root nodulation suggesting that nitrogen fixation occurred. Our results indicate that the microbial community of the Mojave Desert can help the plants survive adverse conditions.

Hung Dang2, Janeva Chung2, Nakin Bhandari2, Nhi Nguyen1

Microbial activity found in the soil of the Mojave desert suggests plant growth promotion

1Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA 900952Department of Molecular Cell, Developmental Biology and Cell Development, University of California, Los Angeles, CA 90095

Abstract

Materials & Methods

Assays for Plant Growth Promoting Activity

Master Chart

Acknowledgements

Discussion

Future DirectionsTrapping Experiment

Because there was presence of Nitrogen-fixing bacteria that only associated specifically with a certain type of plant species, it is best to employ Koch’s postulate. Thus, the isolates should be re-inoculated into Siratro to see if they can again nodulate the plants. Further, PGPB assays testing for activities are also needed for those particulate nodule isolates. Finally, because these strains come from extreme climate conditions, an experiment to test the durability of these bacteria to know what optimal conditions for later use is necessary. Finally, once abilities are finalized, a list of recommended strains of bacteria should be composed as a reference for bio-inoculates in dryland farming.

● We would like to thank the following:○ Dr. Ann Hirsch, Dr. Maskit Maymon, Dr. Pilar

Martinez, and Paul Yang for their tutorage. ○ Dr. Kris Reddi and Anjana Amirapu for assisting us in

the setup of materials for our experiments.○ The Department of Molecular, Cellular, and

Developmental Biology for funding this project.

Phosphate Solubilizing Activity

Using PVK plates as medium, we discovered that 8 out of the 30 isolate exhibited signs of phos -phate solubilizing activity, with most of the activity not covering more than 20mm in diameter. The strain that showed highest level of activity is G1.

Siderophore ProductionUsing both LB and TY plates, bacteria

was plated from liquid culture into 5 equidistant spots. Once the bacteria grew, Cas overlay was poured over each plate and halo formation was analyzed after waiting for the Cas overlay to set. 17 out of the 30 isolates exhibited siderophore activity. Isolate 21 has the highest calculated amount of siderophore activity.

Antibiotic ProductionWe discovered a con

-taminate in 3A liquid culture that most likely came from our soil. This strain exhibited anti- biotic activity as it killed of the lawn growth (evident in the halos). No other colony exhibited activity.

16S Identification

Of the assays, the Cas Assay had the highest amount of positive results. In addition, Cas plates were only used to confirm Cas overlay positives, resulting in many unplated Cas plates. Straings G1, G2, G4, 1A, 2A, and 2 were capable of more than one activity.

Multiple strains of bacteria that were isolated displayed phosphate solubilizing activity, cellulase activity, and siderophore production. With G1 and G2 showing very prominent capabilities. These we believe could be good candidates for future use as bioinoculates. Two distinct bacterial colonies were isolated from the nodules of the siratro plant in the trapping experiment. One of them is characterized to be a Rhizobium species which is known for their ability to form endosymbiotic nitrogen fixing association with root plant. In regards to our contaminate strain, we believe that the reason why it became so prominent is due to its antibiotic production which could have wiped out the native strain.

Out of five plant species that were inoculated with the Mojave desert, Siratro is the only plant that nodulated. Even though there is no significant difference in biomass, the plant’s physical appearance (greener than control) indicates that the bacteria associated with the plants through root nodules did promote plant growth. The squash of the nodules yielded colonies which were then analyzed. The following bacteria were characterized:● Kocuria rhizophila strain DC2201- 100%● Rhizobium sp. strain X2Ac9- 100% .

The figure shows phylogenetic relationship of the closest sequence matches from our cultivable isolates. Of the 9 bacterial isolated from soil sample, the majority were proteobacterial species (strain 1, 7,9, 12, 18). The rest were actinobacteria (strain 17, G2, G3) and firmicutes (strain 2 and 3A).

Cellulase ProductionBacteria was plated from liquid culture

on TY-CMC plates. Once grown the plates were then subsequently washed with Congo Red, NaCl, and then finally HCl. Cellulase activity was not well defined. 7 of the 30 isolates exhibited cellulase activity with strains A3 and A4 exhibiting the highest ratio of halo to plaque. [Picture: Negative result]