Microorganisms are ubiquitous in nature. They can be found almost everywhere in soil, water, air, and even flora and fauna. On bats and birds, microorganisms are also common because of the guano that are produced by these flying animals.

Guano is nutrient-rich because it harbors diverse assemblages of microorganisms. When guano accumulates in an area, it can provide sustenance to other organisms such as minute insects that are food of bigger predators. Aside from serving a big part in the ecological balance of environments such as karsts, guano, when extracted from caves can serve as organic fertilizer.

In the Philippines, there is a dearth of information on the beneficial and harmful effects, as well as ecological importance, of guano because only a handful of Filipino scientists have focused their researches on cave microbes. Dr. Marian P. De Leon, Curator for food and cave microbes and extremophiles in the UPLB Museum of Natural History's Microbial Culture Collection is one of those few scientists.

"I have been fascinated and curious about the expanse of knowledge that can be discovered in extreme, biodiverse sites like caves," Dr. De Leon shares.

As part of a fieldwork for a cave ecology course at the University of the Philippines Los Baños which was done in the province of Pangasinan in 2015, Dr. De Leon observed that Cabalyorisa Cave, a limestone cave in Mabini town was home to thousands of bats that produced mounds and mounds of guano.

"It was a very interesting site which, at that time, I considered very diverse and potential source of microorganisms particularly that of bacteria," she recalls.

The one-year postdoctoral fellowship granted to Dr. De Leon in 2015 by the DA-BAR and UP-NSRI allowed her to work on the bacterial diversity of bat guano from Cabalyorisa Cave, Mabini, Pangasinan using metagenomics.

The resulting paper published in PLOS One last July 2018 (https://doi.org/10.1371/journal.pone.0200095) was the first report on bacterial metagenome of guano from a cave in the country.

"The study can serve as reference to future studies specially that we have already established the protocol for collecting samples and analyzing the metagenome especially in extreme ecosystems such as caves," Dr. De Leon emphasized.

However, Dr. De Leon cautions people interested in collecting guano from caves for whatever purpose. "There are also potentially pathogenic bacteria in guano, as shown by part of our results, that pose health hazards to tourists, researchers and guano harvesters alike," she explained.

Some pathogenic bacteria can cause diseases such as gastroenteritis, respiratory and skin infections. What is further alarming is that some of the bacteria profiled from the guano were antibiotic-resistant. Dr. De Leon however said that infection by these bacteria can be avoided and prevented by proper precautions when visiting caves, and especially, during the process of getting samples.

But on a more important note, the study has "stirred scientific interest for possibilities of isolating and characterizing novel bacteria with multiple functions for production of antibiotics and enzymes."

Examples of novel bacteria that has been discovered in Cabalyorisa Cave are Streptomyces sp. strains AC1-42T and AC1-42W. Recently published in Microbiology Resource Announcements of the American Society for Microbiology (https://doi.org/10.1128/MRA.00904-18), the near-complete genome sequences of these two Streptomyces strains were determined by Dr. De Leon and her co-researchers from the Philippines, Korea, Spain and Canada.

The Philippines has more than 2,000 caves and only a small percentage of this is explored. "Our caves are rich resources of potential microorganisms of industrial and biotechnological importance," Dr. De Leon shared.

According to their paper, both strains showed antagonistic activity against Bacillus subtilis subsp. subtilis KCTC 3135T. More than that, Dr. De Leon's team reported that the sequences may be used for "genome-assisted discovery of novel bioactive secondary metabolites with potential antibacterial, antitumor, or antiviral properties."

The whole-genome sequences of Streptomyces sp. strains AC1- 42T and AC1-42W have been deposited in DDBJ/ENA/GenBank under the accession numbers QKWX00000000 and QKWY00000000, respectively. Currently, it is also being phenotypically characterized.


Image courtesy of Balincaguin Conservancy whose members accompanied Dr. De Leon during her collection trips in Cabalyorisa Cave in 2016.


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