Microsoft CEO Satya Nadella smiles at a meeting of the Economic Club of Washington in Washington, D.C., on Oct. 4, 2017.

Microsoft on Thursday said that it's acquiring Citus Data, a start-up that has commercialized open-source database software called PostgreSQL. Terms of the deal weren't disclosed.

The deal could help Microsoft make its argument that it supports open-source technologies, particularly in the cloud, while continuing to make money from popular proprietary software like Windows and Office. In the cloud business, Microsoft wants to use openness as a way to pick up business amid competition from Google, market leader Amazon and others.

Microsoft has also sought to bolster its reputation in the open-source world by making its products work better with the Linux operating system, which is widely used to run applications in public clouds. It also acquired GitHub last year in a $7.5 billion deal. GitHub is a place where developers collaborate on, explore and access open-source projects.

Currently, Citus Data's website advertises a version of its database software that's hosted on Amazon Web Services. Microsoft's blog post announcing the acquisition mentions the competing Azure cloud 10 times.

"Working together, we will accelerate the delivery of key, enterprise-ready features from Azure to PostgreSQL and enable critical PostgreSQL workloads to run on Azure with confidence," Rohan Kumar, corporate vice president for Azure data at Microsoft, wrote in the blog post.

Microsoft doesn't have plans to change Citus Data's business at this time, a spokesman told CNBC in an email.

Microsoft did not immediately respond to a request for comment about whether Microsoft will continue to offer the Citus Cloud offering on AWS.

The start-up was founded in 2011 and had offices in San Francisco and Turkey, with 40 employees, according to LinkedIn data. Citus Data's investors include Silicon Valley accelerator Y Combinator, Data Collective and Khosla Ventures.

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