Why did this website disappear from Google's SERPs?

[VentaMarketing]

For the first several months this website, WEBSITE, ranked well in Google for several local search terms like, "Columbia MO spinal decompression" and "Columbia, MO car accident therapy." Recently the website has completely disappeared from Google's SEPRs. It does not even exist when I copy and paste full paragraphs into Google's search bar. The website still ranks fine in Bing and Yahoo, but something happened that caused it to be removed from Google.

Beside for optimizing the meta data, adding headers, alt tags, and all of the typical on-page SEO stuff, we did create a guest post for a relevant, local blog. Here is the post: Guest Post. The post's content is 100% unique. I realize the post has way to many internal/external links, which we definitely did not recommend, but can anyone find a reason why this website was removed from Google's SERPs? And possibly how we should go about getting it back into Google's SERPs?

Thanks in advance for any help.

[Francisco_Meza]

You have to stay updated on penguin.

You have a sitewide footer link pointing to http://www.prokellseo.com/

I wouldn't risk external link in the footer even if it is an exact match domain.

There are many factors that can make a website lose rankings. We don't know what it could be with the information you provided.

Maybe you need more content on the home page, it only has 6 sentences.

Check out your GWT to see what you can uncover.

[VentaMarketing]

Thanks for checking this out Francisco. Per your suggestion and after a little research, we actually went through today and removed our signature from all of the websites we manage. It is a tough pill to swallow since it seems like almost every design firm does this, but we want to do it right. And you are 100% correct, the footer link to the design firm's website is not best for SEO or the client, which is always our first priority.

Thank you again for your response.